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Old 01-09-2007, 06:42 AM   #31
BavarianWheels
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Quote:
Originally Posted by Bronxie
So a bigger contact patch is more desirable? And if so, why are larger tires more desirable than smaller tires?

They look cooler...
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Old 01-09-2007, 08:25 AM   #32
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Quote:
Originally Posted by vwhobo
Yeah, be real careful about having too much "unstrung" weight.

Now I remember one of the reasons I stopped logging in.

because you wear boxer shorts?
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Old 01-09-2007, 08:39 AM   #33
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Originally Posted by My Life, My Era
You guys are making it easy for vwhobo and ChrisV to appear uber-intelligent. Most of you...lack....knowledge.

Most of you guys joined this car forum months ago because you like cars...why haven't most of you researched about cars during those months? Do you really like cars? Some of your answers are just completely wrong...but you are so sure of them.
Holy Crap he's right this time!
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Old 01-10-2007, 04:31 PM   #34
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Quote:
Originally Posted by giant016
If wider tires reduce accelerative traction, than skinnier ones would improve it correct? Perhaps dragsters should run skinnies all around

Notice that dragsters run tires with extremely low tire pressures. And ALSO notice that when a dragster actually runs, the tires increase in diameter and the contact patch gets narrower..

Notice the wrinkles in the sidewalls:



The tires are running very low air pressure (and they have to be screwed to the rim, as well). The ultra low air pressure allows more of the front to back contact patch to be utilized for accellerative traction.

But when running hard, the tire expands and the contact patch gets skinny side to side:

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Old 01-10-2007, 04:44 PM   #35
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Quote:
Originally Posted by Bronxie
So a bigger contact patch is more desirable? And if so, why are larger tires more desirable than smaller tires?

Larger wheel size with shorter tire sidewalls give increased cornering/steering response, at the expense of ride quality, up to the point where the wheel itself adds too much unsprung weight and you go backwards. The shorter sidewall is like having a short pencil eraser: it flexes less side to side, thus being more precise in it's response to your input. Wider tires increase lateral grip due to the shape of the contact patch, and in general, larger tires are also designed more for performance with better rubber compounds and tread block design.

Lots of factors go into the choice of tire. For road racing, a very short sidewall tire, allowing room for the largest brakes, and the best cornering/steering response is ideal. For this reason, so many sporty cars follow this pattern.

Now, often, the rubber is heavier than the alloy of the wheel, so by increasing diameter of the wheel but using a lighter alloy, the overall weight can go down, giving less unsprung weight. And by reducing the weight of the tire by having it have shorter sidewalls (at the same or similar overal diameter) you reduce rotational mass at the farthest point from the hub, reducing the effort necessary to turn it, freeing up some horsepower. Thus a larger diameter wheel with a short sidewall tire can free up horsepower AND increase cornering response AND improve overall suspension efficiency.

At some point however, you run into the law of diminishing returns, and can actually go backwardfs, so you have to be careful IF you are looking for ultimate actual performance. In real life on the street, however, the difference between slight improvement and slight detriment is small, and often unnoticeable. So a slightly heavier large diameter wheel will not really hurt the performance enough to be noticeable, but might look better enough to the owner that it's negative effects are immaterial.
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Old 01-10-2007, 10:40 PM   #36
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Quote:
Originally Posted by ChrisV
Larger wheel size with shorter tire sidewalls give increased cornering/steering response, at the expense of ride quality, up to the point where the wheel itself adds too much unsprung weight and you go backwards. The shorter sidewall is like having a short pencil eraser: it flexes less side to side, thus being more precise in it's response to your input. Wider tires increase lateral grip due to the shape of the contact patch, and in general, larger tires are also designed more for performance with better rubber compounds and tread block design.

Lots of factors go into the choice of tire. For road racing, a very short sidewall tire, allowing room for the largest brakes, and the best cornering/steering response is ideal. For this reason, so many sporty cars follow this pattern.

Now, often, the rubber is heavier than the alloy of the wheel, so by increasing diameter of the wheel but using a lighter alloy, the overall weight can go down, giving less unsprung weight. And by reducing the weight of the tire by having it have shorter sidewalls (at the same or similar overal diameter) you reduce rotational mass at the farthest point from the hub, reducing the effort necessary to turn it, freeing up some horsepower. Thus a larger diameter wheel with a short sidewall tire can free up horsepower AND increase cornering response AND improve overall suspension efficiency.

At some point however, you run into the law of diminishing returns, and can actually go backwardfs, so you have to be careful IF you are looking for ultimate actual performance. In real life on the street, however, the difference between slight improvement and slight detriment is small, and often unnoticeable. So a slightly heavier large diameter wheel will not really hurt the performance enough to be noticeable, but might look better enough to the owner that it's negative effects are immaterial.

one of the best has spoken again
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Old 01-10-2007, 10:50 PM   #37
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Here's a video of a drag car taking off in slow motion (1000 FPS)...Pretty interesting.
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Old 01-11-2007, 12:17 AM   #38
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So basically, these things have a range of effectiveness, and too much in either direction can hurt the objective at hand.


How can you calculate if you are getting the most out of your tires & wheels, for example, if you are in the market for these things.


How heavy is too heavy, how short is too short and how big is too big relative to the vehicle it goes on?


Like I'm sure this set up isn't very effective.


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Old 01-11-2007, 02:38 AM   #39
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Learn something new everyday. Who needs school when you've got CF?
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Old 01-11-2007, 03:19 AM   #40
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Originally Posted by giant016
Learn something new everyday. Who needs school when you've got CF?
I suggest you and other members cross-reference what you have "learned" in this topic with a more reputable source, preferably a book.
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Old 01-11-2007, 07:29 AM   #41
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Thanks for the advice, but I know enough about the subject not to reference books. Perhaps you have a recommended reading for the others though?
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Old 01-11-2007, 01:41 PM   #42
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Quote:
Originally Posted by Bronxie
So basically, these things have a range of effectiveness, and too much in either direction can hurt the objective at hand.

How can you calculate if you are getting the most out of your tires & wheels, for example, if you are in the market for these things.

How heavy is too heavy, how short is too short and how big is too big relative to the vehicle it goes on?

It all depends on what you are going to be doing with your car. if you are going for that extra hundredth of a second on an autocross course, or road race course, then as light as possible, with as sticky a tire as you can find is what you are looking for, preferably as wide as can fit under your fenderwells. Like this Miata that Ron Baur drives in SCCA autocrossing:



275 Kumho's on 18x9.5" wheels. A bit on the radical side, but it works. Of course, with any racing, you have to work within the rules, and stock class cars are limited in wheel sizing. One thing about this, there are usually experts that have gone through the calcualtions and teh trial and error phase of testing to tell you what will work best on your car. Of course, you can get a few different recommendations based on who's done the actual testing and their particular location/surface/event, but it'll give you an idea of where to start. Your own driving style will also play a part in determining the best setup. I personally prefer a slightly taller sidewall for a bit of flex. This gives me a more gradual breakaway at the limit, making driving at or past the limits easier. Thus I'll use a 50 series tire on a 1 or 2 inch diameter smaller wheel, rather than a 45 or 40 series tire on the larger wheel when going for autocross performance. On the street looks are more important to me, so I might go for that 40 series tire on the larger diameter wheel.

On the street, if you are into corenring, you can go in a similar route, butremember, street tires are different and that much change may be worse for your car than something closer to stock. Again, on the street, for most people, the negatives are not usually enough to actually notice.

Quote:
Like I'm sure this set up isn't very effective.


For a race car, no. For a street car, it'll have a slightly jarring ride, and be subject to hitting potholes and getting damaged. For a show car, it's plenty effective.
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Last edited by ChrisV : 01-11-2007 at 02:19 PM.
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