Tires

One area that I needed to address were the tires that were on the car. They were Pirelli CN 36 in 215VR60-15 size. The spare was a bald 225VR70-15.

One problem that I always had was that the 60 series tires dropped the ride height by almost an inch and one-half. That was enough that one ended up scraping on driveway entrances, speed bumps, etc. The original tires were 205-15. These were the original type of radial tires which had an aspect ratio of .80 or would be a 80 series tire in today's nomenclature.

The aspect ratio is the sidewall height divided by the tread width. The lower the number, the wider the tire is relative to the sidewall height.

The problem is that the 205/80-15 size tire is no longer available. Coker Tires does make old sizes of tires, but not in that particular size. They are also quite expensive and more appropriate for a concours car than for mine. So I was left to find an appropriate tire that would restore the ride height.

To help in finding the right size, I found a website that computes tire specifications based on tire sizes. Here are the results for the tire possibilities I was looking at.

Specification	Sidewall	Radius	Diameter	Difference
205/80-15	6.5 in	14.0 in	27.9 in	0.0%
215/75-15	6.3 in	13.8 in	27.7 in	-0.8%
215/70-15	5.9 in	13.4 in	26.9 in	-3.8%
225/70-15	6.2 in	13.7 in	27.4 in	-1.8%
235/70-15	6.5 in	14.0 in	28.0 in	0.1%
215/60-15	5.1 in	12.6 in	25.2 in	-9.9%
225/60-15	5.3 in	12.8 in	25.6 in	-8.2%
235/60-15	5.6 in	13.1 in	26.1 in	-6.5%

As you can see, the original tire had a radius of 14.0" and all of the others got smaller. By increasing the tread width for a given aspect ratio, the radius (ride height) also increases. But you are putting more rubber on the road, making steering at low speeds more difficult. You also run the risk of having the tire hit fenders, heat ducts or shields at full rebound.

70 series tires are quite common and are available in a lot of speed ratings. 75 series tires are less common and none (that I could find) had a very high speed rating. So you are left with being able to go across speed bumps other than at a crawl or going very fast. Given that I've never had my 330 above 110 mph, going very fast wasn't a high priority for me. So I ended up looking for a 215/75-15 sized tire. Since these are a tire size that is popular on larger American cars, most come in white-wall. I wasn't particularly interested in having the white-wall exposed or mounted on the inside (where it could still be seen by anybody looking under the car), I limited my search to black-wall tires.

I ended up with Michelin Symmetry P215/75R15. The speed rating on this tire is S, which goes up to 112 MPH. The radius is only .2" smaller, so the car will be back very close to the original ride height. And no, just because they are M&S certified, I don't intend to drive in the snow or go 4 wheeling in the Ferrari.