Tire width on 8" rim

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moparstud440

moparstud440

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Does anyone have what the actual tire width measurement is with the following size tires on a 8" rim:

275/60R15 (advertised as 10.8")
255/60R15 (advertised as 10")

My dad has some Mickey Thomson Sportsman Pro 28x10.5 mounted on 8" wheels. They are advertised as a 11.2" sec width, but they actually measure 11 5/8". He let me borrow than just to see how they fit and I like the 28" tall tire, but the tire hits the leaf spring. So I measure the actual width and its wider than advertised so was curious about the 2 tires sizes above that I'm looking at getting.
 
It is totally dependent on who makes them. There is no set standardized measurement for tires. Each brand makes them differently.
 
The 2 brands I've been looking at are Cooper Cobra G/T and Mickey Thompson Sportsman S/T Raidal
 
I have 275x60x15 Nitto drag radials on 15x8 with 4.25 BS and they fit on the rear of my 68 Barracuda with no problems. Stock leaf spring location.
 
moparstud440 said:
Does anyone have what the actual tire width measurement is with the following size tires on a 8" rim:

275/60R15 (advertised as 10.8")
255/60R15 (advertised as 10")

My dad has some Mickey Thomson Sportsman Pro 28x10.5 mounted on 8" wheels. They are advertised as a 11.2" sec width, but they actually measure 11 5/8". He let me borrow than just to see how they fit and I like the 28" tall tire, but the tire hits the leaf spring. So I measure the actual width and its wider than advertised so was curious about the 2 tires sizes above that I'm looking at getting.
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Wheel-Tire size comparer
 
Ifyou peruse the catalog you will find the the tire manufacture lists a checking rim of 70% which was used to achieve the branded size. But the branded size can be rounded up or down to the nearest 5mm on the 5s.
For example a 275 can actually be anywhere from 270.1 to 279.9 both round to 275, Because there are no 280s nor 270s.
The checking rim for a 275 is; (70%x275)/25.4=7.58 Which rounds down to a 7.5 rim. But good luck finding one. If they used an 8" then the sidewall cross-section will grow by about one-half the increase so .2 inch/5mm in this case. So, your 275, if it ever was a 275 will now be a 280. Or in reality anywhere from 275.1 to 284.9.. Which maths out to in the range of 10.8 to 11.2

I highly recommend, for street work not to install 275s on a 7.5 rim; you will not be able to run a low enough air-pressure to not burn the centers off. In my experience 8.5s are about right; and for sporty driving 9s would be better. These will allow you to bump up the pressure and better control sidewall roll-over in the corners.
 
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F7720F03-DE4A-4F86-8A0F-FCDB86B1B7D0.png
295 55 Cooper Cobras on 15x8” rims.
 
Dennis H said:
View attachment 1715292308 295 55 Cooper Cobras on 15x8” rims.
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They look damn good on there. How are you liking that setup?

I know the goals for drag-oriented cars are a bit different but for handling purposes, you usually wouldn't want anything larger than a 255 or so on an 8" wide wheel. Are you noticing any extra sidewall roll under cornering? I suspect that if you compared how the car drove with the same tires and a 10" wide wheel, the handling would be much improved...but that may not be what you're looking for.
 
MRGTX said:
They look damn good on there. How are you liking that setup?

I know the goals for drag-oriented cars are a bit different but for handling purposes, you usually wouldn't want anything larger than a 255 or so on an 8" wide wheel. Are you noticing any extra sidewall roll under cornering? I suspect that if you compared how the car drove with the same tires and a 10" wide wheel, the handling would be much improved...but that may not be what you're looking for.
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I just posted about putting 295 60 d15 hoosier quicktimes on my 68 fastback , "looks great" . They are designed for 8-10" wheels , Hoosier even has the section width measurements for an 8" wheel in their nominclature .
I don`t have room for more than 12" section width, was some effort to get that , w/o any tubbing---wish I could post pics, but it wont work for me, phone pics only.
 
E2025EA1-BF0A-47A2-969E-BBA414475FF9.png
MRGTX said:
They look damn good on there. How are you liking that setup?

I know the goals for drag-oriented cars are a bit different but for handling purposes, you usually wouldn't want anything larger than a 255 or so on an 8" wide wheel. Are you noticing any extra sidewall roll under cornering? I suspect that if you compared how the car drove with the same tires and a 10" wide wheel, the handling would be much improved...but that may not be what you're looking for.
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Have not compared to 10” rims. Car handles well at speed. One extra leaf each side, Bilsteins. There is some sidewall flex. When pushed real hard in curves or at Willow Springs, the left rear tire inside wall did kiss the leaf spring. Put a spacer on and it was cured. No downside noticed in real world driving. I like to push it in the Canyons on the way to L.A. to try to keep up with my pal in a fast and light A Body.
 
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famous bob said:
I just posted about putting 295 60 d15 hoosier quicktimes on my 68 fastback , "looks great" . They are designed for 8-10" wheels , Hoosier even has the section width measurements for an 8" wheel in their nominclature .
I don`t have room for more than 12" section width, was some effort to get that , w/o any tubbing---wish I could post pics, but it wont work for me, phone pics only.
Click to expand...

Good to hear that it's working out for you too. I don't doubt that it could be totally fine, especially if a tire was designed to be used that way but that would be considered to be a very "pinched" tire in most applications.

If a tire is pinched or stretched (run on a rim that's on the wide end of the range, it usually won't put down the optimal contact patch nor will it have the sidewall rigidity that you could get with a wider wheel.

I'm looking at this from a handling perspective. For straight line drag strip applications, I can imagine that fitting the max tire that the wheel/wheel well will hold, and playing with air pressures could be a viable approach.
 
RPMagoo said:
-- Looks good. -- I'm glad that You posted, and commented, on that set-up. -- I'm considering that set-up 295/50-15" (Coopers on 8" Weld - Pro Star Wheels) on My Brand X car.
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Again...not sure what your goals are but you'll have an even shorter sidewall, making the pinch more severe. It's almost a sure thing that you'll have less traction with those 295s than you would with a 275 or 265, especially when turning.

Just my opinion but the cost of a wider wheel is worth every penny.
Or, consider running the optimal tire size for your wheel which may sacrifice some width in favor of allowing the tire to operate as it was designed to.
 
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