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      12-13-2012, 02:06 AM   #1
SlamMan
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Tire Width and Sidewall Height VS Performance?

How do different tire sizes typically affect performance? For instance, how will a 275/35/19 feel and perform compared to a 275/30/19?

On the surface I would assume the smaller tire will be lighter and will be able to apply slightly more force to the ground having a smaller diameter. What about turning and grip performance? Will the taller or shorter tire grip better in a turn?

Do you think the original 245/35 265/35 tires that come on the car were chosen for the best lap times, comfort or price as a priority?

In full disclosure I'm replacing a pair of 295/30/29 rear tires with a pair of 275/30/19 which seems to be somewhat rare size for rear tires. Figured I'd try something different. I've got 265/30s up front.
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      12-13-2012, 02:43 PM   #2
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Taller tires have better fore/aft grip. Shorter (and presumably stiffer) sidewalls increase effective spring rate.

I think the stock tires were chosen to increase rear acceleration traction (tall and wide) and provide understeer and a nimble feel (narrower and shorter).
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      12-13-2012, 04:02 PM   #3
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Hmmm. I wonder then if the difference between a 275/30/19 and 265/35/19 going to be significant? Good or bad?

A lot of people go from 265/35 rears to 295/30, myself included, and I wonder if that's really a positive for lap times. I don't know myself.
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      12-13-2012, 05:08 PM   #4
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I don't know either but look forward to any information someone can provide.
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      12-13-2012, 05:27 PM   #5
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Quote:
Originally Posted by SlamMan View Post
Hmmm. I wonder then if the difference between a 275/30/19 and 265/35/19 going to be significant? Good or bad?

A lot of people go from 265/35 rears to 295/30, myself included, and I wonder if that's really a positive for lap times. I don't know myself.
Can't speculate on the first part, but I can tell you 295/30 will have more grip laterally and on accel than 265/35, resulting in faster lap times (assuming on a proper wheel width of course).

If I could fit wider than 275 in the front i'd run 285 or 295 square, but the front can only handle 275 slicks on my 18x10's so I do 275 square on track.
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      12-13-2012, 08:02 PM   #6
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Comparing 275/30 vs 275/35: the sorter sidewall will yield better acceleration due to the increased gearing effect (smaller diameter). It will be lighter, so less unsprung mass (better reaction to changes in load) and less inertia (better acceleration and braking). The shorter sidewall will also make the tire stiffer, which will make the tire react faster to inputs (steering, brake, throttle) but may also make the tire less compliant to adhere to road surface imperfections.

An important element to consider is that changing the front to rear tire diameter ratio will impact the DSC calculation. For instance, if you reduce the rear diameter compared to the front, the traction control will intervene more often. Due to the smaller size of the rear tires, the DSC is tricked into thinking that the rear tires are spinning faster than they actually are.
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      12-13-2012, 08:07 PM   #7
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Quote:
Originally Posted by Porschefile View Post
Can't speculate on the first part, but I can tell you 295/30 will have more grip laterally and on accel than 265/35, resulting in faster lap times (assuming on a proper wheel width of course).

If I could fit wider than 275 in the front i'd run 285 or 295 square, but the front can only handle 275 slicks on my 18x10's so I do 275 square on track.
Not sure about this.

As a general rule, for a given inflation pressure, a wider tire will provide better lateral traction at the expense of longitudinal traction.
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      12-13-2012, 09:27 PM   #8
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Not sure about this.

As a general rule, for a given inflation pressure, a wider tire will provide better lateral traction at the expense of longitudinal traction.
Absolutely... assuming you can put the power down. With 265 street tires and 420 odd hp that can be tricky. I agree with you at higher speeds, but coming out of slow corners you can come on the gas much sooner with 295 on an 11 than 265 on 9.5. If you're in a drag race from 60+, sure. But overall the 295 is quicker around a track.
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      12-13-2012, 09:36 PM   #9
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Good info.
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      12-13-2012, 10:43 PM   #10
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Quote:
Originally Posted by Porschefile View Post
Absolutely... assuming you can put the power down. With 265 street tires and 420 odd hp that can be tricky. I agree with you at higher speeds, but coming out of slow corners you can come on the gas much sooner with 295 on an 11 than 265 on 9.5. If you're in a drag race from 60+, sure. But overall the 295 is quicker around a track.
Agreed
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      12-13-2012, 11:52 PM   #11
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Interesting stuff. I'm still looking forward to trying the 275/30 PSS. If they offered a 285/30 in the PSS I'd really like to try that. The 295 PSS was just a little too tight of a fit for my taste.
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      12-14-2012, 09:13 AM   #12
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Keep your eye on recommended wheel widths as a lower profile usually requires a wider wheel for a given tire section width.
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      12-14-2012, 09:28 AM   #13
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I think you'll find that you lose a good amount of grip in the rear. I went from a 255/40 to a 245/40 on my 330 and that was a huge difference. Not sure if it was from the decrease in width and height (25" to 24.7").

I'd like to go 295s on my 18s but there isn't much of a selection in street tires

Quote:
Originally Posted by SlamMan View Post
In full disclosure I'm replacing a pair of 295/30/29 rear tires with a pair of 275/30/19 which seems to be somewhat rare size for rear tires. Figured I'd try something different. I've got 265/30s up front.
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      01-03-2013, 11:05 PM   #14
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Quote:
Originally Posted by CanAutM3 View Post
Comparing 275/30 vs 275/35: the sorter sidewall will yield better acceleration due to the increased gearing effect (smaller diameter). It will be lighter, so less unsprung mass (better reaction to changes in load) and less inertia (better acceleration and braking). The shorter sidewall will also make the tire stiffer, which will make the tire react faster to inputs (steering, brake, throttle) but may also make the tire less compliant to adhere to road surface imperfections.

An important element to consider is that changing the front to rear tire diameter ratio will impact the DSC calculation. For instance, if you reduce the rear diameter compared to the front, the traction control will intervene more often. Due to the smaller size of the rear tires, the DSC is tricked into thinking that the rear tires are spinning faster than they actually are.
Extremely accurate info.
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      02-16-2013, 09:00 PM   #15
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Quote:
Originally Posted by CanAutM3 View Post
The shorter sidewall will also make the tire stiffer, but may also make the tire less compliant to adhere to road surface imperfections.
Spot on.

For the race tracks the shorter sidewall will be of benefit as discussed.

For the drags however a taller sidewall is preferable. This is the reason why drag slicks have such tall high profiles, you want a soft flexible sidewall to allow more contact area and grip on take-off.

For the street, depends on the quality of the streets in your area, if you do a lot of country driving I would go for the 35's.
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