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Need some help with spring rates


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Hey guys,

I need some help figuring out spring rates for my 2005 Yz250 2t. I weigh 235 on my bathroom scales which I believe to be accurate, so figure 250-255 in gear. I replaced the stock fork springs (.44s) with (.48s) and replaced the factory 4.9 shock spring with the factory spring off my 2008 YZ450f (pink code 5.5). With the race sag set at 100mm, I only have 13mm free sag, indicating the spring is to light for my weight. However, when I plug my info into the spring calculators on race tech or mx tech, it tells me I should run a 5.3 spring. What's going on here? Have you guys ever seen a factory spring that's really weak? Any ideas on where to go from here would be greatly appreciated.

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yeah I'm still scratching my head on this one. I thought if anything the spring would be too stiff for my weight based on the calculators, but it's actually a little light. Time for me to get on a diet I guess, lol.

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With the race sag set at 100mm, I only have 13mm free sag, indicating the spring is to light for my weight. ...

try to let the bike sag slowly by its own weight and measure the sag, then push it down and let it rise slowly, take the measurment.

is 13mm the mean value?

do both values differ much? so is your linkage tight or is it ok?

Edited by kawamaha
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ok, remeasured again this morning and has 87mm race sag! So with the help of two other coworkers, I backed some preload off the shock spring to get to 100mm race sag, which left me with 19mm of free sag. I understand that this spring is still just a tad light for my weight but probably ok, correct? Any strange handling surprises that this may cause? I did notice that this past week riding (this bike is new to me guys) that I was flying front-end high off most of the jumps. Is this a setup issue or just me getting used to throttle control of the two-stroke? I have a 08 yz450f that flies level but I hit jumps usually at a constant speed. It seems the yz250 2t is either always accelerating or decelerating, its hard to hold at a constant speed. Thanks for your help guys.

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It seems the yz250 2t is either always accelerating or decelerating, its hard to hold at a constant speed.

don't compare twostrokes to fourstrokes🤣

2-T's are much more nervous, thats why I prefered gnarly pipes and run them one gear higher than experts 👍

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