Originally Posted by
njkayaker
Sort of.
Note that the result you are looking for is the
horizontal distance the center of the axle moves with a full rotation of the wheel.
This is related to the patch radius (the distance of the axle to the ground directly under it). With a load, the patch radius is smaller than the tire radius.
The axle is rotating around an "imaginary" circle that has the patch radius. That is, this circle would be the size of the wheel if the wheel was perfectly rigid (no patch deformity).
The
(C) distance the axle moves horizontally in a full rotation is
equal to the
(C) circumference of the patch circle.
(Imagine the patch radius below rotating full circle.)
The only number that matters is the vertical patch radius.
Your theory is incorrect. The effective radius of a tire is less than the unloaded radius, but greater than the loaded ("patch") radius that you show.
You really only need to measure this number (accurately). That's kind of hard to do. So, people measure the roll-out distance instead (which is the circumference of the patch-radius circle).
Actually, measuring the "patch" radius in your diagram is trivial -- it's the distance from the center of the hub to the ground. If you measure it and the roll-out distance of a tire, you'll quickly find that the effective radius of the tire is greater than the loaded radius, and the difference increases as the tire is more heavily loaded.