Opinions on specs for 7-13 axle setups - your dream HH truck

3.36 rears in heavy haul??? That would suck.

I don't haul over 80K, but this truck has 3.36 rears, they're great on the flat. But I'm in the mountains all the time, and they suck. Sure I can run up hills fast, but no faster than I could with 3.70 rears. And the fuel mileage is horrible.

 

And this was the question that made the other thread go south. GEAR RATIO. The Forbidden Subject.


Hey people, do you know how gear ratio work? Do you understand the importance of gear ratio? The forum is HEAVYHAUL. The topic is a truck that can pull 7-13 axles. A 13 axle rig loaded will be in the 250000+ range. You dont say 3 anything with 13 axles. 4 is the magic number.

Gear ratio. 3.08:1. The axles spin 3.08 times to every 1 time the driveshaft turns. 3.36:1 is a lower gear gear than 3.08:1.

"How is that possible, Six...it looks bigger. I am confused."

Of course you are. If a drivetrain has the axles turning 3.36 times every time the driveshaft makes afull turn, compared to another that makes 3.08:1, the 3.36 is turning faster right? Lost?

Father and son are walking together. Dad is 7 ft tall and son is 4 ft tall. Who is taking more steps? Son. If dad takes 4000 steps per mile and son takes 5500 steps per mile, the ratio looks like 4000:1 vs 5500:1. Who is walking faster? Neither. They are traveling at the same speed. But son having to take more steps to run the same speeds gives him the lower ratio.

You are not going to pulla loaded 13 from a start up a hill with a 3.36 gear. You may get a 7axle, but my money is on you grenading the drivetrain at least twice a year.

Someone wanted to argue about engine torque for hill pulling. Going up the hill is only part of it. Lower gears also allow you to crawl that monster down the grades SAFELY.

Heavyhaul 101...let the GEARS do the work. Gears. Transmission and rears.

 

Good info Six.
A good way too think if gear ratio is to think of it as a lever. The longer the lever, the more force you can apply. The bigger the number, the longer the lever.

3.36 rears are like a 3/8" drive short handle ratchet
3.70 rears are like a 3/8" drive standard handle ratchet
4.10 rears are like a 1/2" breaker bar
4.56 rears are like a 1" breaker bar with a 3' snipe

The heavier the load, the bigger the bolt. A 1-1/2" socket just won't be very effective with a 3/8" drive short handle ratchet on it.

 

series 60 detroits never did like tall gears even moving general freight you'll be wishing for some 3.90s when you hit a hill

 

I think you have that backwards. The 3.36 means the drive shaft turns 3.36 times for one time the axle turns. Not the axle turning 3.36 times for every revolution of the drive shaft.

 

The thing people seem to overlook when specing truck is the intended purpose. If you're running 7+ axles and oversize loads, your fuel economy is going to suck regardless. Why double screw yourself and run 3.08 rears? Put 4.10's or 4.33's (heck even 4.56's if you need to) in it. Especially if your work takes you off road. That extra oomph down low is going to help save drivelines and clutches.

 

Believe you may be right.