Hey guys, was hoping someone could share some info/advice on shim stack tuning setup. Running Ohlins 20mm FPK valves in OEM 2007 Gsxr 750 carts. 160lbs rider, A group, trail braker. Ran the ohlins reccomended stack plus some extra face shims to try and help mitigate brake dive. Bike handles pretty well as is but I am sitting on the end range for clickers at .75-.5 turns out on rebound and compression adjusters. I was thinking of going from 8mm to 10mm on clamp shim but I dont want to increase hs damping too much and end up with a harsh ride. Yes. I know, go talk to a tuner is besr advice but this is for my personal bike just because I like tinkering and tuning for fun. Any advice is greatly appreciated!
Forgot to add. Reasoning for shim stack change is this. I was fighting Corner entry/mid corner push and vagueness (didnt want to rotate to the apex or would loose front end on entry). This was mititgated by harder trail braking (front end too high in corner??)...but too hard on trail braking and the front end starts to pogo(bottoming out I assume). The solution (or what felt better) was increase rebound damping and reduce preload. Made it almost perfect but now I am only running 2 turns of preload in (from full soft). And almost have rbd/comp valves turned all the way in. If it helps any mid-corner pictures show that I am around halfway in the suspension stroke currently. I think this is telling me too much spring and not enough damping. So, I am going to go from 1.0/1.0 fork springs to 1.0/.90 to see if that will help but ( I think) I will need more damping as well being as the ohlins shim stack is "one size fits all". I know the general rule of what should do what In a shim stack just not much expirience trying it. My plan is to either increase clamp shim size from 8mm to 10mm (which should increase damping everywhere) But my fear is making hs damp too stiff. Or I was contemplating adding a few more face shims to hopefully increase more damping on ls side while only slightly increasing damping on hs to keep it riding decent. Geometry wise I am 535mm/ 328mm ride height. Penske triple rear. Bike has no problem finishing corners on the throttle the rear feels great besides a little spin up on knee to knee on throttle transitions (like vir) but my rear shock is due for rebuild hoping that will help spin up, I will asses that issue after rebuild and front end is sorted a little better.
You have a similar setup to what I have. What fork oil are you using and what oil height are you setting. I found the stack to work well for me with .95 springs (kind of what you are suggesting going to) and silkolene pro rsf 5wt at 118mm (prettyvsure it was 118 I'll check my notes later) also as far as pace goes, I'm not the fastest or the slowest. At VIR north for example I am usually in the high 37s or 38s during a sprint. 39s if it's a longer race with more laps.
Ahh cool deal. Our pace is almost the same. I need to reference my notes on oil level, I think I am at 120 as well. Was running redline 5 and 10w mixed so 7.5. Very close in cst to the Ohlind 5w which I am planning on running this time. I like the oil level where its at, I just (think) I need more help on the damping side if I am going to lighter springs. I am really hard on the brakes I am told lol I may try this shim stack with a few more face shims or a bigger clamp to increase damping everywhere. Probably one of those have to just try it situations.
Yea unfortunately I really don't have the knowledge on setting shim stacks and the changes that will make to be able to help you out. Kind of as you mentioned consult a suspension tuner. You could try throwing some money at one of them for the knowledge, typically I have found that if you are willing to pay to play they will help you even if you are going to diy it.
You should change one thing at a time. You may be surprised at how little damping changes, if any, you need when swapping springs. Id swap the springs and ride the bike. Then session-by-session, start adding preload. Then when you are satisfied with the static height, start experimenting with lower oil level. Then revisit preload and/or springrate. I wouldn't even touch the damping. Also, the speed of your inputs have a much larger effect on the speed of the suspension motion than a 5% springrate change.
Yes I am curious about the spring rate change effects but im not thinking it will be much of a difference. I was really interested in the dynamic behavior difference with a 5% spring change. My biggest goal for this shim stack change is to put my damper adjusters in a more "middle range" as currently my happy range is only a half to one turn off of full closed on reb/comp... which Is OK but not ideal. I do agre, I try to only make one change at a time but I will set bike at same baseline with the only difference a damping tweak and a 5% spring rate change. Same oil and height as before.
The needles in those OEM cartridges are shit. The only real adjustment is in the range you're talking about. If you looked at the needle, you'd understand why.
Ah, so I am on to something lol You are being nice calling it a "needle" So basically I should just not mess with good enough here. Current stack is close to what ohlins calls for with my random guess of shim additions... worked "well enough" 18x.2 16x.15 16x.2 (2) 14x.2 12x.2 Clamp 8mm
I'm not an expert suspension guy, but my 2 cents is that you're experiencing spring related issues more than damping. My goal with spring and preload is to get the fork or shock working in the portion of the stroke where you're having issues. Installed preload on an ohlins kit is 6 turns- Not sure about the stock fork with the ohlins valve, but on the 3omm that would basically be like no preload on your 1.0 spring. As others have said I would try the .95 and don't touch anything else first. Sometimes I go to my suspension guy with my theories and he tells me that's all wrong so take it with a grain of salt. How much do you weigh?
I presume you're using the FPK102, did you ever run it as specified by Ohlins? COMP REB 18 X .25 18 X .2 16 X .25 16 X .2 14 X .25 14 X .2 12 X .25 12 X .2 w/8 clamp w/8 clamp 1.75 turns out 1.5 turns out 107 oil height 7 turns of preload on 9.5 springs 1309 fluid Can you confirm bottoming? I would use oil height to prevent bottoming if that's happening, and softer springs to start. Possibly geometry, maybe raise the forks few mm. Just curious..
The vast majority of the time someone describes "bottoming" their forks to me, it is being prompted by where their data acquisition zip tie is, not because they have a specific handling issue or because they actually experienced the sensation of their forks bottoming out. Most of the time, they are simply using their available suspension stroke, which is a good thing.
Hey guys thank you so much for replies. I ended up reassembling before I saw these last few. Just had my first track day on new setup. Oil at 117m 1309 fluid went to the ohlins specified shim stacks on c/r sides except with a 10mm clamp and daaang does it work much better than the last stack. Metric, I started with 39f/25r sag Running 328r e2e 537mm top clamp to axle (full preload/extending topouts as much as possible) Bike is rock solid, holds a line in and out. Really no complaints. More time on the setup for fine tweaking is needes. Only thing I can try to be picky about is I do miss a little bit of the front damping I had before. I want to play with the oil height, I can feel it bottom when I get on the brakes purposely hard (you know, not using any technique type slamming on them) but only intentinally so I think im pretty dang close here where I am at. Its much better then before
