E-thirteen built its rotational-inertia demonstrator to assure its wheel customers that the slight amount of additional weight of its Chubb hubs is easily offset by the use of a lighter-weight spokes and rims. Their science experiment, however, has greater ramifications.
Almost every cyclists insists that, if two wheels weigh the same, the one with the lighter rim and tire will accelerate faster - but where is the proof? Every wheel review worth reading either states or implies that there is a noticeable difference when accelerating a lighter or heavier wheel, but just how significant that effect may be, or whether it is largely a figment of the test rider's imagination has been cause for an endless round of debate. Add the wheel-diameter war to the equation and the discussion becomes less scientific and more emotional. Until now, however, the argument has been an intellectual one.
Because the tire is wheel's heaviest component, by nature, a 29er wheel should be the worst offender of the three diameters, yet the 29er's popularity among XC racers, where quick acceleration and climbing are of paramount importance, suggest that some of the advantages that big-wheel users espouse as scientific fact would be better classified as cycling religion. Evidently, e-thirteen has provided a definitive answer and, while the conclusion should not come as a surprise, when the results are physically demonstrated, arguments to the contrary are laughable.
Watch and Learn E-thirteen, came to Eurobike 2014 with a simple science project, inspired by a hands-on display at the San Francisco Museum of Science and Industry. The experiment consists of two identical wheels of equal weight and diameter that roll down a steel track. The plastic wheels are weighted with brass cylinders. One with the cylinders positioned at the outer extreme of the wheel and a second, with the brass inserts positioned near the hub. If you don't want to bother watching the 15-second video, the wheel with the mass situated near the hub accelerates dramatically faster than the one which is configured in the opposite way.
Draw your own conclusions, but the results of e-thirteen's demonstration suggests that proponents of 26-inch wheels should not be discounted as the sport's angry villagers, reticent to accept any sort of change. The past two World Cup XC races were won on mid-sized wheels, which further undermines the once solidly held belief that big wheels are destined to rule that category. Perhaps the wheel debate deserves a less emotional and a more scientific re-evaluation.
The torque required to spin a wheel with a certain angular acceleration is equal to the cross product (multiplication for simple cases) of the desired angular acceleration and the moment of inertia. Angular acceleration is just a rotational form of linear velocity. the radius of the wheel multiplied by the angular acceleration is the linear velocity (bike speed).
The moment of inertia for a round object is just the total weight of that object (well, mass..) multiplied twice by the radius of the wheel. So, if you consider the torque you apply to the wheel as your effort or "how hard it is to pedal" and assume you want to accelerate at a certain rate, the ONLY way you can argue that a wheel accelerates faster is either that it is lighter, or has a smaller radius. By this we also see that the effort(torque) is way more dependent on the radius of the wheel than it's mass.
In laymans terms, the size of the wheel, has a ton more impact on how hard it is to accelerate that how much it weighs. 29ers are waaaay lighter than normal rims, and that's how they compensate for the added radius
"Works on paper...I don't see the problem..."
Lol...
27.2...for trendy pussies who can't commit...
I should be in advertising... lol
And @dirteveryday,
You should only hate on engineers that gradually increase tech, when they can just go to the top end products without any added effort. We are here to make things better, not extort the public.
In this case I think it would be better to put it as dω/dt x I = τ. This always holds true, regardless of the terrain. For a bike dω/dt = (dv/dt)/r, where r is the radius of the wheel. For a bike, all of this is purely linear so the cross product can be simplified to mr(dv/dt) = τ. Taking that a step further, the trail exerts some resistance on your wheel, which I will just call τ (it's really r x F_trail). So the equation for the amount of force you need to apply to the pedal can be written as mr(dv/dt) = τ-(r_crank x F).
Also, you said "the radius of the wheel multiplied by the angular acceleration is the linear velocity". This is false. That would equal the linear acceleration.
THE TAKE AWAY:
The force you need to make your bike accelerate a certain amount is directly proportional to the mass of the rim (because this is simplified) and the radius of the wheel. Decreasing wheel mass offsets increasing the radius. With 27.5" wheels, you would have to buy rims that are about 95% the weight of 26" rims to get the same acceleration.
The weight is placed 2-3 times further out (200-300%), where when we talk wheel size from 26-29 we are only talking about a increase in 9%. This test unless I am mistaken is hugely exaggerated at least if we discuss wheel size.
As for the hub argument they are proving their point that more weight center to the wheel allowing a reduction in the outer weight is beneficial.
@taquitos and @bullitproof
Is there not a point where the more inertia from the larger wheel will promote faster acceleration at a specific speed and therefore we receive a cross over effect.
Really the question is, what wheel size is more effective for my average speed over the track. faster here and there means nothing its all about the overall time. Hence the 29er xc move.
No. Bigger wheels at the same mass are always harder to accelerate.
rims for each purpose (compare XC rim with XC rim, or DH with DH) would always be lighter in a smaller diameter.
Roval Traversee 29'er rim in aluminium alloy on my XC bike is 412 grammes, I only know because I stripped the wheel to rebuild with new spokes and nipples and was surprised how light the rim actually was for its size, its quite wide too.
I have not weighed any comparable 26" or 650b rims in this category recently
all my previous rims were FR / DH so obviously heavier even in the smaller 26" size
And yeah, it's essentially the same, but a lot of people don't seem to get that "carrying speed better" is just the same as "accelerating slower" (deceleration is just negative acceleration)
Just a reminder that the inertia thing cuts both ways. The same inertia that makes the 9er harder to get up to speed is going to make it retain speed better than a smaller wheel, and that's without even taking into account the rollover (angle of attack) characteristics of each size.
"yet the 29er's popularity among XC racers, where quick acceleration and climbing are of paramount importance, suggest that some of the advantages that big-wheel users espouse as scientific fact would be better classified as cycling religion."
This, like the whole article, is just pointless provocatuer shit. It's not that there's some 29er religion or that people haven't known all this LITERALLY SINCE THE FIRST DAY 29ERS APPEARED. The point is that XC racers have determined that the more difficult acceleration is an acceptable tradeoff for the rollover and traction advantages. And especially for bikes that are meant to be ridden on rough terrain, the rollover will have a much greater impact on overall efficiency and energy expenditure than the inertial mass of the wheel (to a point.... I don't expect XC 32" wheels to be a thing anytime soon).
Yes, many recent XC races have been won on smaller wheels, but this only reinforces the point that there is an optimal diameter (specific to the rider, probably) that balances the terrain-smoothing efficiency of a larger wheel with the snappy acceleration of a smaller one. That, along with bike geometry implications, will drive people's wheel choices. But XC racers won't be going to 26" or 24" wheels for snappy acceleration anytime soon, because acceleration isn't the only variable in the equation.
But I think the real advantages of bigger wheels is the improved geometry it allows: you're not going to get 15mm of BB drop on a 26" bike, you can usually steepen the head angle & reduce travel while still retaining the same level of descending ability, etc.
After testing a few 29ers I can say one thing: if you want a fun bike not a freaking train wagon: you need carbon rims and light ust single ply tyres. Another thing I know about big wheels: roll over is bullshit - just let out some tyre pressure of your small wheels and tadaaaaa!
Yeah, getting a 29er spinning is slower than a 26er, but on a hardtail the acceleration and power transfer are so snappy that I don't notice too much. I've had an awesome time riding my roommate's 29er HT. And I love riding my CX bike on singletrack, which is more less a rigid 29er. I've yet to ride a 29er FS that didn't feel tippy and handle like a canoe though. For FS bikes I definitely prefer 26" or 27.5", especially cuz you can get similar "rollover" from the suspension and tires. Soon I hope to own a 27.5 hardtail though.... I think that would be my ideal bike. I've really liked the few 27.5 bikes I've tried.
www.sjbmw.com/_images/parts/28_lg.gif
#shutthef*ckupaboutwheelsizes
and yes the derivative form is actually the correct (mathematically) way to write these equations. there is no measure of velocity that we have (yes, bombshell) velocity is just the rate of change of position (acceleration, the rate of change of the rate of change of position)
yeah I guess acceleration was the wrong word. My point was that the heavier object might reach a given speed faster because it suffers more inertia and therefore less deceleration. So the time it takes to get back up to speed may actually be faster than that of a lighter wheel due to the improved inertia. We never ride stop start we are always rolling or have some momentum.
If the inertia of the heavier wheel results in less deceleration than the time ti takes to get back to speed X may be shorter than that of a smaller lighter wheel as it suffers more from deceleration. Once we add in bumps and uneven ground the argument that a larger wheel is better continues to grow.
www.bike-advisor.com/wp-content/uploads/2013/01/wheel_27_5_650B_1.jpg
the difference of less rolling resistance is scientifically correct, but is it effective? without tests, i say a ~1 degree change in attack angle does not constitute a better platform.
in response to the inertia comment, it is the LINEAR momentum of the bike that we are concerned about. when a bike impacts a bump, it produces a force that acts 90 degrees to the surface of the wheel (this is actually what makes wheels useful). this does not create any torque on the wheel, which does not affect its rotational speed. what you have to consider is the horizontal and vertical components of that perpendicular force. the vertical component will not interact with the horizontal motion of the bike, and gets stored as gravitational energy/dispersed by the dampers. the horizontal force will change the bikes velocity, regardless of magnitude. the size of the horizontal component is determined by the angle of attack (defined above in the link) that the bump creates with the wheel.
to take away:
slowing the wheel down has less of an effect on the linear velocity of the bike than the horizontal force acting on the bike as a whole (through the wheel). heres a nifty home experiment (for everyone, at your own risk): try skidding to a stop (a stoppage of the wheels angular momentum), and then hit a brick wall (a horizontal force) at the same speed.
1) if given the SAME diameter round objects (both objects in video are the same diameter, the only difference is weight distribution),
2) and if ignoring opposing forces from the "trail" (the only opposing force demonstrated here is at or near the axis of objects, not friction at the radius due to the trail which is what most of us call rolling resistance, and air I guess, negligible)
3) and constant acceleration due to gravity (the linear and static track, not dynamic like trails, with bumps and more so infinitely long)...
Drum roll please: More weight toward the center of a object will accelerate that object more quickly laterally than if the if that same weight is positioned to the outside of an object of similar size and overall weight. Assuming the above^^^which this experiment represents. So to relate to bikes...if two 26" wheels that weight the same are rolling down a flat hill, the one with a higher mass density near the axis (light rim/ heavy hub) will ACCELERATE more quickly than the one with higher mass density near the rim (heavy rim/light hub).
A longer track with bumps and variable elevation would show that the outside weighted object would have a higher lateral speed and not decelerate at bumps and hills as quickly as the other.
www.pinkbike.com/photo/11354970
Angle of attack difference between 29" and 26" for a 6 cm obstacle is about 4 degrees (which isn't too far off from what's quoted in Giant's literature). More importantly, if you look at the cosine of that angle, which determines how much of the impact force will oppose your forward movement ("slow-down force") you can see there's a pretty big difference. Obviously if the object is much taller than a few cm you'll be lifting the front wheel or bunny hopping over it, so the difference will be less meaningful. But basically for objects in the 4-10 cm range the 29er or 650b will slow down a lot less than a 26" would.
Anyway, this is a lot more detail than this article requires, but I just wanted to show that rollover isn't some myth or something you can only "feel", you can actually calculate it.
Ah and the actual roll over (how much energy is lost by encountering an obstacle) depends also on tyre pressure and suspension quality (hardness, setup)
Let's say;
26 wheel takes 5seconds to accelerate 10mph. (0.5/1mph)
29 wheel takes 7seconds to accelerate 10mph. (0.7/1mph)
The smaller lighter wheel will always accelerate faster, but if we are riding a trail doing 20mph and we hit and obstacle or corner and the wheels slow down.
26 slows down to 10mph
29 suffer less deceleration and slows down to 13mph.
Now to get back to 20mph the the 26 will take 5seconds. But the 29er will only take 4.9seconds. Hence faster. While the 26 has a fast acceleration rate, the time it takes to get back to speed is actually less for the larger wheel due to its other benefits. For riders the critical number is the overall not one isolated factor.
If it slowed down say to 12 it would take 0.6sec longer but than you need to consider that the bike is travelling 2mph faster in the section prior before acceleration which more than likely will off set this and reduce time overall.
My point is acceleration is a factor but it's part of the larger equation.
>The same inertia that makes the 9er harder to get up to speed is going to make it retain speed better than a smaller wheel
>The point is that XC racers have determined that the more difficult acceleration is an acceptable tradeoff for the rollover and traction >advantages.
All the clue is in these words. That's all I wanted to write untill read that.
Well done, bkm303!
Look at the video: note how longER the second wheel rotates.
Ofcourse! Naturally! because of greater inertia caused by it's periferial weight.
Accelerates slower, rotates longer. Accelerates quicker, rotates shorter.
About rollover and traction - that just obviously: there is much more probability you fly over your habdlebar hittihg the border stone with 26" wheel than 29" wheel. (fork the same, bike the same)
Just try.
I personally have an isuue 2 time with 26": first time flipp over bars uncontrolled and fall down, the second - almost flipped, just controlled and not falling down.
On 29" - never flipp over the same border.
That's just one of the example of rollover.
So the acceleration is not the main goal. It's just a ONE OF.
Moreover, you need to accelerate-and-accelerate again and again on smaller wheels than on bigger!
Isn't it obvious ???
On the bigger wheels you accelerate slightly slower but when got accelerated you see the speed is becoming terryfying and you think: oh, shit, I need to slower down a little!
Isn't it ? I notice that every time riding.
I personally like both 26' and 29'
Just buy reliable 26 and as much reliable and light 29. Thats all.
I have never ever went over the bars because of the wheel size, cockpit setup, frame geometry or suspension quality. I do not think anyone ever did. People fall because A they make mistakes, and B-sht happens. While 29e rmay save you from 2% of OTBs, it will punish you somerhwere else, like in corners. If you get your balance wrong in the corner on 26", then it is relatively saveable, slight countersteer, hip adjustment, weight shift - things can turn out ok. On a 29er, due to inertia and BB drop stability it is not as easy (given similar wheels, cockpit and frame/suspension design). Once set on certain course, the 29er will always have a mind of it's own, even the best one. That is particularly visible when you want to change your line on a wide trail, or avoid an obstacle. Short note here: I experienced 275 wheels to be much closer in that respect to 29er than to 26.
> the test shows ONLY the acceleration.
Yep, and NOTHING MORE. Did I tell the contrary?
It was obvious without any "scientific" test-video-shows that higher weight accelerating slowly than lower weight whatever it could be: wheel or etc. But the same time lighter wheel stops ALSO FASTER than hevier. And this has much more meaning.
Acceleration is NOT THE MAIN GOAL, but just the ONE OF parameters.
Want to accelerate faster ? Shift to larger rear gear. You've got a damn 9-11 pcs of them for what, how do you think ?
>In Xc the human factor is so dominating that the size does not matter for efficiency.
Phuhahh! What are you talking about...This Just about nothing - finger in the sky.
And by that logic the DH crowd are just differrent bunch of the equaly acting subjects ????
They ride what are they told to ride: expensive suspension bikes, that bad on pedalling, with fat heavy tires, 3.5kg heavy forks.
That's it ?
Man, let's talk about real parameters in comaprision. Otherwise it just a flooding non usable text.
Look at fresh videos on pinkbike: the same guys that done a slopstyle 2 weeks ago now running the DH rampage these days.
I'm pretty sure they could blast the XC trails as well.
Size of the wheel do matter.
And the "efficciency" is very wide definition. What is it is this case ?
If your goal to accelerate faster - go 26". But don't forget about you will slower faster also, and worse to rollover the obstacles.
But with 26" the bike is more compact and better controlled on the very cool corners.
That age common known obvious things. Anyone was absent at school riding bikes???
Same time, who cares obstacles when flying over ?
The wheel size is objective measurable parameter. It IS in reality and one could measure and try it.
***One should/must choose the wheel size&tires, geometry for the given terrain/trail - that is the goal.
***So one who does not race at highest level may wish to take it easy. And remember that Should is a weapon invented by teachers and preachers, Musts are always optional, Mays are closest to reality
based on the argument you make,the logical conclusion would be for xc racers to make their bikes as heavy as possible, in order to make their bike retain speed better. this is obviously wrong.....
No it's not. That is a ridiculous exaggeration. We are talking about the offset of wheels here and the trade off. You know that making a frame heavier would hurt the ride rather than help it.
In the argument for wheel size what I am saying is correct but don't blow that up and start exaggerating that and applying it to everything. Your focusing too much on one aspect and not the overall picture.
>With all due respect, I do not care much for parameters,
Much...how much ? That becomes obvious from your last posts. Bad luck.
>as the sole fact of possessing any wider knowledge in the subject makes it very hard for you to attain any serious riding skills, >UNLESS you work in bicycle industry.
It is only when one have very bad understanding and visualising skills.
Or, if you want, stop to be a user - become a producer. (designer, manufacturer)
I personally do not make anyone to possess deep knowledge here.
But there are a fundamental things anyone should know(even must). They just obvious and must not be perverted by bla bla bla even when this bla bla bla armed with the words about a deep knowledge.
Understanding a fundamentals( = be able to visualise) one then make a choice according to terrain or etc., go riding and then using his own natural means gets the skills. Then binding the fundamentals' sceleton with the skills one reach the goals.
>***So one who does not race at highest level may wish to take it easy.
If one take it too much easy, he rescue to crash. Very often from the second try, cause the first try often lead by the God ))
One must not take it easy. But at the same time one should not be stu..rictly a user who just buy only THAT $1500 26" wheel "STRICTLY BEST FIT TO DH" as manufacturer suggests.
Again - stop to be a user, try to be designer. And you'll see many things.
Please, do not mess Teachers with preachers.
If we had no Teachers(means real teachers) we have no modern bikes.
...But for what is it all and what about ?
The hevier wheel will always accelerate slower, and so roll-on longer than lighter (in the simple words that everyone can imagine)
These are one of fundamentals nevermind what you MUST OR SHOULD OR MAY OR CAN think about it. I hope till the end of times.
Just know and use it.
***One should/must choose the wheel size&tires, geometry for the given terrain/trail - that is the goal.
erm....no? i was infact looking at the bigger picture rather than just focussing on one small aspect. many people in this thread have made the statement that increased inertia will result in better maintenance of speed and you have been the strongest proponent of this stance. i merely applied this view to the whole bike rather than just the wheels in order to point out how flawed an argument it is. i exaggerated nothing, and calling that ridiculous is, well, ridiculous....
It was adressed for all.
Good luck to you being gigled only by this.
Again, it depends how big you're talking. Mathematically, angle of attack is really straightforward to calculate, but it's really only relevant out to a certain obstacle size. For tiny obstacles (millimeters, for example) the difference is negligible and all the wheels roll over nicely. Then for things in the 1-4" range (roughly) the differences in AoA are pretty significant. Then obviously as you get out to the limiting case (obstacle height >/= wheel radius...a wall) they're all the same again. But beyond around 3-4" angle of attack is not so relevant, because while a 29er might technically roll over an 8" log better than a 26er, only an idiot would just go smashing into it. Same goes for the rock gardens in your example, at a certain point it becomes a matter of technique and not wheel size. Rollover will technically be better in the rock garden, but you'll suck at mountain biking if you rely on it But fire roads and small chunks on trails are where the 29er shines, because of the small obstacles (as you've observed in real life). Which is also why the XC dudes like them, for the long semi-chunky pedaling sections where small efficiency gains are crucial and bike handling technique isn't the main factor.
I said you were looking at one factor with your statement of "that logic suggest xc riders should make their bikes heavier, which we know is not true", That statement is not looking at the whole picture. You focused on my argument of inertia and the advantage of the wheel size based on deceleration than applied it in a one directional argument that " if more weight is better, we should have heavier frames then if that's the case". The bigger picture you would not have said that because as you know in the big picture adding weight to the bike would not make it faster and you know that the argument of the larger wheel is not just down to its weight but its size. In the big picture for wheels though the increase size is beneficial in some instances. I don't think they will be faster for all tracks, it will be track dependent, at least until larger wheels becomes so popular that tracks are tailored to the larger size.
The argument you made was not looking at the big picture and you know that, you took one factor and applied it to suit your argument.
I really don't care who you are. But seems like you have had REALLY BAD teachers )))))
Do you hate your school times ?
I really can't understand why are you started to write to @me and what are you trying to prove ?
Could you explain your goals in strait simple way without bla bla?
You are not agree with a simple natural thing that the hevier wheel accelerates slower but rotates longer ?
You are not agree larger diameter wheel "eats" THE SAME obstacles better than smaller ???
And after that all you call yourself a designer ? Huh, the designer, who are "not much into the parameters" ????!
OMG!!!
You made me giggling I knew a bunch of such, oh, they always think about themselves as a BIG persons.
Could you show us the WORKING READY REAL WHOLE bike of your DESIGN-without-much-into-the-parameters ?
Notice: the DESIGN-without-much-into-the-parameters - that's obligatory!
Or show me the bike of any company or designer-constructor that made without "much into the parameters".
Huhuhu
By the way, the guys you pointed here all know about that fundamentals.
Because TO KNOW is to have experience.
And I KNOW what I wrtie about.
Now, the word MUST - as I always knew, has an obligatory meaning. Not you choose.
And SHOULD - is kind of an optional meaning, if you want something, you should....if not - shouldn't. You choose.
MAY has always the mirrored tweeny called "OR MAY NOT"
But that doodling is already bored me really. I like both wheel sizes really and moreover, I know the reason why they act like they do and why I LIKE IT!
Who don't want to know the reasons - let them don't. Their time will come.
I have a proposal for you: make me a full suspension frame of my design. The design will be based bsically on Mongoose Pinn'r but with some improvements/mods to have more versatility.
What could you say about that?
www.youtube.com/watch?v=7m1h0Hf5uMs
a) flattens out and then
b) includes a small "bump" in the track over which the weighted discs roll
otherwise the lambasting will likely continue.
The rougher the track the bigger the 29" advantage.
Pointing out that Nino won the last two World Cups? Sure he's the best XC rider in the world so what a surprise that is! Oh and by the way, Absalon won the overall, on a 29".
29 wheels may accelerate slower, but they don't need to get to as high an RPM - a 29er at 20km/hr is going to have wheels which are rotating at a lower RPM than the equivalent 26' bike. Does this balance out though? Dunno.
While the weights need to be off set obviously you cant have 100 gram hub and only ave 10grams at the rim, if the saving is comparable this just shows that having central weight is better.
As for the wheel debate factor, its massively skewed. the weights are placed about 3times (300%) the distance apart, when in reality a size change from 26 to 29 is only about a 9% increase. Really they need a to scale wheel set up with realistically placed weight.
Has no one learned that a good trait is good in balance with other traits? EVERYTHING is a trade off. No one rides 24" wheels to get extra maneuverability at the WC level do they? It trades off too much. In DH 29" wheels trade off too much on the other end. That leaves 26 and 27.5" wheels. It seems the teams and the market are speaking very loudly.
Man, it's not as much needed if just to notice how longer rolls-out the wheel with the masses on the periferial.
It is stopping much longer, noticably longer without any additional means
And one who has a brain can think and imagine the futher results of it.
But you are rightly have set your question! Espacially for blah-blah-ers who just flooding here.
@Willie1
>It seems the teams and the market are speaking very loudly
Oh, man, how you're right!!!
That's what I've been wondering lately, so many new "OmG BeSt ReVoLuTiOn EvEr!!!!111!" stuff but it's mostly slight variations of pre-existing products or moto rip offs. Cassettes with a few extra teeth, handlebars a little wider, slightly bigger wheels, parts a tad lighter, barely noticable damper performance increase, different chainring teeth configuration...
Where's the true innovation? Are bikes really that perfect (hello drivetrains...) or is marketing getting the biggest slice of the budget?
Mexico? Care to chime in on science down there?
"Because the tire is wheel's heaviest component, by nature, a 29er wheel should be the worst offender " So thus a larger wheel would be slightly heavier.
But in this example the weight is to the center of the 1st wheel which would indicate that the hub and not the tire is the heaviest part of the wheel. So therefor I dont see how this experiment would conclude that a larger diameter wheel rolls slower.
The experiment rather suggests that if you can lose weight at the rim and tire thus forcing the hub to contain the most weight; you would then get faster roll. Which makes sense as if you look at the amount of force required to push the weight round a larger circle versus a smaller one.
But to your point, just building up two wheels, one with their hub and a generic brand, would evidence an actual accurate display of their "thesis".
They built a neutral setup - the plastic or whatever wheels of the same size and weight - added equal mass to both wheels with one representing a more spaced weight distribution from the center of mass and of rotation and another representing a closer spacing.
Thus showing that with wheels of equal mass the inertia is hugely different for different radial distribution.
For a true comparison of the different wheel sizes other experiences/demonstrations would be needed taking into account the different angular speeds the wheels have for the same linear displacement on the ground.
What then?
So the take home lesson is buy a marsh guard.
Ride what you want to ride. All I ask if that the if bike companies produce 27.5 & 29" bikes, please keep making 26" wheels because Pisgah National Forest is one tight, twisty unforgiving mistress who rewards me and my short wheelbase and itty bitty wheels for my efforts.
Look at BMX's...they come in a bunch of different wheels sizes, yet at the end of the day, the pro racing is being done on the smaller wheel size. I now have bigger wheels on my bike and Im pretty much guarantee it just a placebo effect... As much I want it to be quicker, it does feels smoother but yet ,some of the same people Ive been riding with for years are still on smaller wheels and they are still on my ass ;-)
"E-thirteen built its rotational-inertia demonstrator to assure its wheel customers that the slight amount of additional weight of its Chubb hubs is easily offset by the use of a lighter-weight spokes and rims."
RC, I like your articles but you just took this demonstration, which could have inspired some interesting points of view from the arm chair engineers, and simply used it to revive the endless 26/650B/29 debate.
this isnt a 26, 275 or 29er issue, its a weight distribution experiment. PB you f'ed up here
The brass weights on the plastic discs show the effect of having weight closer in to (aka smaller wheel size) or further away from (aka larger wheel size) the hub.
The big wheel have more inertia, mainly because the big tires are heavier. nothing related with this experiment.
The only thing shown here is the impact of mass distibution.
What people in the 26er camp should be arguing is that you can get a lighter stiffer wheel in 26 for much less money and that to get a wheel that is just as stiff and light and therefore accelerates the same will cost prohibitively more. Or that the roll over benefit (A comparison of which would be the difference in slopes of a line drawn tangentially through a point of impact from objects of equal height on the two wheels) is not enough to offset that lowered cornering ability of the longer wheel base, or something else that is actually physically true. Not acceleration.
Take a rock tie it to rope and spin it in a circle. now shorten the string by half it will spin easier and faster.
Acceleration is the speed of change not the speed. We constantly speed up and slow down. This is what they are showing.
Once you put tires,gearing, etc in the mix it much more complex. However you can't dispute basic laws of physics.
Uhhh... there's no "Museum of Science and Industry" in San Francisco. Probably they were drunk.
I distincly remember feelings of dread verging on suicidal tendencies when, way back in the day, the word "moment" re-appeared on my A level maths room's blackboard. All those coins spinning off LPs at 33 and 45 (told you it was back in the day), friction co-efficients of vinyl and ...aaaagrghrh. It used to do my noggin and still does, since I never really understood why you would NEED to know at what point from the centre of the said record your variously weighted coins would spin off.
Had they used examples of MTB wheels of different sizes I would probably have instantly understood it!!! Take note teachers of the world, make it real.
en.wikipedia.org/wiki/Moment_of_inertia
This is a physical law, and it's not new. In fact, this is an ultra-basic law of physics. It's known as "2nd law of motion" by Isaac Newton (around 1687). Sum of forces = mass * acceleration (in a translation movement) or in our case : Sum of Torques = Inertia * Angular acceleration.
If the repartition of the mass on your wheel is increasing inertia, you have less "angular acceleration" for the same torque. In other terms, if you push by the same amount of force on your pedals, your bike is reacting slower if you have more inertia and you will take more time to reach a given speed (but also take longer to stop).
End of story.
So you can have 26", 27,5", 29" or even 20", it's not a question of size, but a question of mass repartition. (that's for the "reactivity criteria"). This experience is only demonstrating that fact.
Now, for the maniability, it seems quite obvious that the smaller, the better.
And finally for the stability of your bike, it's not a question of wheel size, it's about the distance between the two points of contacts (wheelbase).
Now in real life, it's obvious that architecture of wheels directly impact on their inertia, and usualy, a 29" wheel will have more inertia than a 20", but it's not a "general principle" or a "law" and it depend on the wheel's construction.
In fact, you could make a 20" wheel that as the very same inertia and mass than a 29" one, so they would react the same, and if you have the same wheelbase, it would have the same stabilty, but certainy not the same manoeuvrability and general comportment.
So make your choices with that, and the more important : have fun on your bike, whatever the size you ride.
For the same increase in linear speed (displacement speed) between 2 bikes with differing wheel sizes the angular speed increase will be different, making the difference between accelerating a bigger wheel not as big as it may seem without including this detail.
That said I still prefer 26 inch wheels as they are stronger, cheaper and demand less skill to maneuver in tight places which is perfect for unskilled fat asses like myself. Also 26 inch quality tires are easier to find and cheaper to buy than they ever were.
The classic scientific hypothesis.
"with all things being equal"
Perhaps he has actually learnt something from this which I find even more worrying.
I give it 2 or 3 years until it is generally accepted that there are no miracle wheels and that many of us haven't enough fitness or skills (or in my case both) to handle efficiently the bigger wheels and that some of the better riders we know really are faster on 29 inch wheels while others have no gain or loss from the choice.
1) if given the SAME diameter round objects (both objects in video are the same diameter, the only difference is weight distribution),
2) and if ignoring opposing forces from the "trail" (the only opposing force demonstrated here is at or near the axis of objects, not friction at the radius due to the trail which is what most of us call rolling resistance, and air I guess, negligible)
3) and constant acceleration due to gravity (the linear and static track, not dynamic like trails, with bumps and more so infinitely long)...
Drum roll please: More weight toward the center of a object will accelerate that object more quickly laterally than if the if that same weight is positioned to the outside of an object of similar size and overall weight. Assuming the above^^^which this experiment represents. So to relate to bikes...if two 26" wheels that weight the same are rolling down a flat hill, the one with a higher mass density near the axis (light rim/ heavy hub) will ACCELERATE more quickly than the one with higher mass density near the rim (heavy rim/light hub).
A longer track with bumps and variable elevation would show that the outside weighted object would have a higher lateral speed and not decelerate at bumps and hills as quickly as the other.
I don't recall anyone regarding 26" fans as 'angry villagers'; I do recall those constantly banging on about the amazingness of 29" wheels as being really annoying and being a mouthpiece for an industry desperately trying to screw its fans out of more cash; a walking talking sales brochure, if you like.
All this just to explain why their hubs are heavy and it won't matter. That's one way to spin it.
Been doing that for about 8 months. 650b front 26 rear aka B6er..
Great rollover on rooty stuff still fast rear wheel acceleration. It works very nicely and it very noticeable If out my 26 front back on adjust my geo so it is the same more or less in both situations via offset shock bushings
WOW DH? Do you ride it in DJ parks all day too?
Be brave and share with the world your secret prototype DH 29-er.
And on the relative subject of acceleration as noted in the topic of the article, coming from BMX background and racing people everywhere on all kind of bikes, nothing comes even close to instant and fast acceleration and speed gain of BMX with good tires and proper gearing ratios - that's why its so much fun. Smaller the wheel and bike - more room and fun on the trail, acceleration in technical climbs, manoeuvrability and control on skinny's, thin sections.
I have not broken rims doing drops or stair cases, maybe its the skill + the right bike and wheels for the terrain = a happy safe rider progressing. Nothing holing you back.
Cheers and don't be hating on 20-24-26er. Have fun on the trail!
But one my of riding buddies is 6'4 and and rides a 29er norco shin obi. he rides black diamond shore trails , whistler bike park , silverstar etc. Has to yet to break a wheel. Just blows up his rear shock routinely(fusion)
I can usually out sprint him on techy uphills he destroys me on anything downhill and smoother...
You probably know better than the guys who designed your 29er. The review of your 29er was probably done by a "stupid" professional, right, because obviously he doesn't know what your "secret" 29'er bike is actually capable of. Because you ride your 29'er like a god right? And you probably got all the medals stashed up somewhere, all dusty in a closet?
But why prove or explain anything, sure your secret 29er and rims are magic, plus your skills, you must be a famous sports athlete, no, maybe?
LOL>
did anyone notice e-13's theory that its ok to make shitty stupid heavy hubs, because you can offset the weight by using lighter spokes and rims?
yeahhhhhhh
thats all i want in life. shittier lighter rims and spokes so i can wreck the important part of my wheel faster and hopefully buy more replacement parts to keep my bike running, all while having shitty feeling flexy wheels.
why doesn't anyone else make huge hubs?
because they're stupid.
quit being stupid
The point is, angular momentum is actually quite similar and is only bigger for larger wheels because they tend to be heavier.
This demo is not valid because the "axle" (what the wheels in the demo are rolling on) is the same size for both wheels. You would need to have a larger axle in order to represent different wheel sizes if you wanted to use a similar demo.
Boy howdy! Doing laboratory tests using actual wheels would be massively unreliable. Using weights suspended by metal rods spinning down metal poles is downright irrelevant. The only even remotely logical take away is that the disk with the more centralized mass accelerates faster when equal force (gravity) is applied to both. Which is something, you know, everyone already knew. 26ers accelerate faster; we get it.
Slow clap E-Thirteen. Way to incite the already insufferably idiotic wheel-size war with something that's somehow even dumber.
Give us a solid few thousand years, and I think well settle on a wheel size that isn't defined by an integer from an imaginary length scale.
I mean, how f*cked would we all be if the inch was a 3/26" longer, right!? Then a 26" would be 29"!
Forget about 26", 650b, and 29". The optimal wheel size likely won't be discovered for thousands of years...and by then we'll all be riding hovering e-bikes anyways so it really won't matter.
Still, if you do the math, a smaller wheel will accelerate faster (if you consider just the tire, it is linear to the diameter). But then there are a lot of factors not taken into account, otherwise XC racers would ride 16" wheels and accelerate rocket-like.
Most scientific tests I came across that did real world testing suggest that 29" is faster for XC use. But then we see that you can win on 650b or 29", so most probably the whole discussion just comes down to personal preferences.
When I change from my 26" MTB bike to my 700c X-cross I notice it is much slower on all surfaces, and when I change from my 700c back to my 26"MTB. Guess what? Yep - I notice it is also slower on all surfaces.
Only the fountain of youth will solve this worsening problem...
See many mtb dirt jumpers or 4Xers on 650b or 29?
So let's take a 26 27.5 an 29er wheel with the same rim an tyre
We both know which wheel is gonna be lighter an due to gyroscopics more agile
Different wheel sizes have different advantages an disadvantages and in all honesty it's a tired debate
None of which relates to the above test
So yeah
Yawn
If you'd have said 24 you'd have a valid point instead of taking my words out of context just to make a bullshit point
You are all neglecting that it is not only the bike that is accelerating, it's the bike and the rider. The difference in thecontribution of rotary inertia to the total moment of inertia of rider and bike is negligible, and the energy required to increase the inertia moment is the same.
As such handling characteristics is a much more important factor.
1. The wheels should be same weight but different outer diameter.
2. For each revolution the 29er wheel will cover 738.84mm (2.3 inch tyre) vs 675.84mm of a 26inch wheel.
So even though the 26inch wheel will spin faster at the hub (Where this experiment is measuring) it won't cover the same distance. Really each full revolution needs to be added to get distance covered.
This will translate to distance covered on the ground and will give you that acceleration number.
Or maybe I am just talking out of my ass.
2 bikes, identical in every way.
2 people One weighs 80kgs.The other weighs 100kgs.
Both going 20 mph on a flat road.
They both stop pedalling at the exact same time.
Who rolls longer/further ?
actually its the person with the shaved legs
why? because most xc bikes lack enough trail to handle correctly. why? because xc riders associate heavy steering with lack of efficiency IMO
In other words: you can compensate a lower wheel size by a higher teeth number.
having said that, how many of you are capable to reach 60mph because it has a 60t ring on his 26 bike? technicaly, as higher wheel size increase the distance run per round, more teeth implies more wheel rounds per pedaling round. (please excuse my english)
But still we can't reach that speed because some of you seem to forget one parameter: the energy you have to put on your pedals.
And suprisingly, the discipline more needy in energy/calories/power is the one which more uses 29" .
more climbing and flat than pure down hill so we can't say that launch those wheels is as easy as on a downhill race.
So now I'm pretty sure that the calories burned are much higher running a set of 29" than the calories burned on a set of 26" (trying to reach the top speed of the smallest set).
To compare it to the teeth number issue, it is obvious that we can't reach 60mph even having an hypotetic 60t ring on a flat road for example, but even at a lower speed it would be more exhausting to maintain a 20mph speed with a 60t ring than with a "normal" 36 or 38t ring... just because you need much more calories, power to turn such a big ring to that speed, the accelaration is less eficient and the top speed is more difficult to maintain on long terme.
Hopefully my english is clear enough to make myself understood..
I have an old gt karakoram that is convert to road use. 1 inch tires and a whopping spesh 54 tooth front ring. In my early 20's I could hit 60km on level road but only maintain 50km
And I would add, yes the circumference of a wheel does has effect on top speed (on same gearing and same pedaling cadence but with 2 different diameter, you definitly cover dirent distances on one pedale round, in other word on the same cadence or time you need to turn your crank you cover more distance so you go faster... end of the story
The balance between fast and slow always lay in the middle.
Reticent: I do not think this word means what you think it means.
2 People On Identical bikes.
1 Person Weighing 80Kgs And the Other weighing 100Kgs.
Both cycling at 20Mph on a dead straight road.
Both Stop pedaling At Exact same time...
Who Rolls Longer/Further ??
Bikes roll on the ground, not on the axle. If the experiment is done correctly (put the wheels on the table and tilt it, or research rolling wheels), you will see that:
For Power required to Accelerate a rolling bike - effect of Rotating weight is the same as Non-Rotating weight. (There is actually like a 0.5% difference).
Therefore, bikes of equal weight with different wheel size require the same power to accelerate.
Regarding turning, traction, rolling over stuff, etc. I have no idea.
There is no miracle wheel.
What was done to sell more bike was all the hype and the "we will not make anymore top of the range 26 inch bikes" some manufacturers did. Now that is stupid marketing.
There are no miracles and if there is a "goldylocks wheel" it will always depend on the rider, his skill and fitness level and what he is doing with it.
I mean wheels!!!!
"Almost every cyclists insists that, if two wheels weigh the same, the one with the lighter rim and tire will accelerate faster - but where is the proof? Every wheel review worth reading either states or implies that there is a noticeable difference when accelerating a lighter or heavier wheel, but just how significant that effect may be, or whether it is largely a figment of the test rider's imagination has been cause for an endless round of debate. Add the wheel-diameter war to the equation and the discussion becomes less scientific and more emotional. Until now, however, the argument has been an intellectual one."
So- I say again, the main point of this article is the conversations that always go on about rotational weight.
Personally I like it.
To the shed!
It's to show their new heavy hub wont slow down a wheel if the rim and tire are light compared to a heavier rim and light rim/wheel combo. Hence the weight at the center of the wheel (the heavy hub) vs the weights on the outer edge representing the heavy rim.