Pirelli p700-z

[Hanuman]

225-50-15 Toyos on mine. The speed/odometer reading is then nearly spot on, compared to the original cars. 215s leave you about 5mph slow at 70. Ie. You think you’re doing 70, but in reality 65mph.

[BackintheFold]

That was an option. They have the correct offset.

I've got nothing against 225's as such, as long as they fit under the arches.
Also, some appear to flex differently, so are practically the same as 215's.

It would be interesting to carry out a proper comparison of a car with 215s vs different 225s-ride height, amount of rubber footprint, wall flex, rolling circumference... I enjoy that kind of detail, but you need cooperation of people with the different tyres and a common measuring method.

[quattrodave]

So guys what do you think of the early cars as until the 84 model year (pre digital dash) the standard size tyre was a 205/60 x 15 on the 6J ronal or optional 7j fuchs.

When I replaced my rims with compromotive split rims (a cheaper copy of the BBS rim with same offset) I upgraded to 225/50 x 15 but even with the 225's (I had to roll the rear arches to avoid contact) the rolling circumference was still 3% less, with the later 215's it would have been more like 5%

I recall I also changed to later spec springs which lowered the car 20cm as again the early analog dash cars rode much higher.

So what does someone with an early UR use now 205/60 still ?

[mikes2]

The early cars had different arches. If you want to run the 8J alloys, the arch lip needs rolled to accomodate or you'll see rubbing.

For me originality is more important so it would be 6J Ronal alloys with 205/60 tyres unless you're loaded and have Fuchs

[quattrodave]

Originally Posted by mikes2

The early cars had different arches. If you want to run the 8J alloys, the arch lip needs rolled to accomodate or you'll see rubbing.

For me originality is more important so it would be 6J Ronal alloys with 205/60 tyres unless you're loaded and have Fuchs

Precisely, thats why I had to roll back the rear arch lip on my 82 year model when I fitted the 8J's with 225 tyres on the compomotives, however no issues with the front arch lips touching. I also remmber the rear apron/bumper being wider on the 84 on model year so as to partially cover the wheel/tyre as with the 8J's on the earlier car the rear apron gets rather dirty at the sides in daily use. Realy must get the car back on the road sometime in the next few years its been sat in a garage now since the mid 90's awaiting some attention.

[Isimmo]

From a vehicle dynamics point of view we’ve run both the Ur and the rallycar on 6Jx15 but with 205/55/15’s, the Ur on 215/50/15’s and 225/50/15’s, whilst the rallycar has run as small as 195/50/15’s. Honest (personal opinion) answer, the smaller footprint makes the car more balanced and nimble, even making 75-bhp per wheel is child’s play for the smallest footprint. Bigger however just dulls the experience and raises the aquaplaning and tramline risk....

Flip side, they do look utterly epic on 225/50/15’s. Proper monoliths of 1980’s street theatre.