2008 YZ250 harsh on high speed chop

[yz426rdr]

Looking for some input on how to tune my forks for less harshness on high speed chop. I ice race this bike and as the race goes on, the track gets much rougher and I'm having a hard time even hanging onto the bars. The forks are stock, including springs. I have a set of 0.48 springs to put in (I weigh 230lbs without gear). I am going to put in the springs but am looking for suggestions on how I might change the valving to lighten up the high speed damping. I'm sure that with my weight the forks are hanging down and that is why they feel so harsh, but is there anything else that I might do? I was thinking of removing 3-6 of the face shims on the base valve or look to turn it into a two stage stack.

This style of racing includes top speeds in excess of 80mph and the track gets quite rough as the ice tires chew down into the ice in the corners.

[Adammoto]

Interesting. I have 0 experience tuning for ice racing...but 80 mph is fast and ice is hard. I'd suggest backing out the rebound clicker adjustment to start. Next add a crossover in the base valve. Then reduce pivot diameter in the base valve. Finally, consider removing shims from the midvalve. Let us know how it goes.

Edited January 31, 2012 by Adammoto

[yz426rdr]

I haven't been into the fork yet, but I've had the shock apart and the valving was identical to what mx tech has listed for the 2011 yz250 shock, so I'm going to assume that the fork will be the same as well. This is what I'm thinking: 1) remove 3 of the 32 x .11 face shims in the base valve, 2) move the 20 x .11 shim up inbetween the 3rd and 4th 32 x .11 face shims to give me a crossover in the base valve, 3) remove one of the 20 x .11 shims in the midvalve to the bottom of the stack between the 17 x .30 and the 11 x .30, 4) Install the 0.48 springs, 5) lower the oil volume to 315cc.

From the reading I've done on here, the valving I'm after would be a lot like desert riding which would need to be stiffer than woods riding but not quite as stiff as motocross.

Base valve

32-0.11*3

20-0.11

32-0.11*10

30-0.11

28-0.11

26-0.11

24-0.11

22-0.11

18-0.11

16-0.25

Mid valve

20-0.11*3

18-0.11

16-.011

14-0.11

12-0.15

11-0.30*2

20-0.11

17-0.30*2

What do you guys think of these valve stacks, will they lessen the high speed chop I'm feeling? Reading more in here this evening has led me to believe that the stiffness I am feeling is in the face shims as the chop I'm experiencing is high speed but short travel. So I need to reduce the damping in the face shims and the mid valve to lessen this up.

Also, if I remove three of the face shims, do I need to replace them somewhere else to make the stack the same overall thickness? Will the valve stack bolt back together without adding more shims or spacers somewhere else?

Please correct me if I'm wrong as I have alway previously relyed on Race Tech valving charts with gold valves when revalving forks. This time I would like to tackle this on my own.

[RBdirt]

I am 229 before gear and stock suspension feels like its rock hard at even 20 or 30 mph... its going to be so much more plush with the correct springs. I have no doubt that valving will help but I would not base it from the feel of the stock springs, we are 50-60 pounds more than these bikes were sprung for.

[mog]

I would be tempted to try just the springs first ( what's the rear sags? ) but if your going to change valving try just the base mod first as its going to be a big change if you do the base and mid

[yz426rdr]

I've got the rear sag at 100mm, forks are raised 5mm in the clamps. I was tempted to just try the springs, I have a 5.2 spring for the rear as well.

If you think this may be all I need, I'm willing to try as it would be a lot less hasle. I've got to do something though as I'm still trying to get over my sore wrists from the Saturday race!

[the jayman]

Here in Finland typical mods for ice racing are lowering the bike and making it stiffer! Speeds are so huge that it's possible that front fork runs all the time with air spring and rear shock on progressive part of the linkage. Ín stock form bike can also wallow when entering and exiting corners. So your mods might make the suspension actually feel worse.

If you still feel that making it plusher is right call, your stacks look pretty good except I would go with 14mm clamp in BV (replace 16 x .25 with 16 x .11), use crossover lower in the BV stack (maybe 8th-9th shim in this case) and drop the 20 x .11 shim from end of the midvalve stack to open up float by 0.1mm and move 12 x .15 shim in MV below 11mm clamps. That MV setup will works really well, I'm using it to woods riding for all 2strk Yamahas.

[yz426rdr]

We run stock suspension as the races are 6 hours in length on a minimum 6km long track. I was running in the 3 hour class. The ice can get so rutted that a lowered bike would be bottoming out, guys have tried it and it hasn't worked for them.

I'll drop in the springs and see if that helps. I was thinking that the bike was too stiff but I can see from your comments that maybe I'm going the wrong way and have to go stiffer. I kept backing out the compression on the pit stops, didn't think it got better, but then again, my wrists were already so sore I probably wouldn't have noticed an improvement!!!

I keep looking at the bike thinking stock motocross valving is the issue, but not taking into consideration my extra weight requires stiffer valving.

[mog]

a video clip would help see if its riding low and blowing through

[yz426rdr]

So I put in the stiffer springs, raised the oil height in the forks to 350cc and cranked in the compression on both ends, worlds of difference!!! Here I thought it was too stiff, but actually is way too soft for my weight, even with stock motocross valving. Might actually have to go stiffer yet as I'm running about 6 clicks out on the compression on the forks. Thanks for the advice all who replied.

[no hand]

Here there are alot of ice racing fans and most racers use 3w shock fluid in their fork. Besides that it's mostly stock... besides fork springs that has been cut 3 inches ;-)