4in vs 4.5in bolt circle rear axle

[Garrett Ellison]

Bolt circle and stud size makes a lot more difference in trucks. That being said, if you are concerned about all out strength, you have the option of upgrading to a given size with an aftermarket axle (flange diameter matters, too, there has to be a certain amount of material outside of the stud). You could have axles made to use later truck drums with 5.5 on 5.5 bolt pattern if you’re staying with drum brakes. New drums are available in 10 & 11 inch sizes.

 

[pishta]

Is a 4in BC as strong as a 4.5in BC

No, There is more mechanical advantage on a 4.5 BC so there is less shear force on each stud. The farther you are out from the axle centerline, the less force is required to apply the same torque 24" breaker bar or a 5" stubby?

 

[Killer6]

I am a Mopar nut , by junk and build it . The avatar is my 500 stroker kicking A### at Road america , yep a BB
My present project is a 68 Cuda notchback
Thanks for all of the replies
I am going to change axles to a 4.5 bolt circle .
what is the easiest most inexpensive way to do this ?

Swap an earlier '66-'68 era B-body rear in, move the perches, get rims with the correct offset/back-spacing.

 

[B3422w5]

4.5 bolt pattern is definitely stronger,and it has the 1/2 studs too.also I've had a lot of small bolt 8.75s with the 489 case in them.

true.
my 70 340 Duster came with 4 inch bolt pattern 8.75 with 489 case delivered from factory that way. I suspect 71-72 was that way as well

 

[B3422w5]

Swap an earlier '66-'68 era B-body rear in, move the perches, get rims with the correct offset/back-spacing.

buy new axles and have Moser drill for 4.5 bolt circle. Have had them do that several times, front and rear.
cheap, quick turnaround

 

[CudaFactHackJob]

ADAPTERZZZZZZ

 

[RustyRatRod]

Is a 4in BC as strong as a 4.5in BC

Well of course not. Physics dictates the larger bolt pattern is stronger. That said, there have been plenty of big block and Hemi cars built using the small bolt pattern.

 

[CudaFactHackJob]

The four inch pattern has proven itself to be somewhat stronger. The conclusion is that the center of the wheel isn't allowed to flex as much as the larger pattern, plus the smaller center alignment hole allows for more accurate centering. Plus the fact that the hardness of the four inch studs is greater than the later studs which were all made from recycled steel.