Calculating Gear Ratio?

Couldn't tell you for sure, but the best way to find out is on a flat surface, have someone else move the truck forward one tire turn and count the driveshaft revolutions. Then you know for sure.

Usually there's a label on the drivers side door opening on the back side telling you what's in the truck.

 

I will try to post a link to roadrangers ratio site but you need to know the trans ratio or check the revs in direct http://www.roadranger.com/ecm/groups/public/@pub/@eaton/@roadranger/documents/content/ct_062746.swf

 

Mack rears or eaton's my SWAG would be 3.87 or 3.90 Mack truck will not have a tag on the cab but will be stamped or a tag on the rear end, or Mack parts man can tell you, all you need is last 6 of the vin

 

http://www.richmondgear.com/101032.html According to this web page it would be about a 3.08 or lower

 

Mack truck with 3.08 gears and a direct drive rockwell I highly doubt it

 

It figures on the calculator to be 3.98, most likely it's 3.90's. if the tack is off 25 and the speedo is off 1 mile you can miss it a little. RPM X 60 divide by tranny top gear (.73 on most tranny's, except Mack, but you said Rockwell) divide by tire rev's per mile(11R22.5 is 4988) divide by rear end ratio = MPH. If you have 4 of the 5 you can find the other.

 

normally mack ratios would be out compared to normal rears like 3.87 or 4.17 and so on, i use to love em