I am changing to a 12 bolt rearend and I want to install 16" wheels. Chances are the rear end could be a 68-72 unit. My question is what back spacing is necessary on the rear wheels if I end up with a 68-72 unit. Also I would like to run all four tires the same size. The velle is a small block with standard suspension.

That's going to be tough if you want them all the same offset. I know I've used 4.25" in the front and 5 or so in the rear, you should be able to find a happy medium. These were Torq Thrust II's.

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-Andrew
through.theloophole@gte.net

David,

The 68 and later axle is 1-1/4" wider thant the 64-67 one. This means you will add 3/4" to each side. Look at your present setup and see what clearances you have right now. adjust the bs on the new rims accordingly.

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Brian TC#1092, ACES#4374
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1964 Malibu SS Convertible (http://www.chevelles.com/showroom/65elcamino64.jpg) (Garage Queen) Before Restoration (http://www.chevelles.com/showroom/65elcamino64a.jpg)
1965 El Camino (http://www.chevelles.com/showroom/65elcamino1b.jpg) (Daily Driver) Before Restoration (http://www.chevelles.com/showroom/65elcamino1a.jpg)
1981 Corvette (http://www.chevelles.com/showroom/65elcamino81.jpg) (Sidelined for repairs)

Got it, I need 5" bs on the rear wheels. Will 5" bs on the front wheels be necessary to have all the wheels appear the same. In other words is there a noticable visual difference between a 4" and a 5" bs? also,I would like to run the same size tire on all corners, any suggestions on tire size?

The following is definitely the case for 64 and 65, I believe 66 and 67 will be the same. Someone correct me if I'm wrong.

To keep the wheels/tires all identical, you will need to stay with a 235 width tire.

The rear rim width should be either a 7" with 4.5" backspacing or an 8" with 5" backspacing to place it in the center of the wheel well. I have 255/45R17 tires on 17X8 with 5" bs rims. I have 1" clearance on the outside without rolling the wheel lip and 3/4" on the inside. Excellent fit on rear. 15"s with the same bs will fit as well, keep the overall diameter the same as my 17" tire setup.

These measurements are based on having the stock width original 64-67 axle. If you have a later 68 and up axle, you need to adjust for the extra width on these axles. I recommend you take care of your rear suspension bushings to prevent a loose or sloppy suspension from ruining new rims and tires.

The front rim width should be a 7" with 4.5" backspacing. I have 8" with 5" backspacing, but if I did it over, I would go with the 7" width. The tire is close to the outside edge of the wheelhouse, the 7" would bring it 0.5" inward away from the outside edge. I have 235/45R17 tires on the 17X8 with 5" bs rims. I have rubbing when the wheel is pushed up into the wheelwell at full turn lock, such as when backing out of the driveway. I have 1" lowering springs on the front so this alos contributes to the rubbing. I have no rubbing problems under normal driving conditions. Same applies here for the 15" size.

Here's an older thread that might help.

16's on a 66 (http://www.chevelles.com/forum/Forum8/HTML/001072.html)

The fit is for a stock 10 bolt rear. Note that I have more clearance between the rear tire & wheel well lip than on the inside. Would probably work with the newer (wider) 12 bolt, but it would be getting close. From my measurements, I could not go 4.75" back spacing on the front - tire hit the front sway bar at full lock.
On my car, a zero offset (that'd be 4" BS with a 7" wheel, and 4.5" BS on an 8") would have centered the wheel in the wheel well - both front & rear. If yours is the same, you should be able to work out what the wider rear end will do to you.
If you can get a wheel & tire that is close to what you want to "test mount" on your car, do it. You'll at least have some measurements to work from.

Wes

Gentlemen (I think) - Thanks for the replys, now armed with this info I am more dangerous then before!