In part 4 of this project, I attempted to fix a high speed brake shudder issue by making my own fully floating discs out of the factory semi floaters. I’ll admit I was a little nervous about grabbing the lever on my first fast lap for obvious reasons. Modifying the brakes on a vehicle should never be taken lightly and should always be tested incrementally. As I starting going faster and gaining confidence I was braking later than ever with this new setup. These are certainly the best brakes I’ve used on a race bike regarding initial feel, braking power and fade resistance.
As speed increased, new issues arise; testing never ends. By the second session of the day I was really feeling comfortable and getting on the throttle quite early coming out of corners leading to higher speeds on the straights. Nola Motorsports Park has a long start/finish straight. On my Triumph 675 I would see an indicated 155 mph or so before braking for turn 1. When building this Ducati 998, I chose gearing that would allow just over 160 mph in 6th assuming the more powerful but heavier Ducati would see similar speeds. I was wrong. The Ducati is apparently a rocket ship, albeit a deceiving one. The twin cylinder engine in the Ducati only revs to 10,500 rpm and creates a very deep baritone sound, whereas the Triumph will go 3,000 rpm further and screams by comparison. This makes the Triumph louder and ‘feel’ faster. I click into 6th gear on the Ducati as I pass the start/finish line and run out of revs approximately 2-3 seconds before my braking marker. The Ducati has no speedometer, but gearing calculators say this should be about 162 mph. Next time out I’ll lengthen the gearing a little bit to resolve this. The current gearing setup is a 15 tooth front and 40 tooth (+4 from stock) rear sprocket; it looks like a 38 tooth rear might be the way to go here.
I also noticed as I braked later with each lap that the rear wheel was starting to come off the ground and create some instability. I tried to most easily curtail this by reducing some rear rebound damping in the shock which would allow the rear spring to push the tire into the ground more quickly and maintain grip. This helped some but wasn’t a complete fix. I decided not to pursue this any farther because when I change the rear sprocket to a smaller size (longer gearing) the rear wheel will have to move farther back on its eccentric adjustment to maintain proper chain tension. Ducatis with single sided swing arms use an eccentric hub for rear wheel mounting. The single sided arm looks great and makes for fast wheel/tire changes but creates some geometrical issues if not adjusted properly. Because the hub adjustment is eccentric, the circular movement means as the rear wheel moves rearward or forward the ride height also changes. When ride height changes, chain pull angle center of gravity and other geometries are also affected. It’s important to check ride height before rear hub adjustment then use this turnbuckle style link to raise or lower it back to the correct position. The rear wheel moving farther back also creates a longer wheelbase which should also help keep the rear wheel on the ground during hard braking. I’ll try this solution out next time before any more suspension adjustments are made.