When those of you, who have switched to the Progressive springs, and have also switched to using 15w fork oil, did you find your suspension to be smoother over bumps?
I really didn't notice any difference. I think the previous owner may have put 15 or 20w oil.. when my fork seals started leaking i dropped in progressives and 15w.. feels about the same.
O.K., I'm 125lbs, so the stock springs were ok (with 10w Bel-Ray fork oil) for a while until I got tired of the dive (it wasn't unsettling, the dive was nice when coming up to turns as it would maintain it's compression through the turn making for the tighter turn-in, better front tire loading, and lower center-of-gravity), then I switched to the Progressives with no preload, had my crash, and then put 3 x 1/8" thick washers in each leg for preload and set my sag (Rider sag; perfect at 1.5inches). All this while having an /80 series profile tire (maintained at 33.5psi) and the forks down (not up)through the triples 2mm; and reeling from sharp bumps on my commute.
So, these sharp bumps are getting to me and I decide to remove 1 washer from each leg. That didn't help. Then I slid the forks back to their factory height; Wow, what a difference in the action! With the forks raked out, even the 2mm's, had caused enough stiction to not allow smooth action of the forks. But, I'm still dealing with sharp bumps. That leads me to the assumption that it must be too much high speed compression damping due to too thick of fork oil.
Now, I want to work with what I have as far as the forks go, so no RaceTech Gold Valves valve emulators, or Katana or GSXR forks. Just the stock springs vs. Progressives, however much preload, and fork oil weight. These are my variables. So, what's your inputs?
Edit: And another concern is that if I do go with a lighter fork oil will I loose so much of my rebound damping that would allow the Progressive springs to "push out" the front end and cause me to run wide in turns?
I've always thought that 15w fork oil was too harsh for freeway droning and such. All the jolting gives me a headache.
Yeah, I'm doing the "Highway Hop-along" over expansion joints. It seems to be better when I scoot forward in the seat. Which again makes me think it's not the springs, because I've been running the same fork oil all this time.
much smoother for normal riding and the brakes work so much better but the 15wt oil is a bit heavy for the highway.
But don't wonder about it if you haven't done it just do it, you will kick yourself for not doing it sooner :thumb: :cheers:
There are very few bikes that share 37mm diameter forks with the GS. The '87-'90 Honda 600 Hurricanes, '86 VFR750F Interceptors and BMW F650's. Edit: And, '88 GSXR750's. I wonder if the stock spings would be a little stiffer, but not as stiff as Progressives? I'm pretty sure that the length of the F650 fork springs would preclude them from this list, and I would think that the springs for the heavier VFR750 would be too stiff...ah, I just remembered that I can check stock spring rates on RaceTech's website.
Edit: Allright, I just checked and the stock spring rate for the CBR600 is .512 kg/mm which is lighter than the .594 kg/mm for the GS. The VFR was unlisted. The F650 is .6 kg/mm. Interestingly, RaceTech suggests Higher rate springs for the CBR than the GS, even though the stock rate for the CRB's is less. The suggested spring rate for my weight (125lbs) is .715 kg/mm.
http://www.racetech.com/evalving/SpringRateCalculation/dirtspring.asp?brand=Suzuki&yr=91-00&ml=GS500&formuse=form1&SpringType=Fork
Edit: GSXR750 spring rate: .751kg/mm.
Basically, what got me started on all this is this website:
http://www.peterverdonedesigns.com/springs.htm
I weigh about 160 and with 15wt and progressives and the caps below the tripletree by 2 mm (extended rake), it seems to ride fine. I havent had bottoming out nor have i seen it to give me a bumpy ride. HOwever i do remember one time giving me a bumpy ride on muholland, but i dont know why it did that.
I just found on the Progressive site the specs for the springs (p/n: 11-1128):
Free length: 19.75"(502mm)
Outside Diameter: 29mm
Rate (soft/hard): .54kg/mm/.80kg/mm or 35lbs/in /50lbs/in
So they're a little softer than stock at first (I believe this is without the .75 inch preload spacer) and then, of course, harder when compressed further.
I'm sorry, but I find suspension tuning so fascinating! I found this while looking up information (free length of stock spring) on F650's: http://faq.f650.com/FAQs/FrontSuspensionModificationsFAQ.htm
Especially: Front Fork Mods - Reducing Fork Tube Torsion during Spring Compression
After changing to Spectro 5w and adding a pair of nylon washers to my preload (+1/8th inch each leg; 1/2 inch total preload for 1 1/2 inch proper Rider sag), the forks have smoothed out the sharp bumps nicely.