That's interesting. I never had a good look at the bogie wheel machines. In addition to the problem of detracking, I imagine the big wheel ST* suffered from snow build up on the belt beneath the tires more so than the bogie-wheel variant. Snow deflectors may be especially important in the big wheel machines. I would imagine that a benefit of the big wheel design is tire longevity, with tire tread against the track belt, and protection from sharp objects below.
I've not de-tracked my ST4 yet, although I had a "situation" where I probably should have. It happened shortly after I bought my ST4. I had climbed up the steep side of a snow berm that lined our road. It was hard snow, left from plowing earlier in the season. I had subsequently widened the road with the unimog snowblower, so the bank now had a vertical edge down to the road 3+ feet high. After tooling along on top of the berm, I decided to "drop" down to the road again. I figured I could slowly angle down, almost parallel to the berm, until I could touch a piece of the downhill track on the road. Well, things didn't work out that way. After I got about half of the downhill track dangling over the "cliff," part of the bank gave way. I thought I was going to roll for sure and braced for impact. Thud! The good news was I didn't roll. The bad news was that I was sort of high centered, with one track down on the road and one high up on top of the bank. Try as I may, I couldn't steer at all, all I could do is go forward or backward with the ST tilted 35-45º with gas leaking out of the tank. I drove along this way for a couple of hundred feet until I reached a turnout that I cut into the bank with the snowblower. This allowed me finally climb down off the bank.
Upon inspecting for damage, I thought I got away scot-free, but later discovered that I snapped several grousers about exactly in two, probably in the initial impact. Considering Lyndon's experience, I guess the remarkable thing was that I didn't de-track.
Speaking of grousers, does anyone know what kind of steel the ST grousers/cleats are made of? They are light and fairly springy, so I assume that they are tempered spring steel. After I welded the grousers, I quenched them and then tempered them in a steel pan filled with waste motor oil at about 700º. The oil burns off at about this temperature, so it's a good thermometer, and results in a temper approximating spring steel.
... They ran the tires directly on the belting, rather than in-between. In trying to correct the weakness of the small front tires, and associated spring loading and tensioning, they created a whole new problem. On Snow Cats that have a single drive sprocket for the track, one can 'tip' the track sideways, almost to 45 Degrees and it will usually stay on. With the wider sprocket arraingement of the "Big Wheel" machine, if you tip the track just a small amount, the drive sprockets catch on the tire guides and it walks right out of the track.....