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Here are a couple of nice early model coupes at the Detroit 2007 CORSA Convention. Same course, same corner. Look closely at the taller tire and how it is deflecting. Now look at the short tire. Keeping the tire's tread on the ground is what we're really after. This is also how more air works to stiffen the sidewall of a street tire.
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| Images courtesy Scott Trunkhill. | |
Phil Raker sent me a pair of photos that illustrates this on his '65 Corsa 140. Phil writes:
Yesterday I received some photos that Norm Witte had taken at the track day at Grattan Raceway (near Grand Rapids) which was put on by the Detroit Alfa Romeo club on Memorial Day 08. That was my first outing with the new wheels & tires.
Looking at one of Norm's pictures I was reminded of one taken by Scott Trunkhill at the 07 Convention Autocross. Scott's picture shows my car rolling way over as the 185/80-13 tires on stock steel wheels flex a lot. Norm's picture shows the same car with the only change being the 7" by 15" Minilite wheels and 205/50-15 tires. In both cases, tire pressures are set at 30 front and 35 rear.
I would estimate that, in the two photos, the level of lateral acceleration (cornering force) is probably about equal. The new tires and wheels flex much less, resultant body roll is significantly reduced, achievable lateral acceleration is much greater, and steering response and vehicle control are greatly enhanced.
I'm attaching both of the photos as I thought you might like an illustration of the difference that low profile tires can make on the SAME CAR - no other modifications.
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| Images courtesy Phil Raker. | |