Ok, got an '02 GMC 2500HD 4x4 ECSB...

Got it with 8300miles on it and the stock 245-75-16 tires. Those lasted 45,000 miles and I hated every mile of it with their wimpy looks.

So then I stepped up to the Goodyear Wrangler MTR's in 285-75-16 and loved the looks. It really helped make the truck.

But I went from about 13-13.5mpg down to 10.5-11.8mpg. (6.0L/4L80E, forget which gears...)

So, now I've put about 25,000 miles on the tires and they are about ready to be changed. Maybe 1/5 of the tread left.

I don't want to go back to stock size, and I'd like a bit better mileage since I do mostly freeway and some in town driving (very little offroad.) So I was looking at the 265-75-16 which is about in the middle of the other two.

Stock = ~ 30" tall
265-75 = ~ 31.5" tall
285-75 = ~ 33" tall

So, does anyone run the 265-75-16 size? Mileage with this setup? Any pics? Are they still small to look puny/wimpy? I'm looking at the Yokohama Geolander A/T + II's... good pricing and 40,000 mile "guarantee"... just don't look as tough as the GY MTR's.

And is my mileage WAY off? I do drive VERY agressive and fast (80-90mph on the freeway and 99% of the time I'm the first off the line and stay that way at stoplights... and I drift my truck around corners in the rain and sometimes in the dry.) I found that if I drove the speed limit and left stoplights like everyone else I get about .5-.75mpg better for a tank. Not quite worth it...

Truck has 70,000 miles now, K&N drop in filter (recent), TR55 plugs, MSD plug wires, Flowmaster catback (3.5" single pipe), Bilstein Shocks, and no other "performance" mods.

 

Now I may not be 100 percent sure about this but if you went up from a 30 inch tire to a 33 inch tire and did not recalibrate the pcm, your miles traveled will be off. Therefore you will be reading less miles traveled then you actually traveled. I hope someone else chimes in because this was my first thought.

 

You would be correct, but I did change the tire size in the pcm... I did the mark the tire/ground and roll the truck method too. For accurate "results"...

The night we bought it and my wife drove the truck home we got 13.4 mpg (freeway) and we've never gotten that same mpg since. I actually got some of my best mileage towing my Z06 on a trailer... 11.8mpg. Probably because I was using cruise control on 55mph (sometimes up to 60-65mph) and was about 100 miles each way on the freeway with hardly and hills.

I am very disapointed in the mpg though. I want a Duramax SO bad.

But then again we are disapointed in the mileage of my wifes '06 Civic auto as well. 30mpg town, 40mpg freeway claims. If we drive good we get 35 mpg on the freeway, 25 in town.

 

I would say that the lower final gear ratio made your truck work alot harder to accelerate and possibly at cruising also since you cruise at such a high speed. I would say that getting a smaller tire would bring you closer to where you were before. You could also stick with the 285s and then change out your gears for something a little lower. I have always heard good things about Yokahama, especially the Geolanders.

 

Well, I have A G80 and GT5 rearend codes. Not sure what the GT5 is, but G80 is the "posi" read end, heavy duty, right?

As for newer/lower gears, I'm not about to spend that kind of money... $1,000-$1,500 for gears. Although if I could be guaranteed some serious mpg improvement then I might be willing to do a gear swap. But then I'd think about a lift kit and 35" or 36" tires. (No body kits... )

I drive about 25,000-30,000 miles a year. That is $5,500-$6,500 a year in gas, depending on fuel prices.

Funny side note, when I was researching cars for my wife and we looked at the Honda Civic Hybrid, there was a calculator on Honda's site that would show you the savings over your current vehicle compared to the Hybrid. It claimed that in 5 years I would save over $27,000 in fuel.

 

I got 33's my HD i get around 10.5-12 in the city depending on how nice I am (I drive about the same as you most of the time) and that went up from 9.5-10 with stock tires. By the way I have 4.10's in mine.

It may sound dumb but doubble check the air pressure in your tires, if there off it can mess with you mpg. Also your truck gets the best mpg below 2,000 rpm, so the closer you are to that number the better off youll be.

 

I check my tires constantly. I run them all at 55psi. Get a nice even wear pattern on my tires (both the crappy stockers and these GY MTR's.)

So, what gears do I have? GT5's?

I like the look of the 285-75-16, but if I can get better mileage with the 265-75-16 I'd give up some look. I don't think I can stand going back to the 245-75-16's though.

 

Ill check my glove box when I get home but sounds to me like you got some 4.10's

 

Ive never herd of an HD not coming with 4.10's.

IF im not mistaken wouldnt the 33"s give you better gas mileage on the high way with 4.10 gears? Like the roll out or something like that would be better. Now this would be unloaded. Pulling anything I would think you would get worse cause its under more strain.

 

I am pretty sure you have 4.10's. The larger tire should help keep your truck below 2000 rpm's on the highway. Do you have a tune? and is your airfilter clean? My truck has the 6.0L, 3.73's and 285/75 BFG's A/T's which gives me about 10 to 12 in town and 14 to 16 on the highway. Turbo doesnt hurt either.