I'm in the middle of moving from Colorado to Missouri. As such, I've run about 5 loads across I-70 to the Show Me State. And one of the nagging issues with my truck that I've wanted to rectify for years is my gearing.

Presently I am sitting on about 6.5" of lift and 37" Goodyear Wrangler MTs. I plan to stick with 37s and have a "new" set of MTRs scheduled for delivery next week.

My issue is that with the stock 3.73 gearing, the truck feels a bit doggy. I'd love to have crisp throttle response without having to force a downshift. And I'd like to be able to tow without feeling like the truck is drowning.

I've done a few calculations, using some online gear calculator sites, and have figured that to get back to a profile that would put me close to stock tires and gearing, I would need to go 4.30. A friend has told me his father had great success with going to a 4.56 gear.

So, who has regeared with 37" tires, what gears did you go with, and how did that decision work out for you?

 

I run the same thing (37's with 3.73's). That ratio drops me down in the 3.50 range so I trade off a little low end/in town MPG for lower RPM at speed and better highway mileage. 4.10's or 4.30's would put you closer to stock but at what cost. In other words, do you tow all the time around town and want more low end or do you drive longer distances at highway speed more often? My tuner makes up a little in the lower end if I need it and have not had issues. Right now I push about 1700 RPM at 70 MPH on the interstate. I would guess that if you went with 4.30's, you would be pushing into the mid 2k range and not only would your mileage suffer, you would be running much hotter temps in your fluids. I thought about going with 4.10's many years ago but everywhere I go from my home is highway/Interstate so I just left it stock. I know, not much help but there are not many others on here that run these tires that have changed out their gearing. I can think of two others that might chime in......

 

Im interested as well, (sorry no imput). However Im only running 35s, contemplating 4.30 as well.

 

Idk about the OP but I find myself only being able to run the highway towing in D. O/D just isn't much of an option the keep EGT in check and pull any kind of grade at all.

 

We run 4.30 with 315 (35).
Towing is great, good power decent economy with load at reasonable speeds.

Unloaded, 4.30 is too much. 70-75mph sucks fuel bad.

Depending on your driving frequency I would look at either 4.10 or 4.30 at most.

If you give me some info I will put a speed/gear/rpm chart together for you.

I will need the most accurate speed rpm numbers on your current setup to create a baseline. TorquePro or AutoEnginuity, etc...

Keith

 

My current commute to work is 23 miles comprising 70% interstate with a speed limit average of 65mph.

According to the gear ratio calculator I am using (Gear Ratio Calculator), 4.30s @ 70mph puts me at 1941rpm, just a tab below where I normally drive on I-70 (83mph/2000rpm). This would give me 75mph/2079rpm, more than enough speed for towing across the wasteland that is Kansas. And, I'm no where near the much hotter temps you mentioned. Or at least I fail to see how I'm going to be doing anything any more extreme than what I currently am.

And to that point...

A regear will, in my opinion, offer the best in towing capability AND longevity of my transmission and engine. Pushing 37s with the 3.73s is torture to the transmission. That torture becomes the Spanish Inquisition with a trailer hanging off the back. There is simply too much tire to overcome with too little gearing (prime example of why the V10s got 4.10s stock instead of 3.73s). Additionally, it is my opinion (and I am sure someone will correct me if I'm wrong) that with lower gears I should see lower EGTs while towing. The engine will be demanding less fuel under load to attain the same results due to a better efficiency of effort from the mechanical aspects of the vehicle.

"In other words, do you tow all the time around town and want more low end or do you drive longer distances at highway speed more often?"
1) No, I do not tow around town all the time. In fact, I don't tow all that often. I would say 2-3 times a month.
2) Yes, I want more low end. For around town. For towing. For not towing. It doesn't matter. My truck is simply not giving me the power I want/expect with the amount of throttle I am providing it. It's not a mechanical or tuning issue; its poor power translation to the rear axle due to a gear profile that does not match the power profile of the drivetrain.
3) I avoid highways whenever possible. And when I am on them, I don't care about setting a land speed record to get to my destination.

 

I have similar issues.

 

I'll see if I can muster up some data next weekend when I make another run across Kansas. No promises though.

Here are the numbers I am looking at from the calculator I am using.

Speed at RPM
3.73
1500/62
2000/83
2500/104

4.10
1500/57
2000/76
2500/95

4.30
1500/54
2000/72
2500/90

RPM at Speed
3.73
55/1323
65/1563
75/1804

4.10
55/1454
65/1718
75/1983

4.30
55/1525
65/1802
75/2079

 

I bought the truck with it already regeared, but I'm running a 6" lift on 18x10's wrapped in 37x13.5 Toyo MT's. With 4.30's, the speedo is almost spot on.

Have Jody tweak your tune if your EGT's are too hot when trailering.

Stewart

 

Great. The issue with the calculators is they use static numbers in certain parts of the equation. Any real data will be more accurate.

I will post up what I mage for my 16. You can see the differences from status to real world .

 

NO MORE THEN 4.30's for 37-38" tires. Period.

I loved driving my truck with the 3.73's and 37's. It was great on the interstate.

The only time the 4.30's shine is stop and go traffic...

4" and 37's here.

 

Gearing is not related to the speedometer. The VSS is mounted to the ring gear, so it spins the same speed no matter what gear ratio it is.

I ran 35's with 3.73 gears for a while and it was ok unloaded, but towing had me hitting the OD button way too often. Winding climbing mountain roads also often put the truck at the wrong rpm a lot of the time. I went to 4.30 and the truck felt way better but rev'd a little higher than I liked on the highway. Now that I am running 37"s the gearing is perfect.

Btw, ive never noticed a change in mileage with the gearing change.

 

What inputs Keith? Speed, rpm, accelerator? Anything else?