275/60/15 woes

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xguard

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I've read you can fit 275/60/15s on a 72 Demon if you nail the back spacing. Looks like I missed it. 15x8s with 4.5 back space. That seemed to be the magic formula. But my car is small bolt pattern with the standard 10 inch drums. Maybe that's the difference. Thoughts? Options? Really limited on wheel options for small bolt pattern. (Btw the back of the car is sitting a little higher because of the weight distribution on Jack stands.) Will probably throw some 255s on the old wheels until I can upgrade to big bolt pattern.

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4.25 bs with the small bolt would of worked, but just use a spacer 1/4 you got long studs already, but you would need to roll the fender lip a bit nothing to crazy, thats if you need too.
 
I've read you can fit 275/60/15s on a 72 Demon if you nail the back spacing. Looks like I missed it. 15x8s with 4.5 back space. That seemed to be the magic formula. But my car is small bolt pattern with the standard 10 inch drums. Maybe that's the difference. Thoughts? Options? Really limited on wheel options for small bolt pattern. (Btw the back of the car is sitting a little higher because of the weight distribution on Jack stands.) Will probably throw some 255s on the old wheels until I can upgrade to big bolt pattern.

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255s are a nice size tire, here they are on the back of a B.

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Here is the thing , they say the backspace is 4 , 4.25 or 4.5 , but is it actually that. I have bought wheels from Jegs and Summit , because Specialty Wheel didn't offer 4.25.
I tried 4.5 , hit the spring with 275's , actual backspace was 4 5/8 and 4 11/16. So I ordered a 4 inch backspace , got 4 1/4 and 4 3/8. Swapped wheels side to side to see what worked best. My Duster has a good 1/8 to 1/4 difference , side to side. Sure would be nice if they followed their own specs.

Frank
 
Something that bit me was not factoring the tires actual section width when I did my measurements. If the tire was no wider than the tread width it probably would have tucked in there fairly well.
 
This is why I went with a 15x8 instead of the 15x7 also. I figured the wider rim would lessen the "sidewall bulge" that the 7" would have.
 
This is why I went with a 15x8 instead of the 15x7 also. I figured the wider rim would lessen the "sidewall bulge" that the 7" would have.
That's opposite what the tire will do in my opinion. larger base will extend the bead width but the cross section is fixed. Going to a more narrow rim may change that sidewall to a more narrow overall width (just because it has to reach back for the rim bead) but that is not recommended as the tire is designed for a specific size bead width. space your rim out 1/4 and roll that fenderlip with the lip roller that swings in an arc off the hub after carefully starting the trim flange to bend up. Looks like you have plenty more room if that lip is cleared, like most A-bodies.
 
How do they fit on the quarter panel side?

I have no issues or concerns at all with the tire fitment. The car is unmodified in the wheel wells, no spacers, and survivor with 23,090 miles.

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4 1/4 backspace with 255's - Don't go bigger unless you want to problems
 
I couldn't agree with slantsix64 more. I love wheels with too much backspace, that can be fixed/adjusted with spacers. Too little, the tire crashes into the fender. As he pointed out, you already have the necessary studs. No brainer in my opinion!
Next, I think the reason that it didn't work, going in, is cause of the narrow brakes on a sbp 8 3/4, the wheel mounting face-spring distance is a little shorter than the average
8 3/4.
 
This is my car 275/60/15 on a factory 15 x 7 with 4.25" back space, plenty of room between the springs and 1/4 panel. No spacers.

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Sireland, I cant believe how much space you have on the outside- You don't get that on a 74 Duster
 
I've read you can fit 275/60/15s on a 72 Demon if you nail the back spacing. Looks like I missed it. 15x8s with 4.5 back space. That seemed to be the magic formula. But my car is small bolt pattern with the standard 10 inch drums. Maybe that's the difference. Thoughts? Options? Really limited on wheel options for small bolt pattern. (Btw the back of the car is sitting a little higher because of the weight distribution on Jack stands.) Will probably throw some 255s on the old wheels until I can upgrade to big bolt pattern.

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The 15x8" with 4.5" of backspace is generally the "magic formula" for a Duster/Demon that has an A-body 8 3/4 that's been converted to BBP axles. With the stock SBP axles 275/60/15's need more like 4.25" backspace. But with the body tolerances on these cars it's always a good idea to measure your own car from the wheel mounting surface back to the springs and out to the quarter lip. It's not unusual to have an axle offset slightly to one side or the other, or the body tolerances to be more than a 1/4" different from one car to the next or even from one side to the other.

Looks to me like a thin spacer will fix the issue, your car is high enough in the back that the quarter clearance shouldn't be a big issue. If you can get to 3/8" or so clearance on the springs you should be ok. Always better to have a little too much backspace than not enough, a 1/4" spacer is no big deal at all as long as you have enough threads on the wheel studs and it's a lot easier to install a spacer than move the quarter lip.

4 1/4 backspace with 255's - Don't go bigger unless you want to problems
Sireland, I cant believe how much space you have on the outside- You don't get that on a 74 Duster

There are literally DOZENS of Dusters/Demons/Dart Sports running 275/60/15's on 15x8's on this board without issue. As I already mentioned the body tolerances on these cars were not super accurate, so it may be that your car can't run tires that size without modifications. But based on my own '74 Duster and many I've seen on this board it's much more likely that 275's will fit without "problems" if the backspacing is done correctly.

I had 275/40/17's on my '74 Duster with decent clearance for the street, and I'm currently running 295/35/18's with a 1/2" spring offset and some quarter lip trimming. 275's are tight, but they will fit most Dusters/Demons/Dart Sports as long as you account for the differences in width of the different axles and bolt patterns available for those cars.
 
Again, when you tell the average guy that 275's will fit, and they end up like the guy who started this thread. There is a problem. It can be very problematic (stressful) to order tires and rims, and then they don't fit after spending a lot of money. When recommending that size, we should always mention that there is probably a 50% shot they could end up like the OP. How many threads have we seen this same problem now? 255's are a better choice unless you are sure you have the space and/or your willing to modify something
 
Again, when you tell the average guy that 275's will fit, and they end up like the guy who started this thread. There is a problem. It can be very problematic (stressful) to order tires and rims, and then they don't fit after spending a lot of money. When recommending that size, we should always mention that there is probably a 50% shot they could end up like the OP. How many threads have we seen this same problem now? 255's are a better choice unless you are sure you have the space and/or your willing to modify something

There are far more Dusters/Demons/Dart Sports with 275's mounted on them successfully than cars that they didn't work on. The OP's car will most likely be just fine with a 1/4 spacer and nothing else.

I'm well aware of problems in ordering rims, I've maxed out the rim and tire widths on pretty much all of my cars. And when I did it there were very few people running the sizes I run with the axle I have, so it was a lot of measuring, math and straight up guess work. I run 275/35/18's on the FRONT of my Duster and 295/35/18's on the back.

We've done this dance before, you can check all the threads. I'm not going to argue that 275's will fit your car, but I'm happy to provide all kinds of examples of them fitting just fine. I know there are more, but I have better things to do than look up every single example. There are plenty more.

Here's a dozen cars. Literally a dozen. Demon Rear Wheels I know you've seen it before because it was in response to you, but you can follow the link for the pictures or expand the quote for the links to each and every car.
So here's a quick list of a dozen other members currently running 275/60/15's on unmodified sport body cars. I only used examples for cars that the owners said were stock, and had posted a picture for, and I left my car with 275's on it out just in case you think I'm biased. There are tons more folks that have said they've done it without posting pictures. And I'm sure there's even more that I haven't found, but I wanted to limit this to 15 minutes of my time. So, either all of these people are lying about their cars, or you're incorrect. That doesn't mean you have to run 275's, do whatever you want. But it can be done successfully, without rubbing, because they will fit with the proper backspace. And now I can just reply with this post anytime you say they won't fit, so folks have evidence to make their decision.

They fit on DakotaDuster's unmodified '74 Post your wheel and tire combos.
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And 1969cuda340 has them on an unmodified '74 Post your wheel and tire combos.
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And petnic01 has them on a '73 Duster (not any different than a '74 for tire clearance) 73 duster 275/60/15????
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And Sweet416 has them on a Dart Sport (not sure what year, doesn't matter, all the same) 275's on a dart sport
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Mopowers runs them "no problemo"Father-Son 1974 Duster Project
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OL DODGE did it on a '73 Duster 340 73 duster 275/60/15????
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Oldmanmopar runs 275's on his Duster 275/60/15 tires on stock Duster
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Fisher runs 275's on his Duster 275/60/15 tires on stock Duster
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Sireland67 runs 275's "no issues" 275/60/15 tires on stock Duster
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71DodgeDemon340 runs 275's on his '71 Demon front tire size advice
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67autocross with a '70 Duster and 275's Post your wheel and tire combos.
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Mguner's Dart Sport with 275's Wheel/tire combo for '73 Dodge Dart sport
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Here's a thread with more
275/60/15 tires on stock Duster

Another one
Duster 275/60/15

You keep disagreeing and more and more members keep running 275's. Measured correctly they will work on the vast majority of Demons/Dusters/Dart Sports. And regardless, you should ALWAYS measure your own car because the body tolerances on these cars are fairly loose. The ballpark is about the same, but when you're maxing out the wheel well a 1/4" can make or break the fit. And you do have to account for the different width axles, because a SBP A-body 8 3/4 is not the same width as a BBP converted A-body 8 3/4. 7.25" and 8.25" rear axles are different from 8 3/4's too. So you can't just copy one person's backspacing, you have to match the whole combination.
 
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I measured incorrectly somewhere. I plan to find exactly where I messed up. For now I just want to get it going with minimal modifications.
 
I actually believe 275 60 15 looks better on a 7 inch rim fits better too

The tire manufacturers disagree about it fitting better at least, both BFG and Cooper list a 7.5” as the narrowest rim a 275/60/15 should be mounted on.

That said, I’m sure plenty of people have run them on 15x7’s. The problem will be that if the tire is squeezed on a narrower rim the tread pattern will be distorted, so you’ll have to run a lower pressure to keep all the tread on the ground. Otherwise it kinda defeats the purpose of running the wider tire.
 
As a side note. The identical Wheel Vintique 15x8 with 4" bs and 275 60r15 were installed on my Dads 1969 Barracuda notchback. They also fit perfectly. He does have Mancini HD springs.
 
Move the springs; you won't regret it; I have fit 325/50-15s, on 10s, into the tubs of my 68 Barracuda, which is lowered. Yeah, I had to massage the inner metal a bit, but I did not roll the lips, just bent them up in one spot on each side.

I'm pretty sure the Barracudas and Duster/Demons share the same inner tubs.
 
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