Tires, Choices Options

[sithot]

My car has 205/50/15's on it which make it squirt out of a turn from low speeds. OTOH, the ride isn't the finest but I can live with it because I have cars that ride nice.
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I've come down with some choices mostly based on dry grip and not so much about ride quality. Sizes are limited.

Dunlop Direzza in 205/55/15 to add some height (although a 50 series is fun!)

G-FORCE SPORT COMP-2 - SIZE: 195/55R15 because that's all they make

Pirelli P6000 185/70/15

Avon in either 175/70/15 or 185/70/15

I'm familiar with the Avon from friends who run them on early 911's. There's a guy who uses them on 4.5 Fuchs in the 175 size and they say he's not easy to get away from on a back road.

Opinions welcome.

[Dougal Cawley]

195/55R15 is completely the wrong diameter

80% of the correct 165 = a side wall height of 132mm

55% of 195mm = side wall height of 107mm so that tyre will be an inch too small in radius. so gearing wrong as well as handling effected.

the lower profile you go and the wider you go the more derogatory effects on handling. With racing cars, (which is totally different to road cars.) these cars are lowered with stiffer suspension, and they change the camber and caster, so it is like a wholey different car. which is then not so suitable for the road.

The effects of putting wider lower, profile, squarer shouldered tyres on a car like that are that because you have relatively soft suspension, and because the wheels stay parallel with the car (instead of adding adverse camber as the car rolls) as you corner and the car leans, it climbs onto the shoulder of the tyre lifting the inside edge, which creates a sudden loss of grip, so the idea that they give more grip, is not as clear cut as it might seem. the tyre itself offers more grip, but only when you have the chassis to suit.

[horizontally-opposed]

195/55R15 is completely the wrong diameter

80% of the correct 165 = a side wall height of 132mm

55% of 195mm = side wall height of 107mm so that tyre will be an inch too small in radius. so gearing wrong as well as handling effected.

the lower profile you go and the wider you go the more derogatory effects on handling. With racing cars, (which is totally different to road cars.) these cars are lowered with stiffer suspension, and they change the camber and caster, so it is like a wholey different car. which is then not so suitable for the road.

The effects of putting wider lower, profile, squarer shouldered tyres on a car like that are that because you have relatively soft suspension, and because the wheels stay parallel with the car (instead of adding adverse camber as the car rolls) as you corner and the car leans, it climbs onto the shoulder of the tyre lifting the inside edge, which creates a sudden loss of grip, so the idea that they give more grip, is not as clear cut as it might seem. the tyre itself offers more grip, but only when you have the chassis to suit.

^ I dunno. There's about 50 years of fast Porsches here on the West Coast that would argue with the conclusions (not the theory, necessarily) of the above—primarily because many (most?) 914s that are still on the road and used in a sporting manner have been set up to take advantage of the best tires their owners could find for their purposes.

And I will say, my car probably drove best on 205/60R15 A-008R TUs or 205/55R15 BFG Comp T/A 3s. The Vreds in 185/70 were truly prosaic and offered so little grip that the car lost a lot of the fun factor, while I am not all that amazed by the (very expensive) Avon CR6ZZ tires I purchased. I should have ordered the softest compound. The CN36 are unlikely to be more sporting than the CR6ZZ.

Out here, all of the fast autocross 914s had one thing in common: short sidewalls and small-diameter tires. And this was true for heavily prepared cars or, like my car, mildly prepared cars. I'd be curious to see some very good testing done with tall vs short sidewall tires per your input above, but I think the other thing those drivers liked about the short tires was the gearing advantage on the autocross. I liked the gearing advantage of 205/55R15 on the street—the car was still comfortable at cruising speeds, and the BFGs offered a wonderful mix of comfort, grip, and near-limit behavior.

So, if I am looking for a performance tire for a narrow 914, the three I'd be looking at are the Dunlop in 205/55R15, the A048 in 205/60R15 or one of the truly aggressive 205/50R15 if soft, warm-climate only rubber was okay for my use, or the Michelin Pilot Sport AS3 in 205/55R16. My setback is a desire for period appearance.

Of course, just about any tire of today is miles ahead of what these cars came on new. We've just been spoiled by some great tires between then and now...