Best diff ratio for highway towing?

[oh1coupe]

I have just began to use a 99 4.6 expidition to tow my work trailer. Average day is around 100 miles. Its my understanding that the truck came with a 3:31 gear from the factory, can anyone confirm this?

Towing on the interstate i run right around 65mph, with OD off, ( the transmision shifts in and out of od excessively due to load otherwise) and get 9-10 mpg.

Anyone with experience please chime in. With 4.10's would I be able to utilize od on the highway? Im guessing the 4.10 setup would reduce load on the drivetrain and possibly net a little better mpg on the highway, and definatly help it pull up hills, and through town.

any advice is appriciated.

 

[pronstar]

Not sure what your factory gears are. My 97 5.4 came with 3.31 which makes no sense...

What size tires do you have?

I run 4.10s with streeet tires, 285/60R18, and it's the second-best thing I ever did.

Normal driving MPG didn't change. Towing MPS went up a bit. Power is increased everywhere.

You will be able to use OD when towing, though I still think it's best to downshift for grades. But when you aren't towing, you may be able to use OD for most moderate grades (not sure because it's still a 4.6 in a heavy truck.)

But you'll love them with stock-sized tires. If you have larger off-road tires, you'll want to look into more gear, like 4.56 or shorter.

 

[ELVATO]

Quick slightly off-topic question.

Ok, a shorter gear gives you better power all around, but does it reduce your top speed?

 

[JUST4FUN]

3.55 gear in my Expy I tow a TT with OD off at 62 MPH 9.6 MPG
Even with a 4.10 gear Ford dose not recomend towing with the OD on you will make to much heat in the tranny. With the 3.31
in it this sounds like it didn't have a factory tow package (poss can too)

IMHO this expy is not a good tow unit the rated capacity is 5900 lbs with a tow package thats max#

 

[JUST4FUN]

Originally posted by ELVATO
Quick slightly off-topic question.

Ok, a shorter gear gives you better power all around, but does it reduce your top speed?

yes you will run out of rpm faster with a taller gear

 

[oh1coupe]

This did come with the tow package...has the reese hitch, trailer brake prewiring done under teh dash,,etc.

 

[JUST4FUN]

does the hitch say reese on it if it does than no it didn't
ford puts there own hitch on them pluse a trans cooler and larger radiator
IMHO in the Florida heat with no trans cooler this expy is doomed

 

[ELVATO]

Originally posted by JUST4FUN
does the hitch say reese on it if it does than no it didn't
ford puts there own hitch on them pluse a trans cooler and larger radiator
IMHO in the Florida heat with no trans cooler this expy is doomed

Hmm, summer is coming up... Guess I might have to get me one of those coolers. Even though I don't tow, I don't exactly take it easy

 

[pronstar]

Originally posted by ELVATO
Quick slightly off-topic question.

Ok, a shorter gear gives you better power all around, but does it reduce your top speed?

On these trucks, you can't get a gear short enough to reduce top speed. You'll never, ever get anywhere near redline in top gear in your truck.

I buddy on another forum has a heavily modded truck, runs 4.10s on 28.5-inch tires. He almost hits redline in top gear, which calculates to almost 155mph.

I once had the balls to try a top-speed run in my truck. 4.10s on 285/60R18 street tires. I was nowhere near redline but was going well over 130mph. And I'll never do that again.

You could put 4.88 gears in your truck on stock tires and you'll never even come close to redline, so in the case of these trucks, the answer IMHO is no, you won't reduce top speed...because they are geared so tall.

THEORETICAL top speed will be reduced, but you'll never, ever make enough power to pull redline with 3.55 or 3.73 factory gears...so THEORETICAL, yes, but in reality, no.

 

[ELVATO]

Ah, OK. Thanks for the info pronstar.

As of right now, I max about 106-107 (speedo indicated) @ 4300ish RPMs (don't know what gear) on a straight road. I'm guessing this is because I'm not producing enough power to overcome the air drag, right? So what you are saying is that with a shorter gear, my thoretical high speed will be reduced, the top speed I will top at will be higher since there is more "power" being transfered to the wheels. Or am I getting this all wrong?

Sorry for the thread hijack