The following configurations have been done on lowered 07 sedans without rubbing:

Car 1-
Front: 20x8.5/+34, 245/35/20
Rear: 20x10/+40, 275/30/20


Car 2-
Front: 20x8.5/+35, 245/35/20
Rear: 20x9.5/+43, 275/30/20




My question, if I try for:

Front: 20x9, 255/35/20
Rear: 20x10, 285/30/20

What should my offsets be to clear fender shifting wheel/tire inboard? Is it +23 front and +35 rear?

 

Wrong way, you need to go higher on the offset to account for the additional tire width.

 

noooo way your gonna fit a 9 up front with a 255 or a 10 with a 285.

If you're gonna go with a 9, then the offset needs to be atleast +40 with a 245/35. The rear can be +40 and higher with a 275, you'll have a world of problems trying to shove more rubber in there, stick with the standard sizes.
-GP-

 

Based on the 2 examples, can you tell me how you calculated +40 for front and rear? Increasing offset moves tire inboard, but increased width moves tire outboard.

 

Ah .. I see. That makes sense. Thanks for straightning me out.

New calculations then -

The Following calculations assume no rubbing on inside.

From rear of car 1,
Given: 20x10/+40 and 275/30/20
Changing from 275 to 285 means 10mm more width (5mm more on each side). To move tire 5mm inboard means add 5mm to offset. Therefore, offset should be +45mm, right?

From front of car 1,
Given: 20x8.5/+34 and 245/35/20
Changing from 8.5” rim to 9” rim the wheel width grows .5 inch or .25 inch (6mm) each side.
Changing from 245 to 255 means add another 5mm to offset.
Therefore, offset should be +45mm as well, right?

On the S, the stock wheel/tire:
18x7.5/+45, 225/50/18 front
18x8.5/+50, 245/45/18 rear

Doing the math for stock wheel, offset+1/2 wheel width=
140.25mm front
265.9mm rear

Doing the math for 9” front and 10” rear, each with +45 offset:
offset+1/2 wheel width=
159.3mm front
172mm rear (means more clearance than stock?)

What did I do wrong?

 

Btt

 

BTT - anyone?

 

all the calculations dont make sense to me, i hate math!

Why dont you just stick with a 8.5F +35-40/10R+40-50 setup like everyone else??
-GP-

 

I didn't see your first bump, but your in depth post confused the hell out of me.

Car 1-
Front: 20x8.5/+34, 245/35/20 24mm wider stance than stock
Rear: 20x10/+40, 275/30/20 29mm wider stance than stock

Car 2-
Front: 20x8.5/+35, 245/35/20 23mm wider stance than stock
Rear: 20x9.5/+43, 275/30/20 20mm wider stance than stock

Your Car-
Front: 20x9, 255/35/20
Rear: 20x10, 285/30/20

Stock
18x7.5/+45, 225/50/18 front
18x8.5/+50, 245/45/18 rear

I don't own a G35 so take this with a grain of salt. Seems to me if you take the least aggressive of the 2 sample car rear offsets you should be fine using the rear tire you're looking to run. Front looks like it would the most to be concerned about since the wheel turns and could rub during suspension loaded turns.

20x9 +45 would give you bring you in 4mm less than the sample cars, but this also makes you inner clearace 16mm less than the sample cars which is 19mm less inner clearance than stock.

20x10 +49 would be equal to 20mm wider stance than stock but the 10" wheel reduces your inner clearance by 18mm.

The good thing for you guys is lot's of tires to choose from and all are relatively in the stock height range.