Need Help with Wheel / Tire set up......Please help !!!!

[aiki99]

Hey Guys....just finishing up a 2 year project on a 1970 Challenger pro-touring with air ride and 4-wheel disc brakes...Finally down to the details and stuck on wheel fitment.......Trying to fit 20" rims on the car and wanted to know what is the maximum size tire for the rear and front without passing wells or turning issues......Any help would be great....also if 20's do not fit what is my maximum rim size......front end is rebuilt stock, ride-tech 4-link rear with stock wells...air controlled shocks all around so able to control height...

Here are the specs i was thinking....

Fronts:
SIZE: 20x8.5
OFFSET: +36 millimeters
BACKSPACE: 6.17 inch
CENTERBORE: 70.8 millimeters

Rears:
SIZE: 20x10
OFFSET: +45 millimeters
BACKSPACE: 7.27 inch
CENTERBORE: 70.8 millimeters

[Chryco Psycho]

No reason why 20" rims will not fit , it is the overall size of the tire that matters , but I believe the backspacing is going to be the down fall , you have .617 back space on the front , typical is closer to 4.5 , same with the rear , the typical would be approx 5.5 on a 10 " rim or the rimm will sit too far under the car & interfere with the leaf spring

[Jamie]

I have 18 x 8.5 front  5.25" backspace with 245 40. rear 18 x 10  6.25 backspace  285 40 tire.  rears could not fit more perfect. fronts are tucked a little too far in wheel well but function great, no rubbing.  front offset at 4.5 would be perfect for me. 
 I am not sure how small of a tire you would need in the front though, 255-35-20?  rear would be 275-40-20 i think

[72bluNblu]

I have 275/40/17's on all 4 corners of my Challenger on 17x9" rims with a 5" backspace. Front was tight on the fenders, I added a little more negative camber to clear everything.

The rims you have listed have too much backspace, front and rear. 20's will clear the tie rod ends, so you can run more backspace than a 17" (max is about 5.125), but you'll probably end up hitting the frame on turning with that much. Obviously it would depend on the width/height of the tires you choose, but I don't think I'd want to start with more than 5.5" of backspace on anything.

As for tire size, your max height in the front is going to be around 26". More than that and you'll run into issues. Even on my car, which is pretty low, I had to remove the fender braces that ran across the inside middle of the fender. And the 275/40/17's I run are only 25.7" tall. With air ride and anything more than 26" tall in the front, you won't get very low. Not to mention hitting the rear corner of the wheel opening.

I am not sure how small of a tire you would need in the front though, 255-35-20?  rear would be 275-40-20 i think

A 255/35/20 is going to be 27" tall tire. Way too tall for the front. A 255/30/20 might work (26" tall), or a 245/30/20 (25.7"). Same with the rear, a 275/40/20 would be 28.7" tall tire! Not a chance that'll fit. You'd have to go 275/30/20 (26.5"). Even a 275/35/20 would be 27.5" tall, which might still probably be too much, especially at that width. I know folks have run 28" tall tires in the back, but that usually requires wheel well mods, or having the suspension sky high in the rear.

[aiki99]

Was hoping to make this set work for this car since it was such a great deal......$600 with brand new tires....basically free rims.. The tires that are on the rims are 255/35ZR20 front and 285/30ZR20 rear. I have no leafs in the rear and want to keep the car at a low stance with the wheels tucked in.....I basically want to fill the wheel wells but also dont want any rubbing or turning issues.......but if 20's dont fit then i guess i will have to go smaller......

Jamie if you could post pics of your 18's that would be great so I can see how the car looks....Thanks

Also if anyone has 20's on their car please post pics and tell me how they fit......

[crash340]

Jamie
are your rear springs set inboard a little or do you have the fender lips rolled to use 18 x 10 on the rear?

[aiki99]

ok....so my plan wont work.....starting from nothing.....what would you guys recommend for a pro-touring car with air ride....front end has air shocks with US tool fender braces installed....stock fenders.....rear end has 4-link set up with stock wells....no leafs...looking for a staggered look. the widest wheels but tucked in so i can keep the car at a low stance.....if you have pics of your cars please post !!!! that would help a great deal......

[aiki99]

just tried to add pictures of my car but files are to big....

[72bluNblu]

As I already mentioned, in the front you can go as wide as 275/40/17. 18's will buy you a little fender clearance if you go with a 9" rim and about 5.25-5.4" of backspace, but I don't think you'll be able to go bigger than 275/35/18 even then. If you're looking for staggered, you might step down to a 255 wide tire, but keep the height to 26". That will give you more room to lower with the air ride too. So that would be a 255/40/18, or a 255/45/17.

With a 4 link in the back and stock wheel wells you can run a 295 without issue, probably even a 305. I don't think a 315 would work on a lowered car. I have 275's on mine in the back with a 1" spring relocation that basically allows full use of the stock wells, and I have a good 3/4" of space on either side I could fill with tire and still have a little clearance.



Front's



Back

[Jamie]

My springs are offset, sheetmetal untouched. I still Have 3/4 " between tire and leaf spring with the 10" wheel.
As far as you front goes I am not sure how much room is available with the braces you mentioned and also to allow for turning with suspension lowered. My front is cranked down a bit and nothing rubs. I would try to find a  wheel from junk yard from a 95-03 mustang and see how it fits under your fenders. Cheap way to test, I think the offset is close? If you lived near me you could bolt mine on and have a look see!

[72bluNblu]

Most of those mustang rims have a 5.72" backspace, which will be too much for an ebody. In a 17" wheel they'll hit the outer tie rod, and with an 18" I suspect they'd hit the frame when turning.

The inner fender braces will have to be removed for just about any large tire if the car is lowered. Keep in mind that the 275/40/17's I run are only 25.6" tall, and my car really isn't that low. My headers still clear most speed bumps. I've raised it up a bit since the pictures I posted, but the inner brace would still need to be out of it. It's mostly the width of the tire, because of the way the brace comes down to the fender. The center of the brace is high enough, but the outer portion reduces the clearance to the fender.