General consensus on wheel sizes?

[landrovered]

It all boils down to physics. Turning is a product of tire deflection and the balance is struck between sidewall height and grip. I personally think that ultra thin sidewalls look bad and they have less ability to deflect due to the physical limit imposed by their smaller size. That being said a huge sidewall is not going to necessarily going to turn better because of the forces will not be as efficiently transfered to the wheel as with a moderate sidewall. Like I said it is a balance.

A practical example of this is modern racing tires. If tiny thin sidewalls were faster then every F1 car would be on wheels with rubber bands glued to them but they are not. Look at racing cars for the most efficient tire construction in terms of wheel size to sidewall/contact patch.

F1 rules state that the front tire must be between 305-355 mm wide with a maximum diameter of 660 mm. These are on 13" rims. The ratio of width to diameter is roughly 1 to 2 with the rim being roughly equal to the width. In short the tires are square. The sidewall height of the F1 tires is roughly equal in proportion to that of a "50" street tire.

So the most badass cars in the world are running on schweet 330/50/13s, how is that going to hang on the street?

[stephen wilson]

I agree, except for the F1 reference. They use such tall tires because the rules limit wheel diameter to 13". Race cars are actually a poor indicator of best practices, because important design aspects are dictated by the regulations.

[landrovered]

I think the key bit of info from the reference is that a 50 is where it is at. In my mind you start with a 50 then work it backwards to your wheel size, height diameter etc.

[blue2000s]

I may be in the minority, but I'm really happy with my 17s. There's more than enough grip for the roads, the ride is stiff but not painful with the M030, the risk of bending a wheel on a pothole is relatively small, and tires are cheaper. I prefer a little narrower tire for minimizing tram-lining and somewhat increased feedback.

I'm not entirely happy with the style of the stock 2000S wheels, but I actually don't think 18s+ enhance the car's looks given the same wheel style, but that's subjective, of course.

[stephen wilson]

In this area, racing tells us Nothing about our "ideal" tire selection. That can only be determined buy comprehensive testing.

For F1 it's easy, build tires to match the maximum allowed height and width, to fit the maximum allowed wheel diameter. Whatever profile that works out to is purely coincidental.

Using your max. diameter and width numbers, the profile would be between a 46 and 54 "series", depending on tire width. Racing tires usually just use a diameter X width designation, such as 26"X13"-13.

[stephen wilson]

Yeah, I didn't think about that issue, my 18's do "tram-line", but I find it acceptable.

[9eighty6]

blue2000s - I may be in the minority, but I'm really happy with my 17s. There's more than enough grip for the roads, the ride is stiff but not painful with the M030, the risk of bending a wheel on a pothole is relatively small, and tires are cheaper. I prefer a little narrower tire for minimizing tram-lining and somewhat increased feedback.

I'm not entirely happy with the style of the stock 2000S wheels, but I actually don't think 18s+ enhance the car's looks given the same wheel style, but that's subjective, of course.

I am going to have to agree with you on this one. I like the 17s for function and asthetics. Tires are cheaper, that is for sure. I just got a new set of wheels for the summer, and again, I went with 17s (though in the BoxS II design).

I love that everyone has their own opinion though. I enjoy seeing what other owners put on their cars in the pics.

[renzop]

Wheel size is a compromise. You are balancing cost, weight, aesthetics and responsiveness to direction change.

Basically:

Cost: 17 is cheapest cost, 19 highest - 17 wins

Weight: 17 is lightest, 19 is heaviest - 17 wins

Aesthetics: 19 is prettiest 17 ugliest - 19 wins

Responsiveness: This really has to do with tire aspect ratios not wheel size. For the same overall tire height the 19 will be most responsive and the 17 least. However the 17 will have less unsprung weight which also contributes to responsive handling. Call this one a wash.

The 18" is probably the best compromise.

If you ignore aesthetics then 17" are best. They are lighter. The key is to not use the stock tire aspect ratios with the 17" wheels but instead use the same aspect as the OEM 18" tire. This will give the same responsiveness as the 18" and will lower the car by about 1/2". The combination of reduced unsprung weight and lower CG will result in a noticeable improvement in handling. The reduced unsprung weight will result in better acceleration and braking performance as well as a slightly smoother ride. The lower rolling diameter will result in improved acceleration at the expense of higher cruising RPM, poorer fuel economy and an inaccurate speedo.

The problem with the factory 17" wheels is that the are also narrower than the 18" or 19" so you can't mount as wide a tire.

[Lil bastard]

Originally Posted by landrovered

I think the key bit of info from the reference is that a 50 is where it is at. In my mind you start with a 50 then work it backwards to your wheel size, height diameter etc.

Well except that the sidewall height isn't a set height, it is a percentage of tire width.

A 50 series tire has a sidewall which is 50% of the width of the tire. And tire width brings you back to the wheels because, as has already been mentioned, the smaller wheels do not generally come as wide.

[landrovered]

Originally Posted by Lil bastard

Well except that the sidewall height isn't a set height, it is a percentage of tire width.

A 50 series tire has a sidewall which is 50% of the width of the tire. And tire width brings you back to the wheels because, as has already been mentioned, the smaller wheels do not generally come as wide.

I don't disagree with you and my comment was not meant to advocate smaller wheel sizes necessarily. Stock 17 OEM tire size is 205/50/17 front and 255/40/17 rear from what I understand. So if you stick with a 50 or a 40 for handling then you must increase diameter with a larger wheel, or you must choose a lower profile tire which will have different characteristics. Otherwise you are opening a can of worms by running larger or smaller diameter tires than stock. Trust me, I know all about the ramifications of tire size changes from my Land Rovers. We have to re-gear two diffs to maintain drivability with 35" tires.

For my purposes though, the stock boxster profile is fine. I am confident that I will get the best compromise of comfort and handling with these sized tires. The fallicy is that lower profile is better, that is what I was addressing.

[mts]

I believe 18's provide the best compromise on asthetics, ride quality, cost & performance.

[Topless]

I agree that 18s look the best but I just hate paying too much for high quality rubber. I run 17s in stock sizes on the street and my track set is 4x17/255 rears all around.