4.30 gears/mileage
- Thread starter rynarnell
- Start date
fordtrucker4life!
I work with waste
I'm not sure since you have a 38's. If your truck was stock and you put 4.30 gears in you would loose mileage. What mileage are you getting currently? With 38" tires you should gain mileage, but I am totally not sure.
"Generally", if you are towing at your peak torque, 2000 rpm, you should get your best mileage. Example, at 2000 rpm "empty" in overdrive (6th) gear, my speedometer is at 71 mph. If I were to only use the truck to pull a 5er or trailer, then I would change my gear ratio so as to be at the legal speed limit while pulling and be at 2000 rpm.
In your situation, at 2000 rpm, 38 inch tires, 3.73 differential, a speed of 61.12 mph is obtained while in direct drive (not overdrive). That looks pretty good to me.
In your situation, at 2000 rpm, 38 inch tires, 3.73 differential, a speed of 61.12 mph is obtained while in direct drive (not overdrive). That looks pretty good to me.
irish4x4
Mayor of Margaritaville
SInce you likely cruise at 1200 RPM-ish at 65 mph. bumping up your ratio will bring the engine closer to its stock power band (higher RPM = More fuel) to a point. So yes, your mileage will go down at highway speeds but, your "Stop and Go" (87% of all driving) will be like night and day better. With 4.11's you could effectivle split the difference.
If you do the math, 4.30 differential with 38 inch tires will act like a
3.73 differential with 33 inch tires.
If your roads are flat, and mostly freeway, and not pulling anything, then you are probably getting the best mileage now.
With 33" tires and 3.73 differential, at 70 mph, 2000 rpm, = 18.5 mpg.
Hope this helps.
3.73 differential with 33 inch tires.
If your roads are flat, and mostly freeway, and not pulling anything, then you are probably getting the best mileage now.
With 33" tires and 3.73 differential, at 70 mph, 2000 rpm, = 18.5 mpg.
Hope this helps.
Last edited:
patrickc
Full Access Member
I run 4.56's in my truck with 38's and the rpms are the same as running 3.73's and stock tires. I noticed about a 1 mpg drop on the highway with the 38's and 4.56's compared to 38's and 3.73's. Where they help the most is in town or stop and go traffic since the truck doesn't have to work as hard to get rolling.
