Here or in the engine forum?? I thought new bigger...

[White Ram1]

I thought new bigger TIRES would lower my RPM's. I went from stock size to 35's and at 70 MPH my RPM's are still dead on 2,000. I was hoping to have them drop quite a bit.



I'm new to this Cummins game, maybe there is some computer deal I need to do to drop the RPM's???



Any input?

 

[surfbeetle]

Unless you recalibrate your speedometer, your truck still thinks that it is going 70 mph at 2,000 rpm. Your speedo is actually reading slower than what you are really travelling because of the larger tires. You could try a GPS and see what your mph is when your speedo says that you are going 70. Also you should recalibrate it because the cop won't care when he writes you up for speeding. I found out the hard way on that one!

 

[XJSuperman]

If your speedo currently says 70 MPH at 2000 RPMs you are actually doing about 78-80... until you recalibrate the speedo as said above.



Once recalibrated at 70 your RPMs will be approximately 1750.