the difference with the sizes you specified is pretty minimal, but the sidewall on the 17 will sag a little more than the 18 with equal tire pressures, so the contact patch on the 17 will be slightly larger.
No reason to be a dick about things dude.Are you seriously a sponsor, or are you just an intern sitting at a computer attempting to sound smart?
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No reason to be a dick about things dude.
If you will do some research, you will notice that there is 1 tire offered a 315/35/18 and there are 10+ tires offered in a 315/30/18. So you would assume that OP is compairing a 315/30/18 to a 315/35/17. Then you would realize that the 315/35 has more sidewall than a 315/30, which would make Sharad's comment correct.
I'm sure Sharad used this same method to come to his conclusion.
The main point is that the type of tire design and compound has more to do with traction than sidewall. A drag radial will hook much better than an all season tire, at the same size.
BTW, I noticed in your sig that you are running some Hoosier drag radials. Ive been thinking about getting some. How do you like them?
Are you seriously a sponsor, or are you just an intern sitting at a computer attempting to sound smart?
So to the original poster: ignore the contact patch and pick a stickier tire and the one that is the most convient for your combination.
I've been saying that for years. Almost every thread I have to point out that friction does not depend on surface area. I would have stuck with the stock 245's if my 275's didn't look so good.
While we are laying out credentials:
- In the health care industry
- A Mechanical Engineering and Chemistry major
- Owned my mustang since 04
- Now the proud owner of 2 mustangs
(just playing with you sharad, I agree with most of what you are saying)
I will disagree with both and say the size of the contact patch really just doesn't matter. But more to the point, I would agree with what Sharad said about suspension and tires. Your traction is going to depend much more on the ability of the car to put more weight on the rear wheels (weight transfer from suspension), and the coefficient of friction of the tires. For those physics majors, notice that contact patch is NOT a variable in the tractive force equations. Just normal force and coefficient of friction (thus, suspension and tire compound).
Case and point: my 88 mustang has a 245-45-17 nitto 555R. The tire isn't known for hooking hard, and that is a really narrow size compared to what most here run... yet I get 1.6 60' times. There are a lot of guys here with much wider, and sticker tires that can't do that, so I really think tire contact patch doesn't matter. Again, tire compound and weight transfer are the main factors.
So to the original poster: ignore the contact patch and pick a stickier tire and the one that is the most convient for your combination.
Sharad said:Take a 275/60-15 tire and a 275/35-20. They both have a section width of 275mm and they're both about 28" tall. However, with both tires at, say, 32psi, the 275/60-15 will have more rubber on the road because the weight of the car will compress that 60-series sidewall more than it will 35-series sidewall.
Let's step away from the textbook for a minute and take a look at some cars in real life. Lower profile tires have stiffer sidewalls. I'm talking, same make and model tire. I assume it's because they don't want bumps in the road to pinch the sidewall against the rim. Regardless of the reasoning behind it, the reality is lower profile tires have stiffer sidewalls. A tire with a fatter sidewall sags more. It just does. Sit a Fox on a 275/40-17 M/T DR and look at how the tire sits. Replace that tire with a 275/50-15 and look at it again. The 15" tire will look like it has less air in it. Must be a softer more pliable sidewall. Surely you wouldn't argue that the 275/50-15 M/T DR has a smaller contact patch at 50psi than it does at 10psi? I know you're gonna cry foul because I brought tire pressure into the equation... but I'm telling you, in practice (away from the physics textbook) the sidewall sags more with the fatter sidewall than it does with the lo-pro tire. The tire with the fatter sidewall looks like it has less air in it than the lower profile tire. Sits flatter on the bottom, more rubber on the road, better traction!That might not fit your physics equations, but the physics equations also imply that a top fuel dragster will hook just fine on a bicycle tire.
I suppose I've wasted too much time beating a dead horse. The OP asked if the car would hook better with 17s or 18s on the same width tire, and I answered the question with firsthand experience.
It still has nothing to do with the size of the contact patch as the amount of rubber on the road is the EXACT same regardless of tire size (assuming equal tire pressures). Like I said earlier the reason a car with 15" drag radials can launch better than the same car on 17" drag radials has to do with the sidewall flex and not necessarily the size of the contact patch (you'll also accelerate quicker w/ a 15" wheel due to the reduction in rotational mass).
BTW, a 15" tire with 50 PSI will have less surface area touching the ground than a 15" tire with 10 PSI. [WHICH IS THE POINT I WAS TRYING TO MAKE]
Now, I don't disagree with you that better 1/4 mile times can be acheived by running a 15" wheel as opposed to a 17" wheel, but the physics you've stated are false and there is a lot more that goes into the method of launching a car other than contact patch. There's friction, rotational mass, weight transfer, traction, contact area, etc... and there is likely a perfect balance of each depending on the application. For example, a bicyclist wouldn't get very far running a 215 tire and on the other hand a 700x23 bicycle tire on a 400 horse fox body Mustang would be completely useless.
Back to the thread topic, the OP was asking about the difference between a 17x10 and 18x10 wheel assuming he'd run a 315 tire on both. The sidewall height difference really doesn't matter in this case. The biggest challenge with the 18" wheel is the added weight and not the reduction in sidewall height. The minimal additional sidewall flex would be hardly noticeable to most. Assume for a minute that both the 17" wheel assembly and the 18" wheel assembly weighed the same. I doubt you could even find a driver consistent enough to demonstrate the difference between the two. Again, this is an unrealistic situation as most 18" wheels weigh more than a comparable 17" wheel.
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