AH64ID

So here is a chart that shows RPM's.. .Everything in red is either above 2900rpms or below 1600 (since there is no point in cruising above 2900 or below 1600). Rpm's are based off the listed ratios and OEM 265/70/17 Tires.

RowJ

Don't quite follow the above chart but.....
like 'Sewman' said .....

With 35" tires on my 3.55 rear end, I figured once I'm actually at 3.42..... if memory serves?
Lot's of us are! Gives 2000 rpm at 80 mph and works well!
Tows well up to say 12,000 lbs. on my automatic. With a 6 speed I know several that tow heavy and have no concerns.

RJ

AH64ID

Shows RPMs in a gear at a speed, even if the truck cant do it... like you can't go 80 in 1st... but if you did you would be at 21835rpms with 3.73s.


If you have 3.73s and 265/70/17 stock this is what tires does to your effective ratio.. using OEM and toyo rev/mile specs... each tire is a little different, but you get the idea.

285/70/17 : 3.605
285/75/17 : 3.481
325/70/17 : 3.378

With 35 BFG's and 3.55's you actually closer to 3.262 if your truck came with 265/75/16, 3.128 if your truck came with 245/75/16 or 3.252 if your truck came with 235/85/16...

ddestruel

figured using a NV5600 transmission which aside from the 05/06/07 G56 with the high OD the new 07 and later G56 shares similar ratios to the nv5600 so i just used a nv5600 to calculate

315/70/R17 35" tire 4.10 gears

55 mph 65 mph 75 mph
4th gear 3065 3622 4179
5th gear 2205 2606 3007
6th gear 1610 1902 2195




315/70/R17 35" tire 3.73 gears

55 mph 65 mph 75 mph
4th gear 2769 3272 3776
5th gear 1992 2354 2716
6th gear 1454 1719 1983


315/70 r17 35" tire 3.54
55 mph 65 mph 75 mph
4th gear 2557 3021 3486
5th gear 1839 2174 2508
6th gear 1343 1587 1831



315/70 r17 35" tire 3.42
55 mph 65 mph 75 mph
4th gear 2646 3127 3609
5th gear 1904 2250 2596
6th gear 1390 1642 1895



285/70/R17 33" tire 4.10 gears

55 mph 65 mph 75 mph
4th gear 3220 3805 4391
5th gear 2316 2738 3159
6th gear 1691 1998 2306




285/70/R17 33" tire 3.73 gears

55 mph 65 mph 75 mph
4th gear 2929 3462 3994
5th gear 2107 2491 2847
6th gear 1538 1818 2098


285/70 r17 33" tire 3.54
55 mph 65 mph 75 mph
4th gear 2780 3286 3791
5th gear 2000 2364 2727
6th gear 1460 1726 1991



285/70 r17 33" tire 3.42
55 mph 65 mph 75 mph
4th gear 2686 3174 3663
5th gear 1932 2284 2635
6th gear 1411 1667 1923


hope that helps

RowJ

Ok, I'm at 3.26! Thanks
So, to answer original question... 3.42 should not be a problem, if towing.... and with smaller tires, should aid mileage, IMO

RJ

AH64ID

Wasn't being a dick... just had the calculator built in excell so I ran it

Yeah you should be ok towing.. .thou it will drop your tow rating by 1K lbs to get the 3.42's... Personally i would take the 3.73's and add a GV over/under drive if you really want mpgs and good towing... gives you 11 fwd gears (really 10 since 5th over and 6th are very close on a NV5600 and even closer on a G56)....

But look at these numbers.. speeds based on 2200 rpms (CR sweet spot)...



And with the gear vendors if you shift at 2200 rpms will be greater than 1600 in the next gear, on every shift (except 1-2)... W/out the GV you have to shift at 2700 to get all the shifts above 1600.


You also have to think about using the EB... with 3.42's your going faster in each gear at max retarding hp... another vote for the GV... look at how many speeds you can choose from, or downshift at with the GV...




The only drawback to the GV is the cost... but if you plan to keep the tuck for a long time it will pay for itself.

therabbittree

3.42's all the away.. thats what i would order with a new truck order... my '92 has a 5spd and i am swapping a '07 G56 in it and I run 3.07 gears its great plows greta towes awesome.. out pulls my friends '01 3500 6spd ho with 4.10's, and my dads '02 355 auto..etc.. and i run 285 tires so my effective final ratio is even lower then the 3.07s..etc..
I'm seriously thinking of a third gen manual...a mega cab 5500 4wd 6spd manual would be perfect for me.. but no mega cab in a 5500 with out doing soem parts swapping from a wrecked truck..when i pay some debts off.. if the truck i find doesn't have 3.42s i'm gonna buy teh r&P sets and swap them in etc.. its worth it that much to me...
Later
Deo

MLB 1

The Gear Vendors is an excellent choice for higher gearing/lowering RPM. BUT...is not reccomended by gear vendors, to be used in a towing/heavy load situation (see gear vendors website). I changed out my 3.73's for 3.42's 25,000 miles ago and am very happy. I have the stock tire size and have noticed a reduction of about 175 rpm at 75 mph.

One other thing to take into consideration is where the torque curve is on the cummins motor. I remember the ford 6.0 reached max torque at around 3500 rpm (hence the need for the lower gear ratio). I can't recall but im sure someone will note that the cummins makes all its torque between 1600-1900 rpm. The 3.42 gears in 6th (g56) put me right above it at 75-80 mph.

Just some food for thought.

AH64ID

Please show me where it says not to tow heavy loads with it... everything I find is the opposite...

IMO 189rpms at 75mph just isnt worth the cost..

bondkx01

don't think you can get a 08 with 3.73 anymore.. all 4.10. That's the only option when I ordered mine

bondkx01

just checked again. You can't get the 3.73 with the new 68rfe Auto. So I guess only 4.10

AH64ID

Yeah the website says that, but they are on the lots???

bondkx01

ahh.. I think those are left overs from when they where offering 3.73's. So I think this is a recent change.

MLB 1

Check under "commercial towing" on the Gear Vendors website. It will also explain about a +/- gain in fuel economy while towing.

Barry Smith

Like lots of others on here I used to gross 32000lbs + with a NV 4500, 265's 3.54s and other than off the line they were great. I can't imagine getting the 4.10's in anything I was going to pull on the highway there's no need.