245/60/15's on 15X8 rims

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68 Coronet RT

68 Coronet RT

68 GTS # 508 in Registry
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Getting ready to purchase my new rims and tires for my 68 GTS but not to sure what will work on the rear. I'm looking at 245/60/15 on a 15X7 or 8 inch rim or 255 60/15's on a 15X8 inch rim. Suspension is all stock except air shocks right now but plan on taking them off and putting regular shocks on and adding a leaf spring to raise the back end. On the left side I have 11 3/4 inches between wheel lip and inner fender and 12 inches on the right side.
 
68 Coronet RT said:
Getting ready to purchase my new rims and tires for my 68 GTS but not to sure what will work on the rear. I'm looking at 245/60/15 on a 15X7 or 8 inch rim or 255 60/15's on a 15X8 inch rim. Suspension is all stock except air shocks right now but plan on taking them off and putting regular shocks on and adding a leaf spring to raise the back end. On the left side I have 11 3/4 inches between wheel lip and inner fender and 12 inches on the right side.
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On your Coronet? They can handle 15x8's easy and the 255's work well on 8" wide wheels/ I have 255's on 7" wide and they work ok.
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68 Coronet RT said:
Nope sold the Coronet last June. My new ride is a 68 GTS # 508 in the GTS Registry
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Whatever rim you use, make sure you have the proper back spacing on the rims it makes a difference. Ideally you want to center the wheel in the available space you have from inner wheel well to outer lip of the quarter panal
 
68 Coronet RT said:
Getting ready to purchase my new rims and tires for my 68 GTS but not to sure what will work on the rear. I'm looking at 245/60/15 on a 15X7 or 8 inch rim or 255 60/15's on a 15X8 inch rim. Suspension is all stock except air shocks right now but plan on taking them off and putting regular shocks on and adding a leaf spring to raise the back end. On the left side I have 11 3/4 inches between wheel lip and inner fender and 12 inches on the right side.
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SBP 8 3/4 in that GTS right?

Keep in mind you don't get to use all of the space from the inner fender to the quarter lip if you have the leaf springs in the stock location. You end up losing at least a 1/2", probably more like 3/4" out of that with the stock spring locations. So, really you should only figure on having about 11", because that's what you'll have on the left side.

That makes a 255/60/15 kind of tough. The BFG T/A's have a section width of 10.2" when measured on a 15x7.5" rim (manufacturer spec), which is on the rubbing side of marginal clearance. Now, on a 15x7, you might end up closer to 10" with that section width, which would give you enough space assuming everything is centered up with the backspacing properly.

I think the 255/60/15 on a 15x7" is about as much as I would try, even that tire on a 15x8" might not work. A 245/60/15 would be a safer bet, run it on a 15x7 with 4.25" of backspace. With a SBP 8 3/4 you might also be able to get away with 4" of backspace, with a BBP 8 3/4 you'll definitely want 4.25".
 
Is the car small bolt pattern or large? If large, with re-drilled axles or large bolt axles.

A 235/60/15 should work safely with correct backspace and rim width.

235/60/15
15x7
4.25 backspacing

Do not run less backspacing. If you need to make fine adjustments, you can add 1/8”, 3/16”, or 1/4” spacers.

I have 245/60/15 15x7 4.25 bksp in my 68 Dart GT and it is very tight
 
The GTS has new LBP axles in the rear with 11 inch shoes, fronts have been converted to disk with LBP. The rims I'm looking at are 15 X 7 with 4.25 backspacing and the 15 X 8 has 4.5 backspacing
 
68 Coronet RT said:
The GTS has new LBP axles in the rear with 11 inch shoes, fronts have been converted to disk with LBP. The rims I'm looking at are 15 X 7 with 4.25 backspacing and the 15 X 8 has 4.5 backspacing
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Oh ok. Well, both of those wheels have the correct backspacing, but I would be leaning to the 15x7's. They're the exact right size for 245/60/15's, and still within the recommended range for 255/60/15's. And honestly, you'll probably need the little bit of section width squeeze that you'll get out of running the 255/60/15's on 15x7's for clearance.
 
So I could safely run the 255's on the 15X7 rims with 4.25 back spacing ? With 3:91 gears I want to try to get as much rubber down without the half inch shackle off set.
 
68 Coronet RT said:
So I could safely run the 255's on the 15X7 rims with 4.25 back spacing ? With 3:91 gears I want to try to get as much rubber down without the half inch shackle off set.
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I would say cautiously that you should be able to, but, it really depends on your car. Toolmanmike does it with that combination, but with the clearances you'll be at it pretty much comes down to body tolerances. I've seen a bunch of cars that have made that combination work, and I've seen a few that had rubbing. The left side of your car being narrower could be a little troublesome depending on where that 1/4" of lost space is.

You should be at about the minimum safe clearance, but, even an 1/8" in the wrong direction at the minimum clearance means it rubs.

If you wanted a better idea before you pull the trigger, measure the distances from the wheel mounting surface (the face of the rear drums) to the quarter lips and the springs. A carpenter's square and a tape measure work well in combination to do that so you're pulling measurements that are all in line. Then you can run the math with the section widths and backspacing to get a better idea of how much clearance you'll have and where. You can cheat the springs down to about 3/8" clearance, but the quarter lip needs a 1/2" minimum.
 
On my Plymouth Scamp I ran 255/60R15’s I ran 8” welds and it fit stock on an 8.25 rear. Fenders the same I think.
 
Tires were up in fenders quite a bit. No air shocks and stock soft suspension. Body lean bad when cornering. Sometimes left rear would just kiss the fender. You could hear it.
 
Fit and worked for 3 years. Then sold the car2 years ago. Still working.
 
68 Coronet RT said:
On the left side from drum face to the lip is 4 3/4 inches right side is 5 inches.
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That's what I was afraid of. That 1/4" came right out of your quarter clearance.

On my '71 Dart I have an 8 3/4 with LBP axles and 11" brakes as well. On the driver's side I also have 5" to the quarter from the wheel mount, and 6" to the springs from the wheel mount (stock spring locations). On the other side I have 5" to the quarter and 6 1/8" to the springs. So, tight side is 11". The LBP axles can typically make use of more backspace than the standard wheels come with, I think Abodyjoe had a set of 15x7's made with 4.5" of backspace for his car...Rear axle upgrade from SBP to BBP

With your car there's two possibilities. The axle is shifted, which means on the side with 4 3/4" to the quarter there's also more room to the spring. Or, it's all in the bodywork. Which means you probably only have 10 3/4" to work with for tires.

If the axle is shifted over you can either fix that, or run more backspace on that wheel. But 4.25" of backspace won't cut it on the side that's tight. If the axle isn't shifted, then you just have 10 3/4" to work with, and that only leave you 9.75" for tire, which is a 245/60/15. Even a 255/60/15 on a 7" rim will be too big.

Some of the 67-69 cars were just tight. I think on the whole the 70+ cars had a little more room, but it's kind of like they ran on the loose side of tolerance and the 67-69 cars ran on the tight side because the chassis is the same.

If you take measurements from your wheel mount to the springs it will tell you if the axle is shifted to one side, or if it's in the quarter lip location.
 
Regardless of which tire you choose I'd run them on the 8" wheels.
 
72bluNblu said:
That's what I was afraid of. That 1/4" came right out of your quarter clearance.

On my '71 Dart I have an 8 3/4 with LBP axles and 11" brakes as well. On the driver's side I also have 5" to the quarter from the wheel mount, and 6" to the springs from the wheel mount (stock spring locations). On the other side I have 5" to the quarter and 6 1/8" to the springs. So, tight side is 11". The LBP axles can typically make use of more backspace than the standard wheels come with, I think Abodyjoe had a set of 15x7's made with 4.5" of backspace for his car...Rear axle upgrade from SBP to BBP

With your car there's two possibilities. The axle is shifted, which means on the side with 4 3/4" to the quarter there's also more room to the spring. Or, it's all in the bodywork. Which means you probably only have 10 3/4" to work with for tires.

If the axle is shifted over you can either fix that, or run more backspace on that wheel. But 4.25" of backspace won't cut it on the side that's tight. If the axle isn't shifted, then you just have 10 3/4" to work with, and that only leave you 9.75" for tire, which is a 245/60/15. Even a 255/60/15 on a 7" rim will be too big.

Some of the 67-69 cars were just tight. I think on the whole the 70+ cars had a little more room, but it's kind of like they ran on the loose side of tolerance and the 67-69 cars ran on the tight side because the chassis is the same.

If you take measurements from your wheel mount to the springs it will tell you if the axle is shifted to one side, or if it's in the quarter lip location.
Click to expand...

I REALLY like the idea of the 15x7 with 4.5 backspace. Especially with 4.5 bolt pattern aftermarket or cut down axles. And gives you options to fine tune with spacers.

You can run 15x7 on 4.5" backspace in front too. And that will help with fender clearance.

8" wide on a 67-69 dart just makes things tougher. Not really needed for 245 or 255.
 
Not needed but it flattens the tread out nicely and stiffens up that sidewall a little more. I run 225's on an 8.5" wheel on my daily and it still sits just outside the wheel at the sidewall.

And yeah, I know the back wheel is on backwards... I'm retarded sand this was the day I put them on a few years back.

volvo.jpg
 
72bluNblu said:
I would say cautiously that you should be able to, but, it really depends on your car. Toolmanmike does it with that combination, but with the clearances you'll be at it pretty much comes down to body tolerances. I've seen a bunch of cars that have made that combination work, and I've seen a few that had rubbing. The left side of your car being narrower could be a little troublesome depending on where that 1/4" of lost space is.

You should be at about the minimum safe clearance, but, even an 1/8" in the wrong direction at the minimum clearance means it rubs.

If you wanted a better idea before you pull the trigger, measure the distances from the wheel mounting surface (the face of the rear drums) to the quarter lips and the springs. A carpenter's square and a tape measure work well in combination to do that so you're pulling measurements that are all in line. Then you can run the math with the section widths and backspacing to get a better idea of how much clearance you'll have and where. You can cheat the springs down to about 3/8" clearance, but the quarter lip needs a 1/2" minimum.
Click to expand...

72bluNblu' I finally got the rear end back together and I took some measurements. This is what I have from the face of the drum to the springs on both sides is 6 1/2 inches. Left side from drum face to the quarter panel lip is 4 3/4 and the right side is 5 inches. So my question is do I have enough space to run a 255/60/15 on a 15X7 rim with a 4.25 backspace or a 15x8 rim with 4.5 back space or would a 245/60/15 on a 15X8 with a 4.5 backspace work, or just stick with the 245/60 15 on a 15x7 to be safe.
 
6 1/2" to the springs from the drum face? If that's right, those aren't stock location springs. That has to be a 1/2" offset. That assumes you took the measurement with the tape perpendicular to the mounting face and parallel to the springs- ie, you didn't measure at an angle. Do you have any pictures of the spring hangers? Or of the wheelhouse, springs, axle etc? Something doesn't add up there, the measurement to the springs should be more like 6" for the stock location and BBP axles and brakes.

Anyway, let's assume the measurement is correct. Working with the side that has less room, that means you have 11.25" to work with. Assuming a 1/2" for clearance to the quarters and springs, that's 10.25", so yes, you have enough room for a 255/60/15. So then there's the backspace. You have 4.75" to the quarter, so, lets work backward from the front space. You need a 1/2" of clearance, 4.25". With a 15x7, you have ~1" of tire overhang past the rim, so, 3.25" is the front space. The 15x7" is 8" wide outside to outside, so, the minimum backspace needs to be 4.75". And really, I assumed the 255/60/15 would be 10" wide on the 15x7, so, if anything you'd want more like 4 7/8" (4.875"). On a 15x8 that would mean 5.375" backspace.

You have a ton of space to the springs according to your measurement, and not that much to the quarters, which is why the backspace numbers are high. The measurements to the quarters make sense to me, 5" is exactly what I have and what I've seen before, the 4.75" side is tight but again not unheard of because that's just bodywork. But the measurements to the springs read like a 1/2" offset, because the drum to spring measurement is usually pretty accurate. If one side was an 1/8" off it would be one thing, but for both sides to be a 1/2" off is a big difference.
 
72bluNblu said:
6 1/2" to the springs from the drum face? If that's right, those aren't stock location springs. That has to be a 1/2" offset. That assumes you took the measurement with the tape perpendicular to the mounting face and parallel to the springs- ie, you didn't measure at an angle. Do you have any pictures of the spring hangers? Or of the wheelhouse, springs, axle etc? Something doesn't add up there, the measurement to the springs should be more like 6" for the stock location and BBP axles and brakes.

Anyway, let's assume the measurement is correct. Working with the side that has less room, that means you have 11.25" to work with. Assuming a 1/2" for clearance to the quarters and springs, that's 10.25", so yes, you have enough room for a 255/60/15. So then there's the backspace. You have 4.75" to the quarter, so, lets work backward from the front space. You need a 1/2" of clearance, 4.25". With a 15x7, you have ~1" of tire overhang past the rim, so, 3.25" is the front space. The 15x7" is 8" wide outside to outside, so, the minimum backspace needs to be 4.75". And really, I assumed the 255/60/15 would be 10" wide on the 15x7, so, if anything you'd want more like 4 7/8" (4.875"). On a 15x8 that would mean 5.375" backspace.

You have a ton of space to the springs according to your measurement, and not that much to the quarters, which is why the backspace numbers are high. The measurements to the quarters make sense to me, 5" is exactly what I have and what I've seen before, the 4.75" side is tight but again not unheard of because that's just bodywork. But the measurements to the springs read like a 1/2" offset, because the drum to spring measurement is usually pretty accurate. If one side was an 1/8" off it would be one thing, but for both sides to be a 1/2" off is a big difference.
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My bad, both sides are 6 inch from the face of the drum to the springs
 
68 Coronet RT said:
My bad, both sides are 6 inch from the face of the drum to the springs
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Yeah that's about what stock should be.

255's are out. You only have 10.75" to work with then on the "tight" side. Even assuming a 255/60/15 is only a 10" section width when it's on a 15x7" that isn't going to work. If you gave the quarter a 1/2" of clearance you'd only have a 1/4" to the springs, and that's not enough.

I would say a 245/60/15 is as big as you can go unless you trim the quarter lip or install 1/2" spring offsets. And 15x7's with 4.25" of backspace won't work. The math to center everything up on the side with less clearance gives you a 15x7 with 4.65" of backspace, so, what I would probably do is order a set of 15x7's with a 4.75" backspace and a set of 1/8" spacers. It will be right about 3/8" to the springs with that backspace, you can play with the 1/8" spacers if it's too tight on the springs.
 
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