Suspension Q...Will adding oil to your forks affect rebound dampening?

[Speedballer347]

Thanks everyone for all of the information, advices and help!!!!!!!

I am going to leave my front rider sag at 30.  With the springs so weak, it still offers a plush ride.  If I went to (correct) 35 it would bottom even worse.

I'll add 5cc per leg of 5wt fork oil, to keep the front end from bottoming and hopefully to dilute the fork oil so my rebound decreases a bit.

Thanks again everyone!  :-)

[Speedballer347]

Since fork oil LEVEL only affects the lower portion of travel, that is how you keep forks from bottoming provided your sag #'s are correct. In other words, if you have the right springs but are bottoming, adding a bit more fork oil will keep from bottoming. Goes without saying though, too much oil will hydro lock the forks and they won't work right.

You know, I am wondering.....
The fork springs were supposed to have been fitted to my weight.  If you pump my forks they feel stiff!  On the track they feel fine, don't seem to dive excessively. The ziptie and bumps are the only thing letting me know they are bottoming.
But they feel stiff pushing on them.  It's like all of the issues are at the very bottom of the travel.

Is is possible when my forks were done, they put an incorrect amoount of oil in them (too little) and now they are bottoming because of the big air gap/volume? ....Not because of too little spring rate. 
Again, the springs feel stiff pushing on them.  Other than on bumps the handling/geometry seems perfect.

Does anyone know the correct oil level for an 05/06 GSXR1000. 


Maybe the forks just have too little and too thick oil?

[gonecrazy]

loose weight, that should fix it

[Super Dave]

GSXR1000 2005. 
Rider sag at 30mm front. 4 lines of preload showing.  Rebound all of the way out.  Compression 6-out (19 or 20 click range)
The forks bottom so hard the zip-tie leaves indentions in the fork's dust-seal.
Don't know if it is bottoming on brakes or bumps, or both.
Bike feels great on the brakes, rear-end is a little light, moves around a little under super hard braking.
Bike packs up on the first bump (feels like it has run out of travel, and the rebound isn't letting it back out).  Just hits, bottoms, and then skips across the bumps.
With the rebound adjusters all the way out, the forks visibly return too slowly, just manually pumping the forks.

I honestly never really thought anything was wrong.
I had the forks/valving done by one of the best, believed it to be dead nutz correct.  Had it adjusted and tweaked by a knowledgable racer to were it felt really good everywhere except on the bumps. Geometry wise the bike is dynamite!
I figured the problems over the bumps was me tightening up and clenching the bars, inducing it.  Always felt like if I was more relaxed over the bumps the bike would be fine.

I finally tried that at Putnam a couple weeks ago, stayed light/relaxed on the bars and carried my speed over the bumps.  Instantly packed up and chattered.  I stayed relaxed and kept doing it, and the same result.  Went faster, same result.
I asked guys that were going the same pace as me if they were chattering in T2 and T9, and they said they couldn't feel any bumps.
Right then I knew something was wrong.  My zip tie was also at the bottom.

I went to Jay Q and he showed me correct rebound action on his forks, and mine is way slower in comparison, and I don't have any adjustment left. It takes about .5-.7 second for my forks to re-extend.
Then I checked the rider sag and I was at 30mm.  I believe I am supposed to be at 35.  I am sure my tuner friend cranked them down due to seeing his ziptie getting crunched when I would pit. I didn't know anything about suspension, all I knew was he made the bike a lot better, even in the bumps.  I figured my ass-clinching in the bumps was mental...I just foound out it's not 


I figured if I could keep the sag at 30mm, add some oil to keep it from bottoming, it would help some.  Also thought I could remove some of the Ohlins 15wt and replace it (and add 5cc) with 7 weight, it would dilute the oil to a lighter vicosity and reduce the excessive rebound.

Was also thinking of adding 1-2 pounds of air in my front Mich to aid in faster rebounding (of the tire at least).

I know this is all a bandaid, but no time to ship out forks till after GIR.  I blame this on me for not learning about suspension sooner so I could have caught the problem...NOT the guy who tuned them.

If you're at 30mm of rider sag, you on the bike compared to fully topped out, and you've got available preload, it almost sounds like the springs are too stiff. 

Stock springs, according to Race Tech, are .95's.  I'm betting that's not bad for someone in the 180 range.  You're making it sound like you weigh more?

Might be worth rechecking sag, certainly. 

Race Tech is also saying that the forks have a long top out spring, thus they say that 35mm of sag is required minimum.

Could be possible that the spring is right to heavy, maybe there's an incorrect spacer in it for racing, or there was a modification done to the top out spring.  Didn't the individual that did the work provide you with a baseline idea of where to start up?

Either way, with talk of the rebound being as slow as you describe, that would cause problems independently.  Too slow of rebound is a good way to toss yourself on the ground.  Could be a mechanical or an assembly issue. 

Oil height?  Don't know off the top of my head at all.  A service manual will give you a number that would probably be lower than what one would set up for on a racing motorcycle.  Might be worth finding that. 

With too much oil, you could have a bottoming problem too when you run out of air compression.

[twilkinson3]

Something is not right with the forks based on the info provided - rebound all the way out would (if memory serves) make the forks as fast as possible and a half second to return to original position from comrpession sounds slow - how much stiction did you find in the forks when you measured sag?

[tstruyk]

I'd look for bite marks on the fork tubes... Jo Jo is one mean son of a bitch!

[Speedballer347]

I'd look for bite marks on the fork tubes... Jo Jo is one mean son of a bitch!

True story!!!   

[roadracer162]

I didn't see any posts about these two points of interest.
1) Make sure the correct adjuster is being used for Compression damping and then rebound damping.

2) It is possible to overtighten the adjuster locking it into a full slow mode. I've had an R1 that I had bought found stuck that way. I've also seen a freshly built set of forks adjusted incorrectly that displayed in the same manner.

Mark

[GSXR RACER MIKE]

Not sure what weight fork and shock oil is suggested for stock suspension or whatever components you have in there, but Racetech suggests using their US1 oil for your bike (3.5 to 5 weight oil). If that's accurate for your suspension set-up as well, then 15 weight oil will definitely cause a rebound problem!

Too heavy of oil should also be effecting your compression damping, even if your springs are too weak for you the excessive damping may be preventing the forks from bottoming out immediately during your hardest initial braking. But even with really slow damping the suspension will still eventually find bottom if the springs are too weak, which may be the case when your turning.

[Speedballer347]

Want to thank everyone here for all of the help with my fork issues.
I took the bike to WFO-Motorpsports and had Jerry go over it.  Everything everyone here was saying was confirmed.  My fork springs are a hair too stiff, the fork oil is too thick for my rebound valving, and the oil level was way too low.  WFO is going to service them and get them correct.
Thank you all again for all of the help!!!  8)

[tstruyk]

And what about JoJo???

[Burt Munro]

And what about JoJo???

Speedy's trying to keep him on a metal free diet.