Help with getting the proper offset (with KW arms, toyota spindles and RX7 IRS)

Originally posted by SinistarCustoms



Im Doing an RX-7 Irs on mine right now too. Non BD with 4x4 sheetmetal. I used my friends 18x7.5 with 45mm back spacing. 235/40s in the back and they tuck awesome but I dont know If they will work on the front.

hmmm now I wonder what that would be on a 18x7

Still havn't had a chance to get those measurements.

Originally posted by iLLairgasm



Originally posted by SinistarCustoms



Im Doing an RX-7 Irs on mine right now too. Non BD with 4x4 sheetmetal. I used my friends 18x7.5 with 45mm back spacing. 235/40s in the back and they tuck awesome but I dont know If they will work on the front.

hmmm now I wonder what that would be on a 18x7

+38.

+45 on 7.5, that is 8.5 wide /2 = 4.25 centerline and 45mm offset = 1.75 inches + 4.25 = 6" backspace = 2.5 inches frontspace.

a 7 inch wide wheel is 8 - 2.5 frontspace = 5.5 backspace. The centerline is 4, 5.5 - 4 is 1.5 inches offset in mm is ~38.1 mm or +38.

got it?

Originally posted by Russ-D



Originally posted by iLLairgasm



Originally posted by SinistarCustoms



Im Doing an RX-7 Irs on mine right now too. Non BD with 4x4 sheetmetal. I used my friends 18x7.5 with 45mm back spacing. 235/40s in the back and they tuck awesome but I dont know If they will work on the front.

hmmm now I wonder what that would be on a 18x7

+38.

+45 on 7.5, that is 8.5 wide /2 = 4.25 centerline and 45mm offset = 1.75 inches + 4.25 = 6" backspace = 2.5 inches frontspace.

a 7 inch wide wheel is 8 - 2.5 frontspace = 5.5 backspace. The centerline is 4, 5.5 - 4 is 1.5 inches offset in mm is ~38.1 mm or +38.

got it?

got it... lol.

So your original number of +39 might be ok then... Still gotta get the back figured out for sure though.

If I get you a hub to hub measurement of the IRS will you be able to compare it to a stock mazda rear and figure it out?

Originally posted by iLLairgasm



Originally posted by Russ-D



Originally posted by iLLairgasm



Originally posted by SinistarCustoms



Im Doing an RX-7 Irs on mine right now too. Non BD with 4x4 sheetmetal. I used my friends 18x7.5 with 45mm back spacing. 235/40s in the back and they tuck awesome but I dont know If they will work on the front.

hmmm now I wonder what that would be on a 18x7

+38.

+45 on 7.5, that is 8.5 wide /2 = 4.25 centerline and 45mm offset = 1.75 inches + 4.25 = 6" backspace = 2.5 inches frontspace.

a 7 inch wide wheel is 8 - 2.5 frontspace = 5.5 backspace. The centerline is 4, 5.5 - 4 is 1.5 inches offset in mm is ~38.1 mm or +38.

got it?

got it... lol.

So your original number of +39 might be ok then... Still gotta get the back figured out for sure though.

If I get you a hub to hub measurement of the IRS will you be able to compare it to a stock mazda rear and figure it out?

yes

I can even do the same if you get a hub to hub measurement from your front setup and get one from a stock mazda.

Originally posted by Russ-D



Originally posted by iLLairgasm



Originally posted by Russ-D



Originally posted by iLLairgasm



Originally posted by SinistarCustoms



Im Doing an RX-7 Irs on mine right now too. Non BD with 4x4 sheetmetal. I used my friends 18x7.5 with 45mm back spacing. 235/40s in the back and they tuck awesome but I dont know If they will work on the front.

hmmm now I wonder what that would be on a 18x7

+38.

+45 on 7.5, that is 8.5 wide /2 = 4.25 centerline and 45mm offset = 1.75 inches + 4.25 = 6" backspace = 2.5 inches frontspace.

a 7 inch wide wheel is 8 - 2.5 frontspace = 5.5 backspace. The centerline is 4, 5.5 - 4 is 1.5 inches offset in mm is ~38.1 mm or +38.

got it?

got it... lol.

So your original number of +39 might be ok then... Still gotta get the back figured out for sure though.

If I get you a hub to hub measurement of the IRS will you be able to compare it to a stock mazda rear and figure it out?

yes

I can even do the same if you get a hub to hub measurement from your front setup and get one from a stock mazda.



Ok cool... the only problem I think is going to be finding the measurements from a stock one.

Edited: 4/7/2006 8:09:55 AM by 1offWizard

Measure from mounting point to mounting point on the front and rear, then mock up your front sheetmetal and measure lip to lip then measure lip to lip on your bed. If you mount the body square that should give you good measurements. Make sure you measure for the contour of the bedside, although with the IRS you should camber enough to clear that.

The body isn't on the frame, and isn't goin on for a little while yet.... otherwise i'd have done that already.

Alright gentlemen...

I got the measurements today finally... im not sure if anyone knows the stock mazda measurements though.

From hub to hub the measurements are:

Front: 56 3/4"

Rear: 59 1/8"

Anyone know what the stock hub to hub measurements are?