[grivera]

My newly acquired 66 Lemans has a 12 bolt rear, supposedly from a 66 Chevelle. Does anyone know the maximum BS one can use with this rear and tire size if using a 15” wheel?

[3X24SPD]

Better check your casting code/dates on the housing to be sure first.
The 65-67 Chevelle 12-bolts were the 1" narrower ones (54.25") vs the 68+ (55.25").

12-Bolt Housing: Casting #
1965 Chevelle 3859140N
1966 Chevelle 3875745N
1967 Chevelle 3894939NF
1967 Chevelle-Late 3917124NF
1968-Early 69 Chevelle 3917124NF
1969 Chevelle 3959038NF
1970-72 Chevelle 3969278NF

For reference, I run a 15X10 with 5.5"BS & 28X12 M/T on the back of my 66.

[grivera]

Thanks- good point and will do.

do your back tires fit under fender lip?

[3X24SPD]

Yes, but be advised that in my case, I also have wagon rear springs, and a later 55.5" width 8.2 10 bolt rear axle in this car.

[grivera]

Thanks - mine has Catalina springs all around and I’d like to lower it between what it is now and factory height. I believe the Weld wheels in rear are 15x8 with 4.5 BS.

[grivera]

The rear has the 66 Chevelle code:

3875745N with date code H215

But it has 4 wheel disc brakes so I assume it picks up about 1/2” from the rotors.

[grivera]

I measured the rear wheels -15x9” with 5.5 backspace, currently 275/60 MT Drag radials with the little screws into the perimeter of the wheel lip. The fronts are 15x7”” wheels with 3.5 BS. I plan to install 15x8” wheels in rear with 255/60 tires and 215/70s in the front. I hope with the smaller rear wheel and tire combo I can put in springs with lower rate to get rid of that gasser look.