Question on Rear End Width for Street/Track Car

[Bulletpruf]

Fellas -

Getting close to ordering a NASCAR full floater 9" for my 71 Javelin. I can fit plenty of tire under the car with stock rear suspension (17 x 9 wheels with 5" backspace, 275 mm tires) so won't need to mini-tub.

Question is what width rear I should go with. Do I want the narrowest rear possible? Widest rear possible? Or does it really not matter as the tire is going to be centered in the wheelwell anyway?

Right now the stock AMC 20 is 55 7/8" wide and 43.5" from center pad to center pad. My default is to go with something about this width, but wondering if I can do better than this since I'm going 100% custom.

Thanks,

Scott

[MrQuick]

depends on if you want a dish on the rear rim or not.

[astroracer]

Are you planning new wheels? It sounds like you have them on hand so I would say stick with what fits. If the rims you have fit using the stock width rear there is no reason to change the equation, right?
Any change you make right now will alter wheel fitment in that direction. If it was me, and I was planning new wheels/tires, I would shoot for the center of the tire opening and then order wheels to fit as big as I could. Ordering width and backspacing to fit.
Mark

[Bulletpruf]

depends on if you want a dish on the rear rim or not.

Does dish have anything to do with stability, handling, geometry, etc, or is it just an issue of whether I like the way a dish looks? That's what I'm trying to figure out.

Thanks

Scott

[Bulletpruf]

Are you planning new wheels? It sounds like you have them on hand so I would say stick with what fits. If the rims you have fit using the stock width rear there is no reason to change the equation, right?
Any change you make right now will alter wheel fitment in that direction. If it was me, and I was planning new wheels/tires, I would shoot for the center of the tire opening and then order wheels to fit as big as I could. Ordering width and backspacing to fit.
Mark

I don't have the rear or the wheels yet, so I can go wide or narrow on the housing and can do lots of backspace or minimal backspace.

[astroracer]

For handling and bearing life you want to keep the wheel offset to the positive side. A small offset, I.E. deeper rim, will side load the bearings more then a deep offset. As an example; I went with 18x12 rims for the rear of my van project and ordered them with a 7" back space. This puts the wheel mounting face 1" outboard of the wheel/tire centerline which greatly reduces bearing load.
Deep rims look cool from the outside but, if track days and handling are more of your goal, go with a deeper offset and put up with the "my rims are deeper then yours" taunts...
Mark

[TheJDMan]

You should decide on your wheels first and buy them. Once you have the wheels you can mock them up under the car and order the rear end in the exact width you need. This way there is no guessing. Just FYI, Moser sells their 9" floating circle track rear ends in any width for $879.

[Bulletpruf]

Edit to original post; rear is 61" from outside hub to outside hub. Not sure where I got 55 7/8" from. Maybe that was outside axle flange measurement. Will probably go 60" or so on the 9" rear.

Anyway, I think I'll order the composite rear leaf springs this week. Once I nail down what I'm going to do about the rear brakes, I'll order the rear.

Thanks,

Scott

[JRouche]

You should decide on your wheels first and buy them. Once you have the wheels you can mock them up under the car and order the rear end in the exact width you need. This way there is no guessing. Just FYI, Moser sells their 9" floating circle track rear ends in any width for $879.

Ka-Ching!!!! Winner, winner... Thats how you build up a car. Tires and wheels first, then think about the axle housing width needed.

I know... Its sounds azz backwards. But when you are lucky enough to be able to choose the wheels and tires that you want cause the axle dims are not set yet you are ahead of the ball.

Take advantage of that flexability.

Find the wheels and tires that you like that will fit inside of the wheel well and THEN find the number that puts the housing wheel flange where you want it.

You are in the best position right now to dictate what you want. JR

[Skip Fix]

I would think a zero offset would be the easiest on the bearings sonce there is similar leverage in and out acting on it, might not be the way things really work, especially since many new performance cars esp Vettes have a really deep offset inwards.

[Motorcitydak]

When I ordered my Moser circle track full floater I got a tire in the size I wanted and put it on the front then set it in the back and measured based on that wheel. Now I can run the same tires and wheels in the front and rear. Im going to run 315's on 18x10's but you mite want to keep that in mind just because its nice to only need one size wheel/tire. I also do not like smaller front tires and staggered size wheels. I prefer symmetry in my wheels/tires

[Bulletpruf]

Ka-Ching!!!! Winner, winner... Thats how you build up a car. Tires and wheels first, then think about the axle housing width needed.

I know... Its sounds azz backwards. But when you are lucky enough to be able to choose the wheels and tires that you want cause the axle dims are not set yet you are ahead of the ball.

Take advantage of that flexability.

Find the wheels and tires that you like that will fit inside of the wheel well and THEN find the number that puts the housing wheel flange where you want it.

You are in the best position right now to dictate what you want. JR

Got to agree that it does sound backwards, but this is my first road race car. Problem is that I don't have any idea on what wheels I want to use at this point. Just have a tire size and wheel size.

Thanks

Scott