Can someone simplify the whole concept with tall/short gear ratios? I understand the basic premise about higher/lower rpms and revolutions but I'm still a bit stumped when it comes to the 10 speed.

For example my F150 has 3.31 gears and still (feels) like it pulls decently well. I guess my question is in regard to how the 10 speed affects gearing and 0-60 time? I don't tow much and live in a generally flat area so hills are not really a concern.

My previous GMC had a 6.2 was 3.23 gears and pulled effortlessly granted it had more torque.

Does a 3.55 or even 3.73 make THAT much of a difference?

 

Just imagine riding a bike...a single speed, versus a 3-speed, versus a 10 speed, vs a 18-speed for example. Generally speaking, once you get into top gear you'll have a certain pedal effort required to maintain speed. But getting there, the more ratios you had to go through, the easier it was on your legs...and if you were climbing a hill you could drop down a gear or two, your legs were pumping a bit more but didn't feel as stressed, right? I've seen more than one thread on here that alleges the final output from the transmission is the same on a 10 speed as it was the 6 speed.
There was a good post or two on what the exact rpms were, for any given rear end ratio...I'll try to find it.
Put it this way...if you had NO TRANSMISSION ahead of the rear end, the higher numerically gear ratios would accelerate much faster.

 

the gears won´t be as wide with 3.73s as with 3.55s, meaning the transmission will shift through gears quicker under normal driving conditions, and wide open throttle shift points will be at a slightly lower speed. thats how lower geared axles work, but 3.55s and 3.73s are pretty close in spec, if you notice any difference at all it will be a slightly higher cruising RPM

 

I posted on this last week.

At 75mph, the 3.31 gear with 265/60R18 tires would run 1,739 RPM's.

The 3.73 would run 1,960 RPM's at the same speed and same tires.

I didn't calculate the 3.55 because it isn't available with the 5.0 I ordered.

 

265/60-18 Wranglers are 685 rev/mile. 75/60*685=856 RPM at 75 MPH.

The driveshaft will turn 2827 RPM at 75 MPH with 265/60-18 and 3.31:1 axle.

My 2018 XLT came with 275/65-18 which is 651 rev/mile. 75/60*651 = 814

 

The best gear ratio calculator is here:
http://www.grimmjeeper.com/gears.html

It will give you every RPM for any transmission gear, transfer case range, and gear ratio that you could want.

Start with the left side chart.

• For the transmission, select the Ford 10R80.
• Leave the setting on manual or auto with lockup torque converter.
• Use the Borg Warner 4401 transfer case (same low ratio as the F150)
• Leave the underdrive unit blank
• Plug in a stock (or aftermarket) gear ratio of interest (e.g., 3.15, 3.31, 3.55, 3.73, 4.10, 4.30, 4.56, 4.88, 5.13)
• Plug in your stock (or aftermarket) tire size. I recommend sizing down an inch in diameter to account for rolling radius deflection. So a 32.6" nominal tire like the 265/70R18 would be best put in as a 31.6" tire. Better yet use the advertised revolutions per mile listed in the tire corporation's web page.

The calculator spits out four tables.

• The first and second tables are crawl ratio and crawl speed in FPM in 4Low. This is more useful for the rock crawling people like Jeep owners than truck owners, but can be interesting. Plug in a target RPM in the second table to see how slow you can go in a given gear in 4Low.
• The third table is speed based on RPM. Plug in a few RPMs of interest. I recommend using a typical cruising RPM (2000 RPM), peak torque RPM (3500 RPM for the 3.5), and peak horsepower RPM (6,000 RPM for most engines). So you can see what each gear is optimal for and limited to.
• The fourth table is RPM based on speed. This is the most interesting table for us. Plug in any speed of interest and you can see what RPM you would be running in any gear. I recommend plugging in a few of your favorite cruising speeds, say 55, 70, and 80 mph.

You can hit the Copy Form button anywhere to duplicate the table. This makes it super easy to do side by side comparisons of different ratios, tire diameters, transmissions, transfer cases, etc. So for example you could plug in 3.31 on one side and 3.73 on the other to see the difference those gears make, all other things the same.

This is a super fun and useful calculator, and I strongly recommend playing around with it and changing gear ratios, tires, etc. to see all the differences those things make.

 

Every transmission gear is a multiplier of the final (rear) gear. In theory, the more gears you have, the more consistent your rpm's become through various speeds. Keeping an engine at peak rpm's for hp/tq generally means quicker acceleration. Of course, there are always exceptions, but that's another discussion....


With a 10AT, no. It's less than 100 rpm difference at 1:1. Underdrive & overdrive gears would be slightly more, but insignificant for 99% of the people driving. And again, there are always exceptions....

For *MOST* of us, rear gear selection in a 10AT F150 is not a high priority. If you are limit towing, or drag racing for money, all bets are off.

 

Can confirm the 5.0 4x4 with these tires and 3.73 gears runs under 2,000 rpm at 75 mph. I have the analog tach but would estimate it's actually more like 1850 rpm.

 

Yes, the taller 4x4 tires would run at fewer RPM's than the shorter 4x2 tire size at 75mph. Sounds spot on.

Use this link:. https://purperformance.com/p-29669-rpm-calculator.html

Remember that the 10th gear is 0.636:1

 

With the 10 speed auto I will buy 3.73 because there is very little mpg downside, while enhancing everyday drivability. My general rule is to always err to the lower rear gear side because I prefer better drivability over a slight potential increase in mpg.