4.10/4l80e with 33" tires - rpm at 70mph?
 

i got my HD a few weeks ago, and the dang thing GUZZLES gas. i havent put the math on paper yet...i just keep putting gas in it lol.

anyways, i'm doing 70mph on the freeway and notice that i'm at 2,400 rpm. i tap the brake and the RPM didnt flare like the converter unlocked. it's been so long since i've driven a truck with a stock converter that i'm not sure if you will see much of a rpm flare with the bump of the brake peddle.

what RPM would you expect me to run at 70mph with 4.10 gears, a 4L80e transmission and 32.8" tires????

My 2002 1500hd at 70mph was right round 2100 IIRC, it had 3.73 gears and 305s.

2205 rpm

2205 is the math.

Did you measure your tires? Bet they are more like 31" if they were advertised as a 33".

I ran that RPM with a 33" and 4.56s, although i had a 4l60e. Your RPM gauge may be off. I know the RPM was every exactly right.

just an online calculator. the tire is a 285/75-16

Measure the tire circumference using a tape measure or a piece of string. Tire diameter varies quite a bit between manufacturers, and also gets smaller as the tread wears down. My tire diameter is about 0.8" less than what the online calculators say it should be, and that's with most of my tread left!

The RPMs are in the correct ballpark. Also, you will still feel the unlock and lock with the stock 80 converter.

i dont see it locking/unlocking when i tap the brake while cruising down the freeway at 70mph. guess i need to find a scanner to manually lock my converter at a red light and see if the truck dies.

where the hell is my buddy charlie! :)

Has the truck been tuned for the bigger tires? If not then actual tire size is irrelevant when looking at speedo and tach.

70 MPH with the stock 245's and 4.10's that 2400RPM sounds right. You may actually be traveling closer to 75 MPH when your speedo is reading 70. Your gas mileage seems and sounds off first and foremost because those tires dont help, but your speedo is probably slightly off, making mileage seem off as well.