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Max tire size / offset for 71 Swinger with 15" x 7"
https://slantsix.org/forum/viewtopic.php?t=18379		 Page 1 of 2
Author:  AnotherSix [ Mon Jul 03, 2006 4:23 pm ]
Post subject:  Max tire size / offset for 71 Swinger with 15" x 7"
This is an old subject, but all my searching has not turned up a definite answer. The car is getting BBP disks in front and the matching BBP 7 1/4" rear end. I want to get tires and wheels ahead of time for the conversion. I want to go with 15" x 7" wheels and the most available have 3.75" and then 4" backspacing, then it starts getting expensive. I would like to run a 225-60 15. Would this be pushing my luck with the 3.75" backspacing? I could go to down to a 215-60 15 if that is a safer bet. With the 2.76 gears the smaller diameter is probably a good thing. I am not at all interested in running a narrow tire in the front as I am looking for all the handling I can get, and want to be able to rotate the tires. I don't want to get too odd of a size tire since the choices in 15" seem to be getting less and less. I am sure someone knows what will fit on this body. Thanks for any input.
Author:  Sam Powell [ Mon Jul 03, 2006 5:08 pm ]
Post subject: 
I have 15x7" wheels with a 3.75" back spacing and 205-60's on all four conrners, with plenty of space to spare, on the car you see here. . My 1970, 360 Dart, which I sold, had the same size wheels, and back spacing with 225 60's on the rear and 215 60's on the front, with no problem. I think you could go with 225's all the way around, but I think these A body cars do better with a bigger tire on the back. My '69 with 205's all the way around has an overstear problem that could be helped if I put 215's or 225's on the back.
Oh yes, both cars have the big bolt disks up front, and the big bolt rear in back.
Author:  Joshie225 [ Mon Jul 03, 2006 7:46 pm ]
Post subject: 
I had 15x7" wheels with 3.5" backspacing and my 215/60R15s rubbed in the back. With 4.25" backspace cop car wheels 235/60R15s fit fine in the back. I ran 205/60R15s in the front, but 215/60R15s would have fit easily and 225s would likely have fit too. Bottom line is don't buy wheels with less than 4" backspace if you want to fit good sized tires under there.
Author:  RossKinder [ Mon Jul 03, 2006 11:28 pm ]
Post subject: 
Quote:
I had 15x7" wheels with 3.5" backspacing and my 215/60R15s rubbed in the back. With 4.25" backspace cop car wheels 235/60R15s fit fine in the back.
What am I missing? An HTML I have (http://www.rsracing.com/tech-wheel.html) measures backspace as the space on the back, from the inner bolt surface to inner flange and therefore it says that the more backspace you have the farther the rim, therefore the tire, will reach toward the inner wall of the wheel well. Are your figures measuring backspace from the front of the rim?

Thanks
Author:  emsvitil [ Tue Jul 04, 2006 1:37 am ]
Post subject: 
Quote:
Quote:
I had 15x7" wheels with 3.5" backspacing and my 215/60R15s rubbed in the back. With 4.25" backspace cop car wheels 235/60R15s fit fine in the back.
What am I missing? An HTML I have (http://www.rsracing.com/tech-wheel.html) measures backspace as the space on the back, from the inner bolt surface to inner flange and therefore it says that the more backspace you have the farther the rim, therefore the tire, will reach toward the inner wall of the wheel well. Are your figures measuring backspace from the front of the rim?

Thanks
I think he means the back tires rubbed. I assumed it was on the outside in the back............
Author:  Sam Powell [ Tue Jul 04, 2006 6:18 am ]
Post subject: 
More back space narrows the track of the car. Less back space sets the wheels further out, or widens the track of the car. Since the achilles heal of these A body cars is the space between the outside surface of the rear tire and the rear fender, this is where you run into trouble first. If the tires sit too far out, (less back space), then they will rub the fender on the outside. I will say, my car handled the best with cop car wheels. They are what this chassis is designed for, and are ideal. I know, I know my car originally came with 13x4" wheels but you know the designer was thinking cop car wheels. He had to be!

Why did I take them off? Just for a change I guess, I got a deal on the alloys, I had money to burn, and thought alloys would look cool. 8) All that glitters is not gold.
Sam
Author:  RossKinder [ Tue Jul 04, 2006 10:20 am ]
Post subject: 
Quote:
Quote:
Quote:
I had 15x7" wheels with 3.5" backspacing and my 215/60R15s rubbed in the back. With 4.25" backspace cop car wheels 235/60R15s fit fine in the back.
What am I missing? An HTML I have (http://www.rsracing.com/tech-wheel.html) measures backspace as the space on the back, from the inner bolt surface to inner flange and therefore it says that the more backspace you have the farther the rim, therefore the tire, will reach toward the inner wall of the wheel well. Are your figures measuring backspace from the front of the rim?

Thanks
I think he means the back tires rubbed. I assumed it was on the outside in the back............
Ah. Must be. Thanks.
Author:  Joshie225 [ Tue Jul 04, 2006 11:04 am ]
Post subject: 
Yes, the outer fender lip contacted the outer sidewall. Those Centerline wheels looked cool, but scraping tires is very uncool. The car in question with cop wheels.
Image
Author:  AnotherSix [ Tue Jul 04, 2006 9:05 pm ]
Post subject: 
Thanks for all the input. It sounds like I should be looking at 4 to 4.25 on the backspace. I was hoping to get away with less and stay with a 225 or smaller tire.
Author:  Sam Powell [ Thu Jul 06, 2006 5:35 am ]
Post subject: 
You can put 225's on 3.75 back space, but your car will handle better with 4.25" back space.
Author:  RDJ [ Thu Jul 06, 2006 7:24 pm ]
Post subject: 
I am a little confused with the backspace/offset measurments. Wouldn't a 4.5" backspace with a +12 mm offset give you an effective 4.1" backspace?
Author:  Joshie225 [ Thu Jul 06, 2006 8:09 pm ]
Post subject: 
Here is an explanation of offset. More positive offset means more backspacing for a given width. More width with a given offset means more back spacing.

http://www.tirerack.com/wheels/tech/tec ... techid=101
Author:  RDJ [ Fri Jul 07, 2006 7:57 am ]
Post subject: 
73 Swinger. I went to a tire store yesterday to buy some basic chrome modular rims and 225/60/15 tires. He had rims with 3.5 and 3.75 backspace. They looked OK in the back, and I could have gone 235 probably, but I have some new 5 leaf springs and new KYBs in the back. The 225s barely cleared (by 1/4? inch) the front of the front wheel well turning the tire back and forth.

The tire guy said they would be fine because the suspension doesn't move that way, but it was too close for me. Also, it looked as if it might rub on the top of the front fender on a big bump. Maybe not a problem, but if it was, I would be kind of stuck with this investment. It looked like if I had more backspace, it would be fine.

I am going to order some rims from SummitRacing. The 4" backspace has more inexpensive choices than the 4.25, but the 4.25 has some good inexpensive choices. Better to spend a little bit more now than get stuck with something that are not working as well as you would like. The rims they sell have all the specs easy to find for each rim. Plus, you can search just using rim specs. Besides, the prices are good.
Author:  RDJ [ Fri Jul 07, 2006 8:06 am ]
Post subject: 
By the way, they have some Cragar chrome rally wheels for $82 with a center bore diameter of 3.190, and some US Wheel chrome rally wheels for $87 with a center bore diameter of 3.3". Thats why I was wondering (in another post) what the center bore diameter is on my car. I am at work, so I can't measure it. I may just order the ones with the bigger bore.
Author:  slantvaliant [ Fri Jul 07, 2006 8:44 am ]
Post subject: 
Quote:
The tire guy said they would be fine because the suspension doesn't move that way
Hmmmm ... Tires, bushings, even chassis flex during use. I'm with you, I'd like more than 1/4" static clearance.

Something else to think about: Tires with the same specs from different manufacturers and even different models from the same manufacturer are seldom actually the same exact size and shape. If you changed tire brands or models, that clearance could go away.
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