Wednesday, July 24, 2013
Just a few little psi
About 3 years ago, I bought the Kawasaki ZRX1200R as the basis for a future project. I figured, I wasn't ready for the project, but I could ride the bike in the meantime. What I discovered was that the ZRX series had a reputation for being a poor handling bike and, upon riding it for a while, I had to agree. Going in a straight line, everything was fine, but go over a dip in the road while cornering, you better hang on. And don't even think about squeezing on the throttle in a turn.
The guy I bought the bike from told me I should make sure to run the factory tire pressures at 36 front/36 rear. So that's what I did.
Trying to improve the handling, I messed with every suspension setting I could think of. I managed to move the handling in the right direction, but she was still scary and I still wasn't confident.
One morning, on a pure lark, I decided to blow the tires up to 40 psi. WOW! What a difference. Suddenly, you could feel the front end and the rear would follow the front. When I got home, I googled ZRX tire pressures and found that lots of other people had discovered that the factory specs were just wrong. They said that the right specs were 36/42. I gave those a try, along with 40/42 which I settled on as best for me. Now I can go through a dip with confidence. Now I can squeeze that throttle on at the apex and track the bike smoothly out of the corner. I had a little surprise when an oncoming car crossed into my lane on a corner. Grabbing the front brake to slow and tighten my line caused a minor steering reaction, but well within control.
How amazing it is that a few little psi could change the character of a bike.
That got me to thinking. What had probably been happening is that the contact patch of the tire in a corner was moving laterally when the vertical load changed going through a dip. There just wasn't enough tire pressure to keep the tire's shape under different loading.
Of course, the current style is big, fat, wide tires on bikes. I guess people think they look good. But doesn't the fat tire cause the contact patch to move laterally when the bike leans? Wouldn't the bikes handling be more consistent if the contact patch didn't move laterally as far in roll? It always has seemed that skinny tires are the best handling on a bike. I can't say it is the whole reason, but I can say that the KLR has skinny tires and keeps up with just about any sport bike ridden at the same skill level. So keep your fat tire style. I prefer skinny any day.
P.S. Note to self. Always Google any question that comes to mind. There is often useful knowledge there and the factory spec isn't always right.