on a 2001 f250 7.3 what gear ratio is appropriate for 37” tires? Thinking about 4:30 or 4:56..Im in the mountains with road grades that I have to climb it’s bot too flat here also I don’t drive much on the freeway most I’ll go is 65 for short periods of time.....I’m pretty sure I have 3.73 right now. I noticed a bit more fuel consumption when I got the bigger tires.. any chips that would help at all? All I have on it is the banks six gun. Also I need to swap my trans cooler because I’m noticing the trans temp climbing faster. Seen a lot of people swapping to the 6.0 coolers would be a nice upgrade anyways...

 

I run 4.88's with 37s in a 6.2 gas set up. I love it and think it is perfect. That being said, we have two different animals, the 7.3 turns half the rpms, has 2 less gears, and makes all its torque down low. I think you would be much happier with 4.30's, which would be very similar to a factory small tire truck with 3.55s.

 

Say you had 31 inch stock tires and 3.73:1 gears. 65 MPH would be at 2628 RPM.

37 inch tires decrease your 65 MPH RPMs to 2203. 4.56:1 gears would bring that up to 2692 RPM.

 

Only reason I’m thinking 4.56 is there are road grades where I live so I would be looking more on the low end two lane road performance rather than a higher freeway friendly gear..

 

If you tow heavy on a semi regular basis you'll want to go with 4.88's. If you seldom or never tow heavy go with the 4.56's.

 

If it will not climb a decent grade in overdrive with 4.30's and 37's, your either loaded heavy, or your down on power and need to address that. If it was gas, I would totally agree 4.88, but not on a diesel. It should be able to get low in the rpm range and chug along no problem. After all, that is the biggest advantage of a diesel. Your never going to get the mileage back up to factory tires, no matter what gear you run.

 

 

I'm really not sure how to answer that. A 7% grade is the maximum grade allowed on an interstate by law. A new 2018 6.7 is going to somewhat struggle on a 20% grade. If your really hitting stretches of 20% grade for any distance at all on a regular basis, then yes, go low, very low. Or except the fact it is going to down shift.

It's very hard to capture grade through picture or video, but here is a video of 20% grade.


I'm sure that video does not do it justice.
I can't imagine having grades like that and being at speed on a highway trying to use overdrive. I live in the foothills of East Tennessee. I can see the Great Smoky Mountains from my back porch. I can only think of a handful of places that steep around me, and they are all short grades.

 

I had 7.3 with basically 35s, going from 3.73 to a 4.30 gearing was fantastic, with 37s your net would be slightly lower than 4.10 gearing on a stock tire. I think 4.56 would be too tall, I’d recommend 4.30, good balance for towing and mpgs

 

I would go at least 4.88's if you tow anything remotely heavy. I run 5.13's and they made a world of difference when towing, I have a V10 so MPG isn't ever a concern. I would rather have the extra gearing than to spend $2k and not get enough.

 

Again, he has a 7.3 diesel. Max torque at 1600 rpm, more than a 1000 rpm less than a 2v 10. The 4.88 gears would have him well over his peak torque at only 55mph! With 4.30's, he would be right in his peak torque at 60mph.

 

People seem to be missing this ^^^ very key point.

4.30s are deep enough. After that you'd be better off looking into power, like larger injectors.

If for some random reason you need to make one certain climb that's 20% with enough weight you can't just climb it normally..... manual hubs and 4Lo works great.