Race Tech oil height speculation/question

[Barbarian]

For my yz250f, Yamaha recomends 150mm fork oil height. I recently installed the gold valves, and Race Tech recomended 90mm, which means about 2.5 inches less air space.
I've noticed that my Race Tech forks are very plush in the first 5-6 inches of travel, but never bottom. I'm guessing that the Paul Theade theory is to run softer valving for plushness, then jack up the oil height so that the fork stiffens later in the travel and doesn't bottom.
It makes allot of sense, but personally I'm not happy with the forks right now, even on "prefers stiff", they seem to dive/wallow, and feel mushy too much.
I want to keep working with the gold valves for now because I'm learning allot, so would it make sense to stiifen up the valving, and then lower the oil height so my forks are not too stiff when compressed far into the stroke.
I'm a little scared to put the mid-valve back in right now, I don't feel like I know enough to work with it.

 

[phoneman064]

For my yz250f, Yamaha recomends 150mm fork oil height. I recently installed the gold valves, and Race Tech recomended 90mm, which means about 2.5 inches less air space.
I've noticed that my Race Tech forks are very plush in the first 5-6 inches of travel, but never bottom. I'm guessing that the Paul Theade theory is to run softer valving for plushness, then jack up the oil height so that the fork stiffens later in the travel and doesn't bottom.
It makes allot of sense, but personally I'm not happy with the forks right now, even on "prefers stiff", they seem to dive/wallow, and feel mushy too much.
I want to keep working with the gold valves for now because I'm learning allot, so would it make sense to stiifen up the valving, and then lower the oil height so my forks are not too stiff when compressed far into the stroke.
I'm a little scared to put the mid-valve back in right now, I don't feel like I know enough to work with it.

Barbarian,

The racetech method of measuring oil levels has you evacuate the oil from inbetween the fork tubes by fully extending the forks after filling with oil. The Kayaba method is to leave the area between the tubes full of oil for the measurement. The racetech recommendation presumes that you extend the forks before a measurement is taken. I believe the area between the tubes can hold as much as 20cc of oil. That is the "technical" difference between the two methods of oil level measurement.

My experience with Kayaba's is that you definitely need the mid-valve for even mildly agressive riding. I believe that Racetech recommends leaving the mid-valve in on 2001 and later YZ's to remedy the problem you are discribing.

good luck,

Dave

 

[Barbarian]

OK, but how will I know what base stack to use in this situation? I am a very aggresive rider, and I prefer a firm front end.

 

[Barbarian]

Also, my inner fork tubes have holes drilled into the top of them, does that mean I don't have to worry about the air chamber between the inner and out tubes?

 

[phoneman064]

Also, my inner fork tubes have holes drilled into the top of them, does that mean I don't have to worry about the air chamber between the inner and out tubes?

The addition of holes would in the Kayabas would mean that the 90mm RT recommendation wouldn't apply to your forks. I would use the Kayaba method and set it around 110 and try it.

You said the midvalve was removed...asuming that you did the removal, I would recommend putting it back in and and not changing the basevalve. I've found the stock mid-valve to be acceptable for int/exp offroad and mx and believe this would fix your diving problem.

Paul Thede has stated that on the 2001 and newer that the mid-valve should remain in for both type 1 and type 2 GV regardless of offroad or mx.

-dave

 

[Barbarian]

ok then I'll do it, it just pisses me off that that was not in my instructions. Thanks for the advise Dave, I really appreciate it. I have 1.5 weeks to get dialed in for the Brown Jug enduro.

 

[Barbarian]

OK I did the deed, I put in a stack like an 01 wr250f, but with one extra big shim by the piston, because I couldn't remember what the yz stack was like. I had written the wr stuff down from my other bike. Can't wait to ride.

 

[Barbarian]

I rode for about 15 minutes today. From what I could tell, you guys were right. Diving problem has disappeared. Thanks.