new GS racer

[GS1150Pilot]

Love those race shots! Post more!

[posplayr]

Another good weekend.

Sunday was wet but I collected a couple points, and am currently sitting in 2nd in 450 Superbike. Still a lot of races ahead though. This photo is our Sanford and Son rig getting ready to head back to the shop. The puddle on the right hand of the photo kept growing with the rain, by the end of the day we had to move our EZ-Up canopy a couple yards away from where we started in the morning.



Saturday was hot and dry, I got down into the teens and even turned a couple 1:18s. I'm still dragging stuff on both sides, mostly the pipe. The added preload and the chamfer we put in the ignition cover seems to have helped somewhat, the bike didn't touch down on the ignition cover this round. Oil consumption has leveled off, barring a catastrophic failure it's something I can live with for the rest of the season.

Joe Pethoud from Vicious Cycles gave me a used Pirelli Rosso Corsa for testing. It worked great, so I'm going to buy a Pirelli SuperCorsa and run that (Joe Signs says it's even better than the Rosso Corsa).

That said, unless folks have suggestions I'm going to shell out some money for longer fork tubes. I think that'll be the biggest bang for the buck as far as ground clearance goes.

Next race in one month!

I have been reading through this whole thread and been very impressed and nothing to add. However since you mentioned changing out fork stantions I will mention now that the 1st gen GSXR 1100 forks are longer than the 1st gen GSXR 750 forks. I run the gsxr1100 on my street bike. The 87-88 GSXR 1100 also have larger 17mm axles, larger brake rotors and use different calipers I think. I use them with race tech emulators and probably progressive springs.
Don't know it it is allowable but JohnKat has experimented with the bandit forks and says that is far better than earlier cartridge emulators.

[posplayr]

If I may, by using GSXR 89 triple clamps you actually increased the trail as you pulled the front wheel backwards.
Off course raising the rear reduced the trail and you probably ended close to a GSXR spec

I wrote this a while ago on the same subject:

Having installed the GSXR 11 K front fork on my GS 1000 ST, I wondered to what extent the rake and trail had been modified?
The OEM specs for the GS 1000 are:
Rake: 27°
Trail: 116mm
First, I'll assume that the bike's ride height remains constant by adjusting the fork tubes in the triples.
This means that the rake will remain constant at 27°.
The formula that links the different variables is:
a=R*sin(rake angle)-d
a is the trail
R is the radius of the front wheel
d is the offset between the fork tubes and the steering axle
So with the 19" front wheel that has a radius with tire of 344 mm, and the GSXR 11K triple that has an offset of 32 mm, the trail comes out at 124 mm.
That's a lot and the bike will feel heavier to turn.
Second, if we lower the front end by 2.5 cm the rake will decrease by 1°.
With this new rake of 26° the formula will give us a new trail of 118 mm
This is almost the same as the OEM spec!
Is this achievable with the GSXR 11K fork legs?
The answer is yes as the loaded length of the fork tubes goes from 745 mm on the GS 1000 to 715 mm for the GSXR 11K resulting in a shortening of 30 mm that translates in a reduction in height of 26.7 mm
In other words a GSXR 11K fork will give you the same trail as the OEM bike while the rake will decrease by 1° which is good.
You loose of course 26.7 mm of clearance in the front that should be negligeable.
__________________

John I don't remember anymore but input many of these calculations into a spreadsheet with various adjustments. Have you done same or did I send it to you already? I think Civilrock has it. It is the easiest way to show the sensitivity of various mods.

[posplayr]

Ozman, good idea about the dropped upper triple clamp. I have a friend who might be able to machine one for me pretty easily.

Per John Kat's measurements, my forks should be 767mm (they're first-gen GSX-R forks.) John Kat's are unladen, I reckon.

I'll grab the sag measurements the next time I'm down at the shop, they're in my notebook.

The steering's just fine at this point, especially at a fast, flowing track like Portland International Raceway (my home track). Might be a different story at tighter tracks, though. The wide bars offset the penalty of slow steering a bit (easier to jockey the thing around compared to a clip-onned bike).

I have a set of 43mm Ohlins RSU forks in my basement, they're even shorter than what I have now, but I'm going to see if longer tubes are available. (When I get some more $, of course!)

You should measure how long yours are. You mentioned .GSXR 750 before which was surprising to me as that makes ground clearance really tough when using 17" wheels.

[John Kat]

John I don't remember anymore but input many of these calculations into a spreadsheet with various adjustments. Have you done same or did I send it to you already? I think Civilrock has it. It is the easiest way to show the sensitivity of various mods.

No, I haven't seen the spreadsheet but I would love to as I'm very weak at Excel...
It would be good to leave one cell open for comments.
I confirm that cartridge forks are a huge improvement over the conventional damping rod forks.
Off course this does not mean that a determined rider could not go just as fast with this old technology
In France, the cartridge forks are not allowed in vintage racing as far as I know?
I personally like the GSXR 1100 86 forks with emulators and the corresponding 18" wheel as it blends nicely with the rear conventional shocks.
The vintage feel is still there despite the radial tires but you can really have fun on the road.
The GSXR 11K RSU fork has too much high speed compression damping in my opinion but blends nicely with a modern monoshock rear suspension.
Last but not least the Bandit 1200 forks are the best compromise for a road going bike with 17" wheels BUT you need to let them extend through the top triple tree to reduce the trail.
Here are the three configurations I'm talking about:







Sorry for derailing this excellent thread
I wish I was with you guys on the track as I used to ...some years ago.

[ozman]

nice sprocket cover on the s model john !

[patrino]

Another photo from Bob Edwards.

This one's from the first lap of the GP Twins race. The chicane means we're all packed closer together at the start.

[patrino]

Good to know PosPlayer, thanks!

I had thought that the 1st-gen 1100 and 750 forks were the same length but now I know better.

I'm not going to have time to do any suspension work before now and the next race weekend. I've got limited time between work and travel, and have a few more pressing things, namely check the valves, adjust the cam chain, change oil and filter, regear. I spent a lot of time above the redline last weekend and I can now hear the cam chain when the bike's cold (couldn't before).

Save the one time I lost both wheels in turn nine I didn't have any noticeable ground clearance problems last weekend. Maybe I was going slower, or maybe my plan to hang off more helped.

[patrino]

p.s. please check my post in the "Performance" section of the site regarding throttle assemblies. Any suggestions appreciated!

[gs58]

How are the front brakes behaving now? Still getting spongy later in the day? One of the issues I found was the harder I braked, the hotter the discs got and the more they cupped. This meant that the lever had to travel more to get the pads in full contact with the disc. In the end I had some cast iron rotors made to solve the problem. Floating discs would have been a cheaper solution but were not allowed in the class that I was running.

[patrino]

gs85, I wish I could say that they felt better but they don't (at least not after the race weekend). Compared to the beginning of the race weekend, it now takes more lever travel to get the same amount of brake bite. I installed the m/c rebuild kit, bled the system. Worked well at the beginning of the weekend but slowly worsened over time. I'm guessing that the problem you had went away when the rotors cooled off?

It's almost as if there's air getting introduced into the system, or the pistons keep retracting into their bores. (I know that the square-section o-ring in the bores are supposed to "reset" the pistons.) I'm going to bleed the system (again) but don't expect to find any air in the lines or banjos. The one thing I need to double-check is the position of the caliper bleed screws relative to the topmost piston of each caliper. Since the calipers are mounted on non-standard brackets I suppose it's possible that there's air trapped in the piston. But that wouldn't explain why the lever travel changed between before raceday and after raceday.

Regardless I want to switch to a 17mm master cylinder. The 5/8" one still wasn't quite big enough, even when it was feeling good. I'll hit eBay up, anyone know who ran a 17mm m/c? I know Brembo makes them, but not sure what models they put them on (I'd love to find a ratty-looking but functional one, to save $).

[patrino]

Full race report coming soon, but safe to say that the weekend started out on the wrong foot! Here's my clutch after the second practice session:

[azr]

ohhh nooooo.......that's a mess indeed. Racing eh

[GregT]

That's...unusual. My best guess is a fiber plate broke and a piece came out and jammed on the cases and then broke the fingers off the basket...

Do you remember what the fibers were or how old ?

[steve murdoch]

Tough luck, patrino.
Hopefully the first session was great. haha.