How to Accurately Calculate What Spring Rate You Need

Feb 22, 2022 at 9:00
by Seb Stott  
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If you have a coil shock, finding the right spring rate can be tricky. In an ideal world, you'd experiment with a few different options until you find the right one. But with some springs running into three figures, that can be very expensive, not to mention time-consuming, so you want to have a very good idea of what spring rate you need before you order one.

For clarity, the spring rate, or stiffness, is the amount of force required to compress the spring by a certain distance. This is usually measured in pounds per inch (lb/in) or occasionally Newtons per millimeter (N/mm). So, for a 400 lb/in spring, it would take 400 lb of force to compress it one inch, or 800 lb to compress it two inches, and so on.

What spring rate you need will depend on your weight and on the suspension design of your bike. In particular, its leverage ratio, which is how far the axle moves for every millimeter the shock compresses. You can easily work out the average leverage ratio by dividing the wheel travel by the shock stroke. A higher leverage ratio means you'll need a stiffer spring to provide the same sag.

When it comes to estimating what spring rate you need, there are lots of online calculators to help you do this. Here are some links to spring rate calculators from TFTuned, MRP, Fox and The Suspension Lab.

These calculators are great - honestly, most people will be happy enough using any one of them. But they don't always agree with one another because they work in slightly different ways. The calculators from TF and The Suspension Lab rely on subjective inputs like riding style and trail speed, which maybe makes more sense to some people but it's hard to be precise with such terms. Meanwhile, the ones from Fox and MRP allow you more control over the objective input parameters like sag and, in particular, how much your weight is biased towards the rear wheel.

Experienced riders usually have a rough idea of how much sag they need based on their riding style. If you want something super comfortable, you might run as much as 35% sag; for a more responsive ride, you'll be nearer 25%. But for most bikes, 28-30% is the sweet spot. But how do you know what your weight bias is? And how do these calculators work anyway?

To calculate the spring rate you need to achieve a given sag, you can use the below equation. Unless you want to play around with different values of the leverage ratio (more on that below), you don't actually need to use this equation because the online calculators from Fox and MRP do it for you. It's just there to show you how they work and what all the variables mean.

Spring rate in lb/in = W*B*L^2/(T*S), where:

W = Your riding weight in pounds. Make sure to add the weight of your riding kit.
B = The weight bias, or the percentage of your weight on the rear wheel when standing on the pedals without any pressure on the grips. This is given by the ratio of your bike's rear center divided by the wheelbase, but a good approximation for most bikes is 65%.
L = The bike's leverage ratio, which is usually just the travel divided by the shock stroke. Alternatively, you could find a leverage ratio graph for your bike (from the manufacturer, a review, a blog or linkage software) and find the leverage ratio at the sag point. This will give you a more accurate estimate of the sag you'll get. But remember, with a more progressive bike you'll usually want to run more sag (and visa-versa); using the average ratio takes this into account to some extent.
T = Your bike's travel in inches
S = The percentage sag you want (e.g. 0.3 for 30% sag)


A note on preload:

MRP and Fox's calculators allow you to see the effect preload will have on sag. But remember that preload does not affect spring rate - it's just a way to adjust the ride height (sag) independently of the spring rate. I'd recommend using zero preload, both in the real world for better sensitivity, and when calculating spring rate because sag is an indicator of the spring rate you need, not a goal in itself. Yes, you'll need a little preload to stop the spring from rattling and there is some breakaway force from the damper to consider too, but roughly speaking, these tend to be cancelled out by the weight of the bike, which is why bikes don't tend to sag much (if at all) under their own weight. That means, to a reasonable approximation, if you ignore the turn or so of preload needed to stop rattle you can ignore the weight of the bike too.

I used the Starling Spur to check the theory matches reality.

Here's an example

I recently reviewed the Starling Spur, which has 170 mm (6.69") of travel and a 65 mm stroke shock, giving it an average leverage ratio of 2.62. Because the leverage ratio barely changes through the travel, we don't need to consider using the ratio at sag instead of the average ratio. In full riding kit, I weigh about 200 lbs, and by dividing the rear center by the wheelbase we get a weight bias of 64%.

Since it's a pretty linear bike with a very active suspension design, I wanted less than the standard 30% sag. If I put 28% (0.28 ) into the equation, along with all the numbers above, it suggests a 467 lb/in spring. If we plug in 26% sag for a firmer setup, the equation suggests a 503 lb/in spring. In the real world, I used a 502 lb/in spring, which gave me bang-on 26% sag.





220 Comments

  • 312 0
 The big problem for bike brands with these online calculators is that they don't take account of the rate curve of the bikes. We had some trouble with coil shocks being fitted to our frames a few years back when people would buy one second hand, switch to coil, but instead of asking us they'd just use a calculator. On a very progressive frame design, you need a much stiffer spring than these calculators tend to give out. And then you get people running too soft a spring, or running tonnes of preload to get the right sag (and therefore making the coil bind before bottom out which overloads the shock) and then they damage their frame. I know it's not really feasible for bigger brands, but we're more than happy to spring calcs for people - even with used bikes - on any of our frames that are coil compatible. Just drop us an email. I'm sure any of the smaller brands out there would say the same.
  • 11 3
 Very true. There is such an immense difference between a shock that is tuned for weight and the bike with appropriate spring rate and a standard tune with calculated spring rate. Craig at Avalanche will make you cry if you try to argue with the science between damper oil flow, spring rate, and bike kinematics.
  • 17 1
 Why would you use a stiffer spring on a more progressive design? Wouldn't that resist bottom out further? Or is that just so that it doesn't wallow into the mid stroke?
  • 4 2
 @ashmtb85: coils have great mid stroke support as is so I'm confused also
  • 2 0
 So true!
I used the Fox calculator for my Capra (170mm /65mm/ 200lbs) and got 500lbs too - it was way too soft.
I had to adjust the calculator to DH settings to match the real world 550lbs spring.

With a more progressive rate the bike did sag into midstroke with the softer spring.
  • 40 0
 @ashmtb85: It's to do with the average leverage vs the leverage around sag point, plus a bunch of other assumptions. For example, the RocketMAX Gen2 was coil compatible and very high progression because it used the old imperial size 200x57 shock to get it's 150mm travel. Now, if you do a straight average you get:

150/57 = 2.6

At the 30% sag point on the leverage curve, the ratio is actually nearer 2.8, so you need a stiffer spring, and I have weight balance data in my calculation too. To take another example, plugging these stats into the TF Tuned calculator linked in the story suggests between 457lb and 485lb spring for an 80kg rider. That rider actually need at least a 530lb spring for that bike according to my data and testing experience. Given that springs generally come in 450 or 500lb options, most are going to choose 450lb, which is going to need 4-5 turns of preload to get the ride height right. And then you're going to be coil binding the spring before bottom out on such a short shock. Less of an issue on more modern metric length shocks, but really you should never wind on more than 2 turns of preload. If you do, you're spring is too soft.
  • 3 2
 @ashmtb85: because the design is progressive, but the shock run is linear, so it has to be able to handle quite low pressure in the beginning and quite high in the end of travel, therefore you need stiffer spring to avoid going thru whole the travel easily
  • 14 23
flag englertracing (Feb 24, 2022 at 8:40) (Below Threshold)
 @Mntneer: or Craig will start crying and screaming if you use any facts that disagree with his facts. He's an egomaniac who doesn't even ride, his tunes aren't good.
  • 28 3
 @ashmtb85: The amount of progression a frame has in and of itself actually isn't what creates bottom out resistance. The three factors that play into bottom out resistance are spring rate, damping, and shock stroke. Progression is all about what it allows you to do with shock setup and have the bike still ride well. If you take a linear bike and bump the spring rate up to increase bottom out resistance it'll have very little sag and track like crap. Now if you take that same spring rate and run it on a more progressive bike, it'll actually have roughly the same bottom out resistance (assuming all other factors are the same) but ride way better because the wheel will have down travel again.
  • 1 0
 @CascadeComponents: I see. So what does the inherent progression of a linkage matter for then? Small bump compliance?
  • 4 4
 @CascadeComponents: Well.. resistance is a force right ? so technically it requires a higher force to bottom out a more progressive bike. What you mean is that it requires the same energy to compress a spring with eg 400lbs in a linear bike as in a very progressive bike. Wich doesnt really matter because you wouldnt run the same spring rate in both bikes
  • 19 1
 @ashmtb85: I guess it depends on how you look at it. If you look at it from the standpoint of "I always set my bike up for the bottom out resistance I need" then the correct amount of progression gives you good small bump without it feeling like it's wallowing. If you look at it from the standpoint of "I always set the bike to 30% sag" then it lets you run a stiffer spring so that it's harder to bottom out.

@emptybox resistance isn't force, it's the amount of energy the shock absorbs between the starting point in travel and bottom of travel. While a more progressive bike exerts greater force on the wheel at bottom of travel, it exerts less at top of travel. So as you move through top of travel it does less to resist that compression but it makes up for it by doing more to resist it deep in travel.
  • 50 1
 Cotic, Cascade.. now I'm waiting for Dave Weagle to enter the chat
  • 16 6
 @englertracing:
So you and your 6 followers need a box of tissues? Craig is probably the most knowledgeable person on the planet when it comes to suspension tuning for any discipline of riding... MX, sleds, mtb and anything else with a shock or fork. He has been at the core of the suspension evolution for the last 25+ years... Riding, racing, building, innovating and tuning wirh best riders and giving them the Avalanche advantage to perform better. That usually means when he speaks, what he has to say is very relevant and you should listen and je learning.
  • 3 4
 @jaydawg69: a coil's rate is linear how can it have great mid stroke support? Surely that is a function of the frame?
  • 6 37
flag emptybox (Feb 24, 2022 at 9:51) (Below Threshold)
 @CascadeComponents: thats your interpretation. so you do say resistance is mesured in energy while i would say its measured in force.
"noun
the act or power of resisting, opposing, or withstanding.
the opposition offered by one thing, force, etc., to another."
www.dictionary.com/browse/resistance
  • 24 2
 @emptybox: I don't know who's right here, but pointing to a general dictionary in the context of a very jargon-y niche of an already jargon-y cycling equipment doesn't mean a ton.
  • 38 3
 @emptybox: It's not my interpretation. In the world of physics an impact is measured as an energy input because they are a force exerted over a distance which equates to an amount of energy. The impact when you go off a drop is absorbed over the entirety of your bikes travel. It doesn't just compress to a given force and that's it. It's all just conservation of energy in the end, which is one of the core principles in physics. Like if you go off a drop to flat the potential energy you have on top of the drop has to be absorbed by the suspension when you land.
  • 3 56
flag emptybox (Feb 24, 2022 at 10:18) (Below Threshold)
 @CascadeComponents: thats right, and i completly agree with you on that. but you still used resistance in a wrong context in your first comment. if there is a word for it and it is even written in a dictonary why not use it in the right way in a technical debate ? You should know better
  • 16 1
 @pakleni: just wait until Peter Verdone comes saying they're all morons
  • 1 0
 Ah yes, snd the great grand mystery calculation continues…..
  • 3 0
 @cotic-bikes: sounds like the key to a more accurate calculation is to use leverage ratio at the sag point, rather than average leverage ratio.

I tried LR at sag point with the formula in the article and it closely matched my current sag and spring rate. I had tried some of the spring calculators listed and the results were indeed all over the map.
  • 4 1
 Online calculators, across the board, tell me I should be on a 350lb spring for my weight on my Sentinel. When I was setting the bike up, I spoke to Lars at Transition and was told "get a 400."

I've got the 400 set up with just a tiny bit of preload, hit a perfect ~28% sag, and am just super happy with the performance of the shock. I for sure wouldn't want to be on a lighter spring.
  • 2 0
 @ashmtb85: because in the initial part of the travel the leverage ratio is high, easily compressing the spring. That's my guess.
  • 5 10
flag SteveWatts (Feb 24, 2022 at 12:23) (Below Threshold)
 @CascadeComponents: To be fair it is your interpretation. The force of an impact is equally as valid to consider as the energy, and as you point out they can be derived from each other. Do you really think ‘entirety of your bikes travel’ is used every time you go off a drop? And without damping the suspension absolutely compresses to a given force. The suspension is performing two functions, the damping is converting kinetic energy into heat and the spring is storing energy before returning it.
  • 4 3
 @plimdaddy: comparatively to a air spring - a coil produces more force in the mid stroke.
  • 5 3
 @SteveWatts: No, the force at the impact is always orders of magnitude higher than what the spring can stand.
Energy is what matter.
Alternative view is to see the suspension as a damped sprung system, and look at accelerations and speeds instead of energy.
If you remove damping, your spring will overshoot it's equilibrium position due to the inertia and the remaining kinetic energy. damping allow for a more controlled stroke that will overshoot less the equilibrium position. Force only tell you about the direction of acceleration, nothing more.
  • 3 4
 @emptybox: a more progressive linkage does provide more bottom out resistance for a comparative amount of sag as you use a higher spring force. More over it effectively adds damping through the travel so your get both more energy stored and more energy converted at the end of the travel.
  • 2 3
 @faul: it is a damped spring system and if you look at acceleration you’ll find force is equal to the mass multiplied by the acceleration
  • 2 3
 @faul: it is acceleration you actually feel - which is a function of force - you cannot discount it and consider energy alone
  • 5 2
 @SteveWatts:
- no it's not a true damped mass-spring system. There is several independent masses (that aren't constant!) , several springs, several dampers. You can approximate when looking at small intervals.
- mass and acceleration tells you the force seen by the mass at a given time, providing the mass-spring system analogy is relevant. You can deduce the force given by the impact if you know the force at the spring and damper, but that isn't relevant to anything and once you've looked at accelerations and speeds you'll know about everything you need without looking at forces at all, and that's the goal of looking at it in this way.
What you can feel is a complex subject. But that's not relevant when looking at your suspension's action.
  • 1 2
 @faul: ok, yes there is sprung mass, the unsprung mass, and the rider in this system - none of that alters what I have stated before. I’m really interested to know what these variable non-constant masses are that you refer to ???
  • 1 3
 @faul: what you can feel isn’t complex. It’s accelerations. Period.
  • 1 3
 @faul: also what you can feel is obviously relevant
  • 8 1
 @SteveWatts:
The "B" in the article's formula. It's not constant.
From the shock POV, the leverage rate variation also vary the "mass" seen by the shock thru the travel. Or if you look at wheel forces, it's the damping coefficients and spring rates that are varying.
But that's the easy take. Now you have legs, tires, wheels... everything flexes, with a "damped-spring-system" model. making things seen by the actual suspension element of your bike, not constant.
The wheels aren't fixed to the ground so even your references points aren't fix, and there is at least three inertial frames.
You can't feel an acceleration actually. You're good at feeling force or distributed force, you're good at feeling relative displacement of your body parts, but you don't feel anything from the bike. absolute movement isn't really felt at low frequencies. But I digress, how what you are feeling is relevant to your suspension action? Makes no sense to me.
  • 2 0
 Thats good advice, and an unfortunate side effect. But anyone who is specing a coil shock, should always know the golden rule of achive sag with the heaviest spring possible, i.e. the least amount of pre load. Every coil shock ive had, ive probably gone through at least 2 springs before finding the right weight.
  • 2 0
 @cotic-bikes: quick question then, if it's that easy to mess up preload why do shock manufacturers put so many threads on the shock body?
  • 4 1
 @mhoshal: I'm not cotic-bikes but spring length does vary and there are manufacturing purposes of having extra threads anyway.
  • 1 3
 @faul: your a pretender - “you can’t feel an acceleration” - but you can feel a force. F=ma.
B is not a constant, but that is not mass, neither is the force seen by the shock or the other things you mention. The masses are constant.
  • 5 3
 @SteveWatts: push a wall the harder you can. High force if you are strong, 0 acceleration if you have strong walls. F=ma is NOT the force you are feeling.
  • 2 4
 @faul: So standing up, what you feel in your legs and feet pushing on the floor isn’t due to the acceleration of gravity? Zero velocity, not zero acceleration.
  • 1 1
 He turned me off super fast. Didn’t wanna talk anything and didn’t wanna do anything more than have me drop money with him. 0/10 @Mntneer:
  • 2 0
 @SteveWatts: look up jerk, also snap crackle and pop. In a complex system there is more than two time derivatives of position in play.

I think it's jerk you feel.
  • 4 0
 @SteveWatts: I ain't no physics expert, but don't you feel force of the ground that is canceling the force of the gravity, but there is no acceleration since your velocity is the same
  • 4 0
 @englertracing: I disagree. I’m not saying every tune he does is perfect, but he has transformed some of my bikes with his shock and fork tunes tunes. My son-in-law, who raced DH at a high level nationally, rode one of my DH bikes after Craig tuned the the RockShox fork it came with and was blown away. He said it was the best fork he’d ever ridden.
  • 5 0
 @mhoshal: Because different springs are different lengths, and because you have to have a thread all the way up the body to get the preload ring up there in the first place.
  • 1 0
 @ashmtb85: I think because there's often more leverage at the beginning and to achieve the right sag you need a bit more spring.
  • 1 0
 @richard01: are you on drugs?
  • 1 1
 @mtbcrosscountry-com: you can have acceleration forces and deceleration forces that cancel to give constant velocity, or zero velocity. The forces are still there though.
  • 1 0
 @mtbcrosscountry-com: There are still 2 accelerations, you feel the force of the ground pushing back (newton's third law) and because this is a force, and acceleration is a required component of a force (newtons second law force = mass x acceleration) the accelerations must still exist.

Perhaps consider that gravity itself is not a force, it's an acceleration, we experience the 'force' of gravity because we are a mass and an acceleration - gravity is acting upon us. In space for instance, we are still a mass, but there is no gravity/acceleration so there is no force. You need a mass and an acceleration to make a force.

So rather than 'cancelling out' the forces, implying to you they are not there, it's probably better to think of them being equal to each other. As the forces of mass and acceleration are the same in opposite directions there is no net velocity.
  • 1 0
 @mhoshal: Good point! ....probably because it's easier to produce shock bodies with extra threads and cut to length for different shock sizes. Just a guess, it would reduce the need for a bunch of different parts. Just grab a full length body and mill it to length. G
  • 1 0
 @cotic-bikes: @mhoshal: totally overlooked needing to get the ring above the spring in order to compress/preload. Good point
  • 47 3
 Springs mostly only come in 50lb increments though, so mega-analyzing what rate you need to within a few lbs is a little bit moot.

You could summarize more as:
1. Get the spring the manufacturer recommends for your weight. Round up if you like more sag, down if you like more. Jf you don't know, flip a coin.
2. See how it rides. If it feels too tall, go down one step in spring rate. If you get tons of pedal strikes or bottom out or etc, go up in spring rate.
3. Once settled, sell your old spring on pb buysell. If you also bought your replacement spring on pb buysell, you are probably not out much money.
4. Ride the bike and stop thinking about it. Unless you get fatter or less fat, then go back to step 1.
  • 6 0
 Sorry can't edit. Step 1 should say round up if you like less sag, obviously. Cheers.
  • 4 0
 Probably worth mentioning that there are a few springs made in 25 lb increments for those who want the exact correct spring rate. EXT, Nukeproof SLS come to mind. Be sure to check compatibility as spring inner diameters vary by manufacturer and scrub large shock bodies.
  • 1 0
 @chrod: Yep thats why I used the word "mostly". The process does not change though.

Progressive springs add yet another variable, but the process is still the same. It just means if you're in a weight range where the manufacturer recommends a 500lb spring, when you round up or down depending on where your actual weight falls within that range, you can round by 25 instead of 50.

If you really want to know actual sag you can always put a zip tie o the shock shaft temporarily but I've always found that with coils it doesn't really matter, better to just tune by feel.
  • 20 0
 That's why I use a Sprindex spring. It's great being able to run a 515 spring and not be stuck too soft at 500 or too firm at 550.
  • 6 0
 @TEAM-ROBOT: I started using a Sprindex last year and it's fantastic. Most of the time I roll with just a bottle but on bigger days when I'm going to run my hydration pack and more gear I can just twist the adjuster and increase the spring rate.
  • 2 0
 It gives me satisfaction to see others use idiomatic language accurately.
  • 6 0
 @TEAM-ROBOT: Sprindex was a game changer for me. wouldn't run coil without.
  • 5 0
 @jamesbrant: I too love Sprindex. I wish they came in diff colors though. If they did, I might not run anything else. I'd prefer to turn the plastic dial vs. mounting & dismounting my shocks frequently. Water, apparel, packs and bowel movements add up.
  • 3 0
 @KennyWatson: not to mention that no 2 springs of a given rate are usually the same.
  • 2 0
 I believe this is why Sprindex was invented.

EDIT: Dang it, left the page up for a few hours and forgot to click submit... I think we're all on the same page here.
  • 3 0
 Well, this is incredibly cool. Sprindex. I had no idea. Similar adjustability to an air spring, without need of a pump! Going on a pedal tour? bump it up. Slaying the descent, drop it down. Damn, and I just bought two new coils. lol
  • 14 1
 @tankthegladiator: Here's a list of the springs I bought before I found the right spring rate for my MegaTower: 600 Rockshox, 550 Rockshox, 500 rockshox, 500-540 Sprindex, then then 450-500 Sprindex that worked at 495 pounds. Total cost: $470, total time to dial in my setup: 1.5-ish months/15-ish rides. What a pain, and I almost gave up on the coil shock midway through the process. This is the huge downside of coil shocks, and I wish I'd started with Sprindex.
  • 1 0
 @TEAM-ROBOT: With far too many things going on personally in 2021.... I just rode the bike how it came / suggested setup. The factory spring at 500 lbs netted 15% sag once I got around to measuring it out in the fall. Below - I wrote about my full experience.. But now that I know where I ballpark need to be, a Sprindex would be ideal!
  • 4 0
 Also. Spring rates are usually way out from the number printed on the side of them. Many are outside the +/-10% you'd expect. Which means one brands firm 450lb/in can overlap another brands soft 550lb/in!
  • 1 0
 @TEAM-ROBOT: I'm a little bit worried that I'm in the middle of options with Sprindex, i.e. the 390-430 might be slightly too soft and the might be 450-500 slightly too stiff. I'm currently running 22% sag on a 500 lb/in spring (just because that's what was available) in a frame with 22% progression, which results in 25% bike sag. This suggests that I'd end up with a bike sag range of 32-29% on the softer option and 28-25% on the stiffer option. Assuming the measurement accuracy of Sprindex and Rockshox is similar...
  • 5 0
 @boozed: The Sprindex ranges aren't accurate. The adjustment works well but you have to measure the rates to see what you're actually getting.
I've measured a Sprindex 610-680 at 590-640lb/in.
  • 1 0
 @Dougal-SC: Thanks, I wonder if that drops the 450-500 into a more favourable range (for what I think I need...) Again assuming Rockshox is remotely accurate, I haven't measured it.
  • 2 5
 @TEAM-ROBOT: imagine if you lived in a time where there was no sprindex lol that's the exact reason most people go for air one big reason I went with it on all my bikes. Honestly coil shocks aren't even worth riding to me anymore. The weight saving is also another good thing. It's funny how people ride coil shocks only for one reason, consistency and honestly air shocks really aren't that far off so I see no point in running one. Cool story though how you wasted a bunch of money to do what one stock air shock could have done.
  • 8 0
 @mhoshal: It's not a waste of money if you rationalize it to yourself. Suddenly it becomes research.
  • 2 0
 @mhoshal: na man my top model super delux felt super harsh or was way to soft.

Changed that to the factory dhx2 and that was completely different. Even with to high or soft spring rate it was better. Could ride further without falling off legs.

Same thing for my converted coil fork. The dive of the airspring on steeper stuff made me Sick. To compensate that the fork was always to stiff.
The smashpot inside with a adjustable hydraulic made it so much better. I don't even need to switch coils to make it stiffer. Mostly the same for me as the sprindex.

My bike weights probably 17 kg and everything is high-end except the pedals so I don't care if my coils make it on kg more heavy..
  • 2 0
 The sprindex has its problems with accuracy as well losing its effectiveness as the spring compresses.

www.bikeradar.com/reviews/components/rear-shocks/sprindex-adjustable-coil-spring-review
  • 1 0
 @Serpentras: Spring type is not the only thing you changed, RS has a tradition of very poorly designed damping circuits (would you try super deluxe coil instead of fox, you would know). Well made air damper is as good as coil, but there are bikes and rider who will feel better with coil, no doubts about that. The funny thing is that the so much praised midstroke support of coil does not work on ever trail.
  • 1 0
 @lkubica: well I got the factory coil, new from an LBS and for less then the actual RS coil online and I got an SLS with it. Just because it got one scratch on the black paint I can only see with a microscope...

Because it is possible to ride in the Alps for me I don't agree that air is good as a coil. Descending fast for an hour straight is something else. Same for brakes at this point.
  • 2 1
 @TEAM-ROBOT: to that extent I'll agree at least you're sharing your knowledge so people reading it have a better understanding of how irritating it can be to set up coils and don't make the same mistakes before going with a sprindex.
  • 1 1
 @Serpentras: 17kg lmao that's dh bike weight. My Giant Reign weighs 28.5 pounds.
  • 1 0
 @TEAM-ROBOT: at last, coil is a bind to set up
  • 5 0
 @mhoshal: well you probably don't have DH tires. I got 3 kg alone for the tires and I don't care because my setup wont give up.
Pedaling uphill is even faster then doing it with a 3kg lighter bike. All bikes with slack seat tubes are not good for me.
No problem to ride that thing for an entire day. This is build to last and mostly for low maintenance. No derailleur , only coils, burley tires and Trickstuff brakes won't need anything.
  • 4 0
 @Serpentras: I would rather ride your 17 kg bike with real tires than a 28.5 pound bike with light tires. Unless I'm racing cross country.
  • 1 3
 @TEAM-ROBOT: so you'd race 2.3 minions xc eh lmao and last time I checked minions were real tires and by no means light.
  • 1 0
 @Serpentras: what frame are you running?
  • 4 1
 @mhoshal: well you must have a very light casing and it doesn't matter if you run minions then, there are Minions who weight 780g and are 29x2,3. Something like that is a joke even on asphalt, other tires dont get a flat that easy and those are even lighter and are slicks.

For my conditions anything is a waste below DD, at least for me IF I want to ride any MAXXIS off-road.
Anything less is just a flat tire.

@mikeetheviking a pimped out Privateer 161 that wasnt cheap overall because of the parts but it is a long term bike for me and the parts stay on it.
  • 3 0
 @chrod: I believe Ohlins tests all there springs and writes the actual rate on the spring. It may be labeled as 400lb but could measure/test at 408# or 413# or any other rate within a small range around the printed rate. I believe I saw it on a factory tour video awhile back
  • 21 0
 Great article, Seb.

Thank you for highlighting our (MRP) spring calculator. It's quite robust, but we recognize it may be too complicated for many users. We are working on a new one, as well as more information and guidance about if and when to choose one of our Progressive Springs.

If anyone has any questions about how to use the calculator or wants a second opinion that takes into account their particular bike, please reach out to us via e-mail or the online chat function on our website.
  • 3 0
 Yep, I had a question. Why are there 3 inputs for rear wheel travel? Am I supposed to put the same number three times? Or a target range?
  • 1 0
 Yes for sure. Spencer over at MRP really helped out recently with the spring rate on the 10.5 x 3.5 Raze you guys built last month for me. I wouldn’t have guessed it, but he was spot on. Thanks MRP!
  • 4 0
 @Will762: because our calculator is pretty old, and back in the day it wasn't uncommon for frames to have different shock mount positions for different travel settings.

It's one of the main things I want to change with our calculator. For now, just enter the same travel number three times.
  • 26 2
 Pick a spring rate and be a dick about it.
  • 4 0
 Or ride a hard tail and don't worry about it
  • 20 0
 Considering the current geopolitical situation Nukeproof Giga with coil shock seem to be the best choice. I may not live long under 30k rentgens but when new kind of engineer apes find my bike in 20000 years, I can hope that they will recognize that I had the correct spring rate.
  • 16 0
 "This is given by the ratio of your bike's rear center divided by the wheelbase, but a good approximation for most bikes is 65%"

All this talk about how the different calculators do things very slightly differently, and how it it could be done better and more precisely, and then you just throw down this approximation? It's one of the easiest things to calculate: as you say, chainstay over wheelbase, two of the easiest measurements to find or make. Except that number is going to be closer to 0.35, so it's really the inverse, front center over wheelbase, that will get you that ~65%
  • 8 0
 THISSSS. I did the math 3 times thinking I was stupid.
  • 2 0
 @kirny6: You're exactly right. @seb-stott, you might update the article with this change!
  • 15 2
 What I've learned over the years = look at manufactures recommended settings, add 50 - 100lb to recommended spring rate.
  • 1 0
 this is actually somewhat correct... I've got a motion instruments set up to tune all my bikes I find that the correct spring rate for my enduro and dh (coils on both - PUSH and EXT) is always 50 or more over what is recommended.. but I also like to just barely snug up the preload ring to the coil and have my sag be right at 30% or a little more, so if anything, I may tighten it a quarter turn.
  • 2 0
 @Msicola: EXT recommend as little preload as possible, 1/4 turn max :-)
  • 1 0
 @stoat: yup. I find that to be the best way to get your correct spring on the coil.. which is why 25lb increments s is a great thing on the coils. You need to turn close to 1/4 just to snug the coil in place once the preload ring is touching.. i don't want anything shaking around. Plus, using a telemetry system to measure everything confirms if your choices are within the measurements you're looking for.
  • 4 0
 @stoat: Simply because their shocks do not have a hydraulic top out.
  • 1 0
 Disagree. Bike manufacturers settings have led me astray numerous times. This last time, manufacturers settings netted me 15% sag, and an uncontrollable rebound for my weight vs spring rate- creating a less than desirable ride experience.

After using TFTuned, they suggested a drop of 150 lbs spring rate from 500 to 350. I conservatively dropped 100 lbs in my spring rate to 400, and am finally at 27%(ish) sag on a 180mm bike. Which i'm okay with, because I still pedal it.
  • 1 2
 @stoat: they only recommend that to compensate because their shocks have an issue with topout clunk. Craig at avy recommends 1.5+ turns... my understanding is having near zero preload means that rebound damping is too slow near topout which prevents the wheel from tracking the ground as well in the sag range resulting in less traction.
  • 2 0
 @Helmchentuned: Should be noted that the e-Storia does utilize a negative spring.
  • 3 1
 @thegoodflow: they do it because it is better in every way, more preload= less initial sensitivity, no way around that. If you talk about tracking, you are either not even close to top out when there is any weight pushing against the suspension or the bike is unweighted and unsprung mass is pulling on the shock together with the spring extending it, far from too slow.
  • 1 3
 So not because it's the only way to keep their shocks from clunking at topout? That's a convenient coincidence.
  • 5 2
 @tankthegladiator: Spring Preload is a tool for adjusting geometry, nothing less, nothing more. Depending on how hard you ride you need, for example, either a 450 or 500 spring to have the correct spring resistance. With the right preload, you can run both of them at the same SAG. Even a 4mm preloaded heavy coil spring feels better and starts into its stroke softer than an equivalent air spring so I see no problem there.

Some manufacturers allow ample preload (for example rock shox), some virtually none (for example EXT).
It comes down to multiple factors like spring design, damper design (especially top out circuit) and a few other caveats I do not want to delve into right now.

When running bigger preload always make sure you have a spring that acutally supports it, so a spring with a 65mm stroke plus preload (up to 5mm for RS) needs to have at least 75mnm of acutal travel so you do not experience coil bind which basically, occuring once, pushes the spring past its design limits resulting in a damaged spring (shortened, not the same rate anymore).

I have dynoed / analysed a lot of springs from different manufacturers with some very peculiar results.
(EXT and SAR Springs are great, SLS only depending on length, others are utter shit).
  • 2 0
 Every online calc I have used tells me to use a weight I know is at least 50lbs too light.
  • 1 0
 @bigburd: This is what I found too. The Suspension Lab was by-far the most accurate, for what I was looking for.
  • 11 0
 I tell the ladies I run a 550lb spring, but really its only a 450lb spring, which is totally average right guys?! GUYS!?
  • 3 0
 Insert Seinfeld episode where Jerry scratches off the 2 on his size 32 Levis to give the impression he is still a 30.
  • 7 0
 It is also worth noting that spring rates are rounded. Springs are rarely ever exactly 450lb or 500lb. They are within a percentage, up to 10% +/-. This can mean you get a 450 spring and a 500 spring and they are identical or actually the 450 is firmer than the 500.
  • 3 0
 this uncomfortable fact makes all these calculators moot for most of us. it's fun to pretend though!
  • 1 0
 @owl-X: The calculators are still very helpful. It is one thing that does make some folks hesitant to run coils. It is a bit more intensive to set up properly for riders versus taking a shock pump out on the first ride and making small tweaks.

I am one that thinks coil shocks typically outperform air so the inconvenience of set up is less significant. Except on bikes where its a PITA to remove the shock to swap the spring.
  • 5 0
 A firm 450 and a soft 550 can overlap!
  • 1 0
 I think öhlins measures every single spring so theirs should be the most exact I guess.
  • 4 0
 Hell Yea Seb! I love these quick tips and tricks. Seb's articles are always super insightful and informative. Not just another opinion from one individual, I love how he uses calculations and actual examples to back up his claims. This is a great resource for us as riders that I am actually going to use, rather than just entertainment if it were merely opinion based. Keep it coming Seb!
  • 4 0
 Oh quick thing I noticed, Bias should be B = 1-(RC/WB)
  • 1 0
 100% More of this!!!
  • 6 0
 Just get a Sprindex coil and all of your issues will be solved Smile . Turn up the spring rate for climbing and turn it down for descending, it’s ingenious.
  • 4 0
 Interesting, as I just ran through this a few weeks ago. (I'm no pro, but think I guessed okay)
21' Shore 1, 165 lbs, 180mm travel, 70mm stroke DHX2, aiming for 28% sag

Norco Ride Aligned in 2021 recommended 500 lbs (15% sag, factory spring)
Norco Ride Aligned in 2022 now recommends 450 lbs
TFTuned recommends 358 lbs
MRP recommends appx 325 lbs
FOX recommends 300 lbs
Suspension Lab recommends 400 lbs for Balanced, or 370 for Plush.

I only knew about Fox and TFTuned, and used their calculators. I thought dropping from 500 to 300 or 325 was crazy talk, so I went with 400 using a Nukeproof spring and ended up with appx 27% sag. The wifes bike dropped from 450 to 350, and she is also around 27% now. Worst case, I could buy her a 300, and I use her 350 in the future if we want to go softer.

What did I learn? Leverage seems to have alot to do with it. FOX and MRP's calculators seem to be too light. Suspension lab, in my case, for my application was the ideal calculator. They were the only ones to factor in weight of bike. I just happened to nail their spring rate upon a guess, wishing I knew about it sooner.
  • 1 0
 Ride align was very accurate in my case (2022 Norco Range VLT)

It suggested 595lb (600lb) and it felt spot on
Even the damper settings for the DHX2 were 90% on perfect for me and I'm very in tune with setting up suspension
  • 1 0
 When I got my '19 Capra 29 it came with the DHX2 coil spring at 375 lbs. It was right around 30-35% sag and I rode it like that for a year, but always felt it was too much sag and not enough support. I used all the calculators and they all said 325... literally all of them. I was pretty confident I needed a 425 lb spring but didn't wanna shell out the money for an SLS spring. Ended up on a 450 lb cheap black Fox spring and it feels so much better than the 375 at my weight. Sag is only like 15%... so I really should get a 425 at some point, but I really like the way the bike rides so I haven't felt the need. I even payed for the fancier Shockcraft spring calculator and it still recommended a 325... same as their free version. I was pretty disappointed. Wish there was a nice coil rental program where I could try a few out and send back the ones I didn't like because coil definitely feels better than air.
  • 1 0
 @Bracher: Ride Aligned on my 20' Range VLT was spot on. The Shore was way out, which was too bad as I rode it at 15% for the year (yuck)

@mnguyen1224: I'd love to see bike manufacturers supply an array of springs - if it is going to ship coil. I just bought a Nukeproof coil for $30 CAD. You know their raw cost would be $5 or less per... When buying a $7000 bike, seems like the least they could do?
  • 8 0
 420.69 lb/in just as I suspected
  • 7 0
 it is only about the color - needs to look good
  • 7 0
 Should probably show your math once at least on your example.
  • 3 0
 Can anyone explain to me why TFTuned's spring rate calculator gives different recommendations for "single pivot/DW-Link" and "4-bar/VPP"?

Of these four designs, single pivot and 4-bar are more alike while DW-Link and VPP are more alike. And why does the patent number on the linkage have any effect? Shouldn't we be looking at leverage curves and progressivity?
  • 3 0
 1st step, calculate roughly what spring you need
2nd step, buy a cheap RockShox coil, or any other steel coil for 20$
3rd Step, Ride it and you will know
4th step, Wonder if buying a light spring is really worth it since you love your bike with the heavy spring.
  • 2 0
 thanks for the article Seb! Ran the calcs in excel for my 130LR and got pretty close to what Push gave me for my spring. I am not sure, but I think that the B coefficient is supposed to be front center / wheelbase as that gave me closer to 65% you mentioned for my bike. fun little science experiment.
  • 3 0
 "But remember, with a more progressive bike you'll usually want to run more sag"

You _want_ to run the sag that feels best. A progressive frame _allows_ you to run more sag if that's what it takes to feel right.
  • 2 0
 The kind of trail you ride is the most relevant variable, and completely missing from the above analysis. Running an air shock you learn what difference changes to spring rates can make to optimise performance across different types of trails.
  • 2 0
 Having recently gone from air to coil I found matching bottom out force more crucial than matching the sag. With air I was running 30% sag (and 3 spacers in a rockshox super deluxe) and on coil I'm running a 450lb spring (higher than the 350-400lb recommended by TF tuned calculator) which gives 26% sag and I feel like it's not quite as high a bottom out force. If we ignore the bottom out bumper it's easy enough to calculate teh bottom out force on a coil shock. It would be useful to have the data to calculate the bottom out force for the air shock. Actually thinking about this the compression ratio calculated from a shockwiz calibration could be useful here.
  • 2 0
 I will say that on my SJ Evo S5 (cause chainstay length/ leverage might be a factor) I found on several instances if you simply multiply the riders weight by whatever the leverage ratio is at the sag point, you'll get the correct spring rate dead on.

For example at on the OEM link multiply my riding body weight 192# times the leverage rate at the sag point of the stock link, 2.85, and I get 547#s. With the Cascade at 3.25 LR I get a 624# spring. Both of these were very close to what I settled on, using the Springdex.

IME, the Springdex works really well on the first few turns of the adjuster, but when you get it nearly tightened all of the way down it's not working as well.

I jacked around with a high end coil for months. Never again. The future of MTB suspension is air, of this I am certain.
  • 1 0
 The formula in the article is the same one that EXT has in their manual for the Storia / Arma shocks. I've found it to be very accurate provided the user is truthful about riding weight, and the rear bias is bumped up to 70%. I think a lot of people underestimate how much weight they carry on their body (or how fat they are). And I think a lot of people ride a bit more off the bike (or maybe ride steeper trails more often). Either way, when friends have asked for help choosing a spring, this calculation seems to be dead on with the 70% bias, while when they use the Fox calculator, it tends to be about 25-50# too light.
  • 1 0
 Has anyone actually tried the equation? For my 2020 Norco Sight with 28% sag, 150mm travel (5.91"), 52.5mm stroke, 3.0 leverage ratio at sag point, 180 lbs rider+kit weight and 65% weight bias I get 50 - I guess it's supposed to be 500 but I get 50?!
  • 2 0
 I found 594 with your numbers. Did you convert the XX% to 0.xx ? Or maybe you didn't apply the formula the right way, there is a little misconception that can be made with the 2/TS at the end, the exponent is only about the L.
  • 1 0
 Has anyone tried out the equation? I get 50?!!? I guess it's supposed to be 500? Could there a bracket in the wrong place or something? Here are my stats:
28% sag, 150mm/5.91" travel, 3.0 leverage ratio at sag point, 180 lbs weight rider+kit, 65% weight bias.
  • 2 0
 Using the formula given in the article with your numbers it gives 636 lb/in recommendation.
  • 1 0
 @notsosikmik: I never really trusted that formula. I guesstimate based on the progressivity of the frame and how heavy you are. What I do that works. Ive used this method on 3 custom builds. Most of my builds I used 550 lb for DVO and a 600 lb for canecreek.

Your riding weight (body weight + gear) * 2 * (1+Sag%). and from there if your frame is more linear, think about a progressive coil or that adapter thingy or just jack up high speed compression.

Like for PaulWolf, with my quick and dirty formula, you get 460.8 lb coil. So I say 450 or 475 lb coil.
  • 1 0
 @kroozctrl: Gee, that seems to be a lot lower than the equation or any of the online calculators suggest. How come that you use a lighter DVO but a heavier MRP spring? Are there manufacturer differences?
  • 1 0
 @notsosikmik: Thanks that's what I got too now! Wow, quite high.
  • 1 0
 @PaulWolf: I am curious what bike is this for?
  • 1 0
 @PaulWolf: both my antidote frames dark matter 27.5 (550 lb dvo “heavy” coil) and my carbonjack 29 (550 lb dvo “light” coil).
The cane creek was when I had my Santa Cruz nomad v4. MRP only fits rockshox.
Dvo and cane creek have the same ID. And fox and ohlins have the same ID. But you can use DVO and CC coils on the latter because it’s a 1mm delta.
  • 1 0
 @notsosikmik: I ride a Norco Sight 2020
  • 1 0
 Here is a thought: As far as I can tell, the Fox coils range from 250 to 800 lbs/in with the average being 525. A quick google search tells me the global average weight of a human is 136 lbs. 525 lbs/in / 136 lbs = 3.86 lbs/in per lbs weight of a person. For my 170 lbs (without gear) x 3.86 that would give me about 656 lbs/in (while the equation gave me 637). To be fair this does not take travel, sag point, leverage ratio etc. into account but I think it could serve as a good sanity check to see whether you are roughly in the ball park.
  • 1 0
 As others state, all these calculators are pretty useless without specific leverage info from the frame.

I just used the MRP version and it put me on a 400# spring for a Spire with Cascade link, I run a 550# on that bike and it's perfect......
  • 1 0
 Thanks for the mention! Coil spring selection is such a subjective thing it can be super tough to know where to start from. Different levels of rising rate can make an "ideal" sag amount tricky to know, or you change the spring by 100lb and see little to no difference in the sag....I've got a different calculator in the works that can deal with leverage rates and give a little more insight in to how it will feel. At the end of the day its on the trail that matters most, and certain methods work great for some frames but can be wildly inaccurate for others!
  • 1 0
 Anybody have any good tips to eliminate too out besides closing rebound?
I like fast rebound, especially on a progressive bike I feel like the setup is really compromised with rebound closed enough to stop top out.
  • 2 0
 subscribed :popcorn:
  • 1 0
 There are shocks with good top out bumpers/ top out damping and shocks with bad top out bumpers or even without
  • 2 0
 If b = ratio of rear center divided by wheelbase of bike and b = 65%, wouldn't that mean the chainstay length of the bike is extremely long?
  • 2 0
 No, it means where the Center of mass sits from thefront wheel
  • 1 0
 I also have a doubt: if I divide the rear center (chainstay) of all the full suspension bikes currently on the market, by their wheelbase, I get values ​​below 50%. maybe the calculation to do is front center / wheelbase?
  • 1 0
 @paoloz: You're right, it's the front center/wheelbase, or 1/(chainstay/wheelbase). Both are correct and should give you similar values, with any variation being due to BB drop.
  • 4 1
 Can you explain the formula in English for the non engineers in the crowd??
  • 2 0
 I think the resultant of the IFP pressure should not be forgotten, on a superdeluxe it is the more than 20 daN of force added to the sping.
  • 3 2
 You don't calculate spring-rate by sag. You calculate spring rate for target natural frequency and use preload to set sag. The maths is far more complicated than any of those calculators run.
  • 1 0
 - why use natural frequencies?
- why sag gives a good indication then, even for bike travels that can double across categories?
  • 2 1
 Is that a motorcycle tuning rule? Preload should be a last resort on bicycles because they generally don't sag without a rider.
  • 2 1
 @faul: Because sag isn't a good indication of anything. For a start everyone tries to measure it differently with a different riding position and it's trying to match the whole bike based on the first inch.
Natural frequency is consistent and is set by the whole mid-stroke.
  • 2 2
 @boozed: Preload is necessary for setting sag. Why would you think otherwise?
  • 2 1
 @Dougal-SC: That doesn't answer how the natural frequency will help anything, and how you measure sag has less variation than modifying your travel has.

And please don't preload shocks, they are already exploding without help.
  • 1 0
 @faul: Natural frequency is setting spring rate by how your whole bike actually responds. Sag is setting spring-rate by how the first inch feels and forgetting the rest.

Sensible preload isn't killing any shocks. Preload is a necessary part of coil suspension. With no preload your coil is loose and rattling.
Shocks blowing up is bad design and manufacturing. Also bike companies offsetting shocks to one side so the whole thing is flexed into a banana under bottom-out loads.
  • 1 1
 @Dougal-SC: That would mean you are setting you bike on an average response thru the whole travel.
The first 20-30% of the suspension stroke is representative enough of the useful stroke for sag to be an efficient method. It doesn't give you a perfect rate, but you can either buy the closest spring and call it a day, or adjust air pressure in the future fore fine tuning. Bonus it gives you a coherent tuning for all the bikes, more or less the progression of the bike or spring/damping curve
Frequency tuning would require extra maths, would require extra basis of reference for each amount of suspension travel, for a result that would be less than 10% different.
You're probably the only one doing that in the mtb world.
Frequency tuning is helpful in some motor vehicles because you have some frequencies that matters, like around 1hz for seated human comfort, or your tire own natural frequency, and so on. On a mountain bike, I have a hard time seing any benefit from looking at frequencies.
  • 3 0
 @Dougal-SC: I guess this is the argument for adjustable rate springs such as Sprindex; you can set sag without pre-loading the spring.

Although on reflection it probably doesn't matter that a bicycle doesn't sag on its own because it also doesn't ride on its own!
  • 3 0
 @faul: The biggest effect on sag is how the shock reacts to that first ramp in. IFP preload force effects can be huge or tiny. Using only sag to check your spring rate puts all the emphasis on the wrong things.

Average response through the travel is what matters.

Frequency tuning by feel doesn't even require maths. Every rider has built in accelerometers which give the acceptable range.

Which is why it works far better than any other system. Including the bollocks that is sag.
  • 1 0
 @boozed: Sprindex requires preload. Every coil does.
  • 1 1
 The numbers aren’t making sense to me.

172lb*.64*2.6^2/(6.49”*0.3%)
=172*.64*6.76/1.947
=744.14/1.947
=382lb/in
At that spring rate I would need about 5 turns of preload to get 30% sag on my 2018 Intense Tracer.
If I try using the leverage ratio at Sag (2) I get 226lb/in at sag. Is there something wrong with my calculations?
  • 2 0
 Yeah, that is what I am getting as well. However leverage ratio at sag would not be 2 as that close to the ending ratio. Just eyeballing from a leverage chart I found it looks like the ratio at 30% sag is ~2.75ish. Using that in the formula would result in recommended spring rate of 464lbs/in. Which makes sense because the leverage chart is relatively flat for the first 40mm of travel.
  • 1 0
 I feel so stupid. WTF does ^ mean in the context of this equation? Is it 172lb*.64*2.6 squared /(6.49”*0.3%) ?
  • 1 0
 @militantmandy: Yup ^ means squared.
  • 3 0
 if i accurately calculate my spring rate, then what do i blame my crappy riding on?
  • 1 1
 The issue here, is that springs are not cheap, and if that calculation turns out to be wrong, it's an expensive mistake. The best option is to go somewhere where you can try different springs. For me, that equation provides a value that is wildly different from the spring rate that I prefer to ride.
  • 2 0
 Gives me a tad over 500lbs at 25% which is exactly what im running in my 141.
  • 1 0
 I'm always a little scared that my spring perch will start to move if I don't run enough preload. Wish they had a second lockring like on a moto shock.
  • 1 0
 Na, progressive frame you run less shock sag because you end up with more sag at the wheel. ie 25% shock sag on a 30%+ progression frame is more like 29% wheel sag.
  • 6 3
 This article reminds me one of the reasons I don't miss my coil shock.
  • 3 0
 Totally agree, this is the huge downside of coil shocks. Here's a list of the springs I bought before I found the right spring rate for my MegaTower: 600 Rockshox, 550 Rockshox, 500 rockshox, 500-540 Sprindex, then then 450-500 Sprindex that worked at 495 pounds. Total cost: $470, total time to dial in my setup: 1.5-ish months/15-ish rides. What a pain, and I almost gave up on the coil shock midway through the process.
  • 1 0
 @TEAM-ROBOT: @TEAM-ROBOT: There's the additional problem of what the actual rates are. Dougal at Shockcraft has started measuring springs (including a Sprindex I think) I know my three Ohlins springs are all over the show.
www.mtbr.com/threads/adjustable-rate-coil-spring-sprindex.1122499/post-15497121
  • 4 1
 All those calculators are way off what I actually run.
  • 1 0
 Given that most bikes come with an air shock is there not a way to translate the air shock pressure, bottom out tokens etc into a spring rate?
  • 2 0
 That could be done, but each shock would have his own chart.
  • 1 0
 Yes, but the graphs change with compression speed.
  • 1 0
 Some manufacturers supply OE partners with these graphs...others don't, so the engineers have to test for themselves
  • 1 0
 @Dougal-SC: got to start somewhere!
  • 1 0
 What about when you have an e bike which does appreciably sag under it's own weight. How does that impact preload and spring weight, if at all?
  • 1 0
 Based on my experience of setting up the Cotic eeb prototypes, I would say add 10kg to your "rider in kit" weight and you'll be somewhere near. A full fat eeb has about another 10kg unsprung mass compared to a regular bike.
  • 1 0
 Take the wheels off and weigh it. Assume it's 50/50 bias and add that into the equation alongside your (65% biased) weight.
  • 1 0
 My shock came with 2 springs 475 and 500. Bought a third 450.
450 = park.
475 = pedal.
500 = Porky. Big Grin
  • 1 0
 I don't get this point: B "ratio of your bike's rear center divided"
Does it means the long of the chainstay length?
  • 1 0
 It's actually the front center divided by the wheelbase. Chainstay over wheelbase gives you the ratio of the wheelbase behind the center, but the weight on that wheel will be the inverse. So you can either do front center/wheelbase, or 1/(chainstay/wheelbase). Both versions gave me very similar values, with the difference being due to BB drop.
  • 2 1
 OK, so… Online calculator it is!
  • 1 0
 That all works as long as you weight doesn't fluctuate
  • 1 0
 hard
  • 1 2
 slightly dyslectic all I managed to get is bla..bla..bla.bla
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