I have an 08 FX4 with stock 18's and was curious of the offset. I wanna stay with 18's but would like a slightly bigger tire. Can someone tell me how I could go about that without having to recompute the ecm? I know the bolt pattern is 6x135 but would like them to maybe stick a bit more, not much.

 

Just going wider on the stock rims will cause the tires to stick out more, pretty common to go up to a 12.50 tire on the stock rims.

If you don't want to reprogram your speedo, you'll just need to mentally adjust for the difference in circumference to know your speed.

 

Its been a while, IIRC, stock offset is around 44mm (5.5" BS on 7.5 Rim)

 

I wanna fill out the wheel well without running obviously...... how would a 315/95/18 work with my 2.5" level?

 

Or will simply increasing the width also increase the height of the sidewall?

 

That's way too big without significant lift.

With metric tires, the first number is the width, the second is the percentage of the width that is the sidewall height (called the aspect ratio).

So a 275/70R18 is 275 mm wide (10.8") and has 275x70% (7.6") high sidewalls for an overall height of around 33".
A 315/95R18 is 315 mm wide (12.4") and has 315x95% (11.8") high sidewalls for an overall height of around 41.5".

A 295/70R18 is probably closer to what your looking for to max tire size on the stock wheel offset with a level.

 

ive got the stock fx4 rims on my 04 and i got 35x12.5s wrapped on mine. got a 3" level in the front. but the 2.5" should be enough. with the stock rims, there will be a lil rub here and there at full lock. but not a huge deal i think.

 

Rub is no good

 

I want the terra grappled maintain good wet traction

 

well of course rub is no good. lol but what i meant is that it will only rub if you go in full lock. so if your careful youll be fine and got nothing to worry about.

and i love my trail grapplers! they are amazing. but they are lil slick on the wet roads. i just make sure not to gas it very hard lol