3 ms·

The calculation applies to the angle between the contact patch and the center of mass. However, since the tire has some radius to it, and the rider typically is

by lutorm 11y ago

The calculation applies to the angle between the contact patch and the center of mass. However, since the tire has some radius to it, and the rider typically is not centered over the bike, that angle is not the same as the bike's lean angle. So that may account for some of the discrepancy between the "60 degree" mu and that coming from the radius of curvature calculation.

bigiain 11y ago
There's two complications to that, one against our favour and one in our favour (assuming we're trying to rationalise a Cf of 1.7 being erroneously high). The rider leans off the bike to the inside of the turn, and since the rider weighs ~30-40% of the bike+rider mass, this moves the center of mass quite a long way to an even higher angle than the lean angle sensors on the bikes frame indicate - the rider moving makes the discrepancy worse not better. The left/right curvature of the tires (mostly that big fat ~200mm wide rear one) means that the location of the contact patch between the tire and the road also moves towards the inside of the curve. This means the frame lean angle sensor is over-reporting the angle somewhat. This moves the discrepancy back the other way. Another thing to consider though. Nobody assumes the rule of thumb that "the coefficient of friction is always between zero and one" applies to sticky tape (which it quite obviously doesn't), but a hot motorcycle racing slick has that same tacky stickiness to it that duct tape does. Look at any bike that runs into the gravel traps. It's tires come out _covered_ in gravel that's quite clearly stuck to them at a coefficient of friction greater than 1. It's perhaps non-obvious, but it shouldn't be too much of a surprise that tire "stick" like that to the track surface as well as the gravel on the runoff areas...
- rdc12 11y ago
  And I assume that when a rider runs off line onto the marbles [1] they stick to the tire as well, which reduces the ammount of sticky tire in contact with the track. They are also probably unstable compared to the tire. [1] Little pieces of discarded rubber
- lutorm 11y ago
  Yeah, I've done a lot of physics and I've never heard the rule of thumb that "coefficient of friction must be between 0 and 1." There is no such requirement anywhere.

by lutorm 11y ago

bigiain 11y ago

There's two complications to that, one against our favour and one in our favour (assuming we're trying to rationalise a Cf of 1.7 being erroneously high). The rider leans off the bike to the inside of the turn, and since the rider weighs ~30-40% of the bike+rider mass, this moves the center of mass quite a long way to an even higher angle than the lean angle sensors on the bikes frame indicate - the rider moving makes the discrepancy worse not better. The left/right curvature of the tires (mostly that big fat ~200mm wide rear one) means that the location of the contact patch between the tire and the road also moves towards the inside of the curve. This means the frame lean angle sensor is over-reporting the angle somewhat. This moves the discrepancy back the other way. Another thing to consider though. Nobody assumes the rule of thumb that "the coefficient of friction is always between zero and one" applies to sticky tape (which it quite obviously doesn't), but a hot motorcycle racing slick has that same tacky stickiness to it that duct tape does. Look at any bike that runs into the gravel traps. It's tires come out _covered_ in gravel that's quite clearly stuck to them at a coefficient of friction greater than 1. It's perhaps non-obvious, but it shouldn't be too much of a surprise that tire "stick" like that to the track surface as well as the gravel on the runoff areas...

rdc12 11y ago
And I assume that when a rider runs off line onto the marbles [1] they stick to the tire as well, which reduces the ammount of sticky tire in contact with the track. They are also probably unstable compared to the tire. [1] Little pieces of discarded rubber
lutorm 11y ago
Yeah, I've done a lot of physics and I've never heard the rule of thumb that "coefficient of friction must be between 0 and 1." There is no such requirement anywhere.