On Sat, 23 Jun 2018 07:38:15 +0100, Andy Burns
wrote:

The Natural Philosopher wrote:

https://www.youtube.com/watch?v=_2l5bOhHNxU
Answer. not by very much, if at all

looked to be half the width of a piece of insulating tape per
revolution, what was even the point of only measuring the rolling
distance once?

This seems to be a perpetual urban myth.
It tyre pressure sensors are using this

And iTPMS systems *are* using it

snip

The problem with Turnip is that he is a left brainer and once he can't
comprehend something, it must be wrong or simply can't happen and he
will find other (bogus of course) examples to try to support his case.
;-)

It's *obvious* such things work because they just do ... and the fact
that he can't understand how or why, doesn't stop that from being a
fact! ;-)

If you want to calculate the rpm of a wheel at a particular mph you
use the 'effective rolling radius' to do so, not the nominal
circumference of the tyre (with conventional tyres [1]).

https://www.tut.fi/ms/muo/vert/11_ty...ing_radius.htm

I did this when designing an electronic speedometer for the electric
racing motorbike I built.

I measured the 'rolling radius' with the tyre at the optimum (high)
pressure and with all the normal loads on the bike (me, batteries,
fairing's etc). I then used that to determine the rpm/mph and used a f
to V converter to take my rotational sensor output and feed it to a
DVM, calibrated to represent the mph (all done on the bench using an
oscillator and DVM). On the track a RADAR gun determined I was doing
37mph and my display said I was doing 37.4. ;-)

At no time did I measure or use the circumference of the wheel
directly. ;-)

Cheers, T i m

[1] With dragsters the driven tyres expand quite a lot to effectively
increase the gearing speed. ;-)