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Old October 17th 2009, 03:12
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staggered wheels

It has been a year and a half since I lost my 1302 in a fire. It dawned on me the other day as I was looking through some old notes and books currently stored in an off-site storage facility I asked a lot questions that were all over the place until I bought my 1302. Oddly, most questions then focused on a 1303 until I made my purchase. Nevertheless, many questions have popped into my head as I try to do some conceptualizing and I need to once again rely on everyone here who has the experience I lack.

The first questions for my second project have to do with staggered wheels. I know some stock Porsche's have wider wheels on the rear than on the front.

(1) Is there an advantage to staggered wheels if applied to a 1303? Would there be disadvantages?

(2) Is there a formula for staggered wheels? It doesn't have to be a genuine mathematical equation ot anything but is it better to be one-inch wider on the rear? One and a half? Two inches?

(3) Is there a point of no return on the advantages of wider wheels? Is an 8/9½ better than a 6½/7½, for example?

(4) Since wider wheels may mean wider fenders (wings), are there advantages and/or disadvantages to going wider there as well? I have seen some wider fenders that require a second look to even notice they are wider, and I have seen some that almost border as an extreme measure. I'd prefer not going the extreme route but if that route would be better, then so be it?

I'll ask other questions in other threads in their appropriate forums. Thanks in advance.
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Old October 17th 2009, 08:22
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Quote:
Originally Posted by oasis View Post
It has been a year and a half since I lost my 1302 in a fire. It dawned on me the other day as I was looking through some old notes and books currently stored in an off-site storage facility I asked a lot questions that were all over the place until I bought my 1302. Oddly, most questions then focused on a 1303 until I made my purchase. Nevertheless, many questions have popped into my head as I try to do some conceptualizing and I need to once again rely on everyone here who has the experience I lack.

The first questions for my second project have to do with staggered wheels. I know some stock Porsche's have wider wheels on the rear than on the front.

(1) Is there an advantage to staggered wheels if applied to a 1303? Would there be disadvantages?

(2) Is there a formula for staggered wheels? It doesn't have to be a genuine mathematical equation ot anything but is it better to be one-inch wider on the rear? One and a half? Two inches?

(3) Is there a point of no return on the advantages of wider wheels? Is an 8/9½ better than a 6½/7½, for example?

(4) Since wider wheels may mean wider fenders (wings), are there advantages and/or disadvantages to going wider there as well? I have seen some wider fenders that require a second look to even notice they are wider, and I have seen some that almost border as an extreme measure. I'd prefer not going the extreme route but if that route would be better, then so be it?

I'll ask other questions in other threads in their appropriate forums. Thanks in advance.
The correct sized wheels for the front or the rear for ANY vehicle is that which is suitable to support the weight of that corner for the application. However, a moderating factor is the slip angles that are provided by each tyre. There are other factors relating to physical fit and gearing that will be ignored here.
IF you could get equal slip angles front and rear then for a bug with say, a 400hp engine you could be looking at a front wheel width of 160-180mm and a rear width of 250+mm. That would be impractical so it ends up as a compromise on slip angles, traction under power and front end slide.

There is no magic formula and you will find that the differences in wheel width are the result of all sorts of suspension perameters and personal preference. For example, some super cars run rear wheels that are ridiculously wide if you consider the front wheel width and slip angles but the compromise with traction under power and suspension set up moderate the effect.

A good starting point with any car is to run equal tyres front and rear at say the minimum width and then increase the width of one end or the other to suit driving preference and power since you are unlikely to vary the suspension geometry too fundamentally.

Remember, too wide is too slow.

Clive
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Old October 19th 2009, 08:49
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400 hp?

I was thinking my next air-cooled car might pack more of a punch than the 2056 in my 1302, but 400 ponies?

Anyway, I get most of what you are saying. My 1302 had 16x6½ wheels on it. The fronts had 195/50-16 tires; the rears had 205/55-16. The only reason I changed the front tires was because I had slight fender fouling and I wanted to keep them stock.

I noticed some stock Porsche's had wheel combinations of 9- and 10-inches wide, front and rear, respectively. (I don't know the associated tire sizes.) The Porsche was likely pushing more power than I intend -- perhaps even more power per weight than I intend. Intuitively, it seems a 180mm to 250mm ratio (~2.75-inch difference) would be an enormous difference -- much greater than the 911 or 996 or whatever raised my attention to staggered wheels.

Let's start with something fairly pedestrian. What is slip angle?

I'm also wondering what starting point of equal-width wheels I should consider, but I will save that for when I get my platform and have more specifics. Let me also ask, though, why do you think the Porsche has staggered wheels?
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Old October 20th 2009, 08:49
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Little bit of light reading for you:
http://www.mgf.ultimatemg.com/group2...slip_angle.htm
I would be interested to know what vehicle you have, its power and supension set up? A starting point would be standard suspension/55bhp = 165 tyres all round
the Porsche has staggered wheels simply because the load on each corner is very different front to rear. They will be after maximum grip at the rear to tame the gross polar moment that is generated by the rear engine and be able to lay down the power effectively. I suspect that the fronts would have been narrower but the difference in the slip angles would have made it very twitchy and also they needed some big rubber to complement the brake performance.

Clive
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Old October 20th 2009, 12:22
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Thanks! I will read the article as soon as I logoff (otherwise, I will be timed out anyway).

You wanted to know specifics of what I will be driving, and I am not there yet. I am leaning towards getting a 1303. Then again, that was my intent the first time and I ended up buying a 1302 (in 2004) that caught my eye, and I am more open-minded this time. I have to think I would go with a Type IV engine again as I enjoyed it in my 1302 immensely.

I will post specifics when the time is right. I was looking to learn, and you are pushing me in the right direction. Thanks again.
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Old October 21st 2009, 11:50
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Certainly not much of an update but more of a comment after reading and learning ... I can only recall oversteering twice in my 1302, and not that dramatically either. We'll see what I get, but I understand the concept and why starting off with equal sizes was the suggested starting point. Thanks.
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