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Join Date: Dec 1999
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Question what size auto-x tire for phone dials?

I have decided that I need to step up to the plate and purchase a set of auto-x race tires and mount them on my stock phone dials. I got beat by a 944 running race rubber at sundays auto-x. I have the stock phone dials (15") that came with my 87 944. What size competition tire should I purchase?
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Old 03-31-2003, 12:03 PM
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What is the width of your wheel?
Based on the width, get the largest width tire that will fit on your wheel. That is the most stable setup.
For example, a 7 inch wide wheel can take a 205/55 as well as a 225/50 tire. You are better off with the 225/50 tire.

HTH,
-Zoltan.
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Old 03-31-2003, 01:44 PM
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I think they are 7". Thanks for the information. I think I will go with the 225/50's
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Old 03-31-2003, 01:49 PM
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Another option would be 225/45R15. The lower profile will make your car a little faster on shorter tracks, assuming that you don't have to take an extra shift. Works for my 924S.
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Old 03-31-2003, 07:31 PM
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how does a lower profile tire make your car "faster"?.. it'll make your speedometer read incorrectly, which will make you "think" you're going faster but, you won't be...... all you will be doing is piling up miles faster.. but not going any farther or faster..
Frank B
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Old 04-01-2003, 09:25 AM
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Well, this is competition only, so miles and spedo error are irrelevant. A smaller diameter tire allows the car to accelerate faster due to a lower gear ratio. This scenerio is good for auto-x because you have very short areas in which to accelerate.

Jay
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Old 04-01-2003, 09:34 AM
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I dunno about that, it may give the impression of quickness, I'm not so sure it's happening like that.. a lower profile tire will help "lower you car a little bit, but not make it faster.... lower gear ratios would make it quicker..
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Old 04-01-2003, 09:54 AM
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Frank B: it is a question of acceleration, not top speed. a smaller circumference wheel/tire will accelerate a car better than one with a larger circumference wheel/tire. The trade off is a lower top speed.

Think back to a 10 speed bicycle: in first gear, you can pedal real fast, but you won't be going that fast. Now, if you are able to pedal at the same rate, but you're in 10th gear, then your bike will be clipping along at a faster pace. (I know there are other factors to 10 speeds, just trying to use a simple, real world analogy)

To correlate: 1st gear is a larger profile tire; and 10th gear is a smaller profile tire. An engine spinning at 3000 rpm's will move a car with a lower profile tire quicker than the same engine spinning at 3000 rpms with a higher profile tire.

For the average autocrosser, going from a 225/50 to a 225/45 won't make much of a difference. But a seasoned autocrosser may be able to use this extra acceleration to his advantage.

Make sense?
-Zoltan.
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Last edited by Z-man; 04-01-2003 at 10:14 AM..
Old 04-01-2003, 10:12 AM
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I just thought back to when we used lower profile tires for hillier mountain bike races.. it was easier to climb.. (smaller diameter tire/wheel) without sacrificing nice gearing.. gotcha..
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Old 04-01-2003, 10:18 AM
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rahter than go up 4 teeth (heavier, you could decrease your tire diameter/size and loose weight and be quicker.. comprende'..
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Old 04-01-2003, 10:19 AM
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On my 84 VW GTi I installed 235/45R13 tires on 13x8 wheels. The car accelerated like a demon, and the stuck like little else. However the top speed of my car was only 90mph. The trade offs depend on the track. If the shorter ratio of the tire makes it so you have to shift more often, you will lose any/all advantage. However, for short tracks, mmm, nothing like stompin on the V8 cars!
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Old 04-01-2003, 06:14 PM
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