Almost Highside? - Sportbike Forum: Sportbike Motorcycle Forums
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post #1 of 2 (permalink) Old 02-08-2006, 05:00 AM Thread Starter
Join Date: Sep 2003
Posts: 76
Almost Highside?

So I was heading out the other day for school, nice morning, little chilly though. There is a 90 degree turn about a mile down from my neighborhood where I merge onto the road to school. Well, as I'm turning, there's a car pulling up beside me on the road I'm turning onto, ok, no big, just give it a little gas. Well, stupid me does just that, forgetting that my tires are not even close to warm yet. The rear tire breaks loose instantly and I start sliding. Well, this is one time that riding dirt for so long actually helped, I just let down a little on the gas, corrected, bike came back (actually, more like snapped back), and I went on my way. Luckily my friends that were behind me thought I did it on purpose! My question is, how fast do you usually have to be going to highside, since the rear breaking loose sometimes leads up to that? I was going maybe 20 miles an hour by the way, just wondering if that's even enough. Also, just so if this happens again, was that the correct way to handle it?

Last edited by 71custom; 02-08-2006 at 05:06 AM.
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post #2 of 2 (permalink) Old 02-08-2006, 05:40 AM
Join Date: Mar 2004
Posts: 8,798
Its not just how fast you are going, its also how far out of line the back slides before it catches, and how violently it catches, and how well you are holding on to the bike. (to a lesser extend also how long your bike is)

Assume you are holding on to the bike with force X, so it will take X+1 to chunk you into the ditch.
Now draw in imaginary line in the direction of the bikes travel, and another line in between the two wheels. When you start sliding you form an angle in between the lines, we'll call this angle alpha.
The force exerted during a highside (or a near highside) is very simular to the torque produced by a crank. Its a combination of the linear force (speed) and stroke (Wheelbase*sin alpha). In other words, the faster you travel, the less of an angle alpha has to be to throw you. Thats the laws of physics and there isnt shit you can do about it.
Now comes the parts you can do something about. If the rear wheel was to gain traction instantationsly, almost any angle would be enough to throw you. but it doesnt, it takes it some time to regain traction. The force thus have to be split up over this time, providing less impulse the longer it takes. Its the same principal that allows boxers to withstand a hit by rolling with the punch.
What does that mean? You want the rear to regain traction as slowly as possible, but not so slow that it never does (lowside). Chopping the throttle will throw you, but slowly rolling off might save you.
Of course how well you hang on to the bike has a great deal to do with it too.

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