Transmission gearing actually. I was wondering about this for a while. I have a ZF-5 in an F350 dually. Came with 4.10 rear end and changed to a 3.55. Still I'm running 2100 rpm at 60. I was under the truck the other day to get the stampings off the tranny anyway and found that my ratios range from 5.88 in 1st to .77 in 5th. In 5th, with the 3.55's that gives me a total ratio of 2.73:1. I realize the Autos will have different ratios, but what abuot the other bolt-actions out there? What do you guys have?
Dave

 

On the ZF-6 the ratio's are 1st-5.79, 2nd-3.30, 3rd-2.10, 4th-1.31, 5th 1.00, and 6th-.72

3.73 rear gears for all single rear wheel Superduty's (with the 7.3) puts the final drive ratio about the same as yours.

 

I running 3:55 gears and an auto at 60mph with 265/75 tires I'm turning 1500 rpm. I'm not sure what the overdrive final gear is but 600 rpm is a big difference.

 

I have the ZF-5 in my 96 dually and 4:10 rear end. But I also have a Gear Vendors overdrive unit which is a 22% over drive. At 70 mph I'm taching 1900. I don't know what the math is on that, but I get great fuel mileage and I'm not screaming at highway speeds.

RubberDuck

 

I was wondering about that. Very soon it WILL pay for me to look into an over/underdrive unit.
Rubberduck: what mileage are you getting with that settup? I think I'm around 2300 @70 mph. That would definitely make a mileage difference. Another thing is that the gearvendors unit wouldn't change the speedo reading either. As opposed to putting taller tires on.

 

The initial cost is hard to swallow, but I can't imagine being without it now.I went from averaging 13.6 mpg to 17.3 mpg. That's what I average. That being said, with all the mods and me loving to see my stacks smoke, it could be better. In other words I usually drive like an idiot. I did manage to drive sanely for an entire fill up once and I averaged about 18.5. I concider that very good for an old body style dually with 4.10's. So in your case if you drive normal it will pay for itself shortly with fuel prices now days. And you are correct, it doesn't change your speedo at all. Putting taller tires would probably hurt your fuel mileage, because it takes more power to turn them with the same gears. Trust me on this one. My only complaint was customer service for me. Since they don't do many single cab installs they really don't have a mounting set up for me. They claim they do, but they don't. I had to fab my own mount using parts of theirs. And it took forever for them to send me what they thought would work. But during this process I got to know them quite well and without a doubt I would do it again. Their techs are spot on about all aspects of the unit and install. I'm just impatient is all. But for your crew cab, the install will be smooth as silk. They acutally sent me a bracket for a crew cab and it would be super easy to install. Anyway if you think you want to get one, pm me and we can cover the ins and outs of it. Hope that helps.

RubberDuck