Pro-Touring charger guys (autodynamic/Mike etc)

[autodynamics]

[HPP]

This test that has been done and reffered to can be explained with 2 theories:

1. They ran both wheel diameters with the same tire diameter, and lost a lot of tire height and tire flex, and got a very unforgiving ride, and got slower lap times that way.

2. Ther ran same tire height, and like that had 1 inch more tire diameter, and suddenly their gear ratio did not fit the track anymore.

This is just a guess, since i have no idea of what kind of car this was done with, and what was done to compensate.

I've seen a couple of tests like this done in magazines. I believe one was a Cooper and one was an BMW M3. In both instanances, it was done as a plus sizing exercise. In plus sizing, the overall tire diameter does not change. What happens is the rim diamter is increased one inch and the sidewall is decresed one aspect ratio. In both tests, they attempted to use identical manufacturers for wheels and tires and compounds. However, manufacturer offerings did require a different set of tires on a size, so they picked the closest treadwear rating they could. In both tests, slalom times and road course times went up as wheel sizes increased. In these test, the changes did have a bigger imact on the Cooper than the BMW. I'm not sure what your trying to say in point 2, btw.

I am not a big fan of very big wheels, but i have decided to go 18 on my 68 charger. The flywheel effect i have strong doubts that will play a factor here, as time you spend on braking down is quite long( on a 26" tire 200mph is just 2590 rpm). If it has an effect, it could be in your favor, allowing some reaction time for brake feel, like on ice, and no ABS.( BTW we have played around with flywheel weight to make it fit engine torque/ gear ratio etc, and got some very interresting results)  On thing that is just a fact, is that braking 4000 pounds of iron down from straightaway speed to cornering speed takes power, and power creates heat! bigger diameter brakes needs less clamping power, but has higher brake pad speed, but also increased cooling. Overall i think we can trust the racecar brake manufactors that bigger brakes are better.
The MOI theory, and the powersteering that steals extra horsepower while janking the wheel will not have any effect at all, simply because turning IN to a turn, you are not on the power anyway, and if you need a "rapid correction" coming out of the turn while beeing on the hammer, your front weels will (or should) have the same direction, as this will just be compensating for ass beeing all over the place, and if it is not, you have bigger problems than wheel diameters.

You may disagree with those theories, but it doesn't mean they don't exist and don't impact your car. They are scientifically proven and do happen with automobiles. I think perhaps a better correlation would be to say their impact is contingent upon the vehicle and the usage. If you increase the MOI of your wheels by 10%, that 10% will have a greater impact on 2500# car with 190 horsepower than it will on a 4000# car with 500 horsepower. The effect is still there, but it is masked by the weight and power and that effect is there as long as the car is in motion. It doesn't go away because you are on or off the throttle, turning in or turning out. It will be noticeable if you swap out your 15" Cragars for some 19" Budnicks on your 318 powered Charger with the old Federal steering systems in it and the OEM suspension. It will not be noticeable on your stroked 6.1 hemi conversion making big power numbers with the late model steering pump in a car with optimized spring rates.

I've seen countless threads debating rim size vs brake size, I've yet to see a universal answer to the question of which is definitively better. Even in the rules limited world of competition, there are anomilies that change up the rules. Some good examples of highly effecient braking systems used in small wheel sizes would be Nascar, Champ car and F1. That is why I said that most pro touring builders don't notice and don't care about the impact they are creating and quite frankly, I don't see why it is an issue for them anway since there is no "pro-touring" racing classes any where that it could matter. You are right, there is always give and take in building a car, the builder just needs to evaluate those wants and desires against the look and performance they are trying to achieve.

[dangina]

17x8 and 17x9.5 i would use 15" rims if the better rubber was available - and the 17" rubber is in my price range....

[autodynamics]

Ohhhh dip