Tires on 71-72 Roadrunner

[Braden]

Im planning on restoring either a 71 or 72 Roadrunner and i was wanting to know the safest, biggest rear tires i could put on the back without having to make tubs. i was looking at 305/35R18 didnt know if this would be to big or if i could go bigger. thanks

[tuffbird72]

The biggest tire I've been able to fit without rubbing on my 72 RR was a 295/35R18 drag radial. This is about 11.7in wide and I run a 10in rim. Unfortunately I completely forgot my offset but I know it's different than the 17x8s I use for cruise-ins. I seem to recall trying to drop a 305 on the rim as a test and I got inner and outer rubbing so we backed it down to the 295.

Not sure if this helps, but make sure the rim you are using is putting the tire spot on center between the inner and outer well and the 295 will fit nicely...just don't try putting a couple of passengers in back and make sure your torsion snubber is in place because the further into the wheel well that tire goes, you WILL get rubbing. I don't have airshocks or anything like that, but if I carry my buddy "big Mike" I have to put on the 275s on the 17in rim to avoid the rub.

[Braden]

thanks tuffbird72 i was going to try and get Micky Thompson Street radials and rims all the way around but i cant seem to find them in 295/35R18. what brand are you using or would suggest ?

[dangina]

to ad to this question, whats the biggest wheels can we put on the front of the car for 18" rims? I'm looking at 18x9.5" +15mm offset wheels and wondering if they'll fit in there

[72bluNblu]

In the front these cars basically use the same suspension as the E-bodies, same UCA's, frame rails, etc. So, with that in mind, I run 275/40/17's on 17x9's with 5" of backspacing (0 offset) on my Challenger. The 17" rim is limited on backspacing because of the outer tie rod end, max is about 5.25".

But, an 18" rim clears the outer tie rod entirely, so backspace is no longer an issue. I think 18x9.5's with a 15mm offset would fit just fine. You might need a small spacer to keep from rubbing on the frame, but depending on your brakes up front that may not be an issue since a lot of aftermarket disks add 3/16" to 1/4" to the track. For the E bodies, 0 offset is about where you need to be, give or take a little. And of course its better to have a little too much backspace as you can always add a small spacer.

As far as tire size, a 285 is the widest you can go on a 9.5" wide rim, and I don't think you'd have any issues clearing a 285 with a small spacer to keep it off the frame. The 275 uses everything out to the fender on my Challenger, but these cars have more fender room. I've heard of a 295 being run up front on these cars. I'd be willing to bet you could run 18x10's up front with 295's with the right backspace, probably pretty close to 0 offset, or ~5.5" of backspace.

In the back, if a 295 will fit between the stock location springs and the quarter, you could easily run a 305 with a set of Dr. Diff's offset hanger/shackle kits. The offset hanger kit adds 1.5" per side on these cars, so a 325 would probably fit pretty easily.

[tuffbird72]

Hi Braden,

I run the BFG g-Force T/A Drag Radial for the 295 setup. I bought mine from Tirerack and had the local discounttire guys install them for me. The specific size was to keep me from having to adjust my speedo gear to compensate. The 295/35/18 lines up within an inch diameter from the original tires so speed at 60 comes out to actual speed of 59.

72blunblu has a great idea on the offset shackle kits. When I came up with my setup, it was before these were available. Thanks for that one blu...I'm going to go back and investigate the shackles idea. I've always wanted to fit 12"+ tires in the back. I was actually thinking of four-linking the rear end, installing a 1 inch tub adjustment to push the inner well against the framerail but the shackles might just get me where I want to be as well.

I may try to get a 335/35/18 in back since I can only find the 325 in 19in wheel size.

[72bluNblu]

Here's a link to the offset hanger/shackle kit from DoctorDiff

http://www.doctordiff.com/71-72-b-body- ... e-kit.html

Looks like he's currently out of stock, but I'm sure Cass will get some more in soon, I've seen them available a few times now.

As far as the tire size, the offset shackle kit will put the outer edge of the leaf springs in-line with the inner edge of the wheel tub. I measure the wheel tub on my '71 Satellite at 14.75", so I think safely you need an 1" of clearance (1/2" on each side) to keep from rubbing. So that puts you at ~13.75" for a tire section width.

A 335/35/18 would be 28.5" tall, and I couldn't find anything in that size anyway. I did find some 335/30/18's, they have a section of 13.5" and a height of 25.9", which is pretty decent. A little taller would be nice, but the next profile up is too tall. Here's the BFG KDW2 in a 335/30/18, that's a great tire. Pretty soft compound, I ran them on my SRT4 for awhile.

http://www.tirerack.com/tires/tires.jsp ... &tab=Specs

Looks like BFG also has a drag radial in a 345/30/18. That has a 13.8" section, and is 26.2" tall. Should be about the biggest thing you could fit in the back with an offset shackle...

http://www.tirerack.com/tires/tires.jsp ... &tab=Specs

[dangina]

In the front these cars basically use the same suspension as the E-bodies, same UCA's, frame rails, etc. So, with that in mind, I run 275/40/17's on 17x9's with 5" of backspacing (0 offset) on my Challenger. The 17" rim is limited on backspacing because of the outer tie rod end, max is about 5.25".

But, an 18" rim clears the outer tie rod entirely, so backspace is no longer an issue. I think 18x9.5's with a 15mm offset would fit just fine. You might need a small spacer to keep from rubbing on the frame, but depending on your brakes up front that may not be an issue since a lot of aftermarket disks add 3/16" to 1/4" to the track. For the E bodies, 0 offset is about where you need to be, give or take a little. And of course its better to have a little too much backspace as you can always add a small spacer.

As far as tire size, a 285 is the widest you can go on a 9.5" wide rim, and I don't think you'd have any issues clearing a 285 with a small spacer to keep it off the frame. The 275 uses everything out to the fender on my Challenger, but these cars have more fender room. I've heard of a 295 being run up front on these cars. I'd be willing to bet you could run 18x10's up front with 295's with the right backspace, probably pretty close to 0 offset, or ~5.5" of backspace.

In the back, if a 295 will fit between the stock location springs and the quarter, you could easily run a 305 with a set of Dr. Diff's offset hanger/shackle kits. The offset hanger kit adds 1.5" per side on these cars, so a 325 would probably fit pretty easily.

That settles it. I'll go with 18's instead of the 17". I'm running a bump steer kit on my car which lowers the outter tie rod even more, so 18" rim would give me more clearance. I'm also running doctor diffs old 13" big brake kit with gen 2 viper calipers. the hub he uses I believe is 3/4" longer than our stock oem hubs. which is why I was looking at a 19x9.5 with a positive offset. I believe it was so they could run stock mustang rims on with no issues(that and mustang rims are so cheap). I think I'll run the 275 tire as the sizes are more common which equals cheaper. That being said what kind of offsets should I be looking for? I mentioned +15 just for the low offset, but should I be looking at a even more +offset like a +20 or +30?

[72bluNblu]

That settles it. I'll go with 18's instead of the 17". I'm running a bump steer kit on my car which lowers the outter tie rod even more, so 18" rim would give me more clearance. I'm also running doctor diffs old 13" big brake kit with gen 2 viper calipers. the hub he uses I believe is 3/4" longer than our stock oem hubs. which is why I was looking at a 19x9.5 with a positive offset. I believe it was so they could run stock mustang rims on with no issues(that and mustang rims are so cheap). I think I'll run the 275 tire as the sizes are more common which equals cheaper. That being said what kind of offsets should I be looking for? I mentioned +15 just for the low offset, but should I be looking at a even more +offset like a +20 or +30?

Well, the offset you'll need will depend entirely on how much distance was added with that brake kit. With the stock rotors, you should be at 0 offset. That's what my 17x9s are at, and with 275's they're pretty close to the frame at full lock. Probably only about 3/8" clearance. So with the stock brakes I would bet that even a +15 offset would require a small spacer to keep the tires off the frame.

But, if the hubs for that kit really widen the track 3/4" per side, then you'd be looking at +20 for an offset. You'll have to determine exactly how far that kit moves the hub face out, and then just add that to the offset on the wheels.

[dangina]

That settles it. I'll go with 18's instead of the 17". I'm running a bump steer kit on my car which lowers the outter tie rod even more, so 18" rim would give me more clearance. I'm also running doctor diffs old 13" big brake kit with gen 2 viper calipers. the hub he uses I believe is 3/4" longer than our stock oem hubs. which is why I was looking at a 19x9.5 with a positive offset. I believe it was so they could run stock mustang rims on with no issues(that and mustang rims are so cheap). I think I'll run the 275 tire as the sizes are more common which equals cheaper. That being said what kind of offsets should I be looking for? I mentioned +15 just for the low offset, but should I be looking at a even more +offset like a +20 or +30?

Well, the offset you'll need will depend entirely on how much distance was added with that brake kit. With the stock rotors, you should be at 0 offset. That's what my 17x9s are at, and with 275's they're pretty close to the frame at full lock. Probably only about 3/8" clearance. So with the stock brakes I would bet that even a +15 offset would require a small spacer to keep the tires off the frame.

But, if the hubs for that kit really widen the track 3/4" per side, then you'd be looking at +20 for an offset. You'll have to determine exactly how far that kit moves the hub face out, and then just add that to the offset on the wheels.

thanks for the reply, sometimes the simplest answers are the best ones at least now I know a 17x9 0 offset fits - I can go from there. Do think its possible to get a 18x10 in there?

second question, whats the lowest you can slam the car down without tire interference? do you think you could still run a 17x9 rim with a 275 tire if you dropped it 2 inches? Curious as I'll be running the magnumforce drop spindles on my car...

[72bluNblu]

thanks for the reply, sometimes the simplest answers are the best ones at least now I know a 17x9 0 offset fits - I can go from there. Do think its possible to get a 18x10 in there?

second question, whats the lowest you can slam the car down without tire interference? do you think you could still run a 17x9 rim with a 275 tire if you dropped it 2 inches? Curious as I'll be running the magnumforce drop spindles on my car...

My Challenger sits with my header flanges ~3.5" off the ground with my 275's, and since I added a little negative camber (-.9*), I haven't had any tire interference issues. So yes, you can drop the car 2" from factory ride height and still run 275's in the front. I actually used to run the car lower, I raised it up about a 1/4" because I got tired of dragging over speed bumps all the time.



As far as an 18x10, yes, I think it can work on a 71/72 B body. A 275 will fit on a 10" wide rim, so I don't see an issue there. As I mentioned before, I've heard of 295's being run on the front of the 71/72 B bodies.

But, I DO see a problem with running an 18x10 with the magnumforce drop spindles. The biggest problem with running wide rims in the front is clearing the outer tie rod end. On 17" or smaller rims, the rim interferes with the outer tie rod starting at around 5.25" of backspace on a B/E suspension. With my 17x9's and 5" of backspace, I only have about 1/4" to the tie rod from the lip of the rim. Maybe a smidge less. A 10" rim at 0 offset has 5.5" of backspace.

Normally, 18" rims solve the tie rod problem. The outer tie rod actually fits inside the lip of the rim of an 18" wheel, so you can run more backspace. So an 18x10 would be a piece of cake. But, since the drop spindle moves the wheels with relation to the tie rods, you go right back to having interference issues, just like if you had a 16" rim on a stock suspension. So no, I don't think you'll be able to run a 18x10 with 2" drop spindles. The offset you'll need on the wheels will put them into the tie rods.

Why do you want to run drop spindles? They aren't necessary to lower the car 2". My Challenger is lowered entirely with the torsion bar adjusters. Yes, it reduces the amount of available suspension travel. But, since I have 1.12" torsion bars, I don't need all that much suspension travel anyway. I run "button" style poly bump stops with less than 1.5" from the bumpstop to my frame, and have never bottomed the suspension on my car. I actually used to run magnumforce drop spindles on my Challenger, before I figured out I didn't need them. My car sits just as low now, lowered with the torsion bar adjusters, as it did with the drop spindles.

[dangina]

But, I DO see a problem with running an 18x10 with the magnumforce drop spindles. The biggest problem with running wide rims in the front is clearing the outer tie rod end. On 17" or smaller rims, the rim interferes with the outer tie rod starting at around 5.25" of backspace on a B/E suspension. With my 17x9's and 5" of backspace, I only have about 1/4" to the tie rod from the lip of the rim. Maybe a smidge less. A 10" rim at 0 offset has 5.5" of backspace.

Normally, 18" rims solve the tie rod problem. The outer tie rod actually fits inside the lip of the rim of an 18" wheel, so you can run more backspace. So an 18x10 would be a piece of cake. But, since the drop spindle moves the wheels with relation to the tie rods, you go right back to having interference issues, just like if you had a 16" rim on a stock suspension. So no, I don't think you'll be able to run a 18x10 with 2" drop spindles. The offset you'll need on the wheels will put them into the tie rods.

Why do you want to run drop spindles? They aren't necessary to lower the car 2". My Challenger is lowered entirely with the torsion bar adjusters. Yes, it reduces the amount of available suspension travel. But, since I have 1.12" torsion bars, I don't need all that much suspension travel anyway. I run "button" style poly bump stops with less than 1.5" from the bumpstop to my frame, and have never bottomed the suspension on my car. I actually used to run magnumforce drop spindles on my Challenger, before I figured out I didn't need them. My car sits just as low now, lowered with the torsion bar adjusters, as it did with the drop spindles.

question would this be true for say oem spindles running 10" rims, but I mentioned that the hub I'm using is 3/4" longer than stock so wouldn't I have to have a rim of 6" backspace before i start to see issues? I only ask because I have the spindles, brakes ect. mounted on my car, I'm running a 13" disk brake viper caliper setup, if I went back to a oem spindles (which I already sold) I'd also have to fabricate a new bracket for the viper calipers on 13" disks.

[72bluNblu]

question would this be true for say oem spindles running 10" rims, but I mentioned that the hub I'm using is 3/4" longer than stock so wouldn't I have to have a rim of 6" backspace before i start to see issues? I only ask because I have the spindles, brakes ect. mounted on my car, I'm running a 13" disk brake viper caliper setup, if I went back to a oem spindles (which I already sold) I'd also have to fabricate a new bracket for the viper calipers on 13" disks.

Yes, you'd be able to run rims with like 6" of backspace because of your additional offset, but you'd NEED rims with 6.25" of backspace to keep the wheel in the same place as an 18x10 with 5.5" of backspace and the stock brakes.

You might be able to get away with it, I haven't done enough fitting with the larger rims and tires to figure out exactly how much extra space there is to the fender vs. the E body. The frame clearance is the same, but because of the larger fenders there's definitely more room on that side. I don't think you'd have any problems with a 275 wide tire up front on an 18x10 with 6" of backspace and your brake set up, but I don't know how much wider you'd be able to go before you had fender problems. And since a 275 will fit on a 9" rim, you could avoid the problem entirely if that was as wide as you could go. Even a 285 on a 9.5" rim would let you keep things in about the same place.

If I get a chance I'll try mounting my 17x9's with 5" backspace and 275/40/17's on my SSP, that should give me a much better idea of how much extra room there is to play with on the fender side.

[dangina]

[quote="72bluNblu"]
If I get a chance I'll try mounting my 17x9's with 5" backspace and 275/40/17's on my SSP, that should give me a much better idea of how much extra room there is to play with on the fender side.[/quote
]
thanks that would be greatly appreciated!!

[dangina]

curious 72blu have you had a chance to do this yet?