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I am forever catching my rear boxes on what I would call minor ridges, I have just read that pirrelli p4000 tyres are actually giving me 1" less clearence than dunlop aquas (205 x 70 x 15w) on wires. Any else heard of this problem because I will change the tyres (ouch £££) if I have to
jon

Hello John,

of your current tyres are 2" smaller in diameter I would say your speedometer will be very inaccurate and your fuel consumption increased. Maybe the fitting of Dunlops will pay for itself in reduced fuel bills?

Alec

I don't think its the manufacturer of the tyre that is your problem but the size of the tyres fitted. The difference in rolling radius (ride height) can be calculated from the tyre profile.

If you have 205/70 X 15 tyres fitted then your side wall height is 143.5 mm i.e. 70% of 205 mm. This should be the case irrespective of tyre manufacturer.

From what you have said then maybe you have 205/60 X 15 tyres fitted, which would give you a 20.5 mm lower side wall.

I don't know what model E-Type you have but the standard tyre for a Series 1 E-Type is 185 x 15 and these have an 80% aspect ratio giving a side wall height of 148 mm. That is why people fit 205/70 x 15 tyres as they give a similar ride height and rolling radius. This helps keep the speedometer calibration more accurate and, indeed, maintains fuel consumption. It also gives a wider choice of tyres.

What people often fail to remember is that lower profile tyres generally have stiffer side walls and that they affect the way the car's suspension works. Many older cars relied upon the flex in the tyre side wall to add to the ride comfort.

if your tyres are 205/70 x 15's then perhaps you should check your ride heights to determine whether your suspension is sagging a little.

Regards