Are there any benefits to narrowing a rear end? Will it make street tires look funny? is it used to run bigger tires?

 

depends on the application,sometimes it is for bigger tires. some people narrow it slightly so they wont have to run 7.5" backspace wheels.

 

Narrowing a rear end will require back halving the car and having wheel tubs installed. Narrowing it enough so that this work doesn't have to be done means only cutting 1-2" off each end. You just need rims with less backspace to keep the tires in the same position but for the cost of narrowing it this tiny amount isn't really worth it. It would be cheaper to install a third gen diff into a fourth gen to have a diff 4" narrower.

Other than being narrowed to allow larger tires under the back end, a narrow rear end has very short axles. High hp cars can easily twist a long axle. A short axle is very hard to twist. Grab a yard stick by both ends and try to twist it. Now grab a 12" ruler the same way and try to twist it. That's the same effect on the axles. The shorter the axles are, the less prone to twisting they are.

 

so its not worth it for me to cut a small amount off of a 12bolt?

Is backspacing the distance from the wheel stud holes to the outer edge of the wheel?

 

If you're modifying a 12 bolt to fit then having the diff shortened could be worth while. Have a c-clip eliminator installed at the same time. Having the stock 10 bolt shortened is a waste of money. Have the diff professionally shortened. If the ends are not lined up properly before being welded on, you can easily break axles. We have a local racer who broke 3 axles this year. He thinks it's because an end isn't perfectly square on the housing.

Flip the rim over so the outside is facing down. Put a straight edge across the bead surface of the rim, not the outside lip. A 15" rim needs a 15" straight edge etc. Measure from the backside of the inner hub, the part that sits against the drum/disk/axle etc to the bottom of the straight edge. That's the backspace.

An 8" wide rim with 4" of backspace will have the axle right in the center of the rim. An 8" rim with 6" of backspace will have the center of the wheel towards the outside of the rim which will tuck the tires inside the fenders and provide a smooth cleaner, flush mounted looking rim. An 8" rim with 2" of backspace will have a rim that looks very deep because the center is so far inside the rim. This will push the tire outside the fenders unless the diff has been narrowed.

The tires should never change position inside the fenders. They will contact inner or outer fenders if the incorrect backspacing is used. The proper backspace is required along with the diff width to keep the tires in the proper location.

If the fourth gen uses 7.5" backspace rims and you use the shorter third gen diff, you will need to use rims with 5.5" backspace to push the wheels back out to the original position.

 

I have had cars that have been narrowed but the cars have also had the other suspension items to go with it. Like cage,4 link,ant-role and what not. If your making enought power to over come the widdest tire possible you can fit under the car and want to go faster I would say narrow it. But it your not and your breaking axles or what not I would call someone like Strange Engineering and ask them if you could possibly fit a pair of there 40 spline axles into your 12 bolt or 9". I have a narrowed 94Z this is buy far the trickest setup I have yet to date ever had.

Take a look at ARE's car if I remember correctly there rearend is only narrowed by 2" and they use all stock suspenson and there car just ran in the 8.50's! To make a car that heavy run that fast they would have to be making over 1100hp. Those guy's are flying!

 

Im buying a 12bolt from strange and was just wondering if i should have it narrowed some by them?

What will my stock wheels/tires look like on it? Wont i need a different backspace otherwise the tires will hit the wheelwell? maybe i should stay with a regular length axle.

 

I don't think Strange/Currie/Moser make 2 seperate bolt-in diffs for third and fourth gens. To my knowledge they're all the narrower version for the third gens so fourth gens need to use different backspace rims or wheel spacers. Someone else can correct me if I'm wrong.