Space saver wheel help...

[Tim Lamb]

Didn't we have this discussion? I thought it was established that you can't have a *point* contact with the road if the wheel is carrying any load?

[The Natural Philosopher]

dominated by a piece of schoolboy artstudent simpleminded fantasy that anything more or less round has a 'radius' defined by the distance of its axle centre from a surface tangential to the circumference at some arbitrary point.

What is the 'rolling radius' of a tank track.....

[Roger Mills]

You're splitting hairs! Maybe "standing height" isn't the correct term. The radius on which the circumference is based is the rim radius plus (tyre width x aspect ratio). OK, the centre of the axle will be slightly closer to the ground than this due to the flattening of the contact patch.

In theory, the circumference is the length of the internal belt (in a radial tyre) and the revs per mile doesn't change as the tyre wears - but I don't entirely buy that.

[The Natural Philosopher]

Bolocks. there is no 'radius' to a non circular tyre. The circumference of a tyre does not change (much) as the tyre deflates. the 'Standing height' dies, massively.

The circumference of the tyre is the length round its carcass - that is greater than the cords, because there is rubber on top. Obviously, but it doesn't change with inflation. apart from stretching slightly. Obviously it does change with wear, a little.

[Roger Mills]

Slitting hairs again. There is an "effective" rolling radius which is the rolling circumference divided by 2Pi - which you yourself referred to as "rolling radius" earlier in the thread!

The theory - to I don't entirely subscribe - says that, for each revolution of the wheel, the car moves forward by the circumference of the belt (like a track-laying vehicle) and that the rubber squishes to suit.