TYRE SIZE

[Robbiet9999]

Hi i have just purchased from ebay a set of banded steel rims for the rear of my morris. going for the fat and thin look. but they have two different size tyres on so im looking to buy a couple of tyres. what size do i need to keep the circumferance the same as the standard tyre. im only asking as the tyres on my moggy dont tell me and neither do the ones on the new wheels. i need 165 r14's thats all it says on the tyres but not the wall depth.

any help gratefully received.
rob

[bmcecosse]

Depends entirely on the width of the rims. Measure them! 165 X 14 tyres will be suitable for 5 or 5.5 " wide rims - in 70 section should be fine. Any lower section will look silly on a Minor.

[rayofleamington]

Standard tyres are '80' profile. If they aren't 80, then the profile will be stated on the tyre (e.g. 45, 50 ... 65, 70, 75)

The 80 profile refers to 80% of the width.
Therefore a 165/80 will have a 132mm profile.
a 165/70 will have a 115.5mm profile.

The outer diameter of the tyre is:
Rim diameter + (2 x profile)

e.g. 165/80 R14
= 14" + (2 x 132mm)
= 620mm outer diameter

To match tyres front and rear you want to get close to the same diameter - however on a Minor there are other considerations!
e.g. very limited tyre clearance to front top trunnion.
e.g.2 tyre clearance to rear inner arch
e.g.3 - what your insurance company will accept.

If you have narrower tyres on the front you may not have an issue with top trunnion.
On the rear you normally need to do something extreme before clashing with the rear inner arches.
For insurance - some underwriters have rules about wheels and tyres. E.g. where they consider significant change of the tyre centre point (vs standard set up) to be a safety issue. I've heard '20mm' to be the limit for some underwriters which doesn't give a lot of margin to play with on a Minor.

[Robbiet9999]

So if i stick to 80's then they should be the same as standard height. The original wheels have 155's. So i can't see 165's being to much of a problem on the rear.

[bmcecosse]

If you stick to 80 section - they will be too tall. 70 section will be ideal for 165 tyres.

[Robbiet9999]

Would 70 section be ok with 155's

[bmcecosse]

No! But in any case - you say these are wide wheels? 155 are ideal for 5" wide rims, and 'ok' on the 4.5" wise van wheels. Would b e too narrow for anything wider than 5". But 80 section is correct for them.

[Robbiet9999]

Id put 165's on the rear wide wheels and 155's on the standard front which i already have anyway

[bmcecosse]

Why would you want to unbalance the car like that? 155 are really too wide on standard 3.5" rims and wobble about badly unless blown up hard....... 145 are better.

[beero]

If you have MS Excel then email me and I will send you a spreadsheet that calculates what size/profile tyres will give you the same circumference, so keeping your gearing the same and your speedo correct. beerowe @live.co.uk

[Roni]

There is a tyre calculator on this page
http://www.carbibles.com/tyre_bible_pg4.html

[beero]

Yes, I think that is where I got it from.

[Robbiet9999]

The 155's were on the morris when we bought her and have never had a problem. If i have 165 70 14's on the rear and 155 80 14's on the front which gives me the same rolling circumference thus my speedo will read correctly.

[Matt]

Standard tyres are '80' profile.

Being pedantic, but its actually '82' profile ;) But virtually the same! Even the MOT testers manual says so!

[Bit of Both]

I am struggling to find 165/80/14 tyres locally. Will a 175/70/14 work? I tried one on the rim and did not look as if it could give any problems.

[daveyl]

According to that rim calculator, cars running with 145x80x14 tyres should have rims, no less than 4 inches wide! And for certain, those exceptionally wide 155x80x14 tyres should never be fitted to a 3.5" rim either.

Joking aside thanks for the info Roni. Very useful.

[bmcecosse]

Yes - that's absolutely correct. The 'correct' size for Minor rims is 135 - but where to get them? And the 155 tyres are fine on later van 4.5J rims - but no wider on these rims!