What’s standard backspace?

 

OK Guys,

I have a simple question. What's the standard backspace on a '69 15x 8 Rally Wheel? I know it's either 4" or 4 1/2", but my car's in the shop and I can't run over.

Thanks,

Matt 

4"

Thanks,

Matt

I'm looking at 15 x 8's with 3 3/4" backspace, with BFG T/A's 225/70's I shouldn't have a problem should I?

Thanks,

Matt 

im not sure, but you might have tire rub on the inside from the rear suspension being too close to the tires. someone correct me if i am mistaken

With 3 3/4" backspace, the tires will stick out farther towards the wheelwell, right? I was planning on putting 1/4" worth of washers to space the wheels out 1/4" since the backspace is 1/4" less, then checking  everything with the car sitting on the ground and turning lock to lock, of course I won't try driving it like that though.  

Matt 

I'm lost on this one too.

Using the logic that a 3.75" backspace would push your tires out another .25" than a 4.0" backspce, wouldn't it then follow that by adding .25" of washers would have the effect of pusing the wheels out even farther? Net effect being a 3.50 backspace?

Help! I'm even more confused than before I started.

Did anyone take bacKspacing 101?

 

 

 

 

This is all gonna depend on where you take your actual measurement. The backspace is the distance from the surface of the wheel that fits to the hub(rotor), to the lip on the rim that the tire bead seats on. If you're measuring out the the edge of the rim, where the weights would go, you would have about a 1/4 inch difference.
I'm going to go out & measure my factory rims, and see what they are....................

OK, my factory installed rally rims measure 3 3/4" to the bead seat.
If I measure all the way out to the edge of the rim, it is 4". Adams' Apple38624.7760648148

And yes, the more backspace, the further back the rims are.  So a 4 inch is closer to the diff than the 3.75. 

And also yes, if you use spacers under the rim, you will position the rim further out toward the body, just the same as less rear offset.   This is of course provided the lug bolts are long enough.  Now the problem is strength.  A spacer does not have as much contact patch, and therfore will be less able to handle rotational torque, and will create more strain on the lugs.  Spacers are okay if the vehicle is not stressed hard.  Otherwise it's much better to use a correct rim.

kstyer38624.8062384259

Just to surmise. The 3 3/4" will be 1/4" farther from the diff, it will also stick out 1/4" more towards the fender lip, right? I was planning on putting the washers behind my rally wheel to "test" the offset of the rims I'm looking at buying. I just want to make sure that sticking out 1/4 more won't rub on the fenders. The torque thrusts with 3 3/4 backspace are $640 for a set, for 4" backspace they're another $160. I'm just trying to make sure I won't have any fir issues before buying them. I'm just a tightwad.

Thanks for the input,

Matt