Tyre sizes - what do they mean

[Lady Godiva]

Could anyone please give me some basic information on how tyre sizes work?

I’ve got an MGF 1.8i, 1999 plate. I was reading through the handbook (don’t ask) and the tyres are given as something like 6/15 and 7/16 (or something like that).

The tyre pressure were given as 26F/28R, unless you are fitting to 7/16 then it should be 24/28.

Firstly, how does the designation work, what do all the numbers mean. Secondly, how do you know which wheel you’ve got, therefore which pressure you need.

Any assistance would be most appreciated. Please remember we are not all knowledgeable, so no sarcasm please about such a basic subject!!!

Regards
Sally

[Yugguy]

These are dimensions for the wheel rather than the tyre. 6 would be the width of the wheel itself and 15 the diameter, in inches.

The tyre will have something like 185/50/15, the 15 being again the diameter of the wheel (or the hole in the donut of the tyre) 185 being the width of the tyre tread, in centimeters this time, and 50 is how high the side of the tyre is (between the wheel and the top of the tyre) as a percentage of the 185 number.

Hope that makes sense.

[GasMonkey]

Hi Sally

The 6/15 and 7/16 probebly refer to the wheel size - width and diameter in inches - It may actually read 6J15 and 7J16, I have no idea what the 'J' refers to other than it is the width of the rim
Easiest way to see what size wheels it to check your tyre size - they will read someting like 205/50R16 82V - anyway the number afer the 'R' is the rim diameter in inches - this should determine tyre pressure from the handbook figures

Hope that helps

GasMonkey

[esselte]

All you needed to know about wheels and tyres but were afraid to ask :

tyre site

Hope this helps

[Lady Godiva]

Gentlemen (I assume!!!)

Many thanks for your assistance above. It is now all quite a bit clearer. One last question. The rear tyres appear to be directional, in that they have arrows around the outside edge. I think the make is Supersa.

What exactly are directional tyres for and do they really make a difference (they were on the car when I bought it). I never really push the car that hard, although I have been known to accelerate (wink wink). Is it worth sticking with these when I next change (probably at the next MOT in May).

Best Regards
Sally

[oe_cosgrove]

Lady Godiva said:

Gentlemen (I assume!!!) Many thanks for your assistance above. It is now all quite a bit clearer. One last question. The rear tyres appear to be directional, in that they have arrows around the outside edge. I think the make is Supersa. What exactly are directional tyres for and do they really make a difference (they were on the car when I bought it). I never really push the car that hard, although I have been known to accelerate (wink wink). Is it worth sticking with these when I next change (probably at the next MOT in May). Best Regards Sally

Directional tyres are designed to produce their best performance in terms of grip etc in one direction only hence the arrows showing the correct way to fit them, ie arrow pointing in the direction of rotation of the wheel. Uni-directional tyres, ie those that can be fitted either way round are compromised in peformance compared to them, ie do not grip as well etc. A good directional tyre is the best choice. If too simplistic an explanation I apologise

>> Edited by oe_cosgrove on Friday 28th April 21:37