8 replies to this topic

[GeoffS]

My 145/70 R12 tyres need changing, thought about going a bit wider if possible - better grip, look and higher gearing (eg 165/70 would turn 957 per mile, not 1009 as now).
Can also see 175/70 (932 rp ml) and 155/70 (982) for sale.
Would appreciate any advice ie would any/all fit to factory steel 12 in wheels, any fouling under arches (prob unlikely?). Thanks

[Steam]

I am not an 3xpert on tyres etc so please bear that in mind but a wheel width is best suited to the correct size tyre. When you go up a size the way the tyre performs must be compromised. That being said I have run 165s on standard rims without any perceivable issues but I wouldn't go any wider.

[mab01uk]

Note: As you go wider the profile/aspect ratio (height of the tyre sidewall needs to get lower)

eg. So the overall diameter of the tyre still fits within the restrictions of the Minis rear radius arms....

 

Aspect Ratio:
The height of your tyre from the base of the tread to the rim, as a percentage of the tread width. Low profile tyres have smaller aspect ratios. Example: height of tyre = 60% of its width.

 

There are online tyre calculators that will give you the overall diameter of any tyre, so you can see if it would physically fit your Mini.

Edited by mab01uk, 23 June 2025 - 11:06 AM.

[timmy850]

You’d want to stick with a standard mini size so that your speedo still reads accurately and it fits properly
145/70R12
165/60R12

https://www.minispar...styres/31/3102/

[Ethel]

Wider tyres don't give more grip, at least not in literal terms. It's obvious, when you think about it, that it's the tyre pressure that dictates how much rubber will be in contact with the road. 28psi will support 28lbs of car on every square inch of contact patch. Stick an extra 280lbs of luggage in the car & the tyres will flatten to put an extra 10 square inches of rubber on the road.

 

What wider tyres do is make the contact patch wider. That means there's less radial  length in the patch that can distort as the tyre rolls. You might translate the distortion as side slip, understeer, through the steering wheel, but at least you know something of the side forces on the tyres - a wider contact patch will give less warning before you reach the limit of the tyre's grip. Side walls distort under cornering too so a 165/60 could well perform better in that respect than a tyre that's 10mm wider, but 10% taller.

 

155/70/12s can fit inside the radius arms, which is usually the limiting factor. There's not much to spare, I haven't tried but I'd be doubtful any wider 70 section tyre would fit. 

 

Guessworks calculator will let you see what effect various tyres will have on your revs per mile, which is the only valid reason I can think of for taller tyres.

[GeoffS]

Thanks all, makes sense to stay 145 width on view of speedo issue that I’d forgotten about…

[timmy850]

The difference in diameter is negligible between the two sizes available in “mini sizes” so there will be no difference to the speedo. It’s only a problem if you go to an alternate size

Mini size
145/70R12 -508mm
165/60R12 - 503mm

Alternate size from your first post
155/70R12 - 521mm
175/70R12 - 549mm

[Cooperman]

I once had to fit 155/70 x 12 to a rally Mini to comply with the regulations. However, the front tyres rubbed on the inner wings at full lock. The spare tyre would not sit properly in the spare wheel well either.

That is also not t type-approved size, not that that's particularly important. 

Stick with 165/60 x 12 and you'll be fine.

[Ethel]

My plaggy car drove nicely on 155/70/12s. The car was supposed to take them though & ride height, wheel offset & tread pattern will all count too.