[Edavid1490]

I think my 1995 SL500 has a problem. When cruising down the road, my speed at 56 MPH is at 2000 RPM on the tach. Do I have a problem? Thanks for any help!

 

[alien883]

That sounds about right I think. My 91 turns about 3 grand at 80 mph.

 

[Swany]

RPM = MPH X Trans ratio X final drive ratio X 336 / Tire Diameter

Assuming a 4 speed auto with 1:1 4th gear and 2.65:1 final drive ratio and stock tire diameter of 25.7 inch

at 56 MPH I calculate 1940 RPM
at 80 MPH I calculate 2772 RPM

As Alien said, sounds about right. There will be some error in the speedo MPH and maybe even some error in the tach RPM.

I found the formula here
Calculating mph/rpm/Gear Ratio/Tire Size | Rare Car Network (rcnmag.com)

 

[Edavid1490]

That sounds about right I think. My 91 turns about 3 grand at 80 mph.

Thanks for the info!

 

[Edavid1490]

RPM = MPH X Trans ratio X final drive ratio X 336 / Tire Diameter

Assuming a 4 speed auto with 1:1 4th gear and 2.65:1 final drive ratio and stock tire diameter of 25.7 inch

at 56 MPH I calculate 1940 RPM
at 80 MPH I calculate 2772 RPM

As Alien said, sounds about right. There will be some error in the speedo MPH and maybe even some error in the tach RPM.

I found the formula here
Calculating mph/rpm/Gear Ratio/Tire Size | Rare Car Network (rcnmag.com)

Thank you for the reply!