I've been doing some digging, but it seems like there's not too many guys that run narrowed rear ends on their stock suspension cars. So just how narrow of a housing can I go with before I run into trouble with brakes and tires hitting control arm brackets or LCA's?

My theory is that I can cut 2" off per side, and run GM Metric calipers (no parking brake, I know). I think I can run the caliper on the front of the wheel, and rotate it up if there's interference with LCA's. I will probably end up making a pair of offset LCA's anyway to clear my tires.


My goal is to run 26" tall tires on 15x10" wheels with 4.5" b.s. on the strip and something wide like a 305 or 325 tire on the street.

 

How narrow you can go will entirely depend on your tire/rim combination. Nobody can give you an exact number. You'll have to get a measuring tape and check distances yourself.

 

Rim and tire is dependent on axle width, not the other way around! Axle length is gonna be determined by largely by the position of the Axle brackets, which can be put inboard a little bit, but not too much since my springs still have to sit on top of them. Phb and LCAs also get in the way at some point, but that's mostly dependent on the brake package.

I'm trying to get ahold of racecraft to get a couple numbers off of their brackets, but I might just have to buy the brackets and then see how close together I can put them.

 

Depends on tire and rim.

You can shorten up the axle tube right up to the first mount on the tube however if the tire and rim you use hit something at that distance then you need a different tire/rim or a wider housing. You could shorten the tube as short as possible. Your rim may not work but a rim with 2.5" or 3.5" backspacing might. Since you already have rims and tires, how much you shorten the diff will depend on what you currently have, not on how much the diff can be shortened.

A 15x10 rim with 5.5" backspacing fits perfectly. Since you already have some with 4.5" backspace, you can easily shorten the diff 1" which would keep the tire in the same position as a typical 15x10 rim would do. Trimming more off then depends on when tire or rim make contact with any suspension components.

With a 26" tall tire, inner fender clearance shouldn't be too much of an issue but the bump stop could be in the way before suspension components are.

Take off the wheel and use a straight edge across the axle flange. Use a measuring tape and while turning the axle, measure distances from the straight edge at different distances out from center.

The first distance from center will be the rim lip at 7.5". The outer edge will be 13" which will be the height of the tire. You'll need to know how much the side of the tire bows out and check between 7.5" and 13" from center. A cut down yardstick bolted to the wheel studs is easy to work with and write on. This is only a ballpark measurement since you need to allow more room for suspension travel. 1-1/2 to 2" outside those distances should be more than enough.

DOT tire width is measured across the section of the tire. Drag slick width is across the tread. If you know the width of the tire across the section and how much backspace is in the rim, you can calculate how far the tire will extend behind the axle flange.

Lets say you have a 12" wide section. Tire is mounted on a 10" rim with 4.5" backspace. With 5" of backspace the inner sidewall will be 6" behind the axle flange 12/2. Since you have 4.5" backspace, you're pushing the tire outward 0.5" from center. The inner sidewall of the tire will then be 5.5" away from the axle flange.

With a straightedge along the axle flange, measure 7.5 to 13" from center and within that distance, measure back to suspension components. The shortest distance less 5.5" is how far the tire can be moved inward before it touches something.

If you do the calculations and measurements and find you have lets say 3" of clearance before the tire touches anything. You can then remove up to 3" off the end of the axle if enough axle tube permits it.

It's not guesswork. You just need to go do measurements.

 

Here's my concern. See how the panhard bar is already really close to some of the brake components?

 

Are you wanting to fit an existing wheel?

Seems like a lot of trouble to narrow the rear move brakes around, if you are not going bigger then something that fits stock.

I could see if you were mini tubbing and going with a 12" wheel, but a 10" wheel will fit a stock width axle fine.


I ran 28"x10.5 Et Slicks on a 15"x10" wheel with a 5" back space, on a stock witch axle, fit in the stock wheelwells.

 

again with the "trouble"... How come everything I build everybody's gotta come in and say "well, that seems like a lot of trouble....." I was doing some research before I built my mitsubishi engine trying to bump compression and everybody was telling me to just to do it the same way everyone else did theirs and get 20psi of boost at 5000 rpm. I managed to bump compression by about .9:1 and am able to spool my turbo by 3000 rpm. How many DSM's you see smoking all 4 tires off the line? Not too many, they're still waiting for their turbo to spool...

Its not a lot of trouble, its just doing a little bit of digging rather than being a sheep and following everyone elses builds. besides, what else am I gonna do while I'm stuck here at work and can't be wrenching on my car?

/rant.


I will run a 10 inch wide wheel with a nice looking lip to it.

 

Sorry, I did not intend to offend you, Judy wonder what the goal was.

I'm guessing from your last line, your goal is to run as little backspacing as possible, is that correct?

 

These 10" wheels with 5" bs had a pretty big lip.

 

I like the effect people get with 6.5" bs rims on stock width rears, I'm looking for that much tire tuck with a lip like you'll get with 4.5" bs rims.

I'm not offended, but honestly I just wish more people would put the effort and attention to detail in their projects as I do. Not saying everyone else is doing it wrong or that people shouldn't buy bolt in parts, but it just seems like people make some unnecessary compromises when they buy a moser rear end or similar. Or maybe I'm just a glutton for punishment lol.

 

I would not put too much effort into worring about the effort and attention to detail other people put into their projects. You're blood pressure will thank you.

 

Lol true dat. It's your car, build it the way you want it! I've never gotten too worked up over the extra effort and "frustration" I bring on myself by not following the crowd either though. Wrenching on my car (or planning projects for my car) is kinda my escape...

 

My new wheels and tires will tuck better then the ones I posted.

Going back to street tires too.

 

Everyone has this in some area. You're willing to go to great lengths to suit wheel fitment. I'm willing to go to great lengths for transmission fitment. Car guys... checking in.

 

Yeah, the first time we narrowed the 9" for my 55, it was to fit a set of wheels I bought.

A couple years later, we sold the wheels, narrowed the rear more, and had wheels made to fit.

I agree, real car guys are gluttons for punishment.

 

here's what I'm goin for:

 

Any idea what the bs is on that wheel?

I'm thinking 1" off both sides and a 4.5" bs should do it for you.

 

That is a 15 x 10 with 4.5" of backspacing, low pad.

 

There ya go! Cut an inch off each side.

 

Yes...you must be a glutton...

I'm not offended either If someone else thinks people that replace rears with stock width aftermarket are making some kind of "compromise". Maybe those people didn't share the same goal when they bought theirs...to lay a hundred dollar bill inside the lip of their rear rims. (see- my attention to that detail was amazing...to realize it was a hundred dollar bill) lol

Either way, sounds like an interesting project!! Good luck with it!

EDIT: BTW, those are some sweet looking wheels!

 

Exactly. The whole point of wanting a narrowed rear is to lay $100 bills in the wheel lip. 2 per wheel, in fact, with the money I'll have saved over the cost of a Moser (cost is a compromise too btw)

 

That's what I did when I did my back half. I had the rims and tires I wanted to use. I didn't have the car cut up yet and wanted to make the diff first. I positioned the tires and rims behind the car where they looked like they would fit the best then measured between the rims. 45" from axle flange to axle flange. The diff housing itself is 40" from bearing end to bearing end. After the diff was made, I cut up the car for a back half and the fit was perfect

15x15 rims with 5.5" backspace. I originally used 32x14 slicks but have upgraded to 32x16. I still have room between the fenders for more width but 16" wide slicks is enough. I'd love to go to a 33 or 34" tall tire but don't have the room at the front or rear of the fenders for a taller tires.

From that above picture, your issue isn't going to be tires or rims but the park brake part of the calipers. If you switch to a set without park brakes then you could shorten the diff. You can always do like I did in my "Disk brakes for any differential" thread and fabricate some new mounts for some aluminum calipers. The Jimmy rear brakes use an internal drum for park brakes so if you do a little more fabrication, you could still retain a park brake system if required. I had no use for a park brake in a drag car.