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Originally Posted by chicane
Is this just "Old" reasoning, that is now considered out of date or is there some factual reasoning for this that I have overlooked?
Old theory... yes. Newer technology is that good.
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That is too vague to arbitrarily be true IMO. Take a magnesium center and carbon fiber barrel and even so, a 16" wheel is less unsprung weight and easier to both accel and brake from an inertial standpoint than an 18". Or use a 14" diam if the brakes can be small enough to work and fit. Only reason for big wheels is to fit bigger brakes from a performance standpoint
that I am aware of. A true race car can be geared to work for any given track and any tire size including small diams.
So, again, if you don't need 14" rotors you don't need big wheels, and 98% of the people that would buy a Vette will never really
need the big rotors even in a racing situation. You mention below working with a record setting Vette, so maybe you (or the driver if you aren't the driver) can actually put so much heat into the brakes you need the large diam for thermal issues. Even then, I would ask if you have ever taken that car and tried a smaller, cryogenic'ed rotor (is that a word? hahaha) and good pad and found you overcooked 'em? If so, then you
need to run the big brakes and therefore big wheels.
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Originally Posted by chicane
A wider tire helps with lateral traction... and a taller tire helps with longitudinal traction. The tires used in per-say... Top Fuel classes... isnt used because its wide, its used because the rotational inertia of the tire itself makes it grow in diameter... which means a longer foot print and an increase in forward traction.
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Not disagreeing from a drag standpoint other than a taller tire doesn't "help" with traction as much as the inertia hinders acceleration. In fact, contact patch is what creates traction period, so wider is better. Watch a TF car launch, the launch is at full width and the growth as rotational velocity increases is a byproduct of the sidewall design that is necessary to reduce launch shock by wrinkling. The car is also so overpowered the transmissions have stacked clutches that slip the entire length of the track and are replaced each round, but if they could keep the tire from growing they could put more power down with the wider contact patch. They have all sorts of clutch designs of course to work with that byproduct. Also note they still use 15" diam rims because the taller the sidewall, the more wrinkle and shock absorption. Of course tire size becomes class limited too. But anyway, I used 28" diam drag slicks on a 68 Mustang because they would fit inside the wheelwells and it had a 2spd powerglide, so the tall tire helped the big end at 9000rpm thru the traps. I would have ran 26" but then to get out the backdoor, the rpm drop was too great between the gears and the car was slightly faster with the large tire and optimal rpm drop in the shift.
From a Lateral g standpoint, you want smaller sidewalls and less wrinkle for overall performance. Smaller diams are easier to accelerate and brake. 'Course, use a 23" diam overall tire on a 69 Camaro and it will look like butt and there is something to be said about liking the way your performance car looks. But, I say get the small tires for the track and the larger ones for the street. I don't care what it looks like as long as it is fast
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Originally Posted by chicane
This is still open for debate. I did some tire testing for Goodyear some time ago at Talladega where we ran a Corvette around the track for a 24 hours (to an endurance record... that still stands to this day). Anyway... we mounted three infared cameras in the leading and three on trailing... and also had a camera focused on the sidewall. It was an interesting study to say the least. Although we were looking specifically at 275, 295 and 315 section widths in the 17" diameter... I am sure the data would cover other diameters as well.
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Very cool, what was the overall findings of the test??
edit - the above TF stuff is what I understand to be the issues, not necessarily gospel so I am open to facts that change that. Also, the growing tire adds extra "gear" that is beneficial.
Also, thanks XcYZ for the kind words, forgot to say that! Kinda shows why I am more of a lurker than poster since it ain't a Lateral G, but my favorite car to this day is Big Red and love the car culture it started, so here I am
