The factory std Axle ratio for MCI 7-8-9 and Eagle is 3.70
The BB 42 w/ 60 series came from the factory std Axle ratio 4.89
The BB 42 w/ 60 series and Alison 4060 has an OD Transmission and the final 6 gear ratio is .64
Look up the Revs per mile below or at dealer location. http://www.michelin.com/us/eng/tire/truck/tires/xza/xza2_sp.html http://www.goodyear.com/ Goodyear http://www.toyo.com/ Toyo http://www.trucktires.com/ Firestone/Bridgestone
Revs per mile will vary with different Tire manufactures Toyo M144 315/80Rx22.5=487 Continental HSL1 Coach 315/80Rx22.5=491 Firestone HP3000 315/80Rx22.5=491 Michelin 315/80/22.5 XZA=492 9R22.5 = 542 = 8.25x20 10R22.5 = 520 = 9.00x20 11R22.5 = 504 = 10.00x20 12R22.5 = 492 = 11.00x20 11R24.5 = 480 = 10.00x22 12R24.5 = 470 = 11.00x22