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  #1  
Old 04-22-2005, 08:16 AM
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Stretched Tires?

I was talking to one of my friends who is building up his porsche 951 (should be up to about 300whp) He said when talking to some guys, that by getting tires that were not as wide as the wheels, and "stretching" them to fit, it creates a diagnal sidewall. basically, i think he has 225s on 8 inch wheels, and 275s on 10 inch wheels. Looking at the tires on the wheels, you can obviously see the sidewall is at about a 60 degree angle instead of a 90 that would be "flat". He said that the people he talked to recommended this, because it doesn't allow any flex in the sidwall, and creates a much tighter handling car. I'm still a little skeptical... anyone shed some light on this?
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  #2  
Old 04-22-2005, 08:38 AM
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I've wondered how well this would work. I think that this will make for a stiffer tire, but I wonder if the tread profile might not be as good.
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  #3  
Old 04-22-2005, 09:09 AM
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Mad tyte JDM drifters yo! do this all the time. He is semi-correct about the reduction of sidewall flex and it's effects on handling - sort of. Stretching the tire doesn't magically create better overall handling balance, it really just increases the willingness of the car to accept sharp directional changes. As the 951 is already an excellent car as far as chassis balance and handling goes, I can't imagine that stretching the tires like it was a lowrider on 13" Daytons will make anything better in terms of real world use, and it certainly will negatively impact the car as far as durability, ride, wear characteristics, and other useful aspects of tire performance are concerned.
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  #4  
Old 04-22-2005, 09:14 AM
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You will lose a little ultimate tire grip, if the tire are to small for the rim, but it should reduce sidewall flex.
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  #5  
Old 04-22-2005, 05:09 PM
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I imagine it works great until you break the bead because the tire wont flex.
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  #6  
Old 04-24-2005, 12:58 AM
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"stretched Tires"

Careful observation of road race cars will confirm that this is common practice. Depending on what you want to do with the car, it would be good to consult with a number of tire experts, from Tire Rack to race teams, if possible. Or you can watch this thread and take advantage of the wide range of experience here.
With wheel, tire and suspension set-ups, there's always a trade off. Having tires slightly smaller on a wider rim enhances feel and provides more precise control but your car feels more like a race car...ALL THE TIME! On the street such a set-up may provide much poorer ride quality due to the much stiffer sidewalls. That's why one of our bretheren who autocrosses his SVX has 225/45's mounted on 16x8 wheels. Same contact patch as stock, but the stiffer sidewalls improve "feel". Depending on the tire and the disposition of the driver this can be a major improvement in handeling without too great a sacrifice in ride comfort or a pain in the ass. Another SVXer has 255/35's on his 18x8 wheels. His focus was on traction in a straight line. However, the small aspect ratio allows an excellent compromise in ride comfort and handeling. Tires vary in their characteristics further complicating matters. Yoko Dba's for example have fairly soft sidewalls, providing better ride comfort at a small loss in handling precision and feel. Ultra high performance tires have the stiff sidewall designed in from the get-go so if you stretch them you feel like your riding on stickey bricks. On the street the best compromise of handeling, ride comfort and expense, for the SVX, in my opinion, is 17x7.5 or 8's and the tire that best fits you needs. There's a certain amount of "art" to suspension tuning that one only learns from experience. This thread should attract input from some of the Networks v. experienced drivers and professional mechanics. It'll be interesting to read what they have to say on this subject.
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Last edited by WGJ; 04-25-2005 at 05:25 PM.
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  #7  
Old 04-25-2005, 12:00 PM
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Someone should ask this guy what he recommends:
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  #8  
Old 04-25-2005, 12:09 PM
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Now all he needs are stiffer springs and softer roll bars and maybe he will keep at least 3 of those (90%) tires stuck to the road.
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  #9  
Old 04-25-2005, 07:45 PM
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Yup, it's a trade off. Tall sidewalls act like lateral suspension. Having that side-to-side movement does reduce the 'feel' of the car, but usually increases performance when it's boiled down to lap times. (Look at the sidewalls on a formula-one car.) When you have undulating road surfaces with rough spots, dirty spots, oily spots, etc., it's nice to have some degree of lateral flex when cornering. On a perfectly smooth track, this is less important. If you look at drifting competitions, where traction is the enemy, they have as little sidewall as possible, and very wide rims.

Modern racing motorcycles have a certain degree of lateral flexibility in their suspension. When a bike is leaning way over in a sharp corner, a bump in the road surface doesn't move the tire upwards because the suspension is tilted sideways with the leaning bike. Instead, it moves at an angle which really isn't ideal at all. Recently, engineers are building a certain amount of flexibility into motorcycle suspension to allow it to flex sideways to accommodate rough surfaces when cornering. This illustrates the importance of the ability for suspension to move in every direction. Although I've never really read anything about car designers incorporating any advanced lateral flexibility into the suspension of cars, I'm pretty sure they do. The SVX's passive rear steering is a pretty good example of how lateral flexibility can be important.

I prefer big, fat sidewalls. It's not uncommon for racers to replace factory 18's with 17's or even 16's to get those faster lap times. Frequently, the only reason this isn't done because the brakes won't fit inside a smaller wheel.
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  #10  
Old 04-26-2005, 01:05 PM
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Quote:
Originally Posted by thundering02
Now all he needs are stiffer springs and softer roll bars and maybe he will keep at least 3 of those (90%) tires stuck to the road.
Are you referring to the guy in the pic I posted?

That M3 posted the 3rd fastest time of the day and 2nd in PAX behind an S2000. That guy is FAST!!

Here's the list of what I'm up against:

http://www.wpg-autox.org/perl/autox/...cgi?event_id=1

Last edited by Earthworm; 04-26-2005 at 01:08 PM.
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  #11  
Old 04-26-2005, 06:55 PM
WGJ WGJ is offline
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M3 Sedan?

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  #12  
Old 04-27-2005, 09:40 AM
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Note in the list of components there was a Skyline and a Silvia...both RHD.
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