Tire Stretch and Maximizing Performance

[DaveG99]

What offset are those. Little more poke than I like but looks good yet.

He said 20 offset and its a 16x8 with a hancook rs4 in 205/45/16

I plan on getting 16x8 with a 40 offset which would be about perfect.

 

[OggiSiMangia]

Sexy. I'm guessing they rub a bit in the rears though right?

They don’t rub in the rear at all. I’m on vogland springs. Just on the driver side front a tiny bit because of weight distribution. Mostly bumps on the highway and street but nothing catastrophic to any parts. Worth it IMO lol

 

[Plainrt]

I'm guessing would rub driving hard during autocross. Any rear shot of setup?

 

[BRGT350]

On an 8" wheel, I have ran as narrow as 225, but prefer a 245. That keeps the sidewall square to the wheel and the sidewall is then pretty much centered. This allows for equal lateral deflection when cornering. For a 7" wheel, I prefer 215, but have had to use a 205 due to tire availability. On a 9" wheel, the max I have used is 275 and the minimum is 245. I changed to a narrower rear tire on a 9" wheel to reduce some rear grip and dial out some understeer.

I question having lap times reduced by having any type of tire stretch. That runs counter to every book I have read on suspensions and tires, every article I have ever read in a racing magazine, and counter to every class I have taken on suspensions and tires. Also runs counter to my experience in racing my own cars and crewing on a race team. I have spent decades around track cars and have never seen anyone go fast with a really wide wheel and narrow tire. I have seen people get by with a wide tire and narrow wheel, but the handling was never great. Turn-in suffers with that configuration. Every bit of data I have seen points to having a sidewall that is as close to square to the wheel as possible. All of my experience has always been around road race, autocross, and rally cars. I can't provide any input on drag racing.

 

[M-Sport fan]

^^^THANK YOU!!

I also believe that one does not have to put a narrow 205 on an 8" wide (or more ) wheel in order to have great turn-in/response and a lack of 'mushiness'.

I also appreciate the less 'ricer stancer' look of a square wheel/tire tread width setup as well.

 

[BRGT350]

I just can't think of a single racing series that a stretched tire would be used. I don't consider drift competition to be racing since the goal isn't to complete the lap in the fastest time possible. I have crewed for a World Challenge team, American Iron driver, Viper Challenge team, and for Team O'Neil at LSPR. Friends of mine have competed at leMans, won SCCA national championships in all sorts of classes, and race vintage cars. I just don't recall ever seeing a wheel and tire combination that wasn't as square as possible on those cars. The ones that weren't square tended to be a wider tire on a narrower wheel. Many of those were popular on vintage Trans Am cars. Even skinnies on drag cars use a narrow wheel with the narrow tire. If anyone has data to show a top level competitive race car being faster on a stretched tire versus square tire, I would like to see it as it would be something new to learn. I don't consider a bro that ran a canyon to be a top level competitive race car. I am talking about a prepared car with a professional driver doing back to back laps with a stretched tire versus square.

 

[DaveG99]

The 205 rs4 I posted a picture of doesnt look stretched at all on the 8" wheel. They are really wide 205's though. I dont know about track times but having a really wide tire on a narrow wheel would allow more give and "mushyness" on turns. And the opposite also makes sense.

 

[M-Sport fan]

I just can't think of a single racing series that a stretched tire would be used. I don't consider drift competition to be racing since the goal isn't to complete the lap in the fastest time possible. I have crewed for a World Challenge team, American Iron driver, Viper Challenge team, and for Team O'Neil at LSPR. Friends of mine have competed at leMans, won SCCA national championships in all sorts of classes, and race vintage cars. I just don't recall ever seeing a wheel and tire combination that wasn't as square as possible on those cars. The ones that weren't square tended to be a wider tire on a narrower wheel. Many of those were popular on vintage Trans Am cars. Even skinnies on drag cars use a narrow wheel with the narrow tire. If anyone has data to show a top level competitive race car being faster on a stretched tire versus square tire, I would like to see it as it would be something new to learn. I don't consider a bro that ran a canyon to be a top level competitive race car. I am talking about a prepared car with a professional driver doing back to back laps with a stretched tire versus square.

^^^EXACTLY!!!

I also want to see the data which backs up the actual gains from an over-stretched tire on a too wide wheel.
Yes, Drift, as popular as it is with the Fn'F, import crew, is NOT a time based, or first across the line 'competition', and I don't consider it anything more than a bias judged form of entertainment.

I remember that some of the older SCCA /Production road race classes used "cantilever" type side walled race slicks to replicate a square wheel width to tread width scenario, since many of those classes had very narrow wheel width rule limitations.
I'm guessing that they still use these setups in the lesser power /Production, and GT-whatever classes.

 

[Meowoosh]

I think you are viewing it at extremes. Nobody will make the claim using terms "over-stretched tire" or "too wide wheel".

It's all about shaping your contact patch

I imagine it has something to do with the shape of the patch, too. Given the same psi, the contact patch is going to be the exact same # of square inches regardless of the dimension of the tire, but the shape will be different for wider tires. 30 psi supporting 1/4 of a 2900lb car is 24 square inches per tire, regardless of what wheel/tire combo you're using. It's very simple physics. Which could be a 6x4" patch on a 6" wide tire, or a 12x2" patch on a 12" performance tire. My physics textbook would say both of these give the exact same friction, but there's obviously something fancier involved, as the 12" tires are well known to give much more responsive handling and stability in the corner than 6" tires. Is it that the wider tires are closer to cylindrical, and don't have to deform as much, allowing them to be stiffer with less flex, and better able to transfer those forces to the ground?

Probably the best, short explanation is from Paul Haney's book "Racing & High Performance Tire" (available on-line at his website for $55 shipped.

"For the same vertical load and internal pressure, a tire with a wider tread has a shorter, wider contact patch than a narrower tire. The area of both contact patches is the same if the internal pressure and the load are the same. . . A shorter contact patch at the same slip angle begins to slip at roughly the same distance from the leading edge as with a long contact patch. But the shorter contact patch has more of its length stuck to the road than the longer, narrower contact patch; and therefore a larger portion of its overall area is gripping." - Why Wider Tires Are Better, p. 101

Paul's book is excellent, although it requires more serious study than most would like to give. I highly recommend it!

 

[M-Sport fan]

Yes, but all too many advocate for having a wheel width at least an inch wider than the tire's tread width, too much for my tastes.

 

[BRGT350]

It is contact patch, tread design, tread compound, sidewall construction, sidewall support, wheel size, air pressure, tire age, temperature, and surface friction.