Which Gears to Run with 37's?

OldschoolPSD · May 3, 2014

The six speed is a lot more forgiving to taller gearing. I've run 3.55s and 35's on a zf and it acts just fine. Actually kind of nice because you can use 1st gear instead of having to take off in second all the time. Reverse is high though.

Strokin89 · May 3, 2014

I've got 315x70 on the truck now and I never really have to use low. I love how it drives with the tires and 373's but hate the wheel gap I have hahaha

2005 F250 6.0 powerstroke, 6 speed manual, egr delete, arp head studs, new oil cooler, aftermarket coolant filter, custom intake, 4" down pipe into dual 6" stacks, 8" lift, TSD super panty dropper tune.

bootcamp · May 3, 2014

I went from 3.73's to 4.10 and noticed very little gain out of even with 35's. To this day I'm still wishing I had went with 4.30's, you will lose some top end, but gain a hole of bottom end and still be able pull something and keep your gets in check a lot easier.

Snake · May 3, 2014

florida 6.0 said:
I have 37's and 4.56 gears . Daily and towing the truck cannot tell the difference between stock and now . On the highway at 80 it runs 2100 rpm and still gets 15 mpg. I went from a 40 to a 38 and then to a 37 and the 37's are a great match for them .

You don't have 4.56's if you're only turning 2100 rpm at 80 mph with 37's. Either that or your speedo is off quite a bit.

Snake · May 3, 2014

true98jeep said:
Florida thank you for the reply. That is what I am looking for someone who has actually run those gears and can comment on it. I am very torn betw. the two one day i decide 4.56's then the next I think 4.30's haha. I was hoping that would take it to right back to stock as that is how these trucks were built to perform so as close as possible I can get it the best I feel I am.

My 05 F-250 Harley Edition came with a 34" tire and 3.73's from the factory. 4.30's and 37's turn about 100 rpm higher on the freeway than where I was stock.

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true98jeep · May 4, 2014

Snake said:
My 05 F-250 Harley Edition came with a 34" tire and 3.73's from the factory. 4.30's and 37's turn about 100 rpm higher on the freeway than where I was stock.

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Thank you snake that is very manageable for me and thinking that is prob going to be the best all around choice for it. To bring it back to a factory type deal and take a lot of extra strain off the trans.

Dave · May 4, 2014

Snake said:
You don't have 4.56's if you're only turning 2100 rpm at 80 mph with 37's. Either that or your speedo is off quite a bit.

Yeah at that your speedo is off by 15mph or so

true98jeep · May 4, 2014

Did a few more calculations compared it to my fathers F350 dually with 4.10 gears and 235/65R16 (32) tires and decided I am going to go with 4.56's. It will get me just under his gearing when I use the 37's 2200 RPM at 75mph versus 2300 for his. And it will be just lower when I put the 35's on which I plan to swap over to for heavy towing which I will want to be geared lower anyways. Looking to have these swapped hopefully in the next month I will provide feedback when I can as to how this set-up acts.

Snake · May 10, 2014

I'll check again today, but I think that's really close to what I'm seeing with 37's and 4.30's at the same speed. Verified via GPS, factory tach, and a Dashboss.

true98jeep · May 10, 2014

Awesome Snake thank you sir. How is that set-up for you? Would you change if you had to do it all over again or do you like the drivability?

06f250powerstroke · May 11, 2014

430s all day long

Snake · May 11, 2014

true98jeep said:
Awesome Snake thank you sir. How is that set-up for you? Would you change if you had to do it all over again or do you like the drivability?

Haven't had a chance to verify the rpms yet, but I wanted to answer your questions. I'd do it exactly the same if I had to do it all over again, and the drivability is perfect for my situation (don't tow incredibly heavy and the speed limit here is 70 mph). I'd go with 4.56's if I was pulling 15k lbs regularly, but I'd recommend 4.30's to the majority of people running 37's with the 6.0.

Dlinzy · May 11, 2014

Have you put any thought into the 37's actually being closer to 36 and with any wear they'll be at 35 quick. Same goes for most 35's start in the 34's. MT's won't last long on the Highway...

D

true98jeep · May 12, 2014

I know the true specs of my tires and they are a true37. That being said when they wear it will turn them closer into 35's. The 35's I will be using are actually going to be about 35.6 new as I am looking at doing a Metric Toyo A/T II tire on 18's. I will only use the 35's in the winter when up north and when towing Heavy for long trips. I do use the truck quite frequently as a truck pulling 10-15K I would not say regularly but def more than prob 75% of the diesel truck owners esp around me. I am going to do the 4.56's as the 100 -200 rpm drop the 4.30's will save me is very very negligible to me. I like the Idea of having The equivalent of 3.73's daily ( 4.56 + 37's) and the option of having 4.10's for towing (4.56 + 35's). I see this as the absolute best of both worlds and best bang for the buck to actually upgrade my rear from a normal stock set-up.