Originally Posted by
tomato coupe
The following diagram shows the relationship between the three radii, where Ru = unloaded radius, Rl = loaded radius, and Re = effective radius.
It's too hard to read. You should provide a link to it.
https://www.sciencedirect.com/topics...%20the%20wheel.
Originally Posted by
tomato coupe
Your illustration shows the effective radius and the "patch" radius as being the same. They are not, in general.
You've finally managed to almost get your point across! You still aren't being clear enough.
So, you are saying the actual radius to use is somewhat larger than the patch radius. So, sure, what I said was not quite correct. It's still explains closely-enough why the unloaded radius is wrong (too large).
So, you are correct but explained it very poorly.
How different is this effective radius from the patch radius?
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So, to be clear...
The actual radius to use for measuring distance per rotation is called the "effective" or ("rolling") radius. You can't really measure it directly, which is why one does a roll-out measurement.
https://www.tractorbynet.com/forums/...2#post-4599241
Talking about the loaded (patch) radius is a simplification. I think it's a useful simplification: it would be impossible to talk about the effective (rolling) radius without being clear about the loaded radius.
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Note that the effective radius is different between "free rolling" and "driven" wheels.
So, there are situations where the effective radius can be smaller than the loaded (patch) radius. (This might not be the case when bicycling.)
https://liu.diva-portal.org/smash/get/diva2:1762057/FULLTEXT01.pdf
While driving, the driven wheels will get a driving torque. This torque will lead to tire slip, which will make the wheel speed larger than if no slip occurred. This will push up the center of rotation and decrease the effective rolling radius, making it smaller than the loaded rolling radius [7]. If instead the vehicle is braking, the wheels will skid and the wheel speed is smaller than if no skid occurred [7]. This means that the center of rotation will be pushed down and the effective rolling radius will be greater than the unloaded radius.