Independent suspension vs solid axle on military utility trucks

I got interested in this question when I was looking a humvees. I see humvees everyday as part of my job, and while I no longer work on them I do remember how their fully independent suspension does take more time to maintain. Most of the time spent servicing a humvee or High Mobility Multipurpose Wheeled Vehicle (HMMWV) is spent on messing around with the hub carrier and the half-shafts. At least they were thinking and relocated the four disc rotors next to the diffs instead of on the edge of the hub assembly, but getting the caliper and rotors out of the way to get to the hub assembly isn't that hard or take that much time. In fact, I hear its better to have your brake calipers as far to the edge of your axles, which increases stopping power or whatever. Anyways, I see humvees driving down the road and the first thing I notice is when it has any type of armor, payload or trailer on it is how much it sags in the rear. I see it and think, thats kinda excessive, why don't they put a leveling kit on it. Hah, not so fast, there are no leafs in the rear and so no AAL kit, no blocks to throw on, no replacement leaf packs. Sure you could add taller coils but then you have a stiffer and bumpier ride when there is no load, negating the benefit of independent suspension altogether. The humvee was designed for smooth and comfortable travel over unimproved roads at fairly high speeds. Its approach and departure angles are a benefit of the chassis design which puts the engine as far as possible into the middle. This engine location also has the added benefit of making it even harder to work on, but at least you can access parts of the engine from inside the cab!

So I thought, why did the Army switch to a fully independent suspension truck? Why not keep the proven solid axle design? I can understand their reasoning but did they not think that maybe someday the humvee may be asked to do every kind of mission the Army requires? There are so many humvee variants nowadays. The new ones have ballistic protection against up to 7.62 mm rifle cartridges. There are two basic configurations for the newer humvees, 2 and 4 seaters. Of the 4 seaters they can be added a gunners turret, of the 2 seaters there can be added multiple configurations of various shelters for cargo, commo, and maintenance. The heaviest of these new ones (M1151A1 w/B1 Expanded Capacity Armament Carrier Armored w/AC) has a curb weight of 10,300 lbs or a little over 5 tons! with a measly 1,800 lb payload.


M1151A1 w/B1 Expanded Capacity Armament Carrier Armored w/AC

Granted its a specific mission oriented humvee, it is telling when you compare that to the base model M1097A2 which has a curb weight of 5,900 lbs and a payload of 4,400 lbs!


M1097A2

For the weight of the M1151A1 you could have got yourself a Unimog U5000 which has a curb weight of 9,500 lbs and a payload of 16,500 lbs it blows away the payload of the M1151A1 by 14,700 lbs and is still a capable off road machine. I bet you could strip off the body and build a dedicated armored gun truck with a turret and mount heavier weapons and carry more ammunition than any uparmored humvee gun truck.


Unimog U5000

Sure the Unimog is a little taller and a bit wider, but when you load down the humvee suspension design that was made for a curb weight of 5,200 lbs on the original M998A0 model, adding on extra 5,100 lbs on it hampers its all terrain capability, whereas the U5000 was designed for its weight and payload. Is it any wonder then why they chose solid axles? Does anyone question the Unimog's offroad capability?

If its heritage isn't proof enough then perhaps the short wheelbase cab over design can convince you with its rally pedigree. The Dakar Rally or "The" off road endurance race. In time, a truck finished fourth overall at 42:22:01 behind three "cars" in another category. It proves that a big solid axle truck can cover harsh terrain just as fast as a lighter independent front suspension 4x4. Perhaps the military should take note...


It's not a Unimog (its a Kamaz) but the design is similar and maybe there's a reason why all these trucks run solid axles, but whats more astonishing is how a truck this size can finish ahead of all other cars but three.

But people say solid axles aren't good for baja-like speeds when high speed maneuverability and control is needed. If that's the requirement then look at two off road series in the states that have many baja-type racing with solid axles. Ultra4Racing and Jeepspeed.
The solid axle trucks below seem to have no problem at high speeds albeit they are a bit modified. But its not too much of a stretch to combine the best worlds of low geared rock crawling with the fast bump absorption into one truck. Shock and spring tech has come a long way.


Ultra4Racing


Jeepspeed

I wonder where the military would be today if they didn't choose the humvee and instead chose a solid axle truck instead. Perhaps a lot of money would've been saved not constantly having to upgrade, improve, and rebuild the old humvee to be more capable at missions it wasn't intended for. Perhaps more lives could've been saved because more protection could've been more easily added to a Unimog-type truck than a humvee. Who knows, the humvee is getting replaced by the 14,000 lb Oshkosh JLTV with another independent front suspension design. The largest capacity variant of it has a payload of 5,100 lbs. Of course though, its supposed to offer the best possible protection to the crew. Maybe its better, maybe its not, I hope the money us taxpayers paid for it, pays off. I wonder what differences there would be if instead of independent suspension being used in the JLTV, if solid axles with the best military spec springs and shocks. To me that seems like a test worthy scenario.

 

Thank you for the under appreciated post. Very informative my friend.

 

Thanks for the info, wish I could help... Bump