|
Originally Posted by tyoneal
To All:
I know this has been brought up offhandedly from time to time, so I thought I would ask it out right.
Why are 17 and 18 inch wheels considered the, "Best" choice for overall performance, (Road Race or Performance Street driving) while larger wheels (> 19 inches, and, < 17 inches) and smaller wheels are generally considered second rate when ONLY handling is considered?
Compliance. If its driven on the street, that is the biggest aspect that shouldn't be overlooked. That... and suspension design (geometry and damper technology) has come ten fold in the past 15 years... so you don't need to run 850lb spring anymore to get the chassis to work at speed. Not to mention that there is suspension in the sidewall of the tire itself.
The new Vette and Camaro etc. all have moved to 19 and 20 inch wheels, and at least the Vette is considered one of the finest handling production cars in the world?
Yes... it is. Without question.
Is this just "Old" reasoning, that is now considered out of date or is there some factual reasoning for this that I have overlooked?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.
Does Staggering the size have any effect one way or the other on the handing of the car, (i.e.. 19 inch in the rear, and 18 inch in the front), or is it just strictly for looks?
One idea is that the smaller front tire and wheel are effected less by gyroscopic effects from the movement of the package weight. This would effect the transitional steering input less. Interesting thought...
I have noticed that many great performing racing cars have a taller, wider tire on the rear and a slightly shorter and thinner tire in the front. (IRL, F1)
Is there any good reason for having the rear of the car higher in the air than the front for a road racing application?
No. Other than an aero package that would utilize the possible down-force created... I don't really believe that there is anything viable.
Is it a function of aerodynamics, while under heavy acceleration and "At Speed" running, that the down force will adjust the downward pitch of the car, so while running normally it will move into a nice level stable attitude?
Uh... no, I don't believe so.
I had heard that depending on the front to back weight ratio of your car, that in some cases this weight differential helps dictate the width of your tires. (i.e.. A car that is heavier in the front than the rear will handle better with a wider tire up front as to help keep under-steer to a minimum. While a car with more weight in the back will benefit from a wider rear tire to help reduce over-steer. Is this correct?
Before answering, the drive wheel/wheels should also favor a wide wheel as well.
For instance. A 68 Camaro with 55% of it's weight to the front/ 45% of it's weight to the rear, AND being a Rear wheel drive car. Would benefit from having wide tires in the rear, say 315's (Due to rear wheel drive) and would handle better with front tires being somewhat similar in size as the rear tires, say 295's because the front wheels are having to work harder at changing the direction of the car due to the front being heavier than the rear. (in other words a natural tendency to try and under-steer)
This one, really needs to be laid to rest. A wider tire doesn't do as much for forward traction as it is speculated. Which is why I generally laugh when people stuff 315's to 345's on the back of a first gen with and 235 to 255 on the front. All that does is induce handling problems... mainly, as you stated, under-steer.
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.
This would be one of the reasons, other than weight and aerodynamics, why Drag racers run skinnys up front and as wide as possible in the rear. (Given of course it is rear wheel drive) Changing direction is not an issue so under-steer is also a non issue.
Whereas, a rear wheel drive, rear engine car while having 315's in the rear, AND having a weight bias also in the rear could get away with wide tires in the rear and substantially thinner tires up front say 215's without having an undue challenge of dealing with car induced over-steer and under-steer.
Is this a correct thought all other influences being static?
Yes... all we are trying to do is control weight and the transfer of it. The hard part is being able to handle it in all directions.
Do larger diameter tires as a rule run cooler than smaller diameter tires because the friction of the tread against the pavement is spread out over a larger surface?
Like compounds and construction ?? Kinda of. If the tire is larger in any aspect, there is more mass to absorb and retain heat. But on the flip side... the taller tire will have timeoff of the surface and will have more time to cool (in theory).
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.
I just wish I could have done the same kind of testing on their drag race brothern. It is somewhat more difficult... to say the very least.
I'm sure this is blatantly obvious to most people, but I wanted to clear this up in my mind while giving some thoughts to some project issues.
Thanks for your patience.
Best Regards,
Ty O'Neal
|