7 replies to this topic

[JonnyAlpha]

Hi;

 

I am trying to research which wheels and Tyre to get but am struggling a little.

I have read the FAQ here but need a little more help especially regarding 10 Inch Wheels.

 

Can someone clarify my understanding is correct.

 

Wheels seem to be advertised by Rim Width and Rim Diameter e.g. 5 x 10 or 6 x 10 this I get e.g. 5 = a Rim Width of 5 Inches and 10 = a Rim Diameter of 10 Inches. 

 

Tyres however, are advertised as 145R10 or 165/70 R10, taking the first size 145R10 (currently fitted to my Mini) according to info I have read the first figure e.g. 145, is the width of the Tyre in mm, I thought the R stood for Rim Width but I now understand it means Radial and the last figure, in this case 10 again means the Tyre will fit a 10 Inch Rim. 

 

To work out the Height of the Sidewall of the Tyre you take 80% of the Width of the Tyre so for a 145 this is 116mm.

 

The 165/70 R10 has an additional figure (the 70) which if present means that the sidewall height is 70% of the width of the Tyre, if the second figure is not present the percentage to work out the height of the sidewall is taken to be 80%

 

Confusion:

 

According to the info I have gleaned for my Tyres (145R10) the tyre width is 145mm that's 5.70 Inches, does this mean the width of the Tyre at its widest part, roughly half way between the rim and the outer edge of the Tyre? So does this mean a 165 Tyre will fit the same Rim as a 145 Tyre but the Tyre will be a lot wider at the centre?

 

Sorry for being thick but everyday is a learning day.

 

 

 

[henri1972]

Hi 145/80/10 will fit on 3.5 j rim and 165/70/10 fit on 4.5 to 6 j rims this is what i was told when i went to pick up my tyres for my mini 

[Minilegs]

Am I missing something here?
I thought a 165/70 r10 meant 165 mm wide , 70mm tall and radial 10 inch.
Your percentage thing to calculate the tire wall height has spun me out as it's stated on the tire as 70mm ?

[Guess-Works.com]

The first number relates to the width of the tread of the tyre, ie that which is in contact with the road.

 

If you go down to your local Maccy D's and look at some of the cars there abouts you will see some of them which have wide wheels with narrower tyres.... the stretched look...

 

This is not ideal and is very much outside of the manufacturers recommendations...

 

In general the wheel width should be less or equal to the width of the tread, within reason

[surfblue63]

The 70 is a percentage, it is known as the aspect ratio.

[Minilegs]

Ahhh I see. Learn something new every day 😀
I'm still a little bit confused though, but I think I'm getting the wrong end of the stick ( sorry op for the hijack , but this had intrigued me lol)
So we are saying that regardless of what wheel is fitted, a tyre for example which is 225/40r18 doesn't have a 40mm tall side wall, as the 40 is the aspect ratio, so it is calculated at 225/100x40 which equals 90. Is the 90 the total height of tyre and so needs dividing by 2 to give a single tyre wall height ?
I'm sorry but I'm being dumb here now, and I apologise for my stupidity 😔

[Guess-Works.com]

No, the 90mm is the section of the tyre from the bead to the tread, so if you wanted to find the total diameter of a tyre you would add the diameter of the wheel it is designed to be fitted to and twice the aspect ratio.... so using your example....

 

225/40r18, tyre diameter = 18 inches ( or 18x25.4 mm ) + 225*0.40 * 2 = 655.2mm

[Minilegs]

You can all stop banging your heads against your computer screens now ,as I get it !!!
I've kinda been getting it wrong it seems, not that I've ever tried to calculate a tyre diameter before, but with my brief dealings with tyres when replacing them, I assumed that the aspect ratio was just the height of the wall in mm
Thanks every one for enlightening me !!! God I feel stoooopid lol