2/26/02
Tiring Issues II

It’s been November since I wrote about my issues with the tires, but I’ve been spending a lot of time researching, listening, and thinking about what to do. Today, I made the best decision with the advice, and opinions of many sources.

I bought a set of 215-75-15 Michelin Symmetry tires. To back track a little bit to explain my decision, I’ll refresh your memory about what originally came on my car: a 205-15 Pirelli Cinturato. Early 250 GTEs came shod with 185-15s mounted on 5.5inch Borranis, but the later 250GTEs came with 6.5 inch rims and the 205 mm width tires. These tires did not have the side wall ratio number, but using today’s p-metric sizing, this would have been an 80 series tire. Since most tire manufacturers don’t make such a tall tire at a reasonable price, I went elsewhere to find a suitable tire.
 
  Specification Sidewall Radius Diameter Difference Original size 205/80-15 6.5 in 14.0 in 27.9 in 0.0% 205/75-15 6.1 in 13.6 27.1 in -2.9% 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%

This chart shows all the tire size combinations that are close to my original specifications. The best compromise in diameter, width, and % of difference (used to calculate speedometer error) is the 215-75-15. I realize that this size is still larger than the original tire fitted to the narrow body of a GTE, but I test fitted a mounted 215-70-15 tire on my car, and fender clearances seemed fine, so let’s hope the added sidewall height clears as well!

The next step was to find a manufacturer that made this size tire that would fit my application. Kerry Chesbro who runs a 330 GT 2+2 site, bought a set of Michelin Symmetry tires, and was pleased with them, but I wanted to first try Pirellis to match what came with my car. From the days of owning a Porsche, I would have never considered buying Pirellis. There are far stickier tires than Pirellis, but when it comes to this old Ferrari, I used another set of standards.

The type of tire available in the early sixties was a very hard compound. Radials were just coming onto the market, and Ferrari was one of the first to use Michelins, and Pirellis. Tire technology has come a long way since then, and a regular passenger car tire can outperform “state of the art” tires from the sixties. One thing to remember, however, even with better technology available, our cars are still old technology. Having better grip from a modern tire puts more stress on a suspension that was not designed to see such loads. Higher stress to bushings, and more importantly, wire wheels will cause failures, so using sticky tires is not really the best choice for these old cars.

Speed ratings are another consideration. Most salesmen will try to get you to buy a higher speed rating because it’s safer to have that margin, but seriously, besides bragging rights, when was the last time you drove at a SUSTAINED 100+mph? Sure, speed ratings are really a measurement of the tire’s ability to dissipate heat generated from friction, but how fast do you want to go on those wire wheels? Pirellis have a “T” rating which translates to 118 mph, the Michelins are “S” rated at 112 mph. I think at those speeds, I have enough room to get myself into plenty of trouble with the law!

Since Pirelli was the O.E. supplier, I first tried finding a set of 215-75-15 Pirelli P400s, but because this was a passenger car tire, they only came in whitewalls! I didn’t want to mount these tires backwards, and risk seeing glimmers of the whitewall from below the car, so the next choice was Michelin. They were a little more expensive, $84 as opposed to $51 bucks for the Pirellis, but the extra money will make me happier not seeing goofy white walls!

Now I realize this is a large tire for my car, but it is only 10 mm wider than what was original. When you look at that on a ruler, it doesn’t look like a whole lot, so lets just hope I have that much extra space in the front wheel wells at full turn and jounce! I ordered these tires from Tire Rack, because I couldn’t find them any cheaper even when comparing shipping with tax. They shipped them today, so I should see them at François’ by Friday!

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