The joys of suspension setup or fun with PVC...

[tomacGTi]

For some reason an epiphany happened yesterday that I just wasn't happy with the way the bike handled. Previous settings were: Progressive front springs with 15wt. oil, stock oil level +10cc, GSXR rear shock adjusted to match in preload and dampening. 35mm front sag/30mm rear sag. 165lbs with gear.

The front end wallowed when under braking even after increasing the oil column 10cc per Jay and the rear settings (GSXR-1000 shock) were matched to the front. I also couldn't add anymore spacer for preload as I could barely get the recommended screwed down. The bike just felt vague. Although things were set to where they were supposed to be, it just felt off and the front end certainly didn't feel "planted", it just felt like it was following along, making it difficult to change lines, etc. It was soft and floaty on the highway and although comfy, it certainly didn't feel very racy in corners although I was trying my damndest to push.

I decided to use the stock springs that I had removed a year ago and cut off the progressive section to make it a straight rate and extend the stock spacer accordingly using PVC (the NCRick mod). I increased the oil column another 10cc+5cc (to account for oil lost by taking out the Progresssive (name brand) springs that were in there before and dicked around with sag till I settled on 30mm in front and 25mm in back.

Results: Bike is much tidier, so much so that hard, high RPM gearshifts no longer upset the bike and it feels like the power is going from the motor directly into the rear tire. There's no more hobble-horse effect from front to rear. Tipping into corners  is pretty much point and shoot and even mid-corner, fully commited line changes are better (had to avoid some odd debris in one or two today). The on-off throttle buck that I used to have seems to be more tamed to the point where I can gently roll on and off as needed to tighten my line mid-corner and braking no longer packs the front end down so much to the point that it seems like it's on the bumpstops. The front and rear just seem to be working much better together and more balanced.

Honestly, I don't know if the results are purely out of riding the damn thing so hard to see if the changes were better or if the changes didn't make that much difference. About the only thing I may try to do is increase the front sag a hair bit: coming over a rise the front end got a hair light under throttle and wiggled a bit. Nothing steering dampener level, but something it never did before. I'm also reluctant now to dig in there again (as I'm also sore as hell from trying to compress a spring and spacers multiple times) as it's the best it's been in the year I've owned it.

I'll give it a week or so and report back with any changes.

-Randy

[BrianM]

Just a couple observations....  

Oil level just controls the Air Spring, which gives a nice, comphy bottoming feeling vs. the hard, hydraulic lock of the built-in devices.  If you're not using the full range of the forks, no sense in adding more oil.  

Sag isn't really That important so long as there's "some" (yes, this is debatable ~ just my experience derived opinion after tuning lots of racebikes).  I certainly wouldn't go back in just to change that.

Sounds like you've got more than the industry standard 10mm of spring preload (based on your comment about being tired from compressing things).  You'd notice some more improvement by going with proper weight springs and 10~15mm of spring preload.  Things you Should notice with that kind of change are a 'softer' ride on the highway over expansion joints and cracks, yet a firm feel when you start pushing on the bike for braking and cornering.  Kind of a "best of both worlds" type thing.

As as for your front getting a bit light, that May be the 15wt. fluid.  I just changed seals and oil in my forks and put 15wt in there and I think the rebound is a bit slow because of it.  I'm definatally going with 10wt if this winter goes by and I don't put cartridge forks on, I suspect it'll be better for rebound.  

Anyway, some of that's opinion, some of it's fact....  but don't change anything if you're happy with it right now.  Maybe just consider the information for the next time you do go in there.

 

[tomacGTi]

My spring preload via PVC was about 15mm or so after factoring in the removed spring section, maybe 20mm on the fat side of things. I also didn't really feel like buying any more oil as 15 was what I had on hand and the oil is about a year old and still looked ok.

I agree, doing it the right way would certainly be the best way but I figured I'd give this a shot first and see how it went. I have some gold valves looming in my future and this is a stop-gap till I get around to it. I had the parts and felt like experimenting but it's like Rob and his carbs: opening another can of worms only leads to more worms...

Any suggestions as far as sag or anything should be Brian? I was also able to top it out to the stops but added the oil mainly to get the air spring to support the bike more under braking. That coupled with the fact that the Progressives that were in there took up so much room (almost twice the amount of steel versus what's in there now).