Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Rear wheel tyre size

I have driven almost 34000 miles with my M3W and replaced the rear tyre several times. Until the last change the tyre sidewall to drive belt clearance has always been close but the two have never touched. The last tyre I fitted was a Goodyear Vector 4 Season Gen 2 in standard 175/65-R15 84H size. With the belt aligned the clearance between the sidewall and drive belt looked closer than usual and in use the sidewall soon showed signs of scuffing by the belt, not bad but enough to be noticeable. I have a Minilite rear wheel rim.

I asked the tyre fitter if it was possible that the sidewall dimensions would vary from one brand of tyres to another by much and he seemed to think they do by up to 10mm overall for the same specification of tyre, Goodyears being generally on the more "bulging sidewall" side of things. I now have a Kumho Solus HA32, another symmetrical 4 season tyre, fitted and the sidewall overall dimension is 5mm less than the Goodyear, or 2.5mm more belt clearance. The Goodyear was 185mm at 28 psi and the Kumho HA32 is 180mm. Hopefully this will prove to be sufficient to prevent any sidewall scuffing by the belt.

If your belt is scuffing the tyre it may be worth checking the overall width of the sidewall. I know that the Bridgestone Weather Control A005, Yokohama Blue Earth and Kumho KH27 Ecowing all fitted without any issues on my M3W. I believe that the Team Dynamics rear wheel rim that some have can be more of a problem that the Minilite for clearance. A max sidewall dimension for a Michelin Cross Climate would be handy as it is a popular choice, if anyone can supply?

I have a Nokian Weatheproof which has not had this problem. I happy with it.

Somewhat bizarrely, I just sat down on the garage floor for a short break before throwing the back wheel complete with scuffed sidewall Vector 4 Season back into the swing arm. Mine measures 187mm across its widest point with 26psi and unloaded. My plan is to run it till it's worn enough to replace...tread or sidewall!

I had the same plan Calum but I also have the MOT test coming up soon and the tester always comments on the tight belt to tyre clearance and I always say that they are close but don't touch. Although the Goodyear only just scuffed the sidewall over the 1500 miles I ran it, I am sure the tester wouldn't like it. Apart from the tight belt clearance it all ran well but I won't be getting another and it will come off the Alternative Parts List next update. Any other info about tyre dimensions and scuffing gratefully received, it's not good having a tyre that won't quite fit.

Just measured my Bridgestone Weather Control A005, it's 180mm wide.

With everything aligned, mine was too close, scuffing at times with the stock tire. I wound up making a spacer and moving pulley away from the wheel a bit.

A spacer will improve the belt to tyre clearance but will make the belt run hard up against the bevel box sprocket guide plate. This will eventually fracture the guide plate attachment screws. You cannot adjust the swing arm further as you run out of adjustment with the left pivot hitting the bevel box sprocket before it and the wheel sprocket are aligned. The problems all originate from the system being designed to run with a narrower 1" drive belt that proved not to be up to the job I think.

I went chain drive last year and put all those clearance issues behind me.
I can claim smug mode surely !

Just measured our Michelin Cross Climate at 182mm and no scuffing to date (original wheel/black hub)...175/65R15 size...one caution is that it is ~4 years old and about to be changed and not sure that Michelin have not updated to a v2 (?)

Remember folks that as well as the tyre bulge causing belt clearance problems, you need to ensure that the tyre fitter uses a short valve stem. Otherwise, the valve stem might hit the belt (twice) with every rotation. This can cause fatigue in the valve stem leading to leaks and in one case I heard of, the constant battering caused the valve core itself to shake loose and eject itself from the valve stem causing rapid deflation at speed and very nearly a serious accident.