The steepest I've ever been on on a major road was 13%. In a overloaded box truck that was come to a complete stop at the top put it in 2nd and creep down. Brakes were getting spongy by the bottom and I was maxing out the rpms to the point that I was getting nervous
Steepest I ever went up with a heavy rig was 13% in a 36 foot diesel pusher coach. We were grossed out around 36-38K pounds, an even with the 8.3L 300HP CUMMINS it was a workout in 1st gear climbing it. Just held it to the floor, tried not to look to closely at the trans temp gauge(think I saw close to 260 which is common when braking with the retarder, but have never seen it that high under power), and creeped up at about 10 MPH. The steepest grade I ever went up was 25% on the way up to Amicalola Falls in North Georgia. What was scary is people were dragging big fifth wheels and stuff up the grade. Saw a newer DODGE stall out trying to climb it with a big fifth wheel because he started out in 2nd at the bottom.
Low side of an 18 speed Fuller, two lane, flashers on, lowboy grossed at 100k, CAT C15 600hp tune, U.S. 30 heading east out of Breezewood, PA bound for Gettysburg. Steep. Narrow. Twisty. Do not miss a shift..
I wish I knew the grade on some of our back roads. Granted the hills are only 1/2 mile stretches but I've had my dmax spin out with a load and slide back to the bottom. Retry in 4x4
Took the big trucks down some of the major mountains. But where I live we have much much steeper grades just shorter distances. Makes for some hairy rides! Had the backhoe on my dually and trued to stop and turn halfway down one.....thats what took reverse out of my 4l80!
Of course different terrain but the South Bend HMMVW Test track and outfield were the biggest grades i have done and on mud to boot. As well i had no low range so the 6.5 was stressing just a little. My wife enjoyed takin the vid, LOL http://www.youtube.com/watch?v=Sh3wxuPNAGE
Looks fun, the test track that is not the 26% grade head gasket checker. I don't know the grade, but I had mine off road on rock face that it lost traction at one point and just slid down hill about 25 yards.