15" Tyres

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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.

History First:
>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.

GTD Tyres
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.

>Radials
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.
 
Thank you very much Andrew, I appreciate your taking the time to look into the subject and posting the info. Brian
 
The Goodyear Blue Streaks that Andrew refers to are available from Goodyears Racing tire division, and are available from five outlets across the US. We use either Carrol Shelby Enterprises in Torrance,CA or Competition Tires East in Reading, Pennsylvania. The tires are made in Chile! to original race moulds.We use 6.00-15 fronts on 9.5"rims and 8.00-15 on 11" rims.These tires are used on original GT40 race cars in vintage racing in UK. They are very light, quite thin, and will puncture if abused, but for track use they are superb, we have not bettered them with any other tire, and we have made each set last a whole season of hard track and competition use.They are marked "for racing purposes only" so dont get caught on the road.These tires are mounted onto PS Engineering peg drive wheels,and is the combination that we will continue to use in the future.Frank
 
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The dunlops I use work very well. In fact my lap times on these tyres are as near as dammit the same as when I ran full Avon slicks. Like the blue streaks that Frank talked about they make a very good track and competition tyre. They might be justa little softer than the blue streaks so will deteriortae over a shorter mileage on long session track days. Hhowever you are not necessarily road legal in being marked up for race purposes only.
From what I hear the dunlops are not so readily available in the US, a bit like the blue streaks not being so readily available in the UK.
Cost wise and having looked in to both blue streaks and the dunlops the dunlops are quite a bt cheaper most likely mainly due to lack of importing costs to UK.
I find the tyres are sensitive to pressure changes and a few pounds here and there really alter the balance of the car. It has taken a little while to get the hang of it but it was worth it in my opinion.
What would be fun is to find a Champ car team that will let you have their old used slicks. The fronts they use would be good on the rear of our cars for 1/4 mile time trials etc.
Malcolm
 

Rick Muck- Mark IV

GT40s Sponsor
Supporter
Andrew,

Go back and double check and I think you will find that the original 60's street cars did NOT come with radials. The tire sizes you list did not exist in 1966/67. The "P metric" tire rating came in the mid/late 70's. The cars from FAV came on Goodyear intermediate/rain type tires, perhaps "bluestreak sport car specials". The lowest profile radial available in the 60's was from Michelin. The first 60 series radials were the original BF Goodrich radial T/A tires-a good tire for the day BUT the nastiest and most devious tire in the wet. The early style had no crosscut sipes and wouls spin if someone spit on the road!

Look at some of the Hoosier tires for combination street/track use. They have a selection of 15" types.

Rick
 

Rick Muck- Mark IV

GT40s Sponsor
Supporter
Andrew,

Go back and double check and I think you will find that the original 60's street cars did NOT come with radials. The tire sizes you list did not exist in 1966/67. The "P metric" tire rating came in the mid/late 70's. The cars from FAV came on Goodyear intermediate/rain type tires, perhaps "bluestreak sport car specials". The lowest profile radial available in the 60's was from Michelin. The first 60 series radials were the original BF Goodrich radial T/A tires-a good tire for the day BUT the nastiest and most devious tire in the wet. The early style had no crosscut sipes and would spin if someone spit on the road!

Look at some of the Hoosier tires for combination street/track use. They have a selection of 15" types.

Rick
 
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