No bike review is complete without a weigh-in and most will attract comments arguing whether the weight is acceptable or not. It's easy to see why: weight is a simple, objective metric that's easy to understand and quantify. Lighter is better - simple.
But how much better? After all, saving weight is insanely expensive - most weight-saving upgrades cost several dollars per gram saved. Picking Shimano's XTR drivetrain over SLX, for example, saves 322g but costs almost $1,000 more (about $3 per gram).
Within a category (XC bikes, enduro bikes etc.), the gap between a light or a heavy one is about 1kg (2.2lb), and that's about the amount of weight you could save from a typical mid-range bike by throwing money at it. So how much difference does 1kg make?Climbing
When climbing, the energy required to overcome gravity is equal to the height of the climb times the system weight - the weight of the bike, kit and the rider combined. Let's say an average rider weighs 80kg, plus 5kg of kit and a 15kg bike, which gives a total system weight of 100kg (these are just rough numbers). So adding 1kg to the bike increases the total system weight by 1%. The time taken to complete a climb depends on the power to weight ratio, so adding 1% to the system weight means it will take 1% longer to complete a climb, or 1% more power to maintain the same pace. So for a half-hour climb, it would take 20 seconds longer carrying an extra kilogram at the same power.
What's more, that's an upper limit. Bike calculator
uses an algorithm to model the forces acting on a bike and rider in the real world, including gravity, rolling resistance and air resistance. It's generally considered to be an accurate representation of real-world cycling while eliminating all unwanted variables. If you plug in numbers for an 85kg rider and a 15kg bike, a 10-kilometre course and a 10% grade, it predicts it will take 77.86 minutes. Change the bike weight to 16kg and it will take 78.62 minutes. That's 0.97% more time, very close to the 1% figure you'd expect from power-to-weight alone. But change the gradient to 1% and the extra kilogram adds just 0.38% to the time; on a 0% gradient, the time difference is 0.2%.
So what's going on? On very steep gradients, air resistance and rolling resistance are pretty negligible, so most of your power is going to overcoming gravity. That means lifting 1% more weight takes (almost) 1% more time (or 1% more power). But on a flatter gradient, speeds increase so these other factors take up a bigger share of your power. Aerodynamic drag doesn't depend on weight, so the faster you go the more aerodynamics matter and so the less that weight matters in percentage terms. With rolling resistance, it's more complicated; adding weight will increase rolling resistance but not necessarily in proportion to the system weight. This partly depends on whether tire pressure is increased in proportion to system weight or not. Either way, rolling resistance does increase with weight; this is why Bike Calculator predicts a slightly slower average speed on a flat course with more weight.
The bottom line is that adding 1% to the system weight (about 1 kg) will impact climbing speed by at most 1% on steep climbs, but less on flatter terrain. For typical riding with a mix of flat pedalling and climbing, adding 1% to the system weight might affect the average speed by significantly less than 1%, perhaps closer to 0.5%.
To put that in more context, the difference in power transmitted to the rear wheel can vary by as much as four Watts between different chain lubes
at an output power of 250W. That's a 1.6% difference in the power reaching the rear wheel. On a steep climb, speed is proportional to power, so the choice of chain lube could make a bigger difference to climbing speed than a kilogram of extra weight. That makes high-end chain lubes look like a bargain next to carbon components.
In the latest efficiency tests
, the times varied by a huge amount (up to 11% between the fastest and the slowest bike), and only a small part of this variation can be explained by differences in weight. Suspension efficiency (pedal bob), drivetrain efficiency and the presence of an idler
could make a bigger difference to climbing speed than weight. Accelerating
You're probably aware that rotating weight has a greater effect on acceleration compared to non-rotating weight. This is true because when the bike accelerates, the wheel needs to accelerate in the direction of travel (this is called translational acceleration) as well as increasing how fast it's spinning (rotational acceleration). Accelerating anything requires adding kinetic energy to the system, but with a rolling wheel, you have to provide both translational and rotational kinetic energy (usually by pedalling).
If your bike is in a work stand you'll notice it takes energy to turn the cranks just to accelerate the rear wheel up to a high rotational speed - this is the rotational kinetic energy. How much kinetic energy depends on the mass of the wheel: a heavier wheel has more translational and rotational kinetic energy for a given speed.
The energy you apply through pedalling is equal to the power you supply to the pedals (minus all sources of drag), multiplied by the time that power is applied for. So, to get from one speed to a higher speed, you'll need to supply more kinetic energy if the wheels are heavier; this will take more time at a given pedalling power (so slower acceleration).
But how much, exactly?
Because wheels roll, they have a fixed relationship between their translational speed and their rotational speed, and this gives them a fixed relationship between the rotational and translational kinetic energy. The vast majority of the rotational kinetic energy in a bicycle wheel comes from the mass at the outer edge (the rim and tire) - the hub and spokes are pretty negligible. A typical tire weighs about 1kg and a typical rim, about 500g, so for a pair of wheels, that's 3kg of rotating mass that matters.
I've included the relevant equations in the box below, but the gist is that the rotational kinetic energy for this 3kg of mass at the outer edge of the wheel is equal to the translational kinetic energy when the wheel is rolling. That means the rims and tires need twice as much energy to get them rolling at a given speed as the same amount of non-rotating weight on the frame or rider. In other words, the mass of the rim and tire count double in terms of their kinetic energy and therefore have twice as much of an impact on the time taken to accelerate.
The math(s) part
The rotational kinetic energy
of a hoop is given by
E=0.5 x M x R^2 x W^2,
where M is the mass of the hoop (the rim and tire), R is the radius of the wheel and W is the rotational speed (RPM) of the wheel.
But W is given by the translational speed, V (that's the speed you're moving down the trail) divided by the wheel radius, R. So, the rotational kinetic energy can be given by
E=0.5 x M x R^2 x (V/R)^2
The radius cancels out, giving:
E=0.5 x M x V^2
This is the same as the formula for translational kinetic energy. So for a rolling hoop, the rotational kinetic energy equals the translational kinetic energy, so the total energy is just two times the translational kinetic energy.
In other words, every gram in the rim or tire has twice the kinetic energy of a gram that's not rotating. The time taken to accelerate from a standstill to a given speed is given by the kinetic energy required divided by the (net) power supplied by pedalling, so every gram on the wheel has twice as much impact on the time as a non-rotating gram on the frame or rider.
But, remember we're only talking about 3kg here. So for a bike and rider weighing 100kg, the rotational component of the kinetic energy is only about 3% of the translational kinetic energy.
Let's say you swapped to lighter rims which were 200g lighter for the pair. Because this affects both the translational and rotational kinetic energy, the mass counts double, and so it will have the same effect on acceleration as saving 400g from the frame or rider. In other words, it will quicken acceleration by about 0.4% for a 100kg system weight. Hardly a noticeable amount.
What if you went the other way and swapped your 1,000g trail tires for 1,300g DH tires, plus 200g inserts in each wheel, so adding a total of 1kg of rotating weight? For a 100kg system weight, that would slow acceleration by about 2%. If you've noticed that swapping to DH tires feels like it has a bigger effect than this, that's probably down to the extra rolling resistance, not the weight. This suggests that fitting inserts instead
of DH tires may be wise in some situations: in either case, the weight isn't noticeable, but the rolling resistance of a stiffer tire is.
One other thing to note is that the rotational kinetic energy of a wheel doesn't depend on its radius, because although a larger radius results in more rotational kinetic energy for a given angular speed (due to higher rotational inertia), the angular speed is lower for a given trail speed, and these two factors cancel out. This means that if you had a 29" wheel/tire that weighed the same as a 27.5" wheel and tire, the acceleration would be the same. Of course, a like-for-like wheel or tire will be heavier in 29", but only by about a hundred grams or so.Descending
Another reason to want lighter wheels is to do with unsprung mass. This is the weight of the wheels and the other connected components that aren't held up by the suspension. When your wheel hits a bump, it has to accelerate upwards rapidly, then accelerate downwards again as it moves over the bump and the suspension rebounds. How rapidly the wheel accelerates back down is limited by the mass of the wheel but also the stiffness of the suspension spring, which in turn is determined by the sprung mass of the rider, the frame and everything else that is
held up by the suspension.
The heavier the wheel, or the softer the spring, the slower it will accelerate downwards on the backside of a bump. The slower the acceleration, the more often it will lose contact with the ground on fast and severe bumps, resulting in less traction and a harsher ride. This is why engineers in all wheeled vehicles refer to the sprung to unsprung mass ratio - the higher the ratio, the better the suspension can perform.
Calculating the unsprung weight of a bike is pretty complicated because it includes a lot of components (wheels, tires, cassette, derailleur, brake calipers, rotors, fork lowers/swingarm etc.) and because the swingarm's contribution to the unsprung mass depends on where the mass is distributed along its length. It can be measured, however, by putting the bike in a stand horizontally, disconnecting the shock and putting the rear wheel on a scale.
Using rough numbers again, the unsprung mass is about 4kg on the rear and about 3kg on the front. Let's say you were to save 100g per wheel by buying lighter wheels - that's about the difference in weight between DT Swiss' EX 1700 and EXC 1200
wheels, which have a cost difference of $1,964. That would reduce the unsprung mass by 3.3% on the front and 2.5% on the rear. It's hard to quantify how much this will affect suspension performance because that depends so much on the terrain, speed and suspension settings, but I've tested different wheelsets with similar or greater weight differences than this back to back and I can't perceive a difference by feel. It seems to me there are better ways of spending $1,964.
For big changes in unsprung mass, you'll need to make compromises, not investments. Swapping trail tires for DH tires with inserts might add 500g per wheel (about a 12.5-16% increase in unsprung mass) but the extra cushioning, damping, and ability to run lower pressures in the tires will almost certainly outweigh any downside in terms of suspension performance. Similarly, going from 200mm to 220mm rotors will add 25g for the rotor plus about 25g for the adapter, so 50g per wheel. That's a negligible difference to the unsprung mass (about 1.4%) but a noticeable (10%) increase in brake power which could reduce arm pump and increase enjoyment and speed.Could a heavier frame be a good thing when descending?
If making the wheels lighter is impractical, what about deliberately increasing the sprung mass of the frame in order to increase the sprung to unsprung mass ratio and thereby improve the suspension performance? I investigated this at my previous employer
, and while the results were inconclusive, the bike definitely felt calmer and less harsh with 3kg of lead strapped to the frame.
At the time. I put that down to the increase in the sprung to unsprung mass ratio. But now I realise a more relevant factor is the ratio of the rigid sprung mass (the frame and other rigidly connected components) to the total sprung mass (the frame plus the rider).
Because the rigid sprung mass of a bike is so light (around 9kg), it accelerates upward rapidly when the bike hits a bump. This acceleration continues until the rider's bodyweight gets involved, which is only after the bike is moving upward towards him/her. This disconnect is what causes MTB suspension to perform so poorly compared to motorcycle suspension; the suspension needs to be stiff enough to support the total sprung mass of the bike plus rider (perhaps around 90kg), but when the bike first hits the bump, the rider is too loosely connected to the frame to provide much resistance. So the 9kg rigid sprung mass starts to accelerate upwards rapidly, without much suspension movement, until this lag is overcome and the rider starts to accelerate with the frame and create enough resistance to compress the suspension. Increasing the mass of the frame reduces this initial acceleration and forces the suspension to move earlier, and so decreases vibration experienced by the rider. This is why e-bikes are far more comfortable to ride on rough terrain, even when running less sag.
I'm not necessarily saying heavier bikes are better overall
when descending - both Jack Reading and the Santa Cruz Syndicate experimented with adding weight to their race bikes, but as far as I know, neither stuck with it - but I am saying there are tangible benefits to heavier frames when going downhill. I certainly wouldn't stress about having a lighter downhill bike, unless you're carrying it to the top!Don't miss out
One common argument is that, yes, a few grams here or there isn't much on its own, but saving weight where you can throughout the bike adds up to a noticeable saving. This may be true, but allowing for burlier parts in your weight budget adds up to big benefits, too. For example, bigger tires offer more grip and cushioning, bigger brakes reduce fatigue and allow you to stop later, stiffer forks can improve suspension performance through chunky terrain. These factors in isolation might not make much difference, but between them, they create a more confidence-inspiring ride.Some good counter-arguements
My overarching argument here is that the importance of weight is overblown, largely because the weight of the bike is pretty small compared to the weight of the rider, so an extra kilogram on the bike might add only 1% to the amount of weight you have to shift up and down hills. But there are some exceptions where this logic doesn't apply. In particular, when bunnyhopping, pumping, carrying your bike, or technical climbs involving manoeuvring the bike up and over obstacles; a kilogram on the bike may count more than a kilogram on the rider here.
I've also been assuming throughout this thought experiment that the system weight is about 100kg, but of course, if you're a lot lighter any additional weight will have a bigger effect.
To conclude, I'm not saying that a 16kg bike is indistinguishable from a 10kg bike, or that lightness isn't a good thing. I am saying that when you run the numbers the benefits of saving a realistic amount of weight are smaller than you might think, while the advantages of heavier components can be far more tangible in terms of descending performance, not to mention reliability and cost.
Then he posted on this link www.pinkbike.com/news/video-jack-moir-celebrates-his-ews-title-with-a-metal-monday-mash-up.html, and was promptly removed within an hour or so.
Community members started calling out certain PB Staff asking why he got banned, and what rules he broke since nothing he said was bad, or inappropriate by any means. Hence #restoreOutsideCEO.
Well, sounds like PB listened behind the scenes, and unbanned the account that now uses the name NotOutsideCEO
Well either way, out of nowhere swoops in the hero I never knew I needed...Brian Park (he's getting a big raise for the BTW - assuming HR lets me do it!), who restored my account under this pseudonym. Please help me keep a low profile so those Downhillers in IT don't come down on me again (pun intended!).
Finally regarding weight...if you're really that worried about it, might be time to get a gravel bike!
Be safe be well,
Also, he needs an Outside+ tag on his profile, but I think they’ve removed those because people were voting them down into oblivion, for the sole crime of existing.
You don't get a Yeti over a GG because it makes you faster, you get it because it increases you social capital amongst your other overweight middle aged peer group.
Don't let Outside magazine use drama to attract readers and increase clicks.
I've actually cracked several alloy bikes, and I'm not a super amazing rider. I think that aluminum's fatigue life is a real issue for bikes.
But two of the cracked frames were Konas, so that could skew the data.
But I do agree that folks focus on bike weight to their detriment.
There is one aspect of the weight/price/strength compromise which doesn't seem to be adressed at all in the bike industry, it's the relationship between rider weight and parts strength.
For example, I'm heavy and when riding XC I can't use XC wheels, and to get a bike which won't break/flex too much, I need to look in the 130-150mm category.
On the other hand, my gf is 50kg and the main thing that is swappable to save weight is wheels and tires. Because she's not going to replace a Lyrik with a Pike/34 to save a few grams... or cranks... etc.
In the end her bike weight / system weight ratio is 14/64=22%, when mine is 17/112=15%.
That's a 7% difference, a lot more than the small numbers mentioned in the article.
Yeah, that's a good point and it goes hand in hand with the disproportionate sizing problems which very tall and short riders face (same crank length, travel, BB height, chainstay length, and virtually the same stack height for 160 or 200cm riders). Light riders often have overbuilt bikes and heavy riders often have underbuilt ones. For a trail bike, you can often up-spec components if you're heavy (fit DH wheels, tires, brakes or a burlier fork), or maybe fit XC parts to a trail bike if you're really light.
For XC or DH though, there's nowhere more extreme to go. If Tanhee Seagrave is better off on the DH casing than SuperGravity tyre, then perhaps someone much heavier like Wyn Masters would benefit from a tyre that weighed 10-20% more?
With bikes in the 5-15k price range nowadays, that little bit of effort is certainly not too much to ask.
Therefore comparing bike weights is irrelevant unless rider weight is also considered.
I'm ~100kg kitted up and my FS trail bike is 41lb (18.6kg) including tools and full bottle and coils both ends. This equates to a 26.6lb bike for someone that is 65kg.
Assuming strength is *roughly* proportional to body mass (which it will be roughly unless you are a skinny bloke with a huge beer belly) she is having to work 50% harder to move the bike around dynamically on the trail.
Although a big long climb, and she will reap the benefits, as Seb's article indicates.
This has confirmed what I thought, my bikes weight compared to by buddies bikes just doesn't seem to make that much difference up or down hill
Feature Seb Scott more.
Also in the PB podcast. Look I like the cast of characters on the podcast and it appears that they work hard on the content ideas and the firmat. BUT it puts me to sleep, literally. My theory: I’m a bike nerd, I like the deep dives into MTB topics. Often times the setup and concept is good on the podcast, but the actual discussion is shallow and a bit lame. Add in Seb Scott…let him go deep. You have a better podcast. For the model of a great podcast I highly recommend you listen to the now defunct original “MTB Podcast” that was great content. They made meaningful deep dives in the way Seb does in his articles.
This website (linked below) is a good resource that measures rolling resistance on a drum. Problem is, the convex drum probably increases rolling resistance compared to a flat road surface and the wheel in these tests is passive, whereas a powered rear wheel may behave differently due to the propulsive friction at the contact patch. They also don't properly model the effect of bumps and how they interact with the suspension and the rider.
I've attempted to rank tires on rolling resistance in the past using roll down tests and climbing to power but it's hard to get repeatable results in the real world (a breath of wind can affect the times too much). Maybe an indoor version would be ideal.
100% agree. I'm running a Tough Trail Boss on my HT and it rolls really well despite the weight (nearly 1100g for a 2.25x29). I would rather ride it on road than a gripper lighter tyre.
I can't live with the super short travel or XC geometry of the current light weight options, the specialized epic evo was close-ish. Maybe when downcountry (lol) gets into more of a swing there will be a better option for me. Fingers crossed.
Even worse, I am a 27.5 guy because I can't figure out how to not buzz my ass tucking off jumps on 29ers so my options are crazy limited, previous bmx freestyle life has made my muscle memory non-conformist
I realize I am a special use case where I just want a light, shortish travel, smallish wheel bike with halfway-to-gravity-bike geometry and minimalist features. The SC 5010 was as close as I could find and it's been great. Just haven't taken the knife to it yet to see how awkward and personalized I can make it lol.
But the easiest to throw around is the 21" TT BMX, which is very heavy for it's small size... 27.33 lbs. It's also the shortest in the quiver.
One note: the RAD across the BMX, DJ, and slopestyle bike is very similar, within half an inch.
My son has been riding since 18 months and five bikes later, I can tell you weight really only matters when it gets extreme. Geometry and fit always matter much more.
I have one question about the stack height : why is it generally so low on DH bikes?
All measures from largest size (all XL except old Rage which is L, and Megatower XXL) :
27" Rage 611mm, new 29" Rage 638mm, Sender CF 29" 636mm, Sender Al 27" 625mm, V10 29" 641mm, Session 639mm, Demo 629mm.
Always lower than the enduro models :
Torque 27,5" 645mm, new spindrift 660mm, Nomad 648mm, Megatower 666mm, S Enduro 638mm.
Is it just that dual crown make a lower stack possible, so designers just make it as low as possible and expect people to use >50mm riser bars if tall?
Or does sag explain this? (if 20% front and 30% rear, the rear drops 20mm more than the front on a 200mm bike vs 15mm for a 150mm bike, and this difference is even bigger if we take into account that the front sag is less vertical than the rear sag).
>Sees some sort of physics calculations
>Shuffles over to light the Bat-signal for all the PB engineers..
In all seriousness though, lighter rubber (when applicable) absolutely transforms my trail bike. Some of the most fun I've had on my trail bike was running 2.4 Ikons F/R. Crazy quick, and surprisingly capable!
That's why I lit the PB engineer signal. I'm not an engineer. I am sharing personal experience. Anyone who has run Minions and Ikons in the same season feel free to share your experiences here.
I switched from a DHR2 Exo+ to a Michelin DH34 on the front of my Dartmoor Hornet, a weight gain of >300 grams.
It was a hopeless pig to bring uphill and accelerate, but a monster on the way down.
It blew my mind not only on the straight line gnar, but also in corners, holding lines like never before. Total confidence booster at 0.9 bar (yes,sidewalls were that stiff).
Once worn, I put on an Exo+ Assegai... just for a ride, immediately replaced with a DH casing one.
And I have to say, while an awesome and faster rolling tyre, it lacks the ferocious, stubborn, smash-it-all feel of the DH34, which I think is due to its sheer weight and rotational inertia.
On my 150mm bike, swapping out the 2.6" tires for XC tires really woke the bike up, felt much more lively. This has inspired me to go after carbon rims.
They are super fast, especially noticeable when accelerating, but there is less than zero grip in turns, especially loose over hard.
So damn sketchy, had a few very close calls due to a lack of grip, never running XC tires again.
DH34 also has absurdly grippy rubber, so much cornering grip.
Currently have DH casing Assegais front and rear, while they have very good grip in most situations, they can't match the absurd grip of my old DH34 tires.
Might be better in muddier conditions, but I don't ride much in mud, so not very relevant for me.
Bike terrain and demands are dynamic - depending on the move, having a bike that weighs 10% more might require 100% more effort to see realized. So I think the linear assumption of weight to effort (energy) is too simplistic. Like most things, it depends.
Everything you said is completely subjective. I find the opposite: heaver tires (which also allow less pressure) tend to stick to the ground more (when well damped), giving me more traction in all acceleration events: straight line acceleration, braking, and when changing direction; meaning it's "crazy quick" and "the most fun", for me.
Where to even begin. Ikons 200g lighter than Minions.. subjective? Wheels that now weigh ~half pound less each and also roll quicker.. subjective? I commented what I did on this article because it was counter to what the article seems to be suggesting--that a little weight here and there is only a small percentage, *and thus not a very big deal*. Would that be an accurate simplification of the thesis of the article? Right, so I stated that I was pleasantly surprised at how going to a lighter tire with smoother tread (re: must know what the Ikon tread looks like) made the bike "quicker", changed the bike, and was fun to ride. I didn't say it was "better" than anything, but it does suggest that even small percentages can have a big difference in feel for a bike. So you know the math calculations in the article are great and all, but what was being missed was real world application. Tire tread AND wheel weight have an affect on how a bike rides. Thank you for proving that point by sharing your anecdote. How or why this became a pissing contest baffles me. I never claimed that Ikons were "better" per se, I said they were 'fun' and 'quick' on my trail bike, enough so to cause me surprise.
So your response is to say you like a different tire and have more fun that way?? Neat. Go off I guess. I don't see where the debate is. People mad that I didn't time myself? Ok. I bunny hopped off the small stuff and jibbed all over the trail and had a blast, bike felt way different, but I guess that counts for nothing. A quantifiable metric like wheels that are a half pound lighter is all placebo I suppose, because math article is smart. Got it.
Everyone knows that changing weight will make things feel different, just like changing tire pressure will make things feel different. But for the longest time everyone thought high pressure meant fast, and it turns out that was pretty wrong. Seb is showing that the same thing might apply to weight: lighter is not always as big an improvement as once thought, at least for the value of energy used to increase elevation (arguably the most important part of climbing, though of course not the only part).
I didn't 'get mad' when people asked if I took objective measurements. I was confused--big difference. But I've already stated that my original comment was qualitative, not quantitative, in fact I've clarified this to you, specifically. I also corrected you when you claimed the entirety of my original comment was purely subjective. But here you are beating dead horses. Did you want an apology that my comment wasn't what *you* thought it should have been? Ok, I apologize. Next time I'll check with you before sharing my personal experiences.
Not policing anything. I have no pull here beyond a negative props (which I did not put on any of your comments). Just trying to explain why people are doing the thing that confuses you.
@justinfoil: "I'm confused why people who have read my actual words "...absolutely transforms my trail bike." and "Some of the most fun I've had on my trail bike..." are asking about a clock?"
The words I used all the way in the beginning of this thread in my original comment should have, I thought, indicated that I was making a qualitative statement. I have indicated this was the case another two times in this thread, but I'm beginning to think a few people do not understand the difference between the qualitative and quantitative in nature. User Ikubica had a valid question in if the differences I noticed might be due primarily to tread pattern, and I clarified. Seb, the author of this article, echoed some of Ikubica's questions, and I clarified my point further for him, with "I think people are missing what I said in my initial comment--my point is not about all out speed, or even primarily speed focused. Quicker rolling due to tread, yes, absolutely. But there is an *entirely different feel* when you knock ~200g a wheel off the bike AND it rolls easier, hence "...absolutely transforms my trail bike". You can pick up the front end and pop the bike all over the place...". Seb's questions were even further confounding because the title of the article isn't 'Why bike weight doesn't slow you down', the title is "Nerding out: Why you shouldn't worry too much about weight". So even in the title it doesn't state that this is a timing/speed-based argument Seb is making. It was after alllll that where you came in and asked:
justinfoil (Oct 20, 2021 at 11:5
@mikealive: same pressure as previous tires? crazy quick proven by a clock, or just feel? (because often chattery or sketchy can seem quicker but not be quicker)
Can you see why I would be confused? How are people commenting in this thread when they apparently cannot read? I had already clarified what I was saying a few times before you even came in to ask your questions. Questions that appeared to still be missing the entire point of my initial comment. *Then* you tell me that you're asking those questions due to the nature of the article...which would seem to imply that because the article uses some 'Bill Nye' calculations to support a hypothesis, that I cannot make a comment that does not align with the article, or one that is not quantitative in nature. Even though it had already been clarified that the tires were *objectively* lighter, and *objectively* faster rolling, which common sense would tell anyone with a functioning frontal cortex will have an impact on how the bike feels and handles. This is what I was commenting on.
The next two major comments below mine are saying essentially the same thing as I was--that weight DOES have a big impact on how a bike rides and handles, timing devices be damned. And the truly hilarious thing about all this is I can go through the rest of the comments on this article and see you making the same misguided replies elsewhere in other threads. Yet you come back 4 days after the fact to gaslight me and tell me 'oh I was just trying to give you an answer because you said you were confused'. Nah dude. I don't buy it. Either you're Seb's cousin, or you see some poorly applied physics calculations and think 'this has to be right' and stroll into the comments section with police nightstick in hand. I don't downvote based on conversations either, so no internet points hate from me. But I can see you getting downed on the other threads. Do you think that might be due to *you* missing the point of what others are saying?
Umm, talking about reading whole comments/stories. If you read the whole story, it's pretty clear it's about simple things like relative power needed to lift a given weight up a given height. Pretty clearly not about how the ride feels.
In the title, THE TITLE. Not the article. I was speaking specifically about the titular claim 'why people shouldn't worry too much about weight'. But that said--for what feels like the fourteenth time, *why* does it matter again? I thought you said you weren't the comment police? Oh that's right, I'm talking to PB comment section Barney Fife. And because the article was about measurements and calculations, a person cannot comment anything to the contrary. Your circular logic is astounding, truly.
Consider it done. And just an fyi, there is an option to unfollow a conversation, at least on desktop version. Hadn't considered the notifications going out, apologies.
“But there are some exceptions where this logic doesn't apply. In particular, when bunnyhopping, pumping, carrying your bike, or technical climbs involving manoeuvring the bike up and over obstacles”
- that is mountain biking. So…I guess the logic doesn’t apply.
Solid theory, a great piece from Mr Stott but I just don’t believe it’s relevant to real world mountain biking.
I'd alway prefer a lighter bike to a heavier one, but if they are within a reasonable gap then it's just one of many checkboxes when it's new bike buying time.
Very subjective. I'm a heavy dude that like to smash trails, to me, too light of a bike feels fragile and too easy to get tossed off line out from under me. I can rely on a certain amount of momentum from the bike allowing easier inference on where it's going to go if/when traction changes suddenly.
Obviously, balance is everything. And I wouldn’t take issue with many of the points in this article. Losing weight if you’ve got too much of it is a much more cost-effective way to increase performance. There are plenty of times when marginal weight improvements in your bike are unjustifiable from a cost standpoint.
Take a look at something like the Transition Spur. Are you getting much “value” upgrading from the 25.2lb X01 build to the 24.7lb XX1 build for an extra $2,700? Not really.
Would any of us notice a significant difference between the 29.4lb Deore build and the 25.2lb X01 build? Absolutely. Worth spending an extra $2k on? I’d say so. If you can swing it.
Which isn’t to say you couldn’t have a blast on a 29lb “Downcountry” bike, or a 35lb trail bike or a 40lb enduro bike. But if you’re going to be pedaling it up, I’ll bet we’d all appreciate taking a few lbs off those weights, and in many cases, find some value in investing in a lighter build, to a point.
Bottom line is climbs can be up to 10% different in times, but most descents are within 1-2% (up to limits for the short travel bike).
Wheel weight directly affects downhill performance, the lightweight wheels of the 26lb bike noticeably slow down through chunder and don’t track as well at speed.
IMO if you could have a 25lb complete trail bike, with the wheel weight of a typical enduro bike, then you could have some magic.
Wow, that's some amazing science you got there bro
Bike-body separation —- on an tech trail, the bike for sure moves differently (more) than I do, thanks to pumping, hopping, lunges, etc. Thats the “million little accelerations” many commenters have touched on.
It’s not science. But it is repeatable and based on some measurable things, which is more than nothing. And yep, for the same power output the climbs can be that different between the 2 bikes, the numbers don’t lie.
It would be great if Seb looked into that.
Remember back to physics when you drag a cylinder across a surface: it takes the same energy to pull it from the center of mass than it does it pull it with a string wrapped around it and thus making it rotate (seemingly more motion).
also the bob is not a result of the pedaling, its just shifting your weight, and compounded that the energy into the suspension is given right back (minus friction yes but not very much),
i find it counterintuitive as well but idk I leave it open
Dylan Johnson's Clips vs. Flats Video: www.youtube.com/watch?v=KUEaN9FKGLE&t=1s
GCN's Clips vs. Flats Video: www.youtube.com/watch?v=CNedIJBZpgM
And in this case, you are the only energy source, so it's your energy wasted.
There would be no loss from suspension if this was an electric moped with constant force applied, since the only loss would be in the initial compression of the shock.
However, on a bicycle, you will never achieve constant force on the chain, force will be roughly applied in a sine wave form, with some pretty large differences in force during the stroke.
This variable force will act on the suspension through the chain in varying degrees based on the instant centre of the suspension design, causing some energy loss.
Really high anti-squat bikes, contrary to popular belief, can have a tendency to bob more since no one pedals perfect circles. I pedal reasonably decent circles (I can pedal one-footed on flat pedals), but I still like bikes with middling (75%?) anti-squat for both that reason, and because I love traction more than I care about raw pedaling efficiency: a tire slip when climbing over a root is usually way worse that whatever minimal losses come from active suspension.
by the way, a dull saw or a dull chisel is not a poor tool. its a worn out tool that is cannot be used as intended. that would be akin to riding a bald DHR II in the rear and blaming lack of control on the DHR II. a DHR II is widely accepted as one of the best tools. run it until it is bald and it's lack of performance has zero to do with it's design. hardly analogous to a carpenter whom can't build a plumb door jamb because he cannot use a bubble level or plumb bob, then blames it on the otherwise performing bubble level or plumb bob.
at the end of the day, pedal stroke efficiency is not binary, and each of us, pros included, can work to improve our pedal strokes in pursuit of the perfect motion....just like every carpenter can hone their skills in pursuit of the perfect cut or angle. an easier way to say it: improve your pedal stroke, and you improve EVERY bike, even the best ones...
technically any piston driven system pulses...turbines and electrical motors do not. but all of those piston driven systems operate at much higher RPMs [than the cadence of our legs] that increase frequency, smoothing out the response.
What? Stop pedaling? If you're not pedaling of course there is no bob. Is that supposed to be some kind of revelation?
if you'd take a break from your obsession with being right for just a second, you might be able to acknowledge that PEDAL bob has many variables, one of which is PEDAL stroke. you admitted you didn't want to consider it, because achieving a perfect pedal stroke is not possible. enjoy being a carpenter whom has no interest in pursuing perfection of your craft. #revelation
Each ticket gives you x amount of KG's.
This includes, checked bags, carry ons and your fat ass.
International is no problem but AU internal airlines are thieves.
If I can get my 5” trail bike in domestic flight luggage without paying the $70 excess I can ride most stuff and put the savings to better use at the pub post ride.
£300 bag, plus bike fee, plus overgeight fee straight away.
A box is 100% the way to go, last saturday I carried my 15.5kg porker, shoes, half lid and pads, all weighted 23kg
BTW, for the euro crowd, Ryanair sucks and bike fee is £60/flight, but their allow up to 30kg
Loving the Norwegian sense of humour (?).
Maybe they should have extended rights then?
Blaming the food industry for trying to do what it's designed to do (making money from selling food) by the typical "make it cheap, sell it fast" model makes it easier to live with our shitty food choices. Truth is, it's on us to eat healthy, there are plenty of options in most places.
Anyone who is obese has no one to blame but themselves. Sorry.
Yes. Sometimes people's lives are hard and things get them down so they might eat.
But it's their choice.
They could do something else to make themselves feel better.
I don't know about everyone else but I feel best after I've exercised.
Not after eating bad food...
They do distribute passengers in a half empty plane to make the thing more stable though.
In classical physics, yes, the system mass is what matters going uphill.
But humans aren't machines, and we are maybe pedaling with a frequency of 1-2Hz up a steep climb. Every pedal stroke cause acceleration & deceleration. How does doing this over and over again play in?
How that weight on the frame is distributed has a huge affect on handling, so it's hard to blanket-condone strapping weight to a bike willy-nilly for downhill handling benefit.
I'd also note that my bikepacking rig handles a lot better if I put as much weight as possible on my back. Getting a comfy hydration backpack for much of my water rather than having it on the bike made it handle a lot better for bikepacking on anything but smooth terrain.
Pumping the bike through terrain, and weighting/unweighting it at appropriate times, hugely affects downhill performance. The heavier the bike, the harder to weight/unweight it at appropriate times to absorb terrain (which is more effective than letting the suspension do it all).
This is mostly relevant to bikepacking, btw. Small amounts of water/tools/etc. has a far less dramatic difference. Smashing through rock gardens with 3L of water and food on your back is way different than if that 3L of water and food was on the bike, moving up and down more with every bike movement.
Rotating weight really is a factor
The one thing I can say, it is a lot cheaper to lose body weight than bike weight.
Your body's strength to weight ratio is much more important than the weight of your bicycle.
Adding weight to a bike affects a lighter rider more than it does a heavier rider - given the same strength to weight ratio between the two riders.
Heavier riders should have better working suspension due to the sprung/unsprung mass ratio, hence the different riding styles between heavier and lighter riders...
Heavier/more robust components are more required for heavier riders as the forces they are putting on the equipment (think hard cornering on wheels & tires) is greater?
The big counterargument is that a bike that feels faster and lighter is more fun, even if it hardly gets you up the hill faster.
But is reducing the roller coaster effect really what we want in mountain biking? For pure racers, yes. But if you're in it for the fun, it's better if it feels fast but is slow, than the other way around.
You explain most of your conclusions based on a "system weight" and while I think that's relevant for sitting and spinning style climbing and maybe sitting and cruising descending (who does that?)... most of other times we're riding our bikes, our bodies and body weight is actually quite disconnected from the bike and it's weight. A lot of the time spent on our bikes is using our body to manipulate the weight of the bike... and so I think many of the percentages you talk about substantially increase when you take away body weight from the system weight.... and there's where you really feel weight differences.
For example... I've been experimenting with various inserts, tire casings and wheel weights for the past few years (I'm an "ambassador" for a few companies which allows me to easily swap stuff around without too much cost)... I've settled on EXO+ casings, Tannus Tubless inserts and a lighter "all mountain" rim (vs enduro). My wheel system weight is actually quite light while being extremely robust and yet supple. Yes, during sitting and spinning climbing, there is almost zero perceivable difference. I thought I could feel a difference at first but that perceived difference seemed to disappear within a few minutes... it was likely psychological. But where I do notice a big difference is on slow very technical climbing sections where I not only need to very quickly accelerate my bike from a very slow speed, but also "hump" my front wheel (followed by my rear wheel) up and over large technical terrain... similar to Pinkbike's "Impossible climbs". That's where system weight, bike weight, wheel system weight and unsrung/sprung mass ratio all seem to separate and you feel the differences. At the same time, I think those percentages multiple exponentially when you also factor "tired-ness" or "fitness" into that same scenario I just described. For a given "impossible climb"... a lighter frame and wheel set is definitely more noticeable once I'm reaching the ending of that climb and I'm breathing through my eyeballs... a 1% difference feels like 50%.
I'd also argue that there are large portions of descending where I smashing through a fast technical descent where I'm pulling and pushing my bike up around and through sections.. sections where the bike is being forced back up into me and I have to control that, sections where you've got to use a lot of body-bike separation to gain grip or control the bike... fast technical corners... slow technical corners, drops, jumps, etc, etc. I'd argue these are other areas where the body weight, bike weight and wheel and unsprung/sprung ratios start to separate themselves from a total "system weight" and various weight differences can be felt more and less in various scenarios.
I don't think comparing the system weight of a bike can be compared to motorsport where the rider/driver is much more a passenger controlling a very heavy machine through much more disconnected means (motocross probably has some crossover there), vs a bike rider who controls a very light (comparatively) bike through very direct means partly with their own weight against the bike's weight.
End of the day... I believe it's much, much more complicated and there are many instances when riding a bike where you can easily feel much more that a 1% difference in various weights. At the same time... I don't think you need to be super careful or spent crazy amounts of money to save weight.. but you do need to carefully consider where you're putting that weight and what ultimately kind of riding you do and what you need out of your total system.
This is coming from someone riding an aggressive 36.5 lb long travel enduro bike.
"In particular, when bunnyhopping, pumping, carrying your bike, or technical climbs involving manoeuvring the bike up and over obstacles; a kilogram on the bike may count more than a kilogram on the rider here."
GMBN on the case a year ago, just changing tyres.
There usually is a rider in the rider-bicycle system, and it is much more fruitful to look at the total moment of inertia of the rider-bicycle-system. The difference with +1-2kg of mass, and +2» wheelsize becomes negligible to the total moment of inertia of the system, your monthly weight fluctuations during the darl hours of Netflix-season are probably more significant.
It is simply a matter of «feel» to the bicycle
So maybe several bike models with similar components and control tires. But have both the carbon and alloy version of the bike. Or at least add 1 or 2 kg to carbon bikes to emulate the alloy. Having several models with different suspension designs would be interesting too.
And while your at it, run the same bikes with both alloy and carbon wheels or add heavy inserts to look at rotating mass.
And finally, don't do just a 3 min climb up a dirt road. Try several roads with different gradients and/or at least make the climbs closer to 30 min long. This may help explain the benefits of weight difference in qualitative terms as well as quantitative. The sluggish 'feeling' of a bike may also be a factor to consider even if the time differences aren't drastic.
I know there have been other attempts to do this but none have been done properly or have been extensive enough to be conclusive.
The simple gravity effect on a pound or two is simple enough and small enough but doesn't even closely to tell the story of actually riding a mountain bike.
Doesn't experience just riding bikes make this obvious?
The Ripmo weighs 31.2lbs (pedals, bottle cage, sealant, ready to ride)
It runs an Assegai up front and a Dissector in the rear.
The Exie weighs 24.7 lbs (pedals, bottle cage, sealant, ready to ride)
I run a burlier tire set up than stock
Dissector up front, Rekon in the rear
There’s a 6.5 lb difference between the bikes, so that should translate to around a 3% differ even in the real world between the two.
I ride the Ripmo on a trail system on a Saturday and then ride the same trail system on the Sunday on the Exie. the idea being I ride the lighter bike when I have been riding for the past 6 days.
Across a 20 km (12.47 miles) ride my average speed on the Exie is 1.8 kph faster (1.11 mph)
- Clearly the Exie is more than 3% faster
- The Assegai tires obviously have more resistance
- The trails clearly don’t NEED the extra capabilities of the Ripmo, and the ones that do, I’m sure the Exie would fair much worse.
- 1.8 KPH never felt so much fun. I love my Ripmo, but on flowing trails with mild rock features, technical climbs and lots of twists and turns, you just cant beat a lighter bike.
Of course there are diminishing returns, and it depends on your disposable income to figure out if its worth it for you.
My Ripmo is a lightest build for a 160/147 bike, but my Zipp 3zeromoto rims are not the lightest because I need the bike to be built strong enough to be reliable for the type of riding it was built to do.
Same with the Exie, I got rid of the lighter tires it came with because they wont work where I ride the bike. I added some weight, but a lot of use ability.
The ultimate solution for the non beneficial unsprung weight on a bike would involve the G word....
People (especially men) like measuring things and comparing the measurements to see which wins. The weight of a bike is one of the very few things we can compare like-for-like.
Worth the watch on YouTube as he discussed the affect of the extra weight quite extensively.
Tl/dr it was pretty negligible on a climb of 1,000 meters that took a little over an hour.
A lot of the weight reduction is in the wheels: 1500gram carbon wheels vs 1800 gram alloy wheels + 900gram single ply tires vs 1100+ gram dual ply tires. My guess is the wheels are where most of the change in feeling comes from. I'd like to try the light wheels on the Smash to feel the difference, but unfortunately the bikes use different dish offsets, so swapping is a pain.
I have a yt capra single speed and no dropper at around 13.5kg, when I jump on my friends whatever enduro bike at 15+kg it feels like a brick and I can't throw it around as easily. Bigger than 1% difference for sure.
Not quite sure that's how it works...
A big reason Brosnan might run 220s in the back is for the extra thermal mass and extra surface area to keep them cool, especially since the air flow over the rear brakes isn't as ideal for cooling.
After a lot of testing I have Long since started not looking at total weight, just focusing om rotational weight/mass.
That's why spec levels such as "Carbon comp", light frame with heavy wheels, are badly spent money.
That's also why I ride a Knolly with light wheels (and optimized tires, light cassette, cranks)
How many more percent of bicep flex to compensate for 1kg of added weight?
How many sets of how many curls needs to be done to make it the same perceived effort?
How many dollars spent on protein supplements?
@seb-stott we need answers!
Those bikes are mountain bikes - not hardcore bikepark bikes.Superb uphill, downhill and carrying performance, over the top and up to date suspension. Long story short: lightweight but including a ton of fun, easy to throw around in tight corners but 160mm of travel.
Made for the mountains and not necessarily the bike parks, but the Bronson is also fun to ride in a park - maybe it needs a different tire setup.
Would I change one of those bikes with a super heavy 15-16kg (without pedals) truck? No way!!!!
Idk that actually knows physics should confirm deny for us ;P.
There are some aspects of reality one cannot translate into physics.
A better example would be to take a 5 lb dumbell and try to move it in a circle with your arms extended, then try to do the same with 8 or 10lbs, it may only be 3-5 lbs but it will feel very different.
With that said I get what everyone means here and why there is such a resentment towards weight arguments. It's somewhat ridiculous when people are arguing over a hundred grams that may noticeably effect the quality of the bike in a negative way (rotors or cranks or something idk). I just think if people truly don't think weight doesn't matter they are fooling themselves because if you've ridden two bikes back to back that are the same other than 5lbs of weight, it's pretty obvious. Weight matters, it's just that function and practicality almost always matter more (not to mention $$$).
You can't cherry pick the parts that support one part of the theory and skip the rest because it doesn't fit or is too complicated.
Either ride your bike because it's fun, whatever bike you have (light/heavy/cheap/expensive/fast/slow).
Ride against 'the clock' and it will tell you what's fastest.
Doesn't that also mean 29ers don't carry more momentum just because they're bigger...
"This means that if you had a 29" wheel/tire that weighed the same as a 27.5" wheel and tire, the acceleration would be the same. Of course, a like-for-like wheel or tire will be heavier in 29", but only by about a hundred grams or so."
... they carry more momentum just because the wheels are heavier.
This is an extreme example but I was recently riding with my son on the shotgun seat up a reasonably steep climb, and anytime my cadence would drop a little too low it got much harder to pedal. That's not only because I was below the optimal RPM range for making power, but also because the bike would slow noticeably between each pedal stroke and every push was accelerating us again. The extra 30lbs on board make that painfully clear.
I'd also chime in with the others that wheel/tire weight makes a super tangible difference in feel. Whether or not it affects your speed, the weight of your tires can really change your bik's manners. Traction and flat protection are obviously higher priorities but lightness is fun!
I dunno… is it tires? Frame?
Im willing to be a 2” tired carbon hard tail at 20lbs would be a rocket ship uphill. Absolute trash on the downs.
I guess my take from it is, you would be better off spending money in to skills lessons, and or fitness training. You'll get more than 1% speed from both easily.
That or chuck the money saved in to some investment and just buy an ebike in a few years...?
I'd point out that a good portion of the rider weight is basically what powers the system - mainly muscles - wheras the bike is "dead mass". The same way you could argue that ride weight does not matter when climbing if you only add muscles. Which btw would also be wrong as a bodybuilder type might be good at sprints but not on usual mtb tracks.
Second thing is that there is much more then purely weight what drives the efficiency of a bike. From geometry to weight discribution and the characteristics of different materials regarding flex etc. (carbon). Not to mention the effects on how a bike handles.
Even downhill bikes got a lot lighter during the past 10 years for a good reason.
I would argue that most riders benefit more from the handling of a lighter bike than from more reliable parts. With my 72 kg naked I have actually never had problems with lighter parts (not super light). Might be different for heavier riders but looking at e-mtb the current parts can take a lot of force/abuse even the top range / light parts.
I've tried 7 different bikes on the same track, recording them with my Garmin.
It's clear that on the road a lighter bike is faster.
Off road it's a mix, a light bike and good suspension is the more efficient. For example the Spark 910 is light but the suspension is too active in trail mode, so the front lifts and it's difficult to have grip on the front.
In the descends the minimal packaging is a real trail bike (not the Spark 910). Bigger bikes are adapted to bikers that are really fast and need a strong bike. Personally with these bigger bikes like the Propain Spindrift, Ghost Riot EN, I was slower compares to my Propain Hugene 2019.
The new one is really better, no bobbing, more sensible suspension, light and funny. For trail bikers like me it's the top.
Get a bike, time it up a chunky climb using a power meter, then start swapping wheels, tires, adding weight, and so on to test the actual results. Of course the power meter is a large part of the story, but adding 3#s to your fork for instance will likely result in extra upper body exhaustion even if it barely registers on the power meter/ stopwatch.
If you race elite XC and you’re getting results (and no sponsor) get a sturdier second bike (or at least some beefier wheels/tires). Otherwise, if speed is what you seek, hire coaches for skills and training and get a powemeter. Get under 10% body fat. If you can’t easily send 2m (6ft) drops and put out sustained 5w/kg climbing, a light bike is just a colossal waste of money.
We are starting to see more success by coasting through rough sections instead of sprinting through the bumps then braking hard for the next corner. Pedalling the smooth line instead of pedalling through bumps then using that saved energy to pedal hard on the fully smooth sections or to absorb a faster line in the rough non-pedal downhill sections. Light bikes helps with bike control
Hardly a 1 kg difference.
(And the equations in this article miss the rotational energy associated with wheels. Heavy wheels are a bigger deal than other heavy parts. And in addition to obvious weight issues, they also have gyroscopic effects.)
But all things said, losing weight off your belly is far better than paying to drop weight from your bike.
Mate, that's a good weight for a mid-range XC bike these days.
With 29in wheels and the stronger tyres and forks we want on our longer-travel bikes, 32lb-34lb is a good weight - and 35lb is quite reasonable for an entry level bike or a heavy duty enduro bike.
And those bikes are WAY out of the common folks' price range. They also have geometry that's too aggressive for most real-world riders.
"Good weight" isn't determined by what is available, it's determined by what actually complements the rider. For someone who's 6'3" 220 lb, 35 lb is one thing. For a 150 lb rider who doesn't need a bike to be bombproof, (or even worse, for a 5'3" 110 lb woman) it's completely different. For me, the ability, ease, & comfort of moving a 25 lb bike beneath me compared to a 35 lb one is significant, and the heavier bike is less fun to the point that it's not worth buying--I'll stick with the old school bikes.
The industry makes premium bikes for racers, for rough terrain, jumping, etc., and the low-end bikes are just cheaper versions of the same thing. Bikes are WAY more stout than they used to be. Big wheels mean everything else gets heavier, too, especially to maintain consistent rigidity. And the same goes for longer travel suspension. All that adds up, and that's why to get lightweight, you have to pay through the nose.
And that's the problem. Not every bike needs to be a Raptor or a Corvette. A Miata is not only perfectly viable, it's actually MORE FUN in most cases despite being slower. That's the hole I see in today's market. I believe for the skill & interest of the majority of riders (and potential riders), and for the intensity that they will actually ride, a simpler, lighter, smaller, less-travel, less aggressive bike would be more entertaining, engaging, and rewarding for them, and you can still get them to pay a mild premium for it.
Replacing the air in your tires with helium will make you faster.
Putting lighter oil in your shock and fork will make you faster
Riding naked ( less weight) will make you faster
Ti water bottle bolts make you faster
Drink water with the heavy water molecules removed will make you faster.
Lessons will make you faster but don't distract from the $/g/speed thing... this is actually the most efficient as g=0 so benefit is infinity...sorry no math...
Loved the nerd out, I am a gram counter on my gear and get great joy from having the perfect $/g/speed for me.
Love the debate we all love to geek out on the cool parts etc… but we never really look in the mirror!
Ps. I'm actually 9.5% BF atm.
Especially since Geometry and bike length has hit its extreme and even snapped back a bit (e.g. the new Capra). You could theoretically keep a bike a long time with some upgrades and be good!
Well, yeah... might be something other than the weight of the bike, son.
Try this: go for a ride with an empty 20oz water bottle on your bike. Then fill 'er up and do the same ride. Better yet, have your wife randomly fill or not fill the bottle (don't use a transparent bottle) a few times.
Can you tell? No, you cannot.
There is actually lots of good research on the "just noticeable difference" though as far as I know nobody has studied it with bikes. If a 1% difference (all other factors like frame geometry/parts/travel being equal) is perceptible it would be... quite a finding.
Here are a few examples from a quick Google search. If you are already small, super light and in excellent condition, bike weight will matter some, but not that much. I just can't see how 8oz/200g of weight makes a big difference. If I was 5'4 and weight 112 lbs, then maybe I might notice something like that. Of course, there's the placebo effect of knowing your bike is lighter.
2lbs/1 kilo of weight in the overall system of rider + bike + load weight total doesn't matter for most people. If a rider weighs 200lbs and their bike weighs 27 lbs., plus 5 lbs. of clothing/shoes/water bottle etc., we get ~235 lbs. 2lb / 235 lbs. = .00851 or 0.851% total weight. That amount is statistically insignificant and will not matter. Downvote me all you want,
Guys are people too...
Off to buy some titanium bolts.
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