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29-12-2006, 10:01am
I'll add my two bob's worth.
The reason you "turn right" initially before the bike turns left is that you have to introduce some instability to start a turn. When the bike is stable, ie in a straight line or even at a constant speed around a constant radius turn, the bike is in a stable condition, ie the centre of gravity is directly above the wheels (going straight) or the combination of centripetal force and weight is acting directly down through the tyres while cornering. You can actually turn a bike without any force on the handle bars, we've all done it riding push bikes with no hands. You actually lean slightly into the corner. The weight shifts over slightly and now the bike will fall over. It will continue to fall over as long as the weight is outside the contact patch, but if we correct the weight angle, the bike steadies at the new angle of lean and turn. By pushing the handle bars the opposite way for a more rapid entry, all that happens is the front tyre moves out to the right, ie the weight is now acting just to the left side of the contact point, the bike will then turn to the left to re-establish stability by generating some centripetal force. Ie you turn a corner.
The rate of turn is dictated by lots of things, the fork angles, the wheel gyroscopics, the crank gyroscopics, the mass of the bike, length of the wheelbase etc etc. There's no easy fix, except, lighter wheels, lighter crank, shorter wheelbase, steeper steering etc. The best way to check what effect steering angles have is ride a normal road bike, then jump on a velodrome track bike. The track bike has a steeper angle and turns on a sixpence, watch some track racing and see how fast they change direction.
OK, over to someone to shoot holes in it all! <i></i>
The reason you "turn right" initially before the bike turns left is that you have to introduce some instability to start a turn. When the bike is stable, ie in a straight line or even at a constant speed around a constant radius turn, the bike is in a stable condition, ie the centre of gravity is directly above the wheels (going straight) or the combination of centripetal force and weight is acting directly down through the tyres while cornering. You can actually turn a bike without any force on the handle bars, we've all done it riding push bikes with no hands. You actually lean slightly into the corner. The weight shifts over slightly and now the bike will fall over. It will continue to fall over as long as the weight is outside the contact patch, but if we correct the weight angle, the bike steadies at the new angle of lean and turn. By pushing the handle bars the opposite way for a more rapid entry, all that happens is the front tyre moves out to the right, ie the weight is now acting just to the left side of the contact point, the bike will then turn to the left to re-establish stability by generating some centripetal force. Ie you turn a corner.
The rate of turn is dictated by lots of things, the fork angles, the wheel gyroscopics, the crank gyroscopics, the mass of the bike, length of the wheelbase etc etc. There's no easy fix, except, lighter wheels, lighter crank, shorter wheelbase, steeper steering etc. The best way to check what effect steering angles have is ride a normal road bike, then jump on a velodrome track bike. The track bike has a steeper angle and turns on a sixpence, watch some track racing and see how fast they change direction.
OK, over to someone to shoot holes in it all! <i></i>