2/3/11
Sizing tires for 60s Ferraris

I was speaking to one of my advertisers about tires, and what is available for 60s vintage Ferraris. Longstone tires is a distributor for Pirelli Cinturato Tires, and was instrumental in having the company reproduce these classic tires. Dougal Crawley explains here:

Pirelli Cinturato In the early Fifties the world of Sports cars was rocked by the introduction of the Pirelli Cinturato. The Cinturato moved boundaries forward as to what could be expected of a tyre as, until then the ‘Michelin X’ had been the only radial tyre. Michelin developed the ‘X’ to enhance tyre longevity using their new radial technology which considerably improved grip. Pirelli tailored this new technology to suit sports cars by developing the Cinturato which are more progressive. It was because of this new progressive radial technology that many of the World’s best cars fitted Cinturato as original equipment; Lancia, MG, Alfa Romeo, Morgan, Maserati, Lamborghini and of course Ferrari. Similarly, many cars throughout the 50’s and 60’s and even early 70’s considered fitting the Pirelli Cinturato as one of the best upgrades one could make to the performance of a car for road use and motorsport. Through Longstone Tyres, the Pirelli Cinturato brand is thriving today with a range of sizes in the CA67 tread-pattern (155HR15, 165HR400, 185VR15 and 185VR16)

Going to the Shows I, I see a lot of Michelin XWX tires on Vintage Ferraris, but this 70s series tire is actually incorrect for early 60s Ferraris. There was a change in tire side walls in the middle of the decade to the “lower profile” of the XWX, but earlier cars still had the higher profile of the Pirellis. The Pirellis have what amounts to an 80s series tire, and the body work of the older cars were made for this tire.

The CA67 tyre, this was the first Cinturato and was original equipment on the 185VR15 and 185VR16 this is the tyre that the 250 cars fitted.

This is the CN72. In 1964 Pirelli developed the CN72 205VR15 tyre. And from then on Ferrari fitted it to the 330 GT2+2 and 365GT 2+2 and the 500Superfast among other cars.

You can really see the difference in tire height in this picture Dougal sent me comparing the XWXs with the Pirelli Tire in the center.

The body work from the mid 60s back were also made to fit the larger diameter tires, so fitting the XWXs on early cars gives the Vintage Ferrari a “low-rider”look, not to mention a lower final drive ratios and speedometer inaccuracy.

Here’s a 365 California with XWXs. There’s a lot of space between the body and the tire. The lower profile tire also lowers the car closer to the ground. Ferraris are low enough as they are, and loosing up to an inch of ground clearance could be enough to catch you exhaust on something.

Here’s a 500 Superfast fitted with the correct size tire.

Dougal also sent an explanation of side wall measurements:
205/70VR15
205 is the width of the tyre at the fattest point in millimeters. This is not the width of the tread as many people think.
/70 This is what’s called the aspect ratio which is a percentage. It means that the height of the side wall of the tyre is 70% of the width of the tyre, in this case 205mm therefore 143.5mm is the height of the side wall. Having an aspect ratio was a new development by Dunlop towards the end of 1968. The first production car to use it was the XJ6 Jaguar. But many of the top cars were soon to follow suit, but they would often change the cars geometry to suit.
V is the speed rating in the case of V it means 149mph for one hour continuously
R stands for radial tyre construction
15 is the diameter of the rim in inches, where the tyre sits on the rim, not the outer flange which is again the common mistake.
Overall Diameter of a 205/70VR15 would be worked out like this (bearing in mind 25.4mm = 1”)
(((205mm X 0.7 = 143.5mm) X 2 = 287mm) / 25.4 = 11.3”) + 15” = 26.3”
 
205VR15
205 again 205mm width of tyre at its fattest point
Aspect ratio before lower aspect ratios were invented there was no need to mention them in the tyre description. However radial tyres did have an aspect ratio of 80% – 82%
VR 149mph radial
15 15” rim size
Overall Diameter of a 205VR15 would be worked out like this (bearing in mind 25.4mm = 1”)
(((205mm X 0.82 = 168.1mm) X 2 = 336.2mm) / 25.4 = 13.24”) + 15” = 28.24”
 
215/70VR15 This is the tyre that is also commonly fitted in place of the correct 205VR15
Overall Diameter of a 215/70VR15 would be worked out like this (bearing in mind 25.4mm = 1”)
(((215mm X 0.7 = 150.5mm) X 2 = 301mm) / 25.4 = 11.85”) + 15” = 26.85”
  

What to do? Check the recommended tire size for your particular model in the owner’s manual and make sure the one’s you buy have the right dimensions. In the past, XWXs were all that were available, but as demand for these tires rise, manufacturers are listening and reproducing more and more vintage sizes. Check with your tire distributor, or go to one that knows what is correct for your car.

Reminder: If you have a Ferrari related project, car, or idea you’d like to explore, I’d love to talk to you. I can also help if you’re thinking of buying or selling. This website represents what I love to do, share, and how I make a living, so if you’d like to do something together, let me know. It all begins with an e-mail!

Save the Date! Fourth Annual Radcliffe/Tomyang.net Spring Car Show on Saturday May 7th 2011. Richard Garre and I are looking forward to planning this show and more details will follow here and the Radcliffe Motorcar Company Website, but if you want to mark you calendar, the date to remember is May 7th, 2011!

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