Cop car rim size

-
Chevy rick

Chevy rick

Active Member
Joined
Jun 13, 2016
Messages
32
Reaction score
2
Location
toronto area
I have a nice set of cop rally rims on my 70 swinger but the clearance on my new amd fenders is scarring the shiz out of me , the car is nearing completion . did they make a 14" or different backspace on the 15x7 . thanks my friends and stay safe EH.

20200313_192607.jpg


20200315_112134.jpg
 
Original cop wheels are 15x7” with a 4.25” backspace. There was a 15x8 version that came on some of the later trucks but I don’t know the backspace on those.

The 15x7” 4.25” backspace works pretty well on the 73+ style BBP brakes with up to about a 225/60/15. What brakes and tire sizes are you running?
 
72bluNblu said:
Original cop wheels are 15x7” with a 4.25” backspace. There was a 15x8 version that came on some of the later trucks but I don’t know the backspace on those.

The 15x7” 4.25” backspace works pretty well on the 73+ style BBP brakes with up to about a 225/60/15. What brakes and tire sizes are you running?
Click to expand...
I am running 11" discs 74 cuda spindles clamp down style calipers , I think my tires are rather large , I will check tomorrow when i get to the shop . Thanks .
 
I dont know of any different ones. All the ones I have/seen are 15 x 7. I think the super coupe used these in a 15 x 8 as well. What was that...a F body roadrunner or something like that?
 
Chevy rick said:
I am running 11" discs 74 cuda spindles clamp down style calipers , I think my tires are rather large , I will check tomorrow when i get to the shop . Thanks .
Click to expand...

no problem! Yeah with the 73+ disks and the cop wheels you should be good up to a 225/60/15. Much bigger than that on a Dart will probably require bodywork in most cases.
 
I have 235 60 15 on front , I cranked up torsion bars a bit for now . Car is front heavy with the 440 .
 
Chevy rick said:
I have 235 60 15 on front , I cranked up torsion bars a bit for now . Car is front heavy with the 440 .
Click to expand...

Yeah 235/60/15's are not a good choice for the front IMO. I ran 225/60/15's on cop wheels for awhile on my Duster, even those were very close to the fenders. And the 235/60/15 is 26.1" tall, which is pretty much the height limit for something of that width.

You may get away with it if you have the ride height raised with the torsion bars, but that causes it's own problems. I would suggest going down to 225/60/15 or 215/65/15 (if you want to keep the tires at 26")
 
Ya I think i will down size the fronts , The rear is tight too with no mods and 255 60 15 . may put front on back and two new for front .
 
Chevy rick said:
Ya I think i will down size the fronts , The rear is tight too with no mods and 255 60 15 . may put front on back and two new for front .
Click to expand...

That’s an idea. 255/60/15 does work on the back of some stock Darts, but everything pretty much has to be perfect and even then some cars don’t have the room for them without some trimming on the quarter lip. The 235/60/15’s should fit well on the back with plenty of room. Depending what that fit looks like you could consider going to 245/60/15’s next time around.
 
How about a pair of 15 x 6 brand new cop wheels. They have between 3 3/4 to 4 inch backspace ( depends on how you read the tape measure ) Let me know.


Frank
 
The true cop car wheels are 15 x 7, inside bead seat to inside bead seat. Someone may be making them in 6" widths, but I'll bet they don't have OEM numbers or the Pentastar on them.
 
duster2 said:
How about a pair of 15 x 6 brand new cop wheels. They have between 3 3/4 to 4 inch backspace ( depends on how you read the tape measure ) Let me know.


Frank
Click to expand...

They're one or the other, "how you read the tape measure" does not determine the actual backspacing. Lay a straight edge across the outer edge of the rim (flat against the rim, not the tire) and measure straight down to the wheel mounting surface, the measurement at the edge of the straight edge is your backspacing.

If they're brand new and 15x6, they're probably these, which have a 3.75" backspace (+6 offset).
Wheel Vintiques 69-5612334 Wheel Vintiques 69 Series Chrysler Police Black Wheels | Summit Racing

225/60/15 would still be the largest you could go.
 
72bluNblu said:
They're one or the other, "how you read the tape measure" does not determine the actual backspacing. Lay a straight edge across the outer edge of the rim (flat against the rim, not the tire) and measure straight down to the wheel mounting surface, the measurement at the edge of the straight edge is your backspacing.

If they're brand new and 15x6, they're probably these, which have a 3.75" backspace (+6 offset).
Wheel Vintiques 69-5612334 Wheel Vintiques 69 Series Chrysler Police Black Wheels | Summit Racing

225/60/15 would still be the largest you could go.
Click to expand...
Ya I saw them too , they dond change the dementions from rotor to fender on any size its all taken out of the back , no good for me .
 
Chevy rick said:
Ya I saw them too , they dond change the dementions from rotor to fender on any size its all taken out of the back , no good for me .
Click to expand...

Actually they have the same offset as the factory 15x7's (+6), so even though the backspacing changes the center line of the rim stays exactly the same. The 15x6's lose a 1/2" of rim on both the inside and the outside compared to the 15x7's.

The only difference might be that because the 15x6's are the smallest rim approved for a 225/60/15, the 225's might be a little more squeezed on the 15x6's than on the 15x7's. So a little clearance might be gained. It would be a fairly small difference though.
 
Modify the bottom front edge of your fender lip and cut it for clearance. I think 70-72 dart/demon has brace you can push out 72blunblu would know.
 
autoxcuda said:
Modify the bottom front edge of your fender lip and cut it for clearance. I think 70-72 dart/demon has brace you can push out 72blunblu would know.
Click to expand...

Yeah the Darts/Demons/Dusters all have these lower fender braces. The bumper end has an oval slot, so you can sometimes gain some clearance at the corner by adjusting the brace all the way out.

img_8970-jpeg.jpg


img_8967-jpeg.jpg


For 225/60/15's the most you should have to do is adjust the brace though. If you wanted to make the 235's fit without having the car raised up with the torsion bar adjusters you'd probably have to cut the corner of the fender lip back at the very least. On my car I did that, and also lengthened the lower brace from about 12" out to 14". That pushes the lower corner away from the tire and allows for more room. In my case that's what was necessary for the 275/35/18's I run up front with my lowered ride height.

These are my braces compared to originals. That's about the most you can push without totally distorting the fender and the fender to lower valance seam.

img_1950_zps72a4664c-jpg.jpg


And this is the corner treatment
8d8321b9-c002-4e8e-aafe-232ae50c7b33-jpeg.jpg


But that's not the only issue with the 235/60/15's on 15x7's with a 4.25" backspace. That combination actually puts the outside of the tire as close to the fender as my 275/35/18's are, in addition to the 235's being taller (26.1" vs 25.6"). At a higher ride height I managed to run the 275's without rolling my fender lips, but as soon as a lowered the car even slightly I had to roll the fender lips. At my current ride height the fender are rolled, as well as "pushed" out using the fender roller. So what I'm saying is the 235/60/15's are going to be tough to keep up front unless you want to start modifying stuff or raising the ride height.

Pictures don't always capture it, but there is an outward bulge on my fenders at the wheel opening. This picture shows it a little, if you look at the front fenders compared to the rear quarters they look similar. And the rear quarters on the Dusters/Demons are flared out.
img_9631-jpeg.jpg


My ride height. If you look at the fender/valance area you can also see how the lower fender corner is pushed out and trying to take the valance with it.
img_9963-jpeg.jpg
 
I do , indeed know how to read a tape measure and have seen so many wheels that are supposed to be one backspace , when you actually measure them , they are not what was advertised. I measured one of the four 15 x 6 cop wheels I have in stock and got 4 inch backspace. Online it says 3 3/4 .

Frank
 
duster2 said:
I do , indeed know how to read a tape measure and have seen so many wheels that are supposed to be one backspace , when you actually measure them , they are not what was advertised. I measured one of the four 15 x 6 cop wheels I have in stock and got 4 inch backspace. Online it says 3 3/4 .

Frank
Click to expand...

online is wrong

they are 4” to the seat. But if you put a flat board across very edge of the rim and then measure to the rim contact edge should be 4 1/4” or little more than 4”
 
duster2 said:
I do , indeed know how to read a tape measure and have seen so many wheels that are supposed to be one backspace , when you actually measure them , they are not what was advertised. I measured one of the four 15 x 6 cop wheels I have in stock and got 4 inch backspace. Online it says 3 3/4 .

Frank
Click to expand...

Sorry, but if most of the wheels you measure don’t have the advertised backspace then it’s most likely that you’re measuring it incorrectly. In this case it’s possible you don’t have the exact wheels I linked, but they still only have one measurement.

Also, just FYI, pretty much all wheels produced in at least the last 30 years have their specifications cast or stamped directly into them. Cast wheels typically have the diameter, width and offset cast into the back side of the wheel where it can’t be seen. Steel wheels are stamped with the same info, frequently on the inside of the hoop so it’s covered by the tire or on the back side of the wheel depending on the style.

Like this. In this case, 17x9, ET 0 (ET is offset). So offset is +0, which is a 5" backspace
img_3647-jpg.jpg


Which is exactly what you get measuring from the outer edge of the lip to the mounting surface
img_3645-jpg.jpg



autoxcuda said:
online is wrong

they are 4” to the seat. But if you put a flat board across very edge of the rim and then measure to the rim contact edge should be 4 1/4” or little more than 4”
Click to expand...

He’s not talking about the original 15x7” wheels that all have a 4.25” backspace. He’s talking about a new set of 15x6’s.

Backspace is properly measured from the wheel mounting surface to the outside lip of the rim, not to where the tire seats. Width is measured tire seat to tire seat. Couldn’t tell you why it’s different, but those are the definitions. If it were up to me width would be outside to outside too, because that's easier to measure. It makes sense that backspace is to the outside, you can't measure directly from the wheel mounting surface to the tire seat. And, by measuring to the outside of the lip the backspace spec gives you the exact clearance of the rim to the springs. So, hard parts to hard parts.

18x9offsetspecs-jpg.jpg
 
my brothers 68 barracuda has the 73 disc brakes we had 15x6 cop rims made with 4.5 backspace and ran a 235 60 15 tire and a 225 60 15 looked good on the fronts. the 4.5 backspace is the ticket
 
You must log in or register to reply here.
-

Back
Top