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Originally Posted by guruerror
IMO it's easier to think about it from a strictly 'backspacing' point of view. Everyone on this site seems to be worried about what 'offset' their rims have, but offset really doesn't tell you much by itself. You still need to know the width of the rim to determine how much of the rim will be under the truck and close to the suspension to determine if you'll get rub. They're using offset and width to calculate 'backspacing,' so why not just talk 'backspacing' from the get-go? LOL!
I found that with the stock rims which are 8 1/2" wide and have a 5 5/8" backspacing (in other words, 5 5/8" of the rim go inward toward the suspension and the remaining 2 7/8" go outward from the hub) my 37x12.5 BFG MTs rubbed in both directions at full lock. When I went to the Rockstars (9" rim) which have a shallower 4 1/2" backspacing I had about an inch less rim/tire going in toward the suspension, so the same tires exhibited no rubbing. This also gave the truck a more aggressive look since it pushed the tires outward about an inch and a half as well.
When trying to figure out what's gonna cause rubbing...it just makes more sense to me to look for the 'backspacing' first...'cause that tells you exactly how much rim/tire is going 'back' toward the suspension. I only look up the 'offset' if the backspacing isn't published.
For 14" tires I'd think you'd need to get an even shallower BS if possible. 'Cause if 4 1/2" BS makes my 12.5s not rub, adding another 1 1/2" to the overall width will put another 3/4" of rubber back toward the suspension. I don't know how much clearance I have at this point, but I'd think you want to at least try to push the tires out another 1/2" to make up for the additional rubber...which would put you at a rim with a 4" BS...3 3/4" would be ideal, but I don't know that I've seen rims wide enough to run 14s with that shallow of a BS. 14s seem pretty damn wide for a leveled truck...I'll see if I can get pwrhse2k to chime in. I think he was running tires close to your size on his truck when it was leveled.
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Okay...this has turned out to be an informative/educational thread. I change my position on BS vs offset. After some extensive research...and ciphering, I believe that offset allows you to better calculate the amount of rubber/wheel on both sides of the mounting pad than BS. It slowly dawned on me that BS doesn't account for
tire width...only the rim width. Using tire width and offset you can figure out exactly how much rubber/wheel will fall on each side of the mounting pad.
So, with 37x12.5s on stock 17x8.5 rims which seem to have an offset of about 35mm (8.5" rim and a 5.625" BS means that the mounting pad is 1.375" off center...1.375" = 35mm) I would have had 7.625" of rubber/wheel going back from the hub toward the suspension. That's the width of the tire 12.5 divided by two (6.25) plus the positive offset of 1.375.
With my current setup, I've got the same 37x12.5s on rims with 0mm offset, so I've got exactly half of the width of the tire going in each direction...6.25" of wheel going in toward the suspension and 6.25" going out away from the hub.
I had rub at full lock with the stock rims when 7.625" of the tire went under, but no rub with the Rockstars which is only putting 6.25" back. So 6.25" seems to be a good target number to avoid rub against the suspension.
Applying this logic to 14" tires...to keep only 6.25" of the tire going back towards the suspension, you'd need a rim with about a -19mm offset.
14 (width of the tire) divided by 2 = 7 (with 0mm offset you'd have 7" of wheel going in both directions.
7 minus 6.25 (the amount of wheel I've got under the truck with no rub) = .75 (the offset you'd need to get the same clearance)
.75" = 19mm
Since you want the wheel to go out more you'd want a negative 19.
One word of caution, I'd try to stay as close to the -19mm offset as possible...if you start going up to offsets like pwrhse2k mentioned (-44mm) you'll be pushing your tires out even further and you may run into rubbing on the outside of the tire...on the fenders.
I'm glad you posted this thread...I feel like I've got a better grasp of offset/BS now...LOL!
Here's a good site to play on to get a visual representation of the measurements, they don't have our tire sizes, but it still helped me figure things out:
http://www.rimsntires.com/specs.jsp