Tyres, Mph & The Onboard Computer

[Remoh1]

Ok my 2004 xt3 petrol rav4 has 235/60 16 tyres on it. when I check tyre sites like national.co.uk they say the standard tyres for my car are 215/70 16 my questions are

1) will the difference between the 60 & 70% profile make much difference to my speedo reading

2) could that 10% explain the difference btween actual mpg and onboard computer mpg (around 20% higher on comp)

3) How much ground clearance am I losing with that 10% lower profile?

[Fujisan]

See post 6 in this thread for a tyre size calculator.

[T V O R]

1; Speedometer reading is 2.8% too slow with the bigger tyre. When your speedo reads 60mph you are actually travelling 61.7mph

2; Not a 20% difference. Revolutions per mile with the bigger tyre will be 744, the new tyre 724 (3%)

3; 19mm

[Remoh1]

excellent link

I'm assuming that the reason increasing the width increases the radius is because wider tyres have a higher profile?

[Remoh1]

1; Speedometer reading is 2.8% too slow with the bigger tyre. When your speedo reads 60mph you are actually travelling 61.7mph

2; Not a 20% difference. Revolutions per mile with the bigger tyre will be 744, the new tyre 724 (3%)

3; 19mm

cheers, great answers