Choosing correct spring rates

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8/28/2017 12:43 AM

Hey guys.

Have a yz250 and trying to work out which spring rate to go on the rear.

I am 85kg's/187lbs without gear, c grade motocross rider

currently sag is set at 100mm race sag, 30mm static sag. I know this kind of puts me in the window but I have the preload wound about half way down the thread on the shock.

The confusing thing is I seem to get different rates depending on where I look.

Checking the racetech calculator puts me on a 5.5 rear spring,
A local suspension guy said a 5.4 but that was with his valving of both the fork and the shock,
MXA says go up to a 5.0 if you are fast or fat and at 85kg's I assume I am heavier than what yamaha set the bike up for.
mx tech's spring chart is with gear and puts me on a 5.1
Q Springs chart puts me on a 5.0

Checking my manual the bike came standard with a 4.9 rear spring. I'm kind of tempted to go with a 5.3 and just split the difference.
With all the different recommendations how do you go about getting the right spring?


8/28/2017 5:50 AM

I can't offer a ton of help, but I have heard that the Race Tech calculator can be a bit off in their recommendations.


8/28/2017 10:19 AM

You're right there with your current spring. What makes you think you need another one?


8/28/2017 2:37 PM

Sheriff245 wrote:

You're right there with your current spring. What makes you think you need another one?

I bottom out regularly on my local track and i seem to have a heap of pre load on the spring. I will keep trying different clickers to get it closer


8/28/2017 3:04 PM

I used racetech for my springs and its been doing just fine.


2009 Kawasaki KX450F
2009 Kawasaki KX250F
2002 Suzuki GSXR 600

8/28/2017 8:45 PM

The race tech calculator was way off for my 2015 Yamaha YZ250F. Some are ok, but get a 2nd opinion or do your own home work. Should be around 100-107 rider sag, then 30 to 40 of free sag. You in that window, you are probably good.


8/29/2017 8:25 AM

5.4 and 5.3 is a half rate difference. There are other variables such as straight rate aftermarket springs vs slight progressive as with most factory springs. The 1st inch of travel as tested with a typical factory spring will be lighter. With a 145lb rider i got 95 to 100mm of sag with 5mm of spring preload, on stock springs. He was tall, so the slightly stiffer springs helped. I would think on the 5.3 if a typical factory spring, you would be at 100mm of sag with 8mm of preload on shock spring.


Livin' the dream, two wheels at a time!