i found out last week that my g80 is now a nice open differential now :) but i also realized that i still have 3:73s :( so i am thinking about running some different gears to compensate for the 40 inch tires. i was thinking 4:10 ? 4:11s ? higher? i want to gear it so it will have more low end but still get good gas mileage and highway drivability. what do u guys think ?

I'd say at least a 4.56

I just did a quick calculation it looks like 4.88s should get you back to a stock ratio when running 40s

4:88s? holy man ! thank you ! what performance could would i possibly see with that kind of gearing? cause right now with my gears it feels like i could go 100 + cause of the rpms at 75. but i do not need to go that fast its a truck. what equation did u use? and what rpms or highway driveability would i see? eg 75 mph . thx

http://www.richmondgear.com/101032.html

I went on another website which has a calculator on it. You just put in oe tire size, tire size your running now, and gear ratio. Then it gives you 3 ratios high, middle of the road, low. The 4.88s are in the middle which Should be somewhere around stock.

The website is www.tyres1.com then click on interactive calculators on the lower left

I would go with 4.56s minimum but probably 4.88s. I run 4.10s in my 08 dually with 33s and 22s.

I say 4.56. I have them with 38's and its dead on stock. since i don't tow over 8,000lbs, i wish i would have went with 4.10 or 4.30's. i got good freeway mileage with my stock gears. when towing i would drop it to 4th and pull the grade easily with 1200 egt's. of course that has alot to do wih my efi live tunes. Going 70 mph now i'm turning 2200rpm. i wouldn't mind it being more in the 1800rpm range going 70mph. I did run 40's for a while and i didn't see much difference in the rpm's like i thought i would. I will say that running 4.56 helped my grade braking alot. I think 4.56 will be fine imo.

After reading this thread I decided I wanted a piece of the action. I just got some 4.56's to go with my 33"s. Stock @ 70mph I'm turning like 1700 rpm's. I want that to be a little higher.

My question: Will lowering the G-ratio also lower my ability to tow heavy?
Can I still tow 15k? with a tongue of 2k?
I want to buy a 5th wheel this summer, but I don't want to GANK myself.
Thanks

After reading this thread I decided I wanted a piece of the action. I just got some 4.56's to go with my 33"s. Stock @ 70mph I'm turning like 1700 rpm's. I want that to be a little higher.

My question: Will lowering the G-ratio also lower my ability to tow heavy?
Can I still tow 15k? with a tongue of 2k?
I want to buy a 5th wheel this summer, but I don't want to GANK myself.
Thanks

It will tow more weight easier with lower gears. You will be running alot more rpms at 70 mph also

So it seems to me this is a win-win. BUT we all know there is no such thing as that on planet Earth. So..... what am I missing?

You will be running high rpms but the engine will be working less to pull the weight. You will probably be seeing like 3500 rpm at 70'with 4.56s. 33s really aren't that much bigger than the 30.5s that came stock on her. I towed a bunch of skid steers and mini excavators with 33s and stock 3.73s no problem.

I have pulled my 13500lbs 5th wheel with 37,s and stock gearing( not stock power) and it pulls it just fine

4:88s? holy man ! thank you ! what performance could would i possibly see with that kind of gearing? cause right now with my gears it feels like i could go 100 + cause of the rpms at 75. but i do not need to go that fast its a truck. what equation did u use? and what rpms or highway driveability would i see? eg 75 mph . thx

Yes, 4.88 will put you back exactly to the stock power range equivalent of 3.73 with 245's. In 5th gear, you'll be turning 2200 RPM at 75 mph with the 4.88's - and 2050 RPM at 75 mph with 4.56 gears. You'll have a lot more power and better fuel economy with the 4.88's, compared to where you are now.

Don't fear the gear! While a certain ratio will get you into "back to stock" ratios, it will not account for the increased strain on your drivetrain from the substantial weight addition of larger wheels/tires.

Brother,
The strain of the weight increase is nothing compared to my programmer and lead foot. :D

<======Is jealous of you diesel boys! Someday, someday...

How strong are stock axle shafts?
Say you have a 600rwhp truck sittin on 40s running 4.88 gears there is going to be a retarded amount of stress on them. How easy would it be to snap one?

The stock axels shafts are strong enough to handle 37 super swampers. I've had my truck in several mud bogs over the years. It now has over 200,000 miles, 130,000 with swampers with the stock axels.
By the way i don't baby my truck!!!! it is a farm truck and play truck.:D:D:D
It sees it all bush trails, mud, rock, rivers, pulls 15,000 lbs regularly. My 02 has been the best truck I have ever owned. I'm still running all the original u joints.

The stock axels shafts are strong enough to handle 37 super swampers. I've had my truck in several mud bogs over the years. It now has over 200,000 miles, 130,000 with swampers with the stock axels.
By the way i don't baby my truck!!!! it is a farm truck and play truck.:D:D:D
It sees it all bush trails, mud, rock, rivers, pulls 15,000 lbs regularly. My 02 has been the best truck I have ever owned. I'm still running all the original u joints.

I've broken more rear end parts on the street than in the mud with my old truck. It had a 255hp vertec 350 with a 30 spline 10 bolt 4.56 gears on 38s. Every time I snapped an axle or blew a carrier apart was in the street.

You will be running high rpms but the engine will be working less to pull the weight. You will probably be seeing like 3500 rpm at 70'with 4.56s. 33s really aren't that much bigger than the 30.5s that came stock on her. I towed a bunch of skid steers and mini excavators with 33s and stock 3.73s no problem.

Are you sure that he would be running 3500 rpm at 70 with 4.56?? People with 35's and 4.56 gears run at about 2000 rpm.

http://www.dieselplace.com/forum/showthread.php?t=229104

I was hoping that was a typo. Cause 3500 would be bouncin near redline:eek:

Are you sure that he would be running 3500 rpm at 70 with 4.56?? People with 35's and 4.56 gears run at about 2000 rpm.

http://www.dieselplace.com/forum/showthread.php?t=229104

Yep typo I ment 2500ish no way it's gonna be 3500