spring rate

[thebig450es]

What is the stock rear spring rate for a 400ex?

[dustin_j]

325 lb/in

[fearlessfred]

Originally posted by dustin_j
325 lb/in and if compressed it 5 inchs ,how many pounds per square inch would you have?

[dustin_j]

Are you testing me Fred :) ? If compressed 5 inches you'd have 1625 pounds of force pushing back on each end of the spring (in theory).

[thebig450es]

Since i put my GT thunder xc link on i need to find a spring with a spring rate of about 355-360

[dustin_j]

Hypercoil and Eibach springs retail for like $110 now (they just went up); they can be purchased through shock builders, check with M@ul Tech ATV.

Otherwise, the stock rear spring rate on an 04-05 450R was 360 I believe. The springs are a little shorter and larger diameter, so you would at least a different upper spring seat. GT Thunder sells different spring seats for $30 I believe, but you could just have some turned down on a lathe.

[fearlessfred]

Originally posted by dustin_j
Are you testing me Fred :) ? If compressed 5 inches you'd have 1625 pounds of force pushing back on each end of the spring (in theory). no ,not testing you . you know way more than I. my reason for asking is because so many heavier riders tend to preload the crap out of there stock springs to get proper ride height and i thought maybe some talk about spring rates might convince them to do otherwise.

[dustin_j]

Originally posted by fearlessfred
no ,not testing you . you know way more than I. my reason for asking is because so many heavier riders tend to preload the crap out of there stock springs to get proper ride height and i thought maybe some talk about spring rates might convince them to do otherwise.

Big450es, let me know if you want this moved to a different thread. Have you tried using the stock spring already, and found it needed too much preload?

I understand what you mean now Fred, haha. Let's say 2" of shaft travel (spring travels the same distance) corresponds to 4.5 inches of race sag (desired). So if a 400 lb/in spring gave the correct 4.5" of sag with no preload on the spring, there would be 400 * 2 = 800 lb of force pushing on the spring at ride height (correct sag, rider on board).

Let's consider adding enough preload to make the stock spring work. Since the spring travels 2" to get the correct sag, you will have 325 * 2 = 650 lb on the spring if there wasn't any preload. Since the force is 150 lbs short, you would have to apply 150 / 325 = 0.462" preload to get the correct sag.

The issue here is that the spring has to be pushed on with more than 150 lbs just to begin compressing (about 70 lb at the wheel); whereas the 400 lb/in spring wouldn't have to overcome this initial force.

Another thing to note is bottom out force. If there is 4.5 inches of shaft travel, the 400 lb/in spring would provide 400 * 4.5 = 1800 lb of bottoming resistance. Whereas the preloaded 325 lb/in spring only provides 150 + 325 * 4.5 = 1612.5 lb.

So yes, you could just preload the stock spring to make it work, but it will feel very rough over small chop since so much force has to be applied just to start compressing the rear end. You would also be more prone to bottoming out since there's less spring force there. To relate this to body weight, the stock 325 lb/in spring will work with a GTT MX link for a rider up to 150 lbs, and a 400 lb/in spring would work for a rider around 225 lbs. I hope this helps some; please feel free to add to the discussion :)

[fearlessfred]

Originally posted by dustin_j
Big450es, let me know if you want this moved to a different thread. Have you tried using the stock spring already, and found it needed too much preload?

I understand what you mean now Fred, haha. Let's say 2" of shaft travel (spring travels the same distance) corresponds to 4.5 inches of race sag (desired). So if a 400 lb/in spring gave the correct 4.5" of sag with no preload on the spring, there would be 400 * 2 = 800 lb of force pushing on the spring at ride height (correct sag, rider on board).

Let's consider adding enough preload to make the stock spring work. Since the spring travels 2" to get the correct sag, you will have 325 * 2 = 650 lb on the spring if there wasn't any preload. Since the force is 150 lbs short, you would have to apply 150 / 325 = 0.462" preload to get the correct sag.

The issue here is that the spring has to be pushed on with more than 150 lbs just to begin compressing (about 70 lb at the wheel); whereas the 400 lb/in spring wouldn't have to overcome this initial force.

Another thing to note is bottom out force. If there is 4.5 inches of shaft travel, the 400 lb/in spring would provide 400 * 4.5 = 1800 lb of bottoming resistance. Whereas the preloaded 325 lb/in spring only provides 150 + 325 * 4.5 = 1612.5 lb.

So yes, you could just preload the stock spring to make it work, but it will feel very rough over small chop since so much force has to be applied just to start compressing the rear end. You would also be more prone to bottoming out since there's less spring force there. To relate this to body weight, the stock 325 lb/in spring will work with a GTT MX link for a rider up to 150 lbs, and a 400 lb/in spring would work for a rider around 225 lbs. I hope this helps some; please feel free to add to the discussion :) you nailed it man.even if you can get correct ride height by preloading,you still dont have enough spring to control bottom out.i just wanted to add that the front springs being correct is just as important because of body roll .the spring should do most of the compression dampening.the spring will hold the bike up when cornering and the shock,because of the slow speed bleed off,will let the bike dive into the corners.dustin you have nothing but respect from me.you help people on here in a respectfull way and never step all over anyone, im taking lessons ,but im a slow learner

[thebig450es]

I enjoy learning about this lol keep it comming

[dustin_j]

Originally posted by fearlessfred
you nailed it man.even if you can get correct ride height by preloading,you still dont have enough spring to control bottom out.i just wanted to add that the front springs being correct is just as important because of body roll .the spring should do most of the compression dampening.the spring will hold the bike up when cornering and the shock,because of the slow speed bleed off,will let the bike dive into the corners.dustin you have nothing but respect from me.you help people on here in a respectfull way and never step all over anyone, im taking lessons ,but im a slow learner

Fred, thank you for the kind words. I still have a lot to learn, and I enjoy reading and learning from your posts as well. I can tell you have a lot of experience and also enjoy theorizing and thinking through things. I'd love to hear/see more of your desertsled :).

I agree, people tend to focus only on ride height since it's the easiest to set/measure. However, that is only one snapshot within the entire wheel travel; fudging to get the "correct" ride height only messes up the shock's reaction during the rest of the travel. Very good points on front spring selection, do you also want to discuss multiple spring rate setups? That's a good example of why there needs to be low speed bleed in both rebound and compression; in other words, you can't run with the rebound needle shut.

Big450es, are you planning to just change the spring to see if your shock works better with the link? If that works well enough, great, but the stock valving is a little soft for that linkage and a heavier spring (both compression and rebound). If you're hoping to just save some money on a revalve, maybe I could help.

[thebig450es]

Yeah i would love to learn and get some help, i know im way to soft right now with the stock spring.

[chronicsmoke]

Sticky this!

Def. a good read. Thanks! (even though it's stilla bit outta my realm :huh haha )

[dustin_j]

Maybe it would be helpful to you and others to just start from the beginning with your current setup. Have you set sag with the stock spring? If you haven't set or gotten a good sag reading, I recommend always starting there when changing setups.

To set sag, put the quad on a stand. I recommend removing spring preload until the upper spring seat is just touching the spring; the spring should rotate easily, but be touching the seat the whole time. Then, have someone else measure vertically from the top of the axle by the rear sprocket, to a place on the subframe (it helps to make a mark with a sharpie for consistency). Call this measurement 1. Next, put the quad on a level surface (cement or similar is preferred). STAND (sitting is hard to be consistent with) on the pegs, bounce up and down, and turn the bars back and forth; this settles the suspension to give an accurate reading. Have the same person take the same measurement, and call it measurement 2. Your race sag = measurement 1 - measurement 2. GT Thunder's recommended sag (also many others and myself included) is 4-5 inches of sag (38-48% of travel). 4 inches will have a higher ride height with more bottoming resistance, and 5 inches will have a lower ride height with a more plush ride.

If your race sag is less than 4 inches, your spring rate is too stiff, and you need a lighter one. If your sag is greater than 5 inches, put the quad back on the stand and add preload 2 turns at a time; make sure you count the number of turns on the spring. If you need more than 6 turns, you need a stiffer spring rate. I prefer to run springs that give 4.5 -5 inches of sag with no preload on the springs {not hoping to confuse anyone, but this is a true zero preload spring setup, unlike the ZPS setups that are actually negative preload, haha}. If you would like to take these measurements and report back how much preload is needed on your spring, we can help make recommendations and others might learn also.

If anything is unclear, please let me know. There seems to be many misconceptions and misunderstandings about our suspension setups. I don't know it all, but I love to learn and try to figure it out.

[thebig450es]

Wow thats really helpful, when i get some time today i'll measure and report back. Thanks for the info

[fearlessfred]

good stuff dustin. I would love to learn more about multispring setup.the one setup that i had for years was off nic grunlands cannondale and it was the best i have ever ridden and never had to touch it, so i had no tuning experence with that set up.and before that,it was my desertsled and that is infintely adjustable.you could even change the rising rate of the air spring by adding oil on the topside of the piston.big 450,im glad your not offended by me jumpin in on your thread. i seen the chance to get more info out of dustin

[dustin_j]

Sorry I've been busy lately and haven't had a chance to respond. Here's a short intro to multiple rate spring setups. The first/main thing to understand is that stacking springs LOWERS the rate of the entire stack. The equation is

1/Keq = 1/( 1/K1+1/K2+1/K3+...)

Where Keq is the equivalent spring rate; force required to compress the entire stack 1 inch. K1, K2, K3 etc are the different individual spring rates. If you have dual rate, only K1 and K2, triple rate K1, K2, K3, etc.

For example, on my stock front end 450R, I have a 225 lb/in Main spring (K1) and a 160 lb/in tender spring (K2). So my equivalent spring rate is:

1/Keq = 1/( 1/K1+1/K2) = 1/( 1/225 + 1/160) = 1/0.010694
Keq = 93.5 lb/in

So as long as both springs are active, the spring rate is 93.5 lb/in. This very low equivalent spring rate is how I get enough sag for my ride height. Crossover spacers are used to "cross out" a spring and change the equivalent spring rate. When my tender spring (the short 160 lb/in spring) crosses out, my spring RATE changes from 93.5 lb/in to 225 lb/in. This rate increase obviously helps with bottoming resistance and "bump" control. We can get into more specifics later, but maybe this will get some thoughts started.

Fred, I am still very intrigued by your desertsled setup. I didn't think to add oil to control the rising rate of the air. I need to look at your pictures some more and think about this, but I'd like to discuss air shocks some with you. That quad is really neat; thank you again for sharing pictures of it.

[fearlessfred]

I assumed that your rate would be 160 until you hit the cross over. well ,you no what they say when you asume.On my desert sled the air spring is only a spring and the shock is seperate. the spring is vary simple.it is built like a shock, but has a solid delron piston with a polypac seal that is used in a hydrolic application. oil is added to the top for lube and to change the rising rate.the oil is measured vary carefully and is kept the same on both sides. nitrogen is added to the springs with them fully extended. and is only about 100 pounds fully extended and you wouldnt dare use the same gauge to check full bump.I had fill valves added to the lower side of the spring to lower the bike,but that was not that great of an idea,because if you get more preasure on the lower side than the top,the preasure wicks up to the top. i tried running running a different piston with poly pacs on each side of piston.but there was to much stiction. thats probably more than anybody wants to know

[thebig450es]

Right now my race sag is about 5.5", but with stock preload, ive never messed with the settings. Whats the best way to adjust the preload out so there is no pre load effecting the race sag.

[dustin_j]

To be honest, just use a big flat blade screwdriver and a hammer to loosen the lock nut (it's std right hand thread). Make sure you thread the top nut up to the top of the threads and out of the way. Put the quad on a stand and you should be able to thread the upper spring seat to the top of the shock. Then set preload so it is flush with the top of the spring and make a mark on the spring and remember it's reference to something on the shock. This way you can count rotations to get appropriate sag.

It's easier to count preload added rather than preload removed. You can also buy a spanner wrench for the preload nuts, but the screwdriver is much faster.

I've never counted or measured to see how much preload comes stock on these, but yeah you'll need a stiffer spring. See how much preload (how many turns) it takes to get 4.5" race sag and we can try to figure out what spring you need. I measured last night and 4 turns is roughly 0.25" preload, so each turn is 0.0625."