Front tyre size to match 275 drag radials

[3Katz 26]

I'm having some trouble choosing rim and tyre size, let me see if I can explain this without confusing you all..

I love the look of the trans am Mustangs, the tyre bulge looks great and from what I understand they ran 8" rims front and back.

I am running 275/60/15 drag radials on the back and I think running them on an 8" rim will give the same look. The problem I have is I'm running an 8" rim on the front but from the looks of the pics I can find they must have run about a 245 tyre on the front and I don't know if this is doable on a street car.

What is the widest tyre I could practically run on the front on an 8" rim? The guards will be rolled and the car will be lowered and has Opentracker upper and lower arms.

If I have to run a 235 or smaller on the 8" rim on the front then the front and back tyre "bulges" won't match. I may be better off running a 10" rim in the rear with the drag radials to lessen the bulge to match the front. 

Any opinions or experience guys?

[latoracing 256]

Your rear tire height is right at 28", quite tall. A 245 tire (depending on the manufacturer) would be 9.646" wide (245 / 25.4 = 9.6456"). Section width and sidewall height will help with the bulge of the side wall and overall height. I don't think it would look right with a 28" tall tire on the front, more like 26". A 245-55-15 would be 25.6106" tall (+/- per manufacturer) without much bulge, but might be similar to the rear on a 7" wide rim (I'm guessing here). The 1" difference in width (275 = 10.8268"  vs 245 = 9.6456") would need to be accounted for. 

Me, I'd do a 10" rim out back with the 245's on an 8" rim on the front. 

[3Katz 26]

It's good to hear your thoughts, thank you. To fit 245s on an 8" rim on the front I had better watch my backspacing. The car has Opentracker upper and lower arms with the upper arms lowered 1.5" as per the supplied template. The fender lips are rolled slightly already and the car is lowered. Would you have a suggestion for the correct backspace for an 8" rim on the front? With 15's I'm guessing the clearance on the inside ie balljoints etc will be the point of most concern?

[RPM 1,190]

I think most guys use 4-1/2" backspace on the front. 

[3Katz 26]

Is that because it's a readily available off the shelf size? If wheels were available in a custom backspace I wonder if 4 1/2" would still be the ordered sizing?

[grendi 16]

On 1/23/2020 at 4:06 PM, latoracing said:

Your rear tire height is right at 28", quite tall. A 245 tire (depending on the manufacturer) would be 9.646" wide (245 / 25.4 = 9.6456"). Section width and sidewall height will help with the bulge of the side wall and overall height. I don't think it would look right with a 28" tall tire on the front, more like 26". A 245-55-15 would be 25.6106" tall (+/- per manufacturer) without much bulge, but might be similar to the rear on a 7" wide rim (I'm guessing here). The 1" difference in width (275 = 10.8268"  vs 245 = 9.6456") would need to be accounted for. 

Me, I'd do a 10" rim out back with the 245's on an 8" rim on the front. 

245-55-15 does not exist, but 235/60R15 does, and they are 26.1" in height, if that is the look you want and yes, the tire "bulges" will be bigger with 7" rims.
while a backspacing of 4.5" (E~0) is correct for 8", you would need a backspacing of 4.0" to get ET~0 with 7" rims.

i would like to mention this tool to find the right rim/tire size for your car.
https://www.rimsntires.com/specspro.jsp
please be aware that you can try out tire sizes that simply do not exist (like the mentioned 245/55R15).

[latoracing 256]

2 hours ago, grendi said:

245-55-15 does not exist, 
 

It does exist https://www.jegs.com/i/M-H/676/ROD-29/10002/-1 in a drag radial. (which shouldn't be used for steering axle applications). Just attempting to convey an idea of bulge and relative side wall height from a visual standpoint. As a "normal" off the shelf, common size tire, I didn't go and see if it did exist.

[3Katz 26]

Thanks everyone that is really helpful info, I am starting to understanding more about offsets and also tyre sizing. There is one question I have though about et~0 (zero offset?). How is it that on an 8" rim to achieve zero offset the backspace would be 4 1/2" and not 4"?

[newstang 388]

I just love we speak the same language and have completely different spelling of words. Tire- Tyre :-)

 

[bigmal 225]

On 1/25/2020 at 7:52 AM, newstang said:

I just love we speak the same language and have completely different spelling of words. Tire- Tyre :-)

 

Colour - color

Gaol - jail

Customise - Customize

And plenty more

 

[newstang 388]

19 minutes ago, bigmal said:

Colour - color

Gaol - jail

Customise - Customize

And plenty more

 

Wow, the Gaol I never heard

[RPM 1,190]

On 1/24/2020 at 12:45 PM, 3Katz said:

 There is one question I have though about et~0 (zero offset?). How is it that on an 8" rim to achieve zero offset the backspace would be 4 1/2" and not 4"?

My understanding is because an 8 inch wheel has an overall width of 9 inches. The 8 inches is measured where the tire bead is located. Half of 9 is 4-1/2.

[3Katz 26]

Thanks RPM that makes sense. I have some wheels on order 15x8 front 4 1/2" backspace and 15x10 rear -9 offset (which is as close as they could do to zero offset).

[RPM 1,190]

 

18 hours ago, 3Katz said:

Thanks RPM that makes sense. I have some wheels on order 15x8 front 4 1/2" backspace and 15x10 rear -9 offset (which is as close as they could do to zero offset).

Ya, -9 offset. Why is every dimension of the wheel measured in inches, but the offset which is metric? Can they get any goofier?

[3Katz 26]

Yeah it's weird... 

[grendi 16]

On 2/2/2020 at 12:32 AM, RPM said:

 

Ya, -9 offset. Why is every dimension of the wheel measured in inches, but the offset which is metric? Can they get any goofier?

no it's not.
while in the US backspacing was common, europe used offset, and now we have a mix of both.... the best of both worlds.
that's why rims are measured in inch, but tires in mm..... ;-)

[grendi 16]

On 1/24/2020 at 7:23 PM, latoracing said:

It does exist https://www.jegs.com/i/M-H/676/ROD-29/10002/-1 in a drag radial. (which shouldn't be used for steering axle applications). Just attempting to convey an idea of bulge and relative side wall height from a visual standpoint. As a "normal" off the shelf, common size tire, I didn't go and see if it did exist.

i guess you found the only tire available in that size, and yes, it is street legal (DOT Certified)!
but unless your planing to convert your mustang to front wheel drive, i don't think putting those on your car is a good idea. :-D

[latoracing 256]

1 hour ago, grendi said:

i guess you found the only tire available in that size, and yes, it is street legal (DOT Certified)!
but unless your planing to convert your mustang to front wheel drive, i don't think putting those on your car is a good idea. :-D

If you're trying to prove you're correct in the fact that they do not exist in a standard tire, then my example is incorrect, you win! Excuse me for not fact checking my "theoretical"  idea of a size that would offer a similar tire bulge before posting. No one in their right mind would put a drag radial on a steering axle for street use, front wheel drive or not. 

[3Katz 26]

I ended up going on the conservative side with a 235/60 on the front. If there's enough room I will change to a 245 later on. Here's how they turned out