Hi alll. I've read a few threads here pertaining to what size gear to go with etc etc. My question is, what is a safe rpm for the highway?

I have an '02 screw with 35x12.50's with a 3.55 diff.

I will be swapping out the gears within the next two weeks and am still deciding on whether I should go 4.10 or 4.56

I'm leaning toward the 4.10's only cuz I don't want to go 4.56 only to find out rpm is to high and I'm smoking my engine.

I can do the calculator's to see what rpm would be but they don't tell me if those numbers are safe.

PS- I MIGHT eventually add a 3" body lift to the 6" fabtech that I already have and upgrade to 37's or 38's down the road.....M-I-G-H-T.

Suggestions?

Thanks a bunch
-Tom

 

folllow up question...

please forgive me for any and all "dumb" questions.....

As a follow up to my original post, let me add this......

I went to ringpinion.com and typed in 4.56 for ratio, 35" for tire height and 70mph for speed.

The resslts were...

3146=auto, 2145 AOD

I'm a little confused. When I look at my tach, what will I see? 3146 or 2145?

2145 is obviously a safe highway rpm. Is 3146 safe as well?

hmmmmm, in contrast to my original post....I'm starting to think the 4.56 may be the way to go.

 

With 35" tires, the 4.10 gears will keep your truck "drive-able" in the sense that you will have the same response & mileage as your stock gears & tires. With the 4.56, you'll suffer loss of MPG, but have much more power at the wheels. A lot of guys here like having more power, and will put up with poor mileage. I'm running 4.10 gears & 35" tires, and I feel that the power & mileage is adequate for my daily driving needs. But if you're taking your truck off-road, or towing & hauling, then you'll gain a lot more with the 4.56. It's the same price to buy & install. You figure out what will suit your needs best. Daily driving? Or off-roading? Or towing & hauling?

 

well why dont you tell him the WHOLE truth.

with 35's id go with 4.56's, those calculators SUCK they arent accurate unless you know all your shift points and you OD RPM. My truck with 37" tires and 5.13's will be under 3k RPMs (v6) so i doubt you will be over 3k. You will definitely be in OD when you are at 70 unless something is broke. OD will bring your cruising RPM's DOWN.

Now onto the mileage question. Gear swaps are EXPENSIVE. You dont want to have to do it twice, IF theres even a slight possiblity for 36+ id go with 4.56 or 4.88's this will save your transmission in the long run. And help out when city driving stop and go.

Now what fifty left out was the fact that your mileage will infact go UP around town with the 4.56's cause the truck doesnt have to work as hard to get moving. However you will loose some while driving down the interstate. IMO the two wipe each other out. Its gonna be an improvement over the stock 3.55's

but its really up to you but you dont want to run 37+ inch tires with 4.10's with the weak transmissions in these trucks. Even 35's on stock gearing will damage them. Especially if you offroad or tow regularly.

that brings me to the last point. If you tow regularly (once every week or two) id definitely go with a lower gear 4.56 or 4.88 it will help pull the trailer, and keep your transmission happy.

 

I agree with Trimble. I don't tow often, but do a decent bit of off pavement driving and a lot of driving at elevation up steep grades, and heavy 35" tires are rough on the Tranny. I'm putting 4.88s in pretty soon.

 

Thanks for the advice. The 4.56 are in! Should be picking it up tommorow..


Heres a look at my truck as is.

Air hog CAI
6" Fabtech
2" Leveling kit front
Edge Evolution
Straight pipes/Y pipe (had magnaflow and thrush..didnt like-took off)
rhino steps
35x12.50x17 Nokian Vativa MT
4.56 Yukon gears

soon to be....
3" PA BL
37x13.50 (undecided which brand)
1.5" spacers
fender flares
Westin Bull bar w/lights

sorry dial up'ers
http://www.aquaprocs.com/truck/PC090090.JPG

http://www.aquaprocs.com/truck/IMAG0031.jpg