Appropriate Wheel Offset for 18" Wheels?

[MuuMuu101]

Hey there, I found some wheels on CL. That seem like they'd fit on my '68 Dart. They're currently on a Mustang, 5 x 4.5" bolt pattern. They're 18 x 8's on the front with a 245/40/18 and 18x10's on the rear with a 275/35/18. The only problem is I'm waiting for a response on what offset they are. If you look at the pictures, it kind of seems like the rear wheel is sticking past the quarter panel, so it might have less of an offset. If I get these, I'd probably spend half as much than if I were to get all new wheels and tires.

As of now I don't have my front end together, but I'll be running the whole Hotchkis TVS with Dr Diff's 13" brake kit with Brembo-style calipers (I believe the center bores on Dr Diff's hubs are suitable with Mustang wheels). On the rear I've got the Hotchkis leafs, a stock length A-body 8 3/4, and Dr Diff's 11.7" Cobra Mustang Caliper kit. The whole car will be lowered approximately 1-1.5". I know it's possible with some work to fit a 275/35/18 on the back of a Dart. It might take some work (like trimming or rolling the inner wheel lip).

Approximately what offset would be desired for the front and rear?

 

[grassy]

If the springs are in the stock location, I think you may have to use spacers....

I am running a stock mustang gt rim w/the oem tires..I can get the size if you need, with 1.25 spacers and it is a tight fit...

 

[MuuMuu101]

He said the wheels were originally on a '72 Mustang and he's using some spacers now.

 

[grassy]

He said the wheels were originally on a '72 Mustang and he's using some spacers now.

Sorry, that is the extent of my knowledge...there has to be bunches of folks on this board that know more...

 

[72bluNblu]

First- you will not fit 275/35/18's on a Dart with the stock spring location. You need the 1/2" spring hanger/shackle offset to make it work, and you'll need to trim the quarter lip as well. With the stock spring location the widest tire you'll fit is a 255, especially if you're lowered, and that will still probably need the quarter lip trim. I test fit the 275's from my Challenger on my '71 GT, with a 275/40/17 and a 17x9" rim and 0 offset (5" backspace). I was physically able to get them bolted onto the car, but they were actually touching the quarter and the spring. Just won't work without a 1/2" offset and quarter lip trim.

As far as backspacing goes, in the front with an 18x8 you'll want an offset between 18mm and 40mm, or about 5.25" to 6.2" of backspace. That will clear a 255/40/18, but 255's are usually only recommended for 8.5" to 9.5" rims. On an 18x8 it will be a little squeezed. A 245/40/18 would be a piece of cake. I have 18x9's with a 35mm offset and 275/35/18's on the front of my Duster with Dr Diff's 13" Cobra caliper set up. Same offset. I actually just added 3mm spacers to keep from just touching the frame at full lock, so I'm at 32mm offset on my 18x9's. I did still need to have the hub bore on the rims machined to fit over Dr. Diff's hubs. They're smaller than the stock hubs, but they still aren't small enough for most Ford or aftermarket rims.

In the back, you basically want a 0 offset rim with the stock spring location. But, if you want the rims you linked to fit with a 275/35/18 on an 18x10, you'll need that 1/2" spring offset. For that to work, I think you'd need about 6" of backspace. I believe that rear disk kit adds a little width to the rear track, so you might be able to get away with up to 6.25" of backspace. I wouldn't want less than 6" though, and more than 6.25" will need a spacer.

 

[MuuMuu101]

First- you will not fit 275/35/18's on a Dart with the stock spring location. You need the 1/2" spring hanger/shackle offset to make it work, and you'll need to trim the quarter lip as well. With the stock spring location the widest tire you'll fit is a 255, especially if you're lowered, and that will still probably need the quarter lip trim.

As far as backspacing goes, in the front with an 18x8 you'll want an offset between 18mm and 40mm, or about 5.25" to 6.2" of backspace. That will clear a 255/40/18, but 255's are usually only recommended for 8.5" to 9.5" rims. On an 18x8 it will be a little squeezed. A 245/40/18 would be a piece of cake. I have 18x9's with a 35mm offset and 275/35/18's on the front of my Duster with Dr Diff's 13" Cobra caliper set up. Same offset. I actually just added 3mm spacers to keep from just touching the frame at full lock.

In the back, you basically want a 0 offset rim with the stock spring location. But, if you want the rims you linked to fit with a 275/35/18 on an 18x10, you'll need that 1/2" spring offset. For that to work, I think you'd need about 6" of backspace. I believe that rear disk kit adds a little width to the rear track, so you might be able to get away with up to 6.25" of backspace. I wouldn't want less than 6" though, and more than 6.25" will need a spacer.

Granted, these are just going to be wheels and tires to get me by for a couple years so I don't have to fork over the $2500-3000 I was planning on spending for new wheels and tires. I already spent quite a bit if you've seen my build thread. So I don't mind running 245/40/18's up front.

Ok, so good thing about these wheels is that they're 2 piece wheels. I've got a buddy who knows a wheel guy who could cut the welds and set them to the offset required. I don't mind trimming or rolling the quarter lip or adding a spacer.

I was doing some measuring real quick and I can see where it could get really tight and bad. Take into note that my suspension is in full droop. The wheel well opening seems to be a little more than 11.5" wide (measured from inside to inside higher up), but with the springs in their current configuration I guesstimate it being closer to 11" making this tight (hard to measure with skinny tape measure). I've also got undercoating probably adding a little less room under there. There's also that weird hump at the top that Darts that could be an issue in full compression.

What about something like a 265/40/18? Just a touch taller (probably no bueno for being lowered) but skinnier? Or a 265/35/18 (might look a touch funky because it will be slightly shorter than the front)? If needed be I guess I could go with some 255/40/18's in the rear and keep the 275/35/18's as a mach up tire for the future. Tirerack has some Hancook V12's on closeout for a touch over $250 and they're rated for an 8.5-10" wheel. I guess 1/2" shackles need to be on my list for things to buy in the future.

 

[moparlover]

this little tool, $75 bucks, will tell you exactly what size you need and can save you $100's if not $1000's

http://www.summitracing.com/parts/php-01201

 

[MuuMuu101]

this little tool, $75 bucks, will tell you exactly what size you need and can save you $100's if not $1000's

http://www.summitracing.com/parts/php-01201

I've seen that before. I never bought it because I thought I'd never use it more than once. Plus, my entire front suspension is out of the car right now so it's hard to measure at the moment.

 

[72bluNblu]

What about something like a 265/40/18? Just a touch taller (probably no bueno for being lowered) but skinnier? Or a 265/35/18 (might look a touch funky because it will be slightly shorter than the front)? If needed be I guess I could go with some 255/40/18's in the rear and keep the 275/35/18's as a mach up tire for the future. Tirerack has some Hancook V12's on closeout for a touch over $250 and they're rated for an 8.5-10" wheel. I guess 1/2" shackles need to be on my list for things to buy in the future.

I don't think a 265 will fit with the stock spring location either. When I mounted the 275's on my Dart for mock up, they were physically in contact with both the quarter lip and the springs at the same time, to the point that the wheel was obviously dragging on both sides when rotated. 5mm of space per side isn't going to cut it for clearance, and I don't think you'll be able to get enough out of cutting the quarter lip to make them work on the road.

A 275 really needs that 1/2" offset, and even then, its still pretty much maxed out with the quarter lip trimmed back. With the stock spring location, I think a 255 is as much as you can safely run. And depending on the tire, car, and spacing, even the 255 might take some trimming.

 

[MuuMuu101]

I don't think a 265 will fit with the stock spring location either. When I mounted the 275's on my Dart for mock up, they were physically in contact with both the quarter lip and the springs at the same time, to the point that the wheel was obviously dragging on both sides when rotated. 5mm of space per side isn't going to cut it for clearance, and I don't think you'll be able to get enough out of cutting the quarter lip to make them work on the road.

A 275 really needs that 1/2" offset, and even then, its still pretty much maxed out with the quarter lip trimmed back. With the stock spring location, I think a 255 is as much as you can safely run. And depending on the tire, car, and spacing, even the 255 might take some trimming.

I'm curious now... Because I know there are quite a few cars with a 275 series tires and I never here them mention needing offset shackles. I've got to do some research. I autocrossed with Tomswheels and his '67 Valiant and he was running 265/35/18's all the way around (granted he had an 8.8 in it). What about the Red Valiant or the Green Brick? Anybody know about those?

What needs to be modified for the 1/2" shackles because the idea of how they work isn't really connecting in my head. I'm assuming the perches need to be moved in and the offset shackles move them on the frame side, correct? If not, it makes more sense to pay $150 for the kit instead of $250 on tires (just back two). If so, I'll just do a mini-tub years down the line and move the perches then.

Also, the car needs to be on all 4 wheels within the next 2-3 weeks or so (before school starts hence the rush).

 

[72bluNblu]

I'm curious now... Because I know there are quite a few cars with a 275 series tires and I never here them mention needing offset shackles. I've got to do some research. I autocrossed with Tomswheels and his '67 Valiant and he was running 265/35/18's all the way around (granted he had an 8.8 in it). What about the Red Valiant or the Green Brick? Anybody know about those?

What needs to be modified for the 1/2" shackles because the idea of how they work isn't really connecting in my head. I'm assuming the perches need to be moved in and the offset shackles move them on the frame side, correct? If not, it makes more sense to pay $150 for the kit instead of $250 on tires (just back two). If so, I'll just do a mini-tub years down the line and move the perches then.

Also, the car needs to be on all 4 wheels within the next 2-3 weeks or so (before school starts hence the rush).

There are also a lot of folks with 1/2" offsets, not to mention the 3" spring relocations. You're welcome to try it, but all I can tell you is that on MY '71 Dart there is absolutely no way you can run a 275 without a 1/2" offset. The only Dart's I'm aware of that run 275's have at least a 1/2" offset and a quarter lip trim. That will be especially true for a lowered car. Also, not all of these cars have the same amount of space. Pre-70 Darts are VERY tight out back, most can't even get a 255 without rubbing. So, its entirely possible the early Valiants have more space than a 70-up Dart.

The 1/2" offset moves the front spring hanger over a little more than a 1/2", so that its up against the frame rail in the front. The offset shackles mount in the same place as the stockers, but they're offset a 1/2" to move the rear of the spring over. That places the spring even with the inside of the wheel tub, so you can run as wide of a tire as will fit in the stock wheel tub. The hangers and shackles bolt on, but you need to move the spring perches in 1/2" on each side, so 42" C-C.

 

[MuuMuu101]

There are also a lot of folks with 1/2" offsets, not to mention the 3" spring relocations. You're welcome to try it, but all I can tell you is that on MY '71 Dart there is absolutely no way you can run a 275 without a 1/2" offset. The only Dart's I'm aware of that run 275's have at least a 1/2" offset and a quarter lip trim. That will be especially true for a lowered car. Also, not all of these cars have the same amount of space. Pre-70 Darts are VERY tight out back, most can't even get a 255 without rubbing. So, its entirely possible the early Valiants have more space than a 70-up Dart.

The 1/2" offset moves the front spring hanger over a little more than a 1/2", so that its up against the frame rail in the front. The offset shackles mount in the same place as the stockers, but they're offset a 1/2" to move the rear of the spring over. That places the spring even with the inside of the wheel tub, so you can run as wide of a tire as will fit in the stock wheel tub. The hangers and shackles bolt on, but you need to move the spring perches in 1/2" on each side, so 42" C-C.

In that case, I'll just get new wheels in the future and do a mini-tub/spring perch move. My rear end and leaf springs are already in the car.

The guy's shop responded with regards to offset. Fronts are +7mm and rears are 0mm. I know I'm going to need at least a spacer for the front (may just ask for the ones he used as he went back to the Cobra wheels). Rears may be fine. If I end up picking these up tomorrow I just may find some tires on closeout from Tirerack and get a new set of 245/40/18 for the front and 255/40/18 for the rear. It will be a little funky looking with bulging sidewalls in the front and straight sidewalls in the rear, but that's just small details.

 

[MuuMuu101]

Just did some measuring and my rear end is approximately 59" rotor face to rotor face. The stock rear end I believe was 57 1/8" drum to drum. That means my new setup sticks out 15/16" on each side or 24mm. Does this make sense? Will a 0 offset wheel work?

 

[72bluNblu]

Just did some measuring and my rear end is approximately 59" rotor face to rotor face. The stock rear end I believe was 57 1/8" drum to drum. That means my new setup sticks out 15/16" on each side or 24mm. Does this make sense? Will a 0 offset wheel work?

Holy crap! That's a lot wider if that's right. Yes, the stock rear end should have been 57 1/8". I didn't realize the rear disks moved things that much, you may want to ask Cass about that.

As far as 0 offset working, nope. If your measurements are right, you'd need a 24mm offset. to put the wheels back in the same place.

 

[MuuMuu101]

Holy crap! That's a lot wider if that's right. Yes, the stock rear end should have been 57 1/8". I didn't realize the rear disks moved things that much, you may want to ask Cass about that.

As far as 0 offset working, nope. If your measurements are right, you'd need a 24mm offset. to put the wheels back in the same place.

Yeah, I've measured it twice now... The rear end is completely assembled in the car including the brakes. I avoided the center section hump by measuring from the top of the pad contact surface to the top pad contact surface (~55.5") on each rotor. Then I measured from the pad contact surface to the wheel surface (~1.75") and multiplied by two. Adding it together gets ~59".

Maybe I should skip on these wheels. That being said, at least I'll avoid a 1.5+ hour drive home from the shop.

I think my best option, as of now, is to find a wheel with a good enough backspacing where I could run no spacer or a spacer on either the front or back. Maybe an 18 x 9" with 255/40/18 and 24 mm offset?

 

[72bluNblu]

Something is wrong with your measurement, or maybe with that drum to drum measurement.

I was thinking about it, so I looked at the kit. Those rotors sit on the axle flanges, and they're the mounting point for the wheels. There's no way they add more than a 1/4" to the track. The axles stay in the same place, so the only difference is the thickness of the rotor compared to the thickness of the drum at the axle flange.

 

[MuuMuu101]

Something is wrong with your measurement, or maybe with that drum to drum measurement.

I was thinking about it, so I looked at the kit. Those rotors sit on the axle flanges, and they're the mounting point for the wheels. There's no way they add more than a 1/4" to the track. The axles stay in the same place, so the only difference is the thickness of the rotor compared to the thickness of the drum at the axle flange.

The bbp axle flanges are about 3/16" to 1/4" thicker than the sbp flange. So there's a potential 1/2" total. I'll measure again to make sure I'm not crazy because this is boggling my mind too.

 

[72bluNblu]

The bbp axle flanges are about 3/16" to 1/4" thicker than the sbp flange. So there's a potential 1/2" total. I'll measure again to make sure I'm not crazy because this is boggling my mind too.

I would disregard that axle flange part, because my measurements are coming off of BBP axles with 11x2.5" BBP brakes...

 

[autoxcuda]

The bbp axle flanges are about 3/16" to 1/4" thicker than the sbp flange. So there's a potential 1/2" total. I'll measure again to make sure I'm not crazy because this is boggling my mind too.

That would be maximum. It's probably less than 1/2". So still far from 15/16"

This is a little far out, but....Do you have adjustable rear wheel bearings? Are you measuring from the adjuster side and have not made your adjustment yet and the axle is adjust way out?

Ask Dr Diff about what you ordered from him.

IMHO, you should be looking at 245 wide rubber front and rear.

 

[MuuMuu101]

That would be maximum. It's probably less than 1/2". So still far from 15/16"

This is a little far out, but....Do you have adjustable rear wheel bearings? Are you measuring from the adjuster side and have not made your adjustment yet and the axle is adjust way out?

Ask Dr Diff about what you ordered from him.

IMHO, you should be looking at 245 wide rubber front and rear.

The rear end is completely set. Axle play has been properly adjusted and the lock was installed.

 

[72bluNblu]

The difference in the track width can't be more than the thickness of the drum where it sits on the axle flange compared to the thickness of the rotor in the same place.

There is a slight difference in track widths for SBP to BBP, but I know all of my measurements are using a set of BBP axles from Dr. Diff, so that's already taken into account. All that would be left is the rotor thickness compared to the drum.

 

[autoxcuda]

The difference in the track width can't be more than the thickness of the drum where it sits on the axle flange compared to the thickness of the rotor in the same place.

There is a slight difference in track widths for SBP to BBP, but I know all of my measurements are using a set of BBP axles from Dr. Diff, so that's already taken into account. All that would be left is the rotor thickness compared to the drum.

Dr Diff wrote this on another forum also about muumuu101's wheel situation...

5 x 4.5" bolt pattern A-body conversion axles increase the track 1/4" per side.

Rear rotors increase the track an additional 1/8" per side, for a total assembly width of 58.175".

 

[MuuMuu101]

I just looked at some pictures of my tape measure before I had to leave for the night and it seems to be closer to 58.175" My approximation was just bad looking at the tape measure at a funky angle. I'll post them tomorrow afternoon.

 

[pauly v.100]

I'm curious now... Because I know there are quite a few cars with a 275 series tires and I never here them mention needing offset shackles. I've got to do some research. I autocrossed with Tomswheels and his '67 Valiant and he was running 265/35/18's all the way around (granted he had an 8.8 in it). What about the Red Valiant or the Green Brick? Anybody know about those?

What needs to be modified for the 1/2" shackles because the idea of how they work isn't really connecting in my head. I'm assuming the perches need to be moved in and the offset shackles move them on the frame side, correct? If not, it makes more sense to pay $150 for the kit instead of $250 on tires (just back two). If so, I'll just do a mini-tub years down the line and move the perches then.

Also, the car needs to be on all 4 wheels within the next 2-3 weeks or so (before school starts hence the rush).

Tire profiles vary quite a bit too. Your friend's Valiant fitted with 265s may have gotten some tires with a slightly narrower tread width, i.e., he may have gotten lucky. I know that 265 BFGs would not fit on my car at it's current ride height, but 255s do.
Herrens old Valiant ran 17x9 Cobra rims, tire size unknown, and near as I can remember, the green brick runs 14" wheels, or did last time I read anything about it.

"There's also that weird hump at the top that Darts that could be an issue in full compression." If this refers to the inner fender, mine received the business end of a big ball peen hammer for extra clearance. Crude but effective.

 

[MuuMuu101]

Tire profiles vary quite a bit too. Your friend's Valiant fitted with 265s may have gotten some tires with a slightly narrower tread width, i.e., he may have gotten lucky. I know that 265 BFGs would not fit on my car at it's current ride height, but 255s do.
Herrens old Valiant ran 17x9 Cobra rims, tire size unknown, and near as I can remember, the green brick runs 14" wheels, or did last time I read anything about it.

"There's also that weird hump at the top that Darts that could be an issue in full compression." If this refers to the inner fender, mine received the business end of a big ball peen hammer for extra clearance. Crude but effective.

He's a long time member here. He said the 265's were almost as wide as the standard 275's. I believe they were Falkens. He was using Mustang style wheels as well.