5Oclock

My 2500 4x4 with 305 tires has 3.54 gearing in it. I occasionally tow a 5ver toyhauler that is probably around 13-4K loaded. My setup does fine and I average around 10-11 mpg. Problem is that some of the long steep climbs in the Sierra's slow me down to 42-45 mph. My my question is, would I get much bang for the buck with regards to climbing ability by going to 3.73 gearing? I've read a lot of posts from guys that really don't like the 4.10's due to the mileage hit when not towing so I figure 3.73 to be a good comprimise. Provided that there would be a noticeable benifit.

pronstar

Someone please correct me if I'm wrong, but those ratios are so close (about 5%) that I honestly don't think you'll notice a difference.

C Schomer

I think you can go to 3.92 with your carrier and the guys with bigger tires who have done that, love them. Craig

J OOPS

3:92 gears will cost more, than 4:10. There harder to come by for the D60 and D70 axles that your truck has. I'm getting ready to install lift and 35 tires. I all ready bought the 4:10 gears and will be changing over soon. If you go to those online calculators that can figure out the ratios to tire size a 35" tire with 4:10 gearing is the same as 3:54 gears and stock tires for our year of truck. So you would end up with stock rpm but with a heavier rotating mass and a little more resistance on the road with the bigger tires. Should not see a big loss of fuel mileage compared to stock.
Anybody else out there that has changed to 4:10 and running 35" see a huge drop in fuel mileage, for our year of truck?

rebal

I dont think you will see anything worth the cost you would would probably do better with a good converter

5Oclock

Great advice. Thanks. I googled the subject and found a site with such a caculator. I bought the truck used with 305's on it and liked the look so I stayed with the size when I put new 'E' rated rubber on it for my 5ver. Anyhow, stock tires are 30.5" tall, 305's are 32.8" tall. Which adjusts my 3.54 gearing to 3.29:1. To achieve a simulated 3.54:1 my ratio would need to be 3.81:1. Probably even harder to get. A ratio of 4.10:1 with 32.8" tires yields an actual ratio of 3.81:1. Darn close to 3.77 gearing.

Cost to change out is approx $600 per axle. So, I'm thinkin' I will wait an see just how much I actually pull through the mountains. I could probably get used to the 40mph climbs but don't want to burn up the tranny in the mean time.

Anyone see a hole with my logic?

stumpjumper

373 gears in my truck works great. i haven't had any troubles pulling hills in so cal with the 373's, and i even put a bit larger tire on mine.

pronstar

That's the same height as my BFG All-Terrains - just a hair under 33 inches. I've got the 3.73, and it's just fine for the towing that I do.

Biggest grade I've encountered was the Grape Vine going up to Gorman, had no trouble at all keeping up with traffic.

You've got a lot more weight that I do, but I'd stick to the stock ratios at first, then upgrade if you aren't happy with how it performs.

Mechanos

You might also check to see the truck's rev/mile setting was reflashed in the computer when the PO put the 305s on it. The computer might still think they're stock sized tires.

5Oclock

I've seen other posts regarding flashing. What is involved with that? Taking it to the dealer? Are there other ways to tell? Thanks

5Oclock

So you are saying that 4K for an upgraded TC and ValveBody would yield better results than 1400 or so to change the differential gearing? I have read/heard that the 47RE trannys are not that strong.

jballou

4k for an upgraded converter and TC? Much less than that 1500 search around.

Find someone with other tires to trial swap to, well try!

Use the smaller tires and get the computer flashed for the tire change. The formula for tires is just numbers, it is mainly a function of leverage, and that is what you are changing with smaller tires. Less leverage.

I went from 35's to 265's and now the truck almost nevers downshifts on hills. It would frequently downshift on slight hills even with power adders. I know big tire downsize and not exactly your situation, yet very educational.

5Oclock

Sorry, got my #'s mixed up. 4K is for a full rebuild with a new TC and VB. TC and VB is about 2500 for parts and labor.

Just spent 1100 for new rubber maybe 1K miles ago. I can consider going back to 265's in about 49K miles or so.

SundayMoney

Whats wrong with 42-45mph?

Pulling 14,000lbs,you can't expect to be able to pull every grade as fast as you want.

Is it really that big a deal to have to slow down once in awhile? IMO I'd keep the extra coin for a diff change or tranny upgrade in my pocket,and learn to live with a slightly slower pull up a steep grade.

$1000+ is alot of money when you're only encountering problems occasionally.

If you really have to be the first guy to the top,thats no problem either. All it takes is money.

CrazyCooter

The 4.10's would help save your trans in the long run regardless of what speed you would gain on the hills.

I just did a 3.54 to 4.10 swap today on a well modded 01 2500 4x4. He has 285/70/17's on his and tows a 13,000 toy hauler.

I didn't think it reved that high after the swap....Still lower than my 06 6spd.

I also fixed his speedo error. All you need is a SnapOn MT2500 with the correct software and a K13 personality key. Almost any shop should have one of these or better.