My lift arrived today so that will be going on next week. I'm not sure if my 4.56 upgrade will be in before the lift is done so I'm wondering how driveability will be with the stock gears and 37" tires. I probably won't do any towing before those gears go in. My '02 HD was pretty good with the same size tires and 4.10s.

2005 Duramax powered Sierra HD (http://www.tbyrne.com/Sierra/sierra.html) - MANY mods going on now!
2002 8.1 Silverado HD (http://www.tbyrne.com/Silverado/02silverado.html) - Full Throttle lift, 37" tires, 4.56 gears, Comp Cam, TOG headers, Volant induction plus more! - for sale!
2002 8.1 Suburban (http://www.tbyrne.com/Suburban/02suburban.html) -Intercooled Whipple supercharger, 22" wheels/tires + more - 407hp/558 ft-lb torque at the rear wheels - 13.93 @ 95.79 MPH - sold!

a friend of mine has a 04 CC LB with a 9" lift, 37" M/T Toyo open country and stock gears. he pulls a 16k trailer everyday so i think you'll be ok for a little while with ur stock gears :)

Assuming that you are upgrading from 265/75/16 the difference in radius is only 14.6%. This would be the same as keeping the 265's and switching to a 3.19:1 rear end. It won't kill you, but the engine will work harder.

As best I can tell, your Sierra is a CC SB 2WD. The stock tow rating per GMC's website is 15500 lbs.

For a 9% difference in gearing on the 8.1 (4.10 vs. 3.73), the tow capacity is reduced by 13%.

Proportionately, we should reduce your towing capacity by 21.3%.

This brings you to an actual towing capacity (based on 15500) of 12200 pounds.

/Missing engineering school over winter break...

I ran mine for around 9000 miles with 37's and 3.73's,towing 6000lbs every weekend. The only downsides seemed to be some lost out of the whole performance and lowered fuel mileage(corrected for the speedometer difference).Mileage came back up to the high teens after gear swap.You shuld be fine until your gears make it in.

a friend of mine has a 04 CC LB with a 9" lift, 37" M/T Toyo open country and stock gears. he pulls a 16k trailer everyday so i think you'll be ok for a little while with ur stock gears
How does he like the Toyos and are they fairly quiet? I have the Xterrain tires on my '02. They are a little noiser tha I'd like but not extreme.

My Sierra is an '05 CC, LB, 4WD. This truck has the 245 tires. Here is a comparison between the new truck the day I picked it up and my '02 -

http://www.tbyrne.com/Sierra/twotrucks.jpg

I haven't done the math yet but there seems to be a pretty big difference in the tire size (7").

the toyos are great tires. he likes em alot. they are much quiter than the x-terrains. he had terra grapplers 35" first and wore em out in about 14k miles.i mean WORE OUT. between me and him and some of our buds we've had a bunch of tires,bfg A/T's,terra grappler,michelin ltx A/T & M/S,to boggers,super swampers,yada yada yada and the open country M/T is definitely the best tire by far. im puttin 315 toyo M/T's on my 05 d-max. another awesome and over looked tire is the **** Cepek F-C-II...sorry for the long post. this was about gears not tires

if you run 37's and re gear the truck how will the truck respond out of the hole?Is their that much of a performance loss?

What lift did you decide on?

if you run 37's and re gear the truck how will the truck respond out of the hole?Is their that much of a performance loss?
The gain is pretty large,before when towing the truck would labor a little starting out on a hill,after the swap it takes of like nothing's behind the truck. Without the trailer it will really set you back in the seat through second gear smoking the tires(boost launched),usually getting traction when it shifts into drive,before it would only chirp the tires without power braking it(boost launched). I would say it was well worth the $600 I had in parts for the swap.

So changing gears will bring back my mileage? My 36" IROK's actually measure out to 36.8" My mileage decreased quite a lot since I installed the bigger meats. With a set of 4.56's will I be back to stock performance? Thanks.

I think you'll be fine, I run 39.5's and 3.73's and tow all the time. The lag isn't as bad as expected and I actually found that I like the feel, with the gears being longer the truck doesn't search for a gear as much as it did stock. I too planned to re-gear at first but after driving it put that thought on the back burner until I bust something.

I've had 37's on mine with the 3.73's now for about 25K miles. My buddy does towing for the movie industry and asked me to help him a few times. The trailers typically weigh 12000-15000 for a tag along.

Lets just say I had fun playing with him (he has a 99 Ford f350 6x6) on the freeways from LA to Semi Valley.

Now if I was towing this stuff regularly, I would surely get the gears ASAP, but considering I am normally only pulling around my car in my 32 ft (8000lbs max), and have enough power to overcome the tires, I just haven't had the concern to go get the new gears.

The reasoning behind the gearing for me is that I want to drag the truck this summer. I want to blast out of the hole like I did with my 285's. Also. if it brings back my mileage a bit that would be a bonus. Nick

ttt

It will still be fun racing with 37"s, didn't lose much power i think with my tires. The juice will take care of you.