We Never Get Tired Of Tire Questions
I ran Michelin Pilot Power 120/70-17 and 190/50-17 on my '99 GSX-R750. The grip level and the mileage of this tire were pretty impressive and I was determined to use it again. However, when the tires were finished I changed to a used set of Bridgestone BT-002 Race 120/70-17 and 190/55-17, which I had been using on another bike for track days. With the Bridgestones on my GSX-R it feels like 20kg less. Steering is so much lighter and it's lot more fun to ride, although stability is compromised. Now I am lost. The BT-002 Race is not street legal, and I do not know if I can get the same feeling with the BT-002 RS in the same dimension. Or is the different feeling mainly due to the change in dimension from 50 to 55? In such case I could use the Pilot Power 190/55-17 or the 190/50-17 and adjust the ride height (I have an adjustable hlins rear shock).
There are several factors combining to make your GSX-R feel lighter with the Bridgestone race tires than with the Michelin street tires, but most important is the difference in size between the two tires. Using a 55-series rear tire will change your bike's geometry for quicker steering, but the front BT-002 is also smaller in diameter than the Pilot Power, likewise making for quicker steering-we usually make a geometry change for the tall front Michelins to work their best. Swapping from the 190/50 Pilot Power to the 190/55 BT-002 combines both those effects. One option, as you mention, is to use the BT-002 RS, the street/track version of the BT-002. The sizes and profiles of the RS tires are the same as the track-only versions, and your GSX-R's handling will be similar. Another option is to use the 190/55 Pilot Power 2CT (the standard Pilot Power is not available in a 55-series) and adjust your shock or fork ride height to account for the slight change in front-tire circumference. In either case you'll lose some of your original Pilot Powers' wear characteristics.
Those Pesky GSX-R Clutch Switches And Master Cylinders
I removed the clutch switch from my '04 GSX-R750 and ran a wire from contact to contact so the starter would work. Does that have any effect on the way the ECU adjusts the fuel and timing? My 750 is great except for abruptness going from off- to on-throttle. At the Pueblo, Colorado, STAR Motorcycle School and at the Racing 2 Save Lives event at Miller Motorsports I had a problem with my front brake fading during sessions. Mr. Lickwar with STAR recommended a Brembo master cylinder to cure this problem. Which one will help with this? The Brembo website lists master cylinders for $300-$1200. I am not a real fast guy, but I do like to push my limits on a track. I would like to fix these little problems to enjoy my bike even more.
On many Suzuki models we've seen a difference on the dyno when the clutch switch is shorted, an indication that the ECU is defaulting to a different map. Bypassing the switch sends a signal to the ECU that the clutch is pulled in, and it may use that different map to prevent the engine from overrevving with no load. In some cases shorting the switch costs a couple of horsepower, and it could also explain your GSX-R's abrupt throttle. Any Suzuki racebike I've worked on (including the SV650 and various GSX-R models) has had the clutch switch left intact and operational.
We had good results with the budget Brembo master cylinder on our '04 GSX-R600 FX racebike ("The FX Project," July '05). While that bike also had aftermarket rotors, you should be able to cure your fading problem without changing the OEM discs. Replace the stock lines with something sturdier, and keep the system filled with fresh fluid that has a high boiling point.