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MG MGA - Mixing tyre sizes

I have standard disc wheels and I need a couple of tyres. This gives me an opportunity to keep my 2 existing 165s on the back but buy new 155s for the front. The reason for gong to 155s on the front is to lighten low speed steering. Have other done this and has it worked well, or please just make general comments?

Paul

Paul Dean

As you probably already know, standard wheel sizes show as 4Jx15 which is a 4" width rim.

Standard tyre was 560-15 crossply which works out as 155/80r15.

Later tyre size was 590-15 crossply which works out as 165/80r15.

155/80r15 and 165/80r15 both have a minimum rim width size of 4".

So technically both fit and 155/80r15 on paper will be a better fit but how much of a steering and driving improvement depends not so much on the tyre size as it's design and construction.

It's difficult even to compare tyres that were fitted only a few years ago to now even if they are the same make and model details of tyre as they now seem to be a "softer" feel with more movement on the road, which might suit your cause.

It deeps on what tyre types are available in the size you want and how you drive and your expectations. I found mid-2021 because of Covid and other factors availability of a sporty 155/80r13 (unfortunately I have 5" rims) for my Spridget very difficult and ended up with a "soft" tyre but accepted the compromise of comfort instead.

If you can find a good 155/80r15 tyre I'd have them fitted to rear too as grip and handling of the tyre is more about its design and compound than it's width size.
Nigel Atkins

Nothing wrong with different size tires on the front vs. the rear, but its always recommended that the same brand, tread pattern & speed rating be used for all tires. Can you mix brands and ratings, sure, but you may not get the same feel and control if everything were matched.
Nick Kopernik

Even the same make and model of tyre with the same tread pattern may vary in construction and speed rating with differences in size.

As an example only, Vredestein Sprint Classic -

155 R15 - 82S (£81.70 inc.VAT)

165 R15 - 86H (£115.05 inc.VAT)
Nigel Atkins

If speed ratings need to be mixed, lower speed rated tires should be on the front, higher on the rear. Realistically, not too many MGA's will reach "S" rated speeds, let alone "H"!
Nick Kopernik

Well I have now implemented my plan and took delivery of 4 Pirelli Cinturatos. I only need to fit 2 at the moment but there was a good saving on 4 and I will need the other 2 later this year or early 2023.
So I will go from driving on 4 Michelin 165s, to 2 Michelin 165s on the back and 2 Pirelli on the front from now, and when the time comes I will go to 4 Pirelli 155s. I will report on any observations but I suspect/hope that what I observe is slightly lighter low speed steering with Pirelli 155s on front but not much else. We will see.

Thanks for input.

Paul


Paul Dean

Be interesting to hear your findings.

I found it took about 1,000 to get used to the set of four tyres tyres that I had fitted last summer which was a lot longer than unusual. I don't know if it was the different 'rubber' nowadays or not.
Nigel Atkins

I took car out yesterday for first good run of year with the new 155 Pirelli tyres on front and the slow speed steering is significantly lighter. I still have Michelin 165s on the back as although I bought replacements to get Longstone discount the rear ones can do another season.

What I don’t know is how much of improvement is down to reduced width and how much is down to construction, after all Longstone recommend these Pirelli’s for lighter steering due to stiffer walls. But lighter slow speed steering is significant and welcome, don’t need to think of power steering anymore!

Cheers

Paul
Paul Dean

Your comment on tyre Speed-Ratings began to get me a little worried Paul about my Firestone Multihawk 15" tyres.

I just checked and my tyres have a V rating (149 mph) so I think they should cope with my driving.

The reason for my concern was that, just the once, my car just barely touched 120 mph for a second of two, but it felt so light at the front end that it seemed like even a sneeze could end up in disaster.

So I will not repeat the experience with the car in present form, I think I would need some special front end aero mods and front suspension mods for it to feel safe at that speed.

Or maybe get "Q" to fit me a James Bond style ejector seat! :^)

Cheers
Colyn
Colyn Firth

Colyn, Talk to Steve Gyles about ejector seats!
Barry
Barry Gannon

Paul
Very interesting to read, as you had hoped, the new tyres led to lighter low speed steering, and to the extent that you have discarded thoughts of power steering. Well done.

I struggle with low speed steering and that sounds a good shout.
Graham V

Tyre pressure will also make a difference to steering feel and obviously rolling resistance.
Nigel Atkins

I agree Nigel about tyre pressures but my comparison is at same 28psi.

Paul
Paul Dean

This thread was discussed between 31/12/2021 and 31/03/2022

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