Having had all three sizes, myself, my observations are:
Stock tires are too narrow and too short (aesthetically) but are probably the best "compromise" for on/off roading. Hummer made a wise choice for a stock tire.
Changing the 315/70's for the BFG 37x12.50's effects a subtle aesthetic change. Most people won't even know you have non-stock tires, but it'll just plain look better than most other stockers running around. These tires fit nicely in the wheel wells/stock flares with no modifications. Like the stock tires, little to no rubbing in moderate off-road conditions. Extreme conditions will cause them to rub a bit sooner than the stock tires, but nothing serious. Noticed about a 1 MPG drop, mostly attributable to needing speedo recalibration. This tire is "only" 36.3" tall, NOT 37". It's about 1/2" - 7/8" wider than stock tires. Performance (acceleration) is affected due to the height/effective gear ratio change, but it didn't bother me much on a bone-stock H2 (my yellow one.) In fact, the 37 x 12.50's on my stock H2 performed BETTER in the Breckenridge <> Denver climb than my unit with intake/exhaust/flashed unit with stock tires. Same "course" (throughout CO) with same modded H2 and the 13.50's was the best overall.
The 13.50's fill out the wheel wells nicely if you have the extended flares. I don't know the brand/name of the flares I have - I just Optioned them at my dealer - but I'll find out and post the info. The FC II 13.50's are 37.2" tall, so you'll notice an acceleration penalty. Not really a problem if your rig is modded from mild -to- moderate (intake/exhaust/flashed -to- Supercharged) unless you're fantasizing about your 6,800 brick besting the local street racers - LOL. Nevertheless, here's the rub (pun intended - LOL)... At maximum steering wheel lock, these tires will rub a little. I can feel the "DC" logo "bumps" through the steering wheel, so I back off a little. My friend who owns the truck accessory shop, Planet Pickup (hate that name) said he had to adjust the front end height by cranking up the torsion bars. This had made the ride rougher and the steering response feels a little odd. Upon investigation, I do not believe they needed to crank them up, at least not that far, so I'll be dropping them soon. I like the aesthetics better with the front end up since I never liked the "down hill" attitude of the stockers.
I believe that when my SUT comes in, I'll just HAVE to go for these tires again since I like the appearance... well, except for the tacky DC logo thing. I'll be looking for a stock-looking wheel with about 1/2" more width and perhaps a LITTLE more offset, perhaps with beadlock. I do not like tires sticking out past the wheel wells/flares. The stock H2 wheel is the minimum recommended width for this particular tire, BTW. Phil D can probably confirm that the minimum recommended wheel width for the only other 37 x 13.50 I know of (X-Terrain?) is 9"... Phil? This shouldn't be a problem except for moderate-wild off-roading.
These tires have about 4,500 miles on them now and I have found them to ride fine with no noticeable increase in highway noise. It's different, but not louder. I think we all (secretly?) like a little tire noise :-) I give DC/MT an "A" on tread pattern. Noticed considerably better off road grip over the BFG AT/KO's (both sizes.) Not as good in moderate/gooey mud as the MT/R's, but OVERALL (for me!) a better tire.
These tires run about $350 each. Comparing this with the avg. price for the BFG AT/KO's at (say) $215, I'm not sure the 13.50's are the best bang for the buck. I'm less sensitive to price than I am performance (incl. looks), so this wasn't a big deal. Your mileage may vary. For what it is worth, I am putting BFG AT/KO 37 x 12.50 x 17 on the stock wheels on my other three units (one already has them, so two more actually) since they are subtly different and still "leaves room" for me to have something just a one small notch different from those units :-)
As to the treatment on my trim, it is actually "Rhino Lining" - very similar to LINE-X. I chose "Black Pearl", which looks more dark/drab green to me, especially with a green H2. I wanted it to, again, just be subtly different from the other three units. Most times, people choose a contrasting/complimenting color (which looks good), but I wanted to be a little different. So far, so good, so I'll probably do the same to my SUT.
Hope this helps. Glad to answer any questions. Sorry if this all reads poorly, I was interrupted several times by Mrs. Apex while writing this, so it kind of jumps around.
-Randall Garrett-
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