I went through this same question. I checked out many tire shops and was told the widest tire to mount on a stock rim was 265. Some said 285 was ok, and the rest said it would work but was pushing the limit pretty good.
A friend of mine has been running 285's on his stock rims now for 3 years now going through some fairly though terrain and hasn't had a problem at all!
I run a couple of sets of 285 BFG AT on stock rims and u should have to do any trimming just tie wrap the inners for clearance.
When I went to the 285-17 on H2 wheels, the wider rim and offset change,I had to trim the bottom of the airdam on my last GMC and the Chevy I have now didn't need as much but still had to cut 1/2" off the bottom corner.
So depending on how much u want to cut will dictate tire size.
The biggest tires I have personally seen on the stock aluminum wheels were 305/70's. I saw the truck pull up, and when the owner came in the store I asked him about them. He said that the truck (02 Chevy 2500HD XCab, SB, 4X4) was completely stock, and it didn't rub or anything. I took a look at it when I got out of the DD, and they looked really sharp!
I've ran LT305/70R16 for the last five years on Z-71's and Duramax's with no problems. The makes were BFG All-Terrains and Goodyear AT/S. Quit using the Goodyears b/c it is a softer rubber and they wear faster. No aftermarket lift or anything and they fit just fine, rubbed a little on the Z-71's and no rub on the d-max.
I put 265 Nitto's on my truck a recently and they work really well with the factory 16 X 6.5" wheels. Time will tell how the tread will wear. Hope to get 50,000 miles out of them. Here are a couple pics:
I had 285 BFG's on my 2000 Z71 stock rims. Ran them for 2 years with no problems, no trimming, and no rubbing. When you go to a wider rim, then you start to get into clearance issues. I would say that either 265 or 285. 265 if you want to be safe.
Has not been mentioned yet, but how about a 255/85?. Are about 1/2 inch taller than the 285s, but narrower. Fits the OEM wheel fine, no rubbing or issues with uneven wear. Let me add that there are lots of guys running 285's and I've only heard a few complain about unusual wear. I happen to perfer the taller, narrower look.
I've had 255/85 Interco TrXus MT's for almost 2 years. Due to be replaced soon and will go with the same size in a different tire. The choices in 255 are limited compared to 265 or 285, but you can find any style of tire(Mud, AT, etc.) you want. Some manufacturers only produce that size in certain tires, an example, BFG AT's are not available, but MT's are. I'm leaning towards Cooper S/T's
That is why I went with the Nitto's so I could get a 265 tire with an E load range. There are a few others tire companies out there that have a 265 tire with E load range. Cooper Tires and Bridgestone/Firestone. I am surprised there are not any 285's that come with an E load rating! At least I have not seen any. Nitto has a 305 that has and E load rating....
There's actually quite a few brands offering 265's with an E rating. Used to be Michelin was the ONLY one, now there is at least a Dozen different tires to choose from in this size, and most are 3415lb rated.
You are correct about the D rating, sorry I forgot to mention it. I was comfortable with the rating as I only pull small trailers at this point, no more than 2500 lbs. If I was pulling a heavier trailer, I would definitely go with E rated 265's.
I called Michelin about the 265 on a 6.5 rim, and was told that it was alright. Nothing bigger though. I still changed wheels to 8 inch as I frequently pull heavy loads and don't want anything to be iffy. That's why I went to the higher rated 265 to start with.
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