74 Road Runner Tire size on 15x6.5 and 15x7

[74Runneer]

I have a 74 Road runner that currently has 205/70/r14 and 245/60r14 tires on crager wheels. The tires are getting old and they also look tiny in the wheel well so I want to upgrade to something bigger. When I bought the car it came with a set of 15" rallye wheels (perhaps original?) that I'm going to use. Fronts are 6.5", rears are 7". I want to find a tire that will fill out the wheel well the best. I'm thinking either 235/60r15s or 235/70r15s for the front and 255/60r15s or 255/70r15s for the back.
Cooper cobra gts. Any know if I can fit the 70s. I see that drop top got them to fit on his 71 so I figured it would work on my 74.

 

[74Runneer]

https://photos.app.goo.gl/ehkWG6jZ9DqzqSAw8

Heres what the car currently looks like

 

[YY1]

255 60 15 on 15x6.5 rallye wheels on back of my 73.

The tires look like they were made for the wheels and the combo looks like that was what the wheel wells were designed for.

 

[74Runneer]

255 60 15 on 15x6.5 rallye wheels on back of my 73.

The tires look like they were made for the wheels and the combo looks like that was what the wheel wells were designed for.

Do you have any pictures of that? What do you have on the front?

 

[GetX'd]

I would stuff some L60s in the back - should have plenty of room for those. F60s x 15 in the front. Goodyear RSWL. ice looking tires on our old iron especially with Cragars. I have that combo on my 68 GTX - But I'm not sure theres much difference in the wells - yours might even be bigger.

 

[74Runneer]

I believe the backspacing on 15x7 is 4" and the 15x6.5 is 3.75". I'm not too worried about the front, but is that enough backspacing in the rear to fit the 255/70r15?

 

[duster22]

15 x 7 wheels are 4 1/4 backspace.
15 x 6.5 wheels are 4 1/4 backspace.
The difference is in the front side of the wheel , there for a 7 inch trim ring will not fit a 15 x 6.5 wheel.

Frank
The Wheel Guy

 

[mopar 3 B]

Where these not factory optioned with G60-15 on all four corners on 15x7 wheels?

 

[74Runneer]

15 x 7 wheels are 4 1/4 backspace.
15 x 6.5 wheels are 4 1/4 backspace.
The difference is in the front side of the wheel , there for a 7 inch trim ring will not fit a 15 x 6.5 wheel.

The Wheel Guy

Maybe I measured it wrong. I could see the 7" being 4.25" bs but the 6.5" definitely looked like it had shallower backspacing. Do you measure from the raised inside edge or the flat inside face?

 

[74Runneer]

I measured them again today and they 15x7 and 15x6.5 are definitely not the same back spacing. The 15x6.5 is either 3.75" or 4" depending on whether you measure from the flat surface or the lip. Here are the pictures explaining what I'm talking about: https://photos.app.goo.gl/FVPRjby4N4GAVh2DA

 

[mopar 3 B]

Wheel width is measured from bead to bead on the inside. Back spacing would be measured from the same surface to mounting pad face.

 

[duster22]

Backspace is measured from the backside mounting surface to the very back edge of the rim.
Now , I just went and measured two of my 15 x 6.5 factory part numbered ralley wheels. , and they both measure 4 1/4 backspace. Now I don't know if you have some one off custom made wheels , or they are not 15 x 6.5 wheels. By what you measured on the back , a factory 15 x 7 trim ring will fit on the front of your wheel.
Which is impossible with a factory 15 x 6.5 ralley. There is approximately a 1/2 inch difference in the 15 x 7 and the 15 x 6.5 trim rings trim rings.

Frank

 

[74Runneer]

Its definitely a 14" wheel. I measured it wrong.

 

[duster22]

Makes sense 14 x 5.5 wheels are 3 5/8 backspace and 14 x 6 close to that , because they both use the same trim ring.

Frank

 

[74Runneer]

Thanks for helping me dodge that bullet...

 

[Bobby Sixkiller]

I have 15x8 4 inch back spacing wheels on my 73 runner. 275/60 15 rear. 255/60 15 front. No problem. Clears great.

 

[SureGrip]

I used to run 255/60/15's on stock 15x7 cop wheels back in the day on my 74 RR

I have 255/60/15 in the rear and 235/60/15s up front now.