Brian McCarthy e-mailed me recently for information on tyres for his GTD and I thought that it is a topic worthy of opening up on the Forum. Availability (or not) of suitable 15" Tyres is a serious problem for many of us and I would be delighted to see information on tyres you are using in the USA, Australia and elsewhere.
>Original GT 40s supplied with wire wheels had radial tyres:
215/60 VR 15 fronts on 8" rims
235/60 VR 15 rears on 10" rims
>GT 40s supplied with aluminium racing wheels for racing use (usually BRM pattern) came with crossply racing tyres:
4.75/10.00-15 fronts on 8" or 9" rims
6.00/12.00-15 rears on 10" or 11" rims
>These crossplys were also used by some owners on the road, in this case the fronts were usually upgraded to 5.25/10.00-15 to gain some extra clearance under the nose.
>on later cars the rears were uprated to 6.00/12.00-15.
>The crossplys cannot be used on wire wheels as they are unsuitable for use with an inner tube.
I can only comment on sizes we know work on a GTD, perhaps the other manufacturers can fill in the gaps for their cars. The tyres and sizes shown are now almost standard among those of us who compete with our cars in the UK.
225/60V15 front Yokohama A520 or Pirelli P6000. 25.6" diameter, 808 revs per mile on 7" to 8.5" rims.
275/55W15 Pirelli P7R rear. 26.9" diameter, 769 revs per mile on 10" rims.
Both these perform well as track tyres and don't suffer from overheating.
Ideally I would like to get some 235/55V15 fronts, can anyone help?
We know that a 305/50-15 rear will also fit, but we can't get them over here in better than an HR speed rating.
>Crossply Historic Racing Tyres
Dunlop still make original CR65 pattern racing tyres in a limited range of sizes and a modern compound. They seem to have conveniently forgotten to mark the two GT 40 sizes "For Racing Use Only" so some of us use them on the road as well. They tramline and have a harder ride than radials but Hey, this is a racing car, right! They are OK in the wet if treated with respect and will last for about 5000 miles of road use. Three of us use them as our primary sprint, hillclimb and track tyres.
4.75/10.00-15 fronts. 24.7" diameter, 817 revs per mile on 7" to 8.5" rims
5.25/10.50-15 rears. 25.7" diameter, 786 revs per mile on 10" rims
I swap between these and the radials above. The car has it's ride height set up on the Dunlops. When I fit the radials it gives a slight increase in ground clearance for road use.
Malcolm MacAdam and Roger Burston use a larger rear size, however this is marked for race purposes only.
Malcolm, Roy Smart and Paul Thompson have all run slicks and Frank Catt has fitted Goodyear Blue Streaks to Robin Batt's car on 11.5" rears with flared arches. Roy has also used a Bridgestone S-02 front which I think is 205/50 and has good turn in. I hope they will add their experiences here and that we will here from all of you. Anybody wanting supplier info, please e-mail me.