I have an M185A3, an M109A3, an M35A2, and am long-term babysitting an M109A3 on 395s. My opinions are based on those trucks.
First, take into account that the M109/M185 weigh roughly 4000# more than an M35, and have even more barn-door-like aerodynamics. M109 and M185 are essentially the same truck, the difference being mainly how the box was wired up.
So -
When the M35 was first acquired, we drove it from Virginia to Texas. It ran like a champ, the truck's "happy" cruising speed, with the tarp on the back, was 54. It would go a tad faster, but didn't seem to like it. Later the stock 9.00s got switched out for 11.00s. This took "happy cruising speed" to 58-59. That's as fast as I want to go in one of these trucks anyway.
There was no noticeable difference in power between the 9.00s and 11.00s; but, counter-intuitively, it became a bit easier to steer.
When I first got the M185, it's indicated cruising speed was 48mph. I soon discovered, using GPS, that it was actually doing 52 when indicating 48. I got it up to the manual listed top speed of 58 - once. That was on a long flat highway. That truck is slated to be re-shoed with 11.00s in the near future, we'll see what that changes.
My M109 has virtually identical performance. It accelerates from a stop a tad faster than the M185, but once going the 185 catches up quickly and is probably 1/2 a mph faster at cruise.
While the M109 and M185 are definitely more top heavy than the M35, they are not in peril of falling over sideways unless you really work at it. I have seen one go around a corner at way too high a speed, and while it tilted at what I considered an alarming angle, it didn't go over.
Now, the M109 on 395s. I picked that up for a friend and drove it 250 miles home. On level ground, it is much faster than the other two box trucks, it will cruise over 60mph with no problems. But...get to a hill, and it slows way down, even on hills where the other two don't. It is also more susceptible to headwinds. I've driven it in convoy with the other trucks, it has to be held back on the flats, but when we get to hills, the other two just walk away from it. Those tires are definitely larger than the power of the truck wants to push.
While the two on 9.00s feel rock steady while driving, the one on 395s feels less stable. We've checked out the front end carefully, everything is well maintained and set as it should be. Braking performance is also reduced on that truck, as it will be on any stock vehicle that you put on bigger, heavier tires with more rotational mass. My personal opinion, which is just that and worth two cents, is that those tires are just too big for that truck.
Looks cool though.
The M35 on 11.00s gets around 9.5 mpg. The box trucks all get around 8-8.5mpg. The one on 395s is getting better mileage on the flats, but works harder and needs to downshift sooner on hills, so loses whatever it gained on the flats.
I think these trucks on 11.00s may be the perfect setup (or 14.5s, which are roughly the same diameter as 11.00s). It is what the military was switching to at the end of the M35's career.
There's my
. Other opinions may vary.
Cheers
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