Difference between 15 and 16 inch tyres

[macafee2]

A search on the internet shows
for 195/65 R15 Diameter of 66.66 cm and Circumference of 193.7cm
for 215/55 R16 Diameter of 62.33 cm and Circumference of 195.8cm

These are the two tyre sizes shown in my handbook.
Did Rover calibrate the cars for these two sizes at the factory?

If I put a 16 inch wheel and tyre on my car, my speedo will show slower (even slower) then I am going but my mileage will not increase as much, is that correct?
If Rover did not calibrate the cars, which gives the most accurate distance reading?
What is the difference over 1,000 miles?

macafee2

[Richard1973]

https://www.tyresizecalculator.com/t...ror-calculator

Very little in it when I put the sizes in. 1mph at 60

[T-Cut]

Originally Posted by macafee2

If Rover did not calibrate the cars, which gives the most accurate distance reading?

Neither - or should I say it's not calculable. All speedometers are designed to read 'fast' by law. How much too fast will vary, so without the calibrated figures, you can't answer the question.
EDIT: I guess you could say that the larger tyre is the more 'accurate', since both are designed to run 'fast'. The speedo will show closer to actual, but both will show substantially fast.

What is the difference over 1,000 miles?

If the '1000miles' were an accurate distance, then the tyre-generated difference would be 1000 x 193.7 / 195.8 miles or 1000 x 195.8 / 193.7 miles depending on which tyre set the datum.


TC