I need someone to check my calculations on gears!!

[AlaskanJack]

Well based on my test this morning and my calculations I have 5.38 gears. Here's what I did. I was driving at 65mph with approx 3350rpm in Drive (not Odrive).

I checked my calculations with the following

(rpm X tire dia)/(diff Ratio X Transmission Ratio X T-case Ratio X 336) = mph

rpm = 3350
tire dia = 35
Diff Ratio = unknown
Transmission ratio = 1:1
T-case Ratio = 1:1
mph = 65

After rearranging the equation and solving for the unknown I got 5.3685.

Can someone re-check my calcs the gearing is not what I was expecting. But then again it does have very good throttle response and is not sluggish as it might be with 35's and higher gears (lower Number).

 

[SteveVB]

Tire size calculation not valid with the speedo

Did you read the speedo for the MPH? Was it corrected for the tire size? It could be 20% off

Have you changed the gears or are they stock?

If the MPH is correct are you sure you were in third gear and not second- if you have the auto- second gear is 1.47:1, divide your figures by 1.47 and you get to 3.55:1 or so. A stock explorer gear. Also in 3rd the torque converter may not have been locked up raising the rpms a bit, so you are calculating your axle ratio, plus some torque converter slip(gearing).

If you want the rear axle ratio, pull the cover and count, or rotate the drive shaft and count the wheel rotation.

 

[AlaskanJack]

I had someone follow me so I know speedo is accurate. The Overdrive is not working so I know I was in 3rd or drive. Wouldn't this be close? Either it has been regeared or the speedo has been replaced. Stock gears are 3.73 according to axle code.

Also I would think that 35 in tires and 3.73 gearing would be a bit sluggish. This truck has some real good pick up and acceleration from stop and on up. Much better than my Ex with 3.27 gears and 31's

 

[CBoug76]

Check out the Gear Calculator in my Signature....

 

[Alec]

According to the chart at 4lo.com, you do have 5.38 if your speedo is correct. It's more likely that you have 5.13.

Damn you have low gears!

 

[CBoug76]

Yeah I was just gonna say go to http://www.4lo.com/ and you'll see on a chart that your RPM's are Ideal for that gear and tire combo....

 

[AlaskanJack]

Thanks CBdoug. That's what I needed that calculator on 4Lo just confirmed my math.

I will eventually pull the diff cover and count the teeth to make sure, but I can't do it now and this was eating away at me. Yesterday I realized that the gearing had to be low when I sqawked the rear tires taking off in a hurry.

This is making my 1,000 dollar investment even more sweet!!

Anyone have any thoughts on what SteveVB was saying about the torque converter not being locked up?

Now I am really anxious to open the diff cover and see if there is a locker installed. I don't know really anything about lockers. Well a little. I know its not lincoln locked I would feel that on regular driving around corners. Otherwise I know some lockers are switchable from inside the cab, but whether there is a mechanical locker without switch. I don't know. I'm learning more and more everyday from this website and other wheelers.