"The Natural Philosopher" wrote in message
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No. The effective radious first of all is almost ********. But if you mean
te circumferenmce divided by 2 PI then that will only change with
pressure, as the belts strech, Not with loading.

Otherwise p[eole would be travvling 30% slower when their tyres were flat,
for the same speedo reading

They *will* be travelling slower - you've got that right. But not by
anywhere near as much as 30%.