I have a 2005 Ducati 800 Supersport track-only bike. The previous owner was a very experienced racer and installed an aftermarket Brembo 19x18 radial master cylinder. It is ferocious. It brakes with amazing violence and I love it, except that there is very little lever travel from no brakes to full brakes. That provides little feel for me and I was looking for something with similar power, but more lever travel. One shop recommended the 19x20 Brembo while another thought the 16x18 Brembo was the way to go. Could you offer your thoughts and explain how all this works?
The first number in the master cylinder designation indicates the piston size, while the second number is the pivot length of the lever. A smaller piston diameter or a shorter pivot length will force you to move the lever more to displace a given amount of fluid through the system, giving you more leverage; in turn, this gives you more lever travel and a softer feel. Your 800 Supersport originally had a master cylinder with a 16mm diameter piston, quite a bit smaller than the Brembo 19x18 master cylinder you have on there now. For more lever travel and feel, the 16x18 master cylinder would be the better choice.
A Wheelie Big Problem
I'm a big motorcycle racing fan and something that I hear all the time is how wheelies are bad for launches from a start and for driving out of a corner. The argument is that you are reducing your forward motion by robbing some engine power and using it to lift the front of the motorcycle rather than to propel you down the straight. I understand that line of thinking, but I'm thinking about what happens after that point. When a motorcycle has the front end in the air under full power it seems to me that the only thing you have done is stored some of that forward kinetic energy as potential energy, specifically the weight of the front of the bike at the height of your wheelie. And if you were to stay on full throttle through the power wheelie until the front settles back on the ground, you would return all that PE back into forward KE, just at a point further down the straight. It seems to me doing that would be getting more power to the ground than using some kind of electronic wheelie control that actually cuts some power to keep the front end down, or I even heard of applying some rear brake to keep things horizontal. (That brings up another question, why would you ever apply rear brake while you're still on the throttle? Wouldn't it just be better to roll off throttle a little bit?).
So what's really the difference between having the front tire skim the ground versus being a foot in the air? The one thing I can think of is that by making the bike taller, you are increasing the wind resistance and slowing the bike down that way, but I have never heard this mentioned, it is always using forward force to lift the bike rather than propel it. Now I realize that I must be wrong, since all the top pro teams use some kind of wheelie control, so the proof is in the electronic pudding. I just can't understand how cutting throttle could increase your forward momentum (unless, of course you've lost traction, and are just spinning the tire). Can you help me wrap my head around this?
Consider a piece of plywood lying on the ground, and you must lift one end. When you first lift, the plywood is very heavy, but as you raise your end higher, it gets easier and easier until the plywood is vertical and it takes almost no effort to hold it there. This is the real problem with a wheelie-as the front end gets higher, it takes less power to raise it further, not more. Even a small wheelie can get quickly out of hand, forcing the rider to close the throttle or apply the rear brake to bring things back under control. Aerodynamics plays a part too, just as it would if you were trying to lift the plywood on a windy day. The earlier you can stop a wheelie and get the front end back on the ground, the less chance things will start to snowball and the more power you can apply to forward motion. Closing the throttle cuts a significant amount of power for a (relatively) long time, and riders sometimes use the rear brake without closing the throttle to cut a slight amount of power for the moment necessary to bring the front end down. Just as with traction control, electronics can manage the small amounts of power and tiny slices of time to stop a wheelie almost right away better than most riders can, leading to wheelie control.
Got a question? Send a note to Sport Rider, Attention: The Geek, 831 S. Douglas St., El Segundo, CA 90245, or e-mail email@example.com.