Hi Niels

Nice to see you here again, btw.

 NP> In the days when I had an FB Ute and got my tyres recapped, I would
 NP> drive to town on nearly bald tyres and come home with a winter tread on
 NP> the rear wheels. The difference in circumference affected the speedo
 NP> reading quite noticeably, and I also had to change back to second gear
 NP> sooner on the 1500 ft climb up the hill to home.

 NP> It also affected the speedo when I blew a tyre on the falcon one night
 NP> and had to use the spare which was a low profile. !!
 NP> The car even looked lopsided as well as affecting the handling.
 NP> The fact that I had 3/4 of a ton of wood in the back and another 1.5
 NP> tons on the trailer didn't really help. :-)

 NP> I can't understand how anyone with a bit of real life experience could
 NP> think that altering the radius of a wheel would NOT have an effect.

Both of the examples you give above included changing the length of
the circumference as well as the axle-to-ground distance. My
argument is that just reducing the pressure in a tyre won't change
the circumference by anywhere near as much as it changes the
axle-to-ground distance, and thus won't change the speedo as much.

 > TB> Simply pulling the integral over the linear distance would
 > TB> solve it conclusively.

 >  Simple my arse... it's impossible. So measure the axle height
 > instead, which will reflect the speedo reading, precisely.


 NP> Roy experimented and only found a small difference on the speedo.
 NP> What he forgot was the DIFF is in between. !!!!

Reread the experiment - I deflated *both* rear wheels, and averaged
them in my calcs. Gimme some credit, I learned what a diff could do
with my Meccano set when I was a small brat.

To Anyone: Does Meccano still exist? Years ago I saw a pretty fair
Taiwanese clone. I've got a bad feeling that the computer craze has
overtaken it, but I exist (formerly: live) in hope.



Cheers

--- PPoint 1.88