My wheels are the 7J x 16 Futura so the specified tyre size is 235/70R16, rather than the 8J that most of the other 16" wheels (and all of the 18") are. Even they look slightly oversize though. I must admit if I was buying tyres for 18" wheels, I'd definitely go for the Pros in standard recommended size.

7J rims are supposed to be for 205 or 215 tyres, max 225, so the 235 is oversize on those too. Has to be a reason for the specifications.

Oversize puts more curve into the sidewall which will alter the stiffness and damping. Most likely in yaw or sideslip as when you run along the size of a lorry rut.

Given the known issues of a P38 on inadequate tyres, like the "death wobble" I don't fancy experimenting. I wonder if there is any tyre size link with the death wobble? I can see mine trying that sort of trick in a few thousand more miles.

Probably doesn't help that modern tyres are designed for independent front suspension systems.

Clive

Where are you finding the info on tyre and wheel sizes Clive? There used to be an excellent website, the wheel and tyre bible that had 4 pages of really useful information but it suddenly went all commercial and now has no useful info at all.

Google pulls up several sources of tyre size - rim size data.

This is the one I used https://www.tyresizecalculator.com/charts/tire-width-for-a-wheel-rim-size-chart as its nice simple list. Hafta assume its right.

Clive