Gear ratio question

[Dfinkler]

Hi all

    I am in the process of setting up a new quad axle dump in Wisconsin. I am getting the MP8 445HP with the M-DriveHD 14 speed overdrive. I will be off road a lot but not in sever conditions and a lot of on road.  The salesman I am working with thinks 3.56 Ratio? I have talked to 2 other Mack dealers and they suggest going to 3.25s or 3.40 ratio?  Any help would be appreciated thanks I only have 1 shot to do this right lol 
 

3.56 Ratio= 1500 rpm at 65mph and 1650rpm at 70mph and 1950 rpm at 85 mph max

3.40 Ratio= 1429 rpm at 65 mph And 1570rpm at 70mph and 1950 rpm at 89 mph max

 

Edited September 29, 2020 by Dfinkler

[Mackpro]

This is probably of no help , But my buddy has 5 GU’s all with the 455 MP8, however all his have Allison transmissions. He’s running 24.5 full size tires and 4.19 Mack rears and runs 87 mph at 1900 rpms . Unsure of the overdrive ratio difference between the two transmissions 

[bts-4120]

i belive the allision is .60 and a mdrive is .78  in other words alot of diffrence  still little shocked about the higher ratios on a dump truck application

[Mark T]

16 hours ago, bts-4120 said:

i belive the allision is .60 and a mdrive is .78  in other words alot of diffrence  still little shocked about the higher ratios on a dump truck application

I don't understand the super high axles in dump trucks either. Salesmen seem to be under the impression the low gear in the transmission can do it.  In my opinion any of these new engines have over 1000 pound feet of torque right of idle ( @ 1100 or 1200 RPM)  even if feathering the throttle.  

[mackcat12]

I had a 2018 with the MP7 425HP and 12 speed MDrive with 3.79 ratio and it sucked off road, you might be ok with the 14 speed creeper gears. I traded mine for a 2020 granite quad axle with MP8 455HP and Allison transmission with 4.19 ratio and this thing is a beast it does awesome off road and pulls like a freight train.