I'm looking for some 17" wheels for my car, a 71 plymouth scamp. Most of the wheels I'm finding are in mm. My rear now is a 14x70x245 and my fronts are 17x70x225. What offset do I need for my rear and front for 17" wheels.
confused on backspacing
- Thread starter coreyg
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69_340_GTS
Well-Known Member
On average, and assuming you don't want to modify the car a lot, these cars like around 4.50" backspacing on 7" wheels (front and/or rear), and 5.00" backspacing on 8" wheels (normally rear only). Does not matter if the wheels are 14", 15", or 17", because wheel diameter has no bearing on backspacing at all. I think where you'll see the metric dimensions is for "offset". A 7" wheel with 4.50" backspacing has 1" of positive offset or around +25mm. An 8" wheel with 5.00" backspacing also has 1" or +25mm offset.
Lustle
Well-Known Member
I would highly suggest you get under there and measure, measure, measure. 1972, my back rims are 15x8 4.75 back space. It centers the tire perfectly. I'm exactly half an inch from the unmoved spring and unrolled fender. But before I picked those rims and tires. I got under there and measured. First make sure the car is level. Then run a plumbob from the two contact points. The spring and the inner fender lip. Measure between the two. Subtract 1 inch (1/2" per side for movement while driving). This is your max section width on a centered wheel. Now measure from the front plumb bob to the wheel mounting surface. Then from the back plumb bob to the wheel mounting surface. This will tell you what back spacing to get. Don't just "assume" that what fit others will fit yours. For all you know that rear is not original and wasn't centered right when it was put in. Or maybe the springs were moved. Or who knows what else. Make sense?
dano
Evil Handy Man
We need to know more bout your car.
Have you converted to LBP or are you still stock SBP?
If LBP how was this done as it will effect your offset front and rear.
Have you converted to LBP or are you still stock SBP?
If LBP how was this done as it will effect your offset front and rear.
What did you use for your two contact points for the measurement?
Lustle
Well-Known Member
Leaf spring and inner fender lip. Those are really the only two things you can hit under there. The wheel well itself is huge, I'll never know why ma mopar didn't make use of it.
I have the wilwood conversion up front so I can pick either one, the rear is still stock drums but I'm planning to do the brake conversion back there also.
This is not accurate whatsoever. On a 14" or 15" wheel you can't run more than about 4.75" of backspacing in the front because of contact with the UCA, regardless of width. That basically limits you to a 7" rim in the front. Yes, if you work it out just right you can use a 15x8", but there isn't much point because you can't run a tire wide enough to matter. You're basically stuck with a 235, and that will fit on a 7" wide rim.
If you step up to a 17" rim, you can run as much as about 5.6" of backspace, the rim clears the UCA (with a low profile zerk on the upper ball joint). Most rims start to interfere with the outer tie rod around 5.6" or 5.7" of backspace if you're using 73+ disks as the reference. Some can run a little more, but not most. 5.6" of backspace lets you run an 8" wide rim with ease, and you can run 245/45/17's or even 255/45/17's without issue or interference.
If you go to an 18" rim, you clear the outer tie rod. An 8" rim can have as much as 6.3" of backspace, again using the 73+ disks as the reference. A 9" rim will now fit up front, usually with the best fit around 6" to 6.2" of backspace. You do have to watch the UCA as full lock with that wide of a rim, tubular UCA's come in handy to run an 18x9 or 18x9.5. But now you can run 275/35/18's in the front, like I do on my Duster.
These numbers are wrong too. A 7" wheel with 4.5" of backspacing has an offset of +13. An 8" wheel with 5" of backspacing also has an offset of +13. Backspace and offset are not measured from the same places.
For the OP, do you know the part # of the wilwood kit? There's more than one, and the offset added by the brakes is different with different kits. What kind of tire width are you looking for? Backspace requirements change with the width of the wheel. Do you want to keep a 225 wide tire up front and a 245 out back and just go to a 17" rim? You could run 245's all the way around pretty easily, although that's probably about as wide a tire as you can fit in the back with the stock spring locations.
Its the 140-11023 wilwood kit. I am running qa1 tubular upper control arms. I want to run the widest tire all the way around so if I can do a 245 on all tires I will. The other issue I'm going to run in the the center bore size that wilwood kit is. It has a 82.3mm center bore size I've notice most wheels are around the 72ish center bore size.
Ok, that kit will increase the offset by .2" compared to the drums. That's actually a little less than what the 73+ brakes add. The center bore could be a problem, I didn't realize those hubs had that wide of a register.
If you want to run as wide as you can go, I would say stick with a 245/45/17 all the way around. You might be able to cram a 255 in the back, but usually that requires cutting/rolling on the quarter lip and even then not all cars can manage it. A 245 is safer, especially if you're already running 245's in the back.
So, you'd be looking for a 17x8. I happen to know of a 17x8 that has a 5.25" backspace, which would work in the front, but it's a BBP wheel.
http://www.summitracing.com/parts/vsw-141h7865gm19/overview/
In the front it's an easy fit, they should leave almost an inch to the frame and an extra 1/4" to the fenders compared to my 275's.
It would work in the back, but only if you switch out to BBP axles (they increase the track width), and obviously you'd need the 5x4.5" pattern. A small spacer might also be necessary to keep you off the springs in the back even after the BBP conversion. Those are the same rims I have on my Challenger (mine are 17x9). The center bore really is 83mm, they clear pretty much any hub register that will fit on these cars.
Here's a larger picture of my Challenger to show the rim design...
69_340_GTS
Well-Known Member
Where did I say he should run more than 4.75" b/s on the front? I said 4.50" b/s with any diameter wheel. How is that "not accurate whatsoever"? On a stock Dart (which one could have only assumed he had based on the OP info) that much b/s will normally cause the tires to hit the frame rails at full lock. Trying to make it simple for the guy... He did not originally mention any suspension modifications, nor did he mention any desire to run
anything larger than a 17" wheel. Now that you have a lot more info on the OP's car, now I'm "not accurate whatsoever" because I posted way before you had all this additional information? Give me a frickin' break!
Yes I blew it on the offsets. Should be +12.7mm. My math sucks when I'm tired.
You didn't say he should run more than 4.75" of backspace on the front. Which is exactly why your information isn't accurate. With a 17" wheel you can run more than 4.75" of backspace, and you SHOULD.
You can run 17x8's, with perfectly stock suspension, with a 5.25" backspace and 245/45/17's and not hit anything. Not the frame, not the fender, nothing. You can't run that much backspace with a 14 or 15" rim because your rim will hit the UCA. So, when you said this
your information was in fact inaccurate. The OP's first post said he wanted to run 17's, which will let you run as much as 5.6" of backspace, even with the stock suspension. You can't do that with a 14 or a 15" rim.
Ok got some measurement from the front of the car.
from the hub mounting surface to the inside fender is 5.25"
from the fender to the frame rail is 16.75"
from the hub mounting surface to fram is 11.25"
and from the hub mounting surface to tie rod is 5.25"
from the hub mounting surface to the inside fender is 5.25"
from the fender to the frame rail is 16.75"
from the hub mounting surface to fram is 11.25"
and from the hub mounting surface to tie rod is 5.25"
So do I need to worry about offset with 17x8 and 5.25 backspacing?
69_340_GTS
Well-Known Member
Nothing I said was incorrect (except for my offset calculation). It may not have been the encyclopedic & comprehensive version of wheels & tires for A bodies, but don't tell me my information was incorrect. All I do is try to tell people what has worked for me. If that isn't good enough, too bad.
71DodgeDemon340
Well-Known Member
Also dont forget if your shooting for 4.5 bs on the rear and find wheels with 5.5 bs you can use a one inch spacer to get the bs you want.
I found wheels with 4.5 backspacing will that also work up front. The wheel that was on there before has a backspacing of 3.75 and its width is 7", will a 8" with 4.5 work up front
The only way they'll work in the front is if you run a 225. Any wider than that and they'll rub on the fenders.
To run a 17x8 on the front and make it worthwhile you really need to have at least 5" of backspace. Any less than that and your tire width is limited to the point that you don't need an 8" wide rim anyway.
In the back they'll probably limit you to a 235. Those are BBP wheels so I assume you're converting. What axle do you have in the back? 8 3/4?
71DodgeDemon340
Well-Known Member
Heres the wheels I'm looking at. They are 17x8 with 4.5" backspacing will these work for both front and back.
Look good, replace the foose center cap with a all black one and youll be set
I still need to do the rear conversion for the bbp but right now I'm just concerned with my fronts since I cant put any wheel on. I'm going to do some more searching today for wheels with a 5" backspace but I really like those wheels so if I can only run 225 up front thats what I'll do. Its not going to be a track so 225 will be fine atleast I think
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