Not sure if I have the manual Allison someone was looking at listed - but a couple of other 6-8 speed medium transmissions are. HEAVY.
Note: Was not aiming for a freeway truck, but to maintain 55 at peak torque (hills etc) so undoubtedly they will allow a M1008/M1031/M1028/M1010 etc to drive a LOT faster, but at a higher RPM with less power.
I also looked at adding a doubler or Atlas etc (only calculated the ORD doubler as same ratios as ATLAS IIRC) Note not all the ratio's are listed when calculating the transfer case final ratio's - I chose the ones that gave the best continuous steps up. Obviously (for example) in the "off road" mode you could stay in "M" (205 low/Magnum 1:1) for the 3M/2M/1M shifts if you chose.
The OEM tire size was also listed with OEM 4.56 ratio ring and pinion set - topping out at 47mph at 1800rpm, but because of the overdrive 6th gear you will hit 55 at 2100rpm, 65mph at 2480rpm and 75mph at 2850rpm (with the original 4.56 and TH400 in 3rd gear 55MPH = 2650rpm)
The dually choice with Michelin XL's is interesting - essentially met target speed with a low rolling resistance tire for highways with good directional offroad traction (a skinny mud tire works well if there is a hard bottom since higher PSI at the ground), or for floatation on sand / snow / muskeg add a 3" spacer and the outside duals then air down to about 5 PSI. Beads are so stiff on OEM rim widths it is not that hard to keep them on the rim without beadlocks but Staun internal air filled beadlocks could always be added. Siping would be a very good idea as they can get squirrelly on wet pavement like Oregon has.
NOTES: Assumes you have swapped dually front hubs and a Dana 70 dually (ideally HD from a 70's or 80's GM) rear end both with a 77" WMS distance as the OEM dually rims have a 8" backspace (H1's have 7"). I also only used OEM 4.56 for comparison and 4.88/5.13 as I plan to use a High Pinion Dana 70 in the front with a M1028A3 Dana 70HD in the rear. Currently the OEM Dana 60 with DRW hubs forces the use of 1.75" spacers on my junkyard '79 C30's dually (drum) 70HD rear axle in order to match the front WMS.
The total contact patch is then the same as the 46" Baja Claws at about 12PSI. WITHOUT so many extensive suspension mods, driveline and brake stress, and retaining more useful torque at the ground. You can also always reverse directionally mount the second set of XL's for a non-directional pattern. Plus you have 4 spares!
In normal use you'd carry 2 spares as rear duallys on the pavement or gravel getting to your hunting or off-road access road, with the other 2 mounted on the back of a camper or a 2" hitch carrier or in the box or whatever. Dismount the rear outer pair and carry until needed for floatation (I am thinking a rear bumper with dual swingaway tire mounts each able to hold a pair of wheels...) Or only carry one with the other 3 in a follow-on trailer with fuel etc and a RTT aka Turtle's Russian expedition.
Just denying the existance of the box that most people try to think out of... screw the design envelope!
