Phil's Blog

2/16/08 – 2/17-08

At last it’s time to go to the track again!  This was a 2-day at Thunderhill, outside Willows, CA.  Typical California; clear skies and warm for February.  I went with two friends, Jason and Cassie.  They both ride, as well as Cassie races in the AFM. 

I support all the Zoom Zoom Track Days, and it was great to see all my friends again.  I usually park in the same spot on the RV pad so folks know where to find me, but this time I couldn’t so I ended up by Brian, the tire guy.  I like Brian and it looks like this year I’m going to park next to him because we were right in the middle of the paddock.

Over the winter I had some experiments going on.  Jason’s 2000 ZX-6 took the brunt of my current experiments: we added a secondary reservoir on his stock shock to help control squat and we did a major revalve on his forks to control brake dive.  The trick is to make the forks comfortable to ride on but not dive under braking.  We did the same thing to my 2000 Aprilia Mille 1000R.  I revalved the Ohlins forks and added a secondary reservoir to the Ohlins shock.  I have a 1995 CBR400RR that I race in 450 Superbike.  I did the same thing to that bike also.  I wanted to see what benefits I would gain by controlling the chassis to a higher degree.  We had a lot of stuff to figure out over two days. 

One thing about working track days is that each one has a theme; there is a defining customer that I learn something from that I never knew before.  This time the customer had a 749 Ducati and a 1098 Ducati.  When he came to me to do a set-up, he said his 1098 was perfect but the 749 was really hard to ride and when he got up to speed he was worried about crashing.  I went to work.  The bike was stiff in the front and soft in the back.  I got the sag in the front without a problem.  The shock was a different story.  I had made a couple of spring adjustment tools but they wouldn’t work, so I had to pull the shock.  On most Ducati’s the foot peg is not in front of the bolt that is the lower shock mount.  On a 749, the peg is right there.  So I couldn’t put the bike on jack stands to pull the shock.  I had to look in the “MacGyver Drawer” for an answer.  I noticed that the frames had a Boss welded in the frame for a motor mount, right above the foot pegs.  I found a 9/16” socket and a ½ extension that fit into the frame boss.  It allowed me to set the bike on jack stands without using the foot pegs.  I had the shock out and adjusted in 5 minutes.  I finally got the magic numbers 1 3/8” for the forks and 1” for the shock.  The other thing I learned is that if I use compression to control the chassis and rebound to control the comfort, the bike always is good.  It was no exception on the Ducati 749.  When the customer came back the next day and said that his 749 was now way better than his 1098, I was very happy.  I worked from 7:30 in the morning till 8:00 at night.  I didn’t get to ride all day on Saturday. 

Sunday started well and by lunch everybody was taken care of.  After lunch I got to ride.  It was the first ride on a bike since my accident on October 5, 2007.  I will tell you that I cracked my pelvis in 3 spots racing a desert race in Las Vegas.  I was very nervous about how my hip was going to feel and if I was going to be able to fold myself up and get off the bike in the turns.  Well, other than being a little stiff at first, it was glorious to be on the bike.

After doing two sessions at a slow pace and getting my mind wrapped around riding again, I was ready to test the bikes.  I rode the Aprilia first and for the first three laps when I would turn in on turn one I hit the inside bumper three times in a row.  What an idiot.  I would have to let off, stand it up and turn in again.  I came off and realized that because the rear wasn’t squatting it was turning in very quickly - much more quickly than I was used to.  I had to digest this.  I had never ridden a bike that didn’t squat.  Now about the forks.  I finally got to use the brakes hard.  The forks move but don’t dip very much.  It was way less than I was used to.  It took a couple of sessions to get used to it.  The thing I noticed is that it took less distance to stop using the same effort on the brakes.  I was amazed.  So I let a few instructors and Jason ride the bike.  They came back and said the same thing.  It was very planted, steered in a precise manner and the big thing is that it wasn’t too stiff.  I did not touch an adjuster during the weekend.  I think that the experiments were a complete success.
I have a track day on 2/25/08 at Infineon Raceway.  I will have more information then.

SETTING UP A BIKE

It’s all about the balance.  It’s how the bike chassis splits the rider’s weight between the front and rear tires.  Too much weight on the rear tire and the front tire pushes in the turns and gives the bike a heavy feel.  If you have too much weight on the front tire, the bike is twitchy and unstable.  This is the reason that there is a measurement called “trail.”  Usually if you set the chassis at the factory recommended height and set the race sag correctly, the trail numbers will be good and the bike will be balanced.

Now you have to set the suspension adjusters to stabilize the chassis.  If you forget what you read easily, then try to remember these two things: compression is the performance side and rebound is the comfort side of suspension. 

Let me explain it better…

Compression keeps the forks from diving too much under braking and it keeps the rear from squatting under acceleration.

Rebound disconnects the wheels from the chassis and allows the tires to roll over the bumps without pulling the chassis down with it.

These two forces, compression and rebound, affect the trail numbers dynamically and can cause the bike to be either quick- or slow-steering at different speeds.  The point of a race sag measurement is to mechanically set the geometry of the chassis.  The suspension dynamically keeps the geometry stable under all conditions. 

That is the point of a set up: to optimize the chassis to make it as easy as possible to ride!