Engine/Transmission (1998.5 - 2002) Gear Ratio Question

[TowPro]

On the way to the dealer last night to trade in my 98 (3:54 5 speed) I run the RPM up to 2000 in 5th gear, and checked the Speed. 65 MPH



On the way home with my new truck (2002 4:10 auto) I run the RPM up to 2000 in OD, convertor locked, and again checked the speed. 65 MPH



I guess the auto has a higher OD then the 5 speed? If this is the case I am really glad I bought the 4:10's with the Auto.

 

[pro99]

Hello, the difference in gear ratio from manual to auto you really should not see. the manual has a 0. 73 ratio in fifth and the 47re has a 0. 69 ratio. What has changed is the tire size from 98 to 2002. The tire size in 98 it was 215/85/16 now they have 235/85/16 and bigger, need to check the size difference from truck to truck. Hope this helps you out at all? If not sorry.

 

[TowPro]

that makes sense. but the 98 had 254/75-16, not sure what the new one has.

Originally posted by PROTURBO

Hello, the difference in gear ratio from manual to auto you really should not see. the manual has a 0. 73 ratio in fifth and the 47re has a 0. 69 ratio. What has changed is the tire size from 98 to 2002. The tire size in 98 it was 215/85/16 now they have 235/85/16 and bigger, need to check the size difference from truck to truck. Hope this helps you out at all? If not sorry.

 

[RADdodge]

The OD on an Auto is 0. 69 compared to 0. 75 for the 5-speed and 0. 73 for the 6-speed. I purchased the 4. 10 ratio because I knew I would end up with larger wheels and tires. With the larger meats, I’m cruising about 72 mph at 2000 rpm. My effective ratio is 3. 69.

 

[fj40charles]

New 2500 comes with 265/75/16 tires.

 

[TowPro]

I guess the tires size is what did this.

old truck 245/75 would be a sidewall of 183. 75mm

new truck 235/85 would be a sidewall of 199. 75mm



In other words, the 235/85 is a taller tires, covers more ground per rev.

 

[RADdodge]

The best way to calculate tire performance as regards to speed and ratios is to use the manufactures Revolutions Per Mile (RPM)rating for a particular tire. Even though two tires are rated as the same size, their RPM is probably different. I've even seen differences between different tire types of the same size and manufacture, small differences but different never the less. FYI.