What is the maximum backspacing on 4th gen fbodies, searching I seen something like 7" in front and 7.5" in rear. Tryin to see how big of a spacer Ill need for some

19x9.5" 57mm offset
19x11" 65mm offset

to fit my 96.

With the given I calculated

w/rims in front 7.25 backspacing
w/rims in rear 8.31 backspacing

so id need the following spacers

.25 Spacer front (or .5)
.81 Spacer rear (prob 1")

if anyone knows if this is correct please let me know. Used a calculation i found on the net.

fronts (9.5/2 + 57mm + .25 (lip) = 7.25 - 7 = .25
rears (11/2 + 65mm + .25 (lip) = 8.31 - 7.5 = .81

 

Check the post in the FAQ showing the ZR1/GS 17x11 50mm setup. That is a 7.93" backspace, and some cars require various combinations of the mods shown. You have ~15mm (~0.59") more backspace (depends on the exact dimension of the wheel lip, which is not a standard or fixed value). There is also a photo of a Torque Thrust II 17x11 45mm offset (7.75" backspace). You have ~20mm (~0.79") more backspace than that wheel.

To me, those are the limits you have to work with. Any more than 7.93" backspace, and the mods to the wheels wells will increase. Any less than 7.75" backspace and the tire will stick out too far beyond the fender.

So... you have to revise your 65mm offset to bring the wheel in the range of 45-50mm, so you need a spacer in the range of 0.60" - 0.75".

All that assumes you have a wheel with a lip similar to the ones mentioned above. Hence, no one can tell you the EXACT dimension of the spacer, without knowing the manufacturer's quoted backspace, rather than your calculated backspace.

 

not sure quoted backspacing but i have 17x11 zr1's, think they are 50mm so that means id just need a spacer that is equal to 15mm correct? Lip is the same asll all above

 

Sounds right. If you actaully have both wheels, measure the difference. That is the only way to be positive.