My 01 E250 2V had 3.73 gearing. I'm now looking at an 06 3V F250 with 4.10 gearing. The van didn't have a tach so I had no idea what the rpms were.

What are most of you typically turning for rpm's at highway speed if you have 4.10 gearing? I know tire size (this looks to have some oversize tires - not sure the size) will affect this too.

Most of my driving will be back country roads - 50-60 mph. Occasional freeway time - speed limit is 70 but I used to drive the E350 at 65.

 

Changing from a 3.73 to a 4.10 will increase RPM by 10%. So if you are turning 1500 RPM now, if nothing other than the gears change you'll be turning 1650 RPM. If you are now turning 2000 RPM you'll turn 2200 with the 4.10.

 

Just found out the truck has 20" wheels with 35" tires - I'm sure that will affect things a little too with the larger, heavier tire than stock

 

The 5R110 w/ 4.10 gears and 35" tires you are looking at approx 1816rpm @ 65mph.(in OD) If the truck had 4.30 gears you would be looking at 1905rpm at 65. At 50mph in OD 1397 for the 4.10s and 1465 for the 4.30s. Nice for highway driving empty but not optimal for towing.

http://www.grimmjeeper.com/gears.html

 

man I enjoy the specificity.

 

That is what the calculator spits out. Probably at least within 100rpm from those numbers. A lot of little variables that can add up.

 

i posted a few years ago the difference in speedometer/tachometer readings with worn out tires and then with new tires. I found that interesting. Can't remember now though.
Funny what a fraction of an inch of tread depth can do.

 

Agree - exactly what I was looking for

 

Also, going from van to F-series, the tire diameter is different.

 

What do you mean by the last sentence? 4:30 Not optimal for towing?

 

Not with 35" tires. With the stock tires that were not even 32" then yeah 4.30s are good. For the V10 and towing I'd rather be running at least 2100 @ 65mph in OD.

 

I'm running stock 20's with stock size 275/65 20 tires. They are 34.5 inch diameter and work well with the 4:30's. I don't have an issue with your theory, just curious what you meant by it.
BTW- My truck shows right at 2k at 65 2100 at 70 so these numbers are pretty close.

 

At 2200-2300 you can usually feel you are getting into the meat of the torque curve. I noticed it in mine. Its good to shoot for at least that rpm at the cruising speed (mph) you want to tow at in OD.

 

As a side note, every duty with 4.10 or 4.30 gears has had the speedo read wrong. Putting 35" tires on these trucks corrects the speedo [based on gps readings]. It like these trucks are all calibrated for 373 gears and no corrections are made at the factory for the lower gears?

 

Gears don't affect the mph output but larger tires will. A sensor reads a tone ring which is bolted on the carrier in the rear diff. My speedo read fast until I put 285/75R16 tires on it, just under 33" diameter. Speedo compared to GPS is right on now.(taken at several speeds) Maybe Ford just sets the speedo for the largest tire for the MY? For later trucks that were available with 20" wheels that is just below 35". If the speedo reads faster than you are going there really isn't much liability there vs if the speedo reads slow.