the how wide can I go debate

63XL500

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Wow. Those look good. But I do notice the 255s on my car now are even slightly pushing out past the rim (Continental DWSs). It gets really hot here, though, so I don't want to have a tire heating up the sidewall too much from bulging out that it causes a blowout.
 

Scrat

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And it's still wrong.

Just because Boltzman posts a picture of an non-recommended tire and wheel combination showing that it holds air still doesn't make it OK for general street use.


Norm

not sayin its ok to run it that way, the op was looking to see if it was done and what it looks like.
 

63XL500

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Its an odd size, but to get a little bit taller tire in an attempt to get the car off the line I think 265/45/18s will work best. It just seems like 275 is too wide. My 255/45/18s should be 27.0 inches tall and the 265/45/18s should be 27.4 (used the Miata forum calculator, just the one I found). The Bridgestone RE71Rs are available in that size and are $246 a piece. They are very close to a drag radial, really meant for autocross but they seem like the best value. Still need to do a little more research on them.
 

tjm73

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problem is that doesn't account for aspect ratio

Aspect ratio doesn't really matter in this rule of thumb. You just need to select an aspect ratio that provides the desired overall diameter that is needed.

Overall section width is independent of aspect ratio.

A 275 tire, whether a 40, 50, 60, or what have you will always be about 10.8"-10.9" in width.
 

Racer47

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There is a ton of bad info on tires and rims on this forum and the internet in general. I’ve tried to resist posting but just can’t anymore. I’m an engr. I’ve worked for 2 OEM’s and 1 major tire company. I normally don’t post much because I don’t like posting my resume to prove that I know what I’m talking about. But here goes. Sorry it got a bit long.

First off, tire manufactures do not establish tires sizes or wheel sizes. The Tire and Rim Association does. It was invented over 100 yrs ago to insure compatibility across manufactures. They also establish speed rating tests plus load and inflation requirements. All the info you see on Tire Rack comes directly from T&RA. 90% of the info tire manufactures publish is straight from T&RA. Some tire manufactures do publish data measured from their tires in production. But they will never publish data outside of the T&RA guidelines. In order to be D.O.T. approved, you must meet the T&RA standards.

l_b7wuQ2bGOMJQdkhMSpFUyU70TjV4-XFditel4rIrCDnYUYloIFU5stCWP0w6q7ndOlPxpUxeRj1wPDIEoWn4ifcOM4c_7mKqTuhTxjnH20GKEFS1LnS7dw_SETZGCm9e2Pv3tr5FK7e-lF8VpO70Y_Es3MzMmna_IRW2cAcfZFqktk1s1por6nahsNwD0yKj0ErkAL-trS6kS-AcZM_rKaw0RZhkBzvHHMSoq5xLP5VBV-QRdtVdNIDKdFfO1dvI0BwGk3aPKzsEHafWn5oNh2VJfgnESyuJQpL6fZ7q1pCr4bAKTtX9T_PTswys2YlH0wEdJDGJ05wJVGSVBhVqfPt4Y9zgOcW_dzq8lKZdBqt3K89WC5pbw2hCRJueJ7rr7rHhRIxQmtbCl_pzSNPN-5M71k25-qLzXybkKbK-M3CE4XTow3tZpDjq4iBniU3FAw5G8627t_4qZFcX_jj9-8X7WCdteavRcDx52L_8mUyIIMn-0LB0dHpVBFLLaCiXVu5iLF4ISq7sbPMAWW5j72MJC4DMB99a-x9d5O_FXedrvNiKnVNiU0ANN7epiHgkhdxt67cOOWN0dn-ZJZQnoDxXf3SMHEWQwC0U4yhP1UFiDJw4mO=w1079-h972-no


Included in the T&RA specs are minimum and maximum tire sizes. And yes, there is enough tolerance such that a tire that is actually a 300 width could be sold as either a 295 size or a 305 size. Car and truck tire sizes are every 10 mm width ending in 5 (275, 285, 295, etc). Motorcycle tires end in 0 (140, 150, 160).

JvWu71XhNKWIKxNGJVdQhk0J07DFLtopKfhLo6YTGhgB6hJUGiJISZfmRbp5cZOmarkJjkP8wjnYWZVnyEr6Mcfmkfv11w_JmWhnpHJHsfkKwF__XsmaCjlnHVdqBqFP7iXc3aUmOoGeMIlcs2nxri57Fmq6vdTRTC85MZOu4ZCDCFez4gxn7qFztBoGyBtNbqGN3j197cBZXTUGSJufLxUrCjJIA-9f4ijJf2cbIbKNCYWejnffws0HI4mUcnr_1lajDAbRewj4N87f4zNvyjuAAdCTJ530vXjdLlbrDWYbIzP_k-nyldfRRsGVZdMlYDXQhtq8y7qzKvWHOCeYmD8RUQj0ZkeRtC9egLozyDJFlI0oB0KCvuvfjVxrHY3_e1XIlR5l2pC0XiU4XvNkg3tBdnnjJF8AgHWM6MtXoXyJJW0w563ooTFgj1SXmYCDPKTstBfi00Gqs3NlBCSZcZPFvuU48i1KgqmG9jmbPxI9OLHJ2MZMH95PVmDR7VPx9eH2qjvz-jK-fd39rZbBeWJ6SkrWJ9m5EGc9TeU93qWZdr8WY97PPPqhysWHV_3JuRUcOMlgez3YwtTh8yYiiUqANbqRjzVenVR96wz2VHEOyYfmKO9N=w698-h883-no



“I've come to the conclusion that tire sizing is basically this....rim width + 1, then multiply by 25.4 and round up to the next closest tire width in the appropriate aspect ratio for the tire height you want.”

“General rule is to stay within 1/2 inch +/- of the tread width (not section width) of the tire. Considering most 275's float around 10 inches of tread width, wheels ranging from 9.5 to 10.5 inches would work best.”

Both of these are false. Aspect ratio is an important factor is determining rim width, especially when going outside of the approved rim width range.


“Aspect ratio doesn't really matter in this rule of thumb. You just need to select an aspect ratio that provides the desired overall diameter that is needed.
Overall section width is independent of aspect ratio.

A 275 tire, whether a 40, 50, 60, or what have you will always be about 10.8"-10.9" in width”

This is completely false. The lower the aspect ratio, the wider the recommended rim width.
245/60 7.0” 7.0-8.5” range
245/50 7.5” 7.0-8.5” range
245/45 8.0” 7.5-9.0” range
245/40 8.5” 8.0-9.5” range
That’s a 1.5” difference in recommend width and 1” difference in the range for the same 245 wide tire varying only the aspect ratio.


“M&H recommends 12" wide rims for that size, and minimum is probably 11"

This is not 100% accurate. M&H simply chose to only publish the T&RA recommended size. A 325/40 tire has a lot of sidewall and can easily go 1 inch outside of the T&RA approved list without failing due to rim width.

Here are a couple pages from the T&RA book.


Ny6nl09VgTXw3_rYXvI6RarJVumE74qbGoLRgWTHtYirfK-jlcKPfAkp4yWhXu8X6BtiD3lRUo_R21CB_vHjSK7AciiMH4_CZ2PgQZQx2oOrl-qLIMh7W_04j46U_FDTNfmb22CvqhXZDsIMlAfkFFwLH6rv5T_RHPUHGyadDJz9kXUfZHEOY_p2CdKMuVJyMpXwPGr0zYs4Zl3wI0PtaOp0TJQP6U4UiJfN-88oTJSxKRH7D_Ac8xo5xHFvB64dINtN7jCmlJI1M06SvaX7FrRVJNSy95wO0XQUKF__fabZhxi43wYkKmszB8VlxlfIvQT3EB5iFkupJkJSD2wR22XoSI5t09yukvm9PGSySLvfks5mh76b75OPDoyr8DA_sIPiTC-Is2VQLY4MhwHnkwlL1PmK5NCeJ29ZvIKKIdrOgfRk4ihyANTurh6fC_5CwaLhkjKOtHmavDXc7GZ1YF3ZoVTpH8v49QRgQp4U-UQpXqRfhSdYZcaIvn_XbF67addF5THgt37zXkRtaUbiu9F2Eoa_8VNbGoaw_qEZFPgjva3fxKzySoWBtn08A7D1qNwFSFLvrxy1OGooOC0DQE6KpA71mNS33lEwWlzWjS6K5ZofT7-z=w912-h740-no



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“but like Frank said, the Mustang world is filled with people who don't think much past getting wide tires and you're at least partly taking their word for it. An 11" vs 10" shootout, same day, same car could prove enlightening whichever way it might favor.”

Sure that tire probably would be slightly better on an 11” or 12” wide wheel. But that’s not the point. You have a 10” wide wheel. A 295/40R18 is the largest size approved by T&RA for a 10” wide wheel. But that 325/40R18 is going to provide more traction than a 295/40R18 on that same 10” wheel (all other variables being equal).


“post 13, 275's on 8.5 rims
And it's still wrong. Just because Boltzman posts a picture of an non-recommended tire and wheel combination showing that it holds air still doesn't make it OK for general street use.”

That’s incorrect. That rim is only ½” below the T&RA approved minimum rim width. It is perfectly safe for road use. There is a huge and I mean huge safety factor built into tire specs.

As an example, most people don’t know that passenger car tires and wheels are designed to withstand 120 psi. That is the max that most home air compressors will put out. This requirement was enacted so that you could not kill yourself by over-inflating your tire at home. However, when you go to auto-x forums and talk about running high tires pressures, say 40 psi, there is always some Dudley Do-Right preaching that the sidewall says 35 psi max therefore you will die if you inflate to 36 psi.

My point is that one half inch is fine. In most cases a full inch too wide or too narrow is fine. In some cases, even more than that is safe. The tire will not fail. I’ve done it. I’ve tested it with lab equipment.


“It gets really hot here, though, so I don't want to have a tire heating up the sidewall too much from bulging out that it causes a blowout.”

This is not true. The bulge (or stretch) will not fail the tire from heat. Low inflation fails tires from heat. That bulge is relatively constant, it is not flexing as it goes around the tire. However low inflation causes excessive flexing as it rolls into and out of the footprint. That builds heat and fails tires.


Lastly, if you keep the rim size constant, the bigger the tire, the greater the traction. This holds true until way past what most Dudley Do-Rights think. Let’s use the 8.5” wide wheel. T&RA says that 255/40R18 is the widest tire they approve. But in practice a 265/40R18 will provide more available traction. So will a 275 and 285 but with decreasing improvements. At some point no further traction will be gained. Yes, the tire bulges (it can easily take it). Yes, there will be a slight reduction in steering feel or more precisely, it’s a delay in steering response because it takes a split second longer to develop lateral forces due to the non-ideal sidewall. But this factor is way less than internet wisdom would lead you to believe. On a racetrack (road course, auto-x, drag) a 275 wide tire will outperform a 255 wide tire on the same 8.5” wide wheel, all other variables being equal (which is never completely achievable).

As an example, look at the top header pic of this SCCA Super Vee forum. http://apexspeed.com/forums/ Do you think that rear tire is anywhere close to the T&RA tire width recommended for that narrow rim width? Wider and wider tires kept being developed to reduce lap times while the wheel size remained the same due to the rules.

However we should also consider the opposite approach. The opposite is to keep the same tire size and vary the rim width. If you do this you will find that there is a sweet spot in performance. And that sweet spot will line up very closely to the T&RA approved rim widths. And this is more like what the OEM’s do. They pick a tire size first and then the rim width or do it at the same time. Most of us already have a set of wheels and then try to put on the best tires that will fit, even if it is outside of the T&RA approved limit.

Ok, I’m done, flame away if you must.
 
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stkjock

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:clap:

best post I've seen in weeks. Also make me happy that you're dissertation backed up my understanding. :party52:


Thank you Racer47
 

tjm73

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Pretty sure we're talking about this wheel.

26983.jpg


It is 18x8.5".

The optimal tire for this wheel is a 245 or IMO a 255. For stock height it would need to be a 45 aspect ratio. You can adjust the aspect number as needed for either 245 or 255. That's all I was saying.

275 is too wide IMO. You need a 9-9.5" for the 275 and while a 10" wheel will take a 275, it is too wide and will look a little stretched.

That said, the hyper tech info posted is awesome.
 
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Norm Peterson

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There is a ton of bad info on tires and rims on this forum and the internet in general. I’ve tried to resist posting but just can’t anymore. I’m an engr. I’ve worked for 2 OEM’s and 1 major tire company. I normally don’t post much because I don’t like posting my resume to prove that I know what I’m talking about. But here goes. Sorry it got a bit long.
Understood. Explaining tech tends to get like that, (I'm a retired engineer myself). No flame intended.


Included in the T&RA specs are minimum and maximum tire sizes. And yes, there is enough tolerance such that a tire that is actually a 300 width could be sold as either a 295 size or a 305 size. Car and truck tire sizes are every 10 mm width ending in 5 (275, 285, 295, etc). Motorcycle tires end in 0 (140, 150, 160).

Thanks for posting this page. I assume that in actiuality that A and B identify the range between which the maximum section width occurs, or is at least supposed to occur. Sidewall shape physically has to be a curved shape under inflation.


M&H recommends 12" wide rims for that size, and minimum is probably 11"

This is not 100% accurate. M&H simply chose to only publish the T&RA recommended size. A 325/40 tire has a lot of sidewall and can easily go 1 inch outside of the T&RA approved list without failing due to rim width.
Understood completely, with one caveat. A M&H drag slick is really not intended for general road use, where the conditions under which the tire is asked to operate are far less controlled than they are at a drag race.


Here are a couple pages from the T&RA book.

qd_Hx6wzfxcCADWcnEUqSsOl_L_eM_itTs5EMQU_lvNXcweG33wgdfhfOSjCM5icQr9Pk-AVJ2Y2nYXHJ6W8ciLqp_PmGj3zy8FdNK08gjmhNX24q2aDT_NJuMuahoimOixsOzz82laCTqo_bJAiCgvX2pux7lgNGHaDaHjrqS3nza8j4A1bfmtY5MwAju0rHtP6L42VdzfRL0rthPJl_NpjNBVhxtnZBrxiO8aeuqdrGv-f0sVDOepXWsIi8erdm5WaTEtCX6urMY5zAnhx3b9UzwX8cpYzRvzpL2JNAolRqHl9xAn7NmxqB2u7vLl4jeOXaYxzmPgVNPgCbOE68C7rRaImeIs_SR2wAbpgZSlwXHoVpwU0IxwEl6kEfLEOoVoX1GayLys17YCUsRN-YtY-3AeQI2xHzW6RD6dKpCs7cIa2VivPAS1ApfzXnPydeOttpD5x_RQEhzmLlzWsPtHbB9YEIBs3pZnr6IrAFjavZRBcVVRgRc1dIUKLZC3Gl2lWk_WxG1DTJdt87S5dtuIIhFeNi2BmqfgCjqkh6xrhhkz7728p2IVNU_g1lbqVDYr5QMnmMWSH8UinHCuDWDrFEUtFM0fGkp82aZQo4h3OJmGJvRyY=w893-h940-no
Thanks much for this page as well.


“but like Frank said, the Mustang world is filled with people who don't think much past getting wide tires and you're at least partly taking their word for it. An 11" vs 10" shootout, same day, same car could prove enlightening whichever way it might favor.”

Sure that tire probably would be slightly better on an 11” or 12” wide wheel. But that’s not the point. You have a 10” wide wheel. A 295/40R18 is the largest size approved by T&RA for a 10” wide wheel. But that 325/40R18 is going to provide more traction than a 295/40R18 on that same 10” wheel (all other variables being equal).
“post 13, 275's on 8.5 rims
And it's still wrong. Just because Boltzman posts a picture of an non-recommended tire and wheel combination showing that it holds air still doesn't make it OK for general street use.”

That’s incorrect. That rim is only ½” below the T&RA approved minimum rim width. It is perfectly safe for road use. There is a huge and I mean huge safety factor built into tire specs.
My point is that one half inch is fine. In most cases a full inch too wide or too narrow is fine. In some cases, even more than that is safe. The tire will not fail. I’ve done it. I’ve tested it with lab equipment.
I know that was mine. Technically I understand what you're saying here. But I'm unwilling to recommend going outside the T&RA guidelines to anybody else (even though I've gone a half inch above the wide end on my own cars a couple of times over the years with no ill effects).

I know the T&RA's "narrow-side recommended limit" isn't a fixed pass/fail boundary. And I'm pretty certain that carcass overstrain and the consequential fatigue effects are involved in how that was determined. What I don't know is how much margin necessarily exists in any given tire make/model regarding fatigue life, or how fast you sacrifice that per half inch of lesser wheel width.

What I'm seeing is when a tire is mounted on a narrower than recommended width wheel, it starts out with a slightly higher amount of carcass strain, together with suspected slightly lower vertical and lateral spring rates - and as a direct consequence of the first a greater amount of flexing as each 'segment' of the tire passes into, through, and out of contact with the ground. IOW, somewhat faster accumulation of fatigue damage (I used to work in an industry where that was a recognized term).


“It gets really hot here, though, so I don't want to have a tire heating up the sidewall too much from bulging out that it causes a blowout.”

This is not true. The bulge (or stretch) will not fail the tire from heat. Low inflation fails tires from heat. That bulge is relatively constant, it is not flexing as it goes around the tire. However low inflation causes excessive flexing as it rolls into and out of the footprint. That builds heat and fails tires.
A tire with a 4.5" tall sidewall (from bead to tread) and a vertical spring rate of 1500 lb/in supporting a 1050 lb corner weight is going to deflect (roughly) 0.7". That does alter the sidewall shape into sharper curvature. Has to. Just like the greater deflection resulting from underinflation does (I did rather recently stumble across an accepted formula for estimating tire vertical spring rate from tire size and inflation pressure).


Lastly, if you keep the rim size constant, the bigger the tire, the greater the traction. This holds true until way past what most Dudley Do-Rights think. Let’s use the 8.5” wide wheel. T&RA says that 255/40R18 is the widest tire they approve. But in practice a 265/40R18 will provide more available traction. So will a 275 and 285 but with decreasing improvements. At some point no further traction will be gained. Yes, the tire bulges (it can easily take it). Yes, there will be a slight reduction in steering feel or more precisely, it’s a delay in steering response because it takes a split second longer to develop lateral forces due to the non-ideal sidewall. But this factor is way less than internet wisdom would lead you to believe. On a racetrack (road course, auto-x, drag) a 275 wide tire will outperform a 255 wide tire on the same 8.5” wide wheel, all other variables being equal (which is never completely achievable).
As an ex-autocrosser I know that autocrossers have been running outside the guidelines for years and relying on driver skill to "drive around" the response downside. It's a lot easier to accept this for such limited use - you'd either wear out or heat-cycle the tire into uncompetitiveness first.


As an example, look at the top header pic of this SCCA Super Vee forum. http://apexspeed.com/forums/ Do you think that rear tire is anywhere close to the T&RA tire width recommended for that narrow rim width? Wider and wider tires kept being developed to reduce lap times while the wheel size remained the same due to the rules.
If, as I suspect, that's a picture of a cantilever slick (designed specifically to "get around" a competition class maximum wheel width rule), that's a whole 'nother discussion and not relevant to this discussion of production street or DOT-rated competition tires.


As far as "opposite approach" goes, I've always worked more like this . . .
They pick a tire size first and then the rim width or do it at the same time.
with a strong bias toward choosing wheel widths above "measuring width" for the tire size(s) under consideration. If there was no other reason (though there is), I've left myself with a car that would be better able to use wider tires should I choose to do so the next time around.


Norm
 
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oldVOR

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There is some good information in Racer47's post and I appreciate the effort put into the composition.

Racer47 says a 275 can be mounted on the OP's rim and provide more traction than either the 245 or 255 under the same conditions. "On a racetrack a 275 wide tire will outperform a 255 wide tire on the same 8.5” wide wheel, all other variables being equal."

Racer47 does indicate there will be a reduction in steering feel and response, which, most would attribute to the narrow wheel/wide tire combination but, what do we know, our opinions are false. Even-though those false opinions would have most using a more optimal wheel/tire combination.

Racer47 also states "that there is a sweet spot in performance. And that sweet spot will line up very closely to the T&RA approved rim widths."

One lister posted - "I've come to the conclusion that tire sizing is basically this....rim width + 1, then multiply by 25.4 and round up to the next closest tire width in the appropriate aspect ratio for the tire height you want." Using this, a 285 section width tire would go on a 10 inch rim.
Per T&RA, acceptable widths range from 9.5 to 11.0 for 285's in 35 & 40 aspect ratio's.

Another lister poster - "General rule is to stay within 1/2 inch +/- of the tread width (not section width) of the tire. Considering most 275's float around 10 inches of tread width, wheels ranging from 9.5 to 10.5 inches would work best." Using this, a 275 section width tire would go on a 9.5 to 10.5 inch rim.
Per T&RA, acceptable widths range from 9.0 to 11.0 for 275's in 35 & 40 aspect ratio's.

Both of the above fall into the middle of the T&RA recommended wheels widths for the respective tire section width and, for all intents and purposes, what most would consider the "sweet spot in performance".

However, per Racer47, both listers comments are FALSE and should not be followed.

Racer47 does state that aspect ratio wasn't taken into consideration by the above two listers. With that, yes, a 275/285 tire with aspect ratios of 50/55/60/70 are available but not many performance oriented vehicle owners are going to mount SUV/Light Truck tires on their cars. This is, after-all, a performance vehicle oriented forum and most would only consider a 35 or 40 aspect ratio tire in the 275/285 section width for their needs.
 

Racer47

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bro-engineering, nice, I never heard that term before but I'm certainly going to use it in the future.

“I assume that in actuality that A and B identify the range between which the maximum section width occurs, or is at least supposed to occur. Sidewall shape physically has to be a curved shape under inflation.”

Yes, but it does not have to be curved. It just can’t have the tread shoulder being wider than the middle of the tire. A major part of T&RA is sizing. There are legal requirements for tire to vehicle clearance. This is just one small part of the rules.

“Understood completely, with one caveat. A M&H drag slick is really not intended for general road use, where the conditions under which the tire is asked to operate are far less controlled than they are at a drag race.”

T&RA does not care about intention. It’s either DOT or not. I believe stkjock’s tires are DOT legal drag radials so they fall under T&RA rules and pass all the requirements.

“I know the T&RA's "narrow-side recommended limit" isn't a fixed pass/fail boundary. And I'm pretty certain that carcass overstrain and the consequential fatigue effects are involved in how that was determined. What I don't know is how much margin necessarily exists in any given tire make/model regarding fatigue life, or how fast you sacrifice that per half inch of lesser wheel width.”

You are giving the government regulators way too much credit. There is absolutely no stress / strain type data as any part of T&RA wheel sizes. There is simply a formula that for a given width and aspect, you get the “measured” rim size and the accepted range. Those are then rounded off to the nearest half inch.

“What I'm seeing is when a tire is mounted on a narrower than recommended width wheel, it starts out with a slightly higher amount of carcass strain, …., somewhat faster accumulation of fatigue damage

Fatigue strength is tested for tires. ½” too wide or too narrow adds zero fatigue damage. 1” may add trivial amounts of fatigue damage. Cornering forces put much more load into a tire than being mounted on a wheel that’s slightly too narrow.

We need to take a wider view of a tire’s limits. Passenger car tires in general have more load capacity than is required for the weight of the vehicle they are mounted on. This is because styling likes bigger diameters and wider tires. But the load capacity requirements go up for those larger tires per T&RA. So we have load capacity (and fatigue damage) to spare. But then, say we go from a 255 to a 275. Now we have even more excess capacity. So whatever trivial amount of damage that 1” too narrow wheel imparts on the tire, it does not matter, we have plenty to spare.

“A tire with a 4.5" tall sidewall (from bead to tread) and a vertical spring rate of 1500 lb/in supporting a 1050 lb corner weight is going to deflect (roughly) 0.7". That does alter the sidewall shape into sharper curvature. Has to. Just like the greater deflection resulting from underinflation does (I did rather recently stumble across an accepted formula for estimating tire vertical spring rate from tire size and inflation pressure).”

I’m not sure where you are going with this but those numbers are believable.
 

Racer47

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......Racer47 does state that aspect ratio wasn't taken into consideration by the above two listers. With that, yes, a 275/285 tire with aspect ratios of 50/55/60/70 are available but not many performance oriented vehicle owners are going to mount SUV/Light Truck tires on their cars. This is, after-all, a performance vehicle oriented forum and most would only consider a 35 or 40 aspect ratio tire in the 275/285 section width for their needs.

So your “general” rule is really that a 275 or 285 tire in only 35 or 40 aspect ratio should only be used with 9.5” to 10.5” wide wheels on only a performance orientated vehicle.



Ok, if that makes you happy.

A 275/70 tire calls for an 8.0” rim with a 7” to 9” range. My point is still accurate, aspect ratio matters in rim width.
 

Thenorm

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Lastly, if you keep the rim size constant, the bigger the tire, the greater the traction. This holds true until way past what most Dudley Do-Rights think. Let’s use the 8.5” wide wheel. T&RA says that 255/40R18 is the widest tire they approve. But in practice a 265/40R18 will provide more available traction. So will a 275 and 285 but with decreasing improvements. At some point no further traction will be gained. Yes, the tire bulges (it can easily take it). Yes, there will be a slight reduction in steering feel or more precisely, it’s a delay in steering response because it takes a split second longer to develop lateral forces due to the non-ideal sidewall. But this factor is way less than internet wisdom would lead you to believe. On a racetrack (road course, auto-x, drag) a 275 wide tire will outperform a 255 wide tire on the same 8.5” wide wheel, all other variables being equal (which is never completely achievable).

and this is why i have a 285 tire on a 19x9. it's more grip and faster around the track. Its also why people were stuffing 275/35R15 hoosier tires on Integra type R 15x6 wheels.
 

Racer47

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and this is why i have a 285 tire on a 19x9. it's more grip and faster around the track. Its also why people were stuffing 275/35R15 hoosier tires on Integra type R 15x6 wheels.

Exactly

When I was working at the tire company I had a 72 Mach 1 fastback with 265/50R15 on the front and 295/50R15 on the rear, all mounted on 15x7 magnum wheels. Every tire engr saw that car and many complimented me on my tire selection. Not one of them ever said anything about damaging the tires or tire failure or blowouts or anything. Because we all saw, in person, just how much abuse a tire can take.
 

oldVOR

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Racer47, apply the rule to some high aspect ratio tires as examples:

325/60-20 with an advertised tread width of 11.0 inches and go +/- 1/2" for rim width. Does that fall within the T&RA specs? Yes

315/70-17 with an advertised tread width of 9.9 inches and go +/- 1/2" for rim width. Does that fall within the T&RA specs? Yes

As a general rule, it works.

Feel free to twist my words around how ever you like, hasn't stopped you thus far.
 

BullittSS

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My practical experience with my last two 'daily driver' Mustangs:

* 2009 Bullitt -- nearly 60,000 miles with 275/40/18's on 8.5" rims -- no unusual wear patterns or handling issues (Continental Extreme Contact DWS and General G-Max AS-03)

* 2014 GT/CS -- 37,000 miles with 275/40/19's on 8.5" rims -- again, no unusual wear patterns or handling issues (30,000 miles on BF Goodrich g-Force Comp-2 and 7,000 on Comp-2 A/S)

Car manufacturers have occasionally exceeded 'recommended' tire specs on OEM wheel applications for high performance vehicles. That would seem to support some of Racer47's comments on the wide range of tolerances built into modern tires.
 

Racer47

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oldvor, You have no idea how much you do not know about tires. Don't pretend like you know something that no one else does with your made up rule.

I clearly explained how it really works. This is a fact, not my opinion. Plus I already gave examples where your rule failed.
 

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