gear ratios

Hey guys,

If all goes well looks like I will be getting a 6.7 crew cab 4x4 this week... I am trying to figure out what gear ratio to go with. This will be my daily driver & will be towing with it as well, but I dont want the motor reved out on the freeway.

If you could post your gear ratio, tire size, RPMs at 75mph & top speed @ what rpm... that would be awesome

3.55's are the highest option you can get in a SRW truck now. But with 20's and 3.55's I am at 1650 at 70mph.

I really wish we could go 3.73's.. these things lose so much power just going to a set of 35's

if you get a 4x4 you have more options. how heavy is your tow rig?

I'm going with a 4x4, I'll be towing up to 12k lbs but up in the mountains @ an altitude of 7k+ft

I have 3.31s and I love them! If I go 60 I get 23 mpg and If Im in town I get 16-18

That is single cab 4x4 with 20" wheels and 33" Toyo MTs on stock suspension...and an AFE intake but otherwise bone stock!

Oh I am at about 1600 RPMS at 70 highway in 6th forgot to mention that

I have 3.31's with 35" tires at about 73 mph im turning 1500 rpms, at around 100 mph im still under 2k rpms.

I tow my gooseneck with are john deere tractor that total weight of deere and trailed is right at 38k lbs and i have no problem getting it moving, i can actually get out of the hole faster than my dads 6.4 with 3.73's.

I average mid 17's around town and highway mid 19's and broke 20 a few times hand cal. Ford claims 3.31 gears holds the engine in peak torque at 70mph. ive never experienced losing power with the 35's i can still white smoke the tires taking off without power braking.

Anyone else got more input?

Im going to be leaving the truck bone stock, mostly towing and probably only a 33 inch tall tire maybe a 35... thanks

Engine mods on my truck are H&S Mini Maxx, aFe Intake and a 4" down pipe back DPF delete.

Mine with 38's and 3.55 gets 13-14 going 70 turning 1500 rpm. This past weekend on the way to Ennis I was getting 15 going 80-85(did check the rpms, but I will tonight on my way home), that was the best my truck has ever gotten. I think there was a tailwind so that may be what helped me.

I haul my 36' gooseneck grossing out at 26k-29k a lot and get about 8 mpg, I don't have a problem getting the truck moving at all either.

ThAnks

So you guys think a truck would tow well with 3.31

Everyone with 3.31's doesn't seem to have problems getting stuff going. If you plan on sticking with stock wheels you shouldn't have a problem with the 3.31's but up in the hills the 3.55's may help a little

These things are double overdrive right? Do they ever kick down two gears on hills to.direct ?

I'm really surprised with the higher gear ratios not having a problem moving loads, the 6.7 is a beast. My father ordered his ec dually with 3.73's and gets 20 mpg mixed driving. Not sure on the rpm/speed, I haven't driven it in awhile.

Seams to me like too far might lug the engine and get worse mileage

My buddy is in the process of buying a 2012 truck but was undecided which way to go, 350 SRWccsb or DRWcclb. We test drive the SRW with his 20ft enclosed (10k) and with the 3.55's and 20's it didn't like 6th gear at 65mph. It was hunting between 5th and 6th to much and lugging pretty hard in 6th. Wouldn't be a problem at 75mph though. He decided to go DRWcclb with 3.73

Checked my RPM's on the way home last night:
70 - 1550
80 - 1775
85 - 1900

I think my fuel mileage suffers from the truck lugging at 1550 going 70, but then when I bump it up to 80 the mileage suffers again from the wind drag that it has. I'm in one of those damned if you do damned if you don't situations.

What about manual shifting into 5th instead of 6th at 70?

SAK said:

Engine mods on my truck are H&S Mini Maxx, aFe Intake and a 4" down pipe back DPF delete.

Mine with 38's and 3.55 gets 13-14 going 70 turning 1500 rpm. This past weekend on the way to Ennis I was getting 15 going 80-85(did check the rpms, but I will tonight on my way home), that was the best my truck has ever gotten. I think there was a tailwind so that may be what helped me.

I haul my 36' gooseneck grossing out at 26k-29k a lot and get about 8 mpg, I don't have a problem getting the truck moving at all either.

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Dzchey21 said:

Seams to me like too far might lug the engine and get worse mileage

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Mine is all stock with 4:30 gears. It runs 2300-2400 going 80 and I get 14 empty. Hauling at 28900 13' high Im getting 7-8 at 75-80. Seem like his is lugging comparing rpm and mpgs.

Rivets are the new duct tape.

Dzchey21 said:

What about manual shifting into 5th instead of 6th at 70?

Click to expand...

I will try it on my way to the ranch this evening from the office, but its only 40 miles, I would try it the rest of the way home but I will have my gooseneck and backhoe in tote.

I will check the RPM too to see if my theory is correct.