OZ ATV :: The Australian ATV Forum

[Clarkie]

I borrowed this from another Forum, thought it was worth a read for people like me who dont realy understand springs ( I know Fox floats dont have springs)


Before understanding the different rates you need to know how springs are rated – springs are rate for the amount of force it takes to compress the spring 1�. The numbers below are simply for ease of math – not necessarily the rates we use in our JET Stealth Conversion Kits.
A single rate spring of 100lbs means for every inch of compression it takes 100lbs – so the first inch 100lbs the next inch – 100lbs more (200lbs total) the third inch another 100lbs (300lbs total) and on we go from there. A single rate spring is very easy to tell since you can see the coils are all the same distance from each other. For several applications a single rate spring is not versatile enough for different types of terrain – if we were all racing on an oval asphalt track, single is o.k., but most of us are hitting rocks, cross roots, bumps, big G-outs, jump faces, big landings and want the suspension to feel good on all terrains. In order to accomplish this we need some type of progression so we can initially be soft enough to take on the stutter bumps, rocks, etc – but also be able to take a big hit. If we simply decrease the rate of a single rate spring to be soft enough for the little stuff – by the time we get further down in the spring – there is not enough support for the big hit. Conversely if we stiffen the spring to take the big hits, everything else becomes harsh and we take a trip to the chiropractor.


Dual rate springs – (I prefer triple for MX – but BIG MX triple may be too soft so we will use dual for big jumps over 70’) since we are looking for progression to be able to be versatile – we can progress by mechanical linkage (rear linkage) or stacking springs. If we stack TWO springs of 100lbs – the rate is softer – which becomes 50lbs per inch instead of 100. So if we have 3� of shock shaft – we can allow the two springs to compress (with a rate of 50lbs / inch) – this will be soft enough to deflect easily hitting roots, rocks, bumps etc – but TOO soft for the big hit. NOW that we have it softer, we will allow the two springs to work together at 50lbs per inch for the first half of the shock travel. Half way through the travel we will install a mechanical stop for the top spring so it can no longer move. Now the only spring that can move will be ONE of the 100lb spring (main spring) which will make the spring rate change (or crossover) from 50lbs per inch to 100lbs per inch. Since we are now at a stiffer spring rate than before – it can take the bigger hits. We can play with this position of crossover up or down depending on preference and conditions. Sorry if I’m being slow, but I get this question several times a week and would like to be thorough.
This can also be accomplished by a dual wound spring – which is one spring that has some coils that are closer (typically at the top) and some further away. The close ones will contact each other effectively crossing over to the next rate. This works well too, but there is no adjustment to the point where it crosses over.


Triple rate springs – (my woods preference for the front by far) if we are still not versatile enough we can stack another spring on. If we stack (3) 100 lb springs on top of each other (yes there is a formula) the initial rate will now be 33lbs per inch (crossover) then two springs 50lb per inch (then crossover) and the final spring - 100lb. we can play with the rates and crossover positions – but we typically will divide the shaft travel by three between the body and the bumper and use all three spring for the first third of exposed shaft, then crossover the top. The 2nd third of shaft travel will now be two springs, then crossover. The third will be the last spring (Main Spring) which will continue to travel until the shock body hits the bottom out bumper which acts like a progressive fourth rate. Why is this my preference for trail riders and woods racers? Because it is more versatile for so many different situations and they way we design our JET Stealth Conversion kit, we can adjust it simply by adding a crossover ring making it stiffer or remove one making it softer.
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