I happened to be driving snowcats during the transition to grooming with combs that leave a corduroy surface. I drove snowcats at Killington VT in 1980, then at Alta UT from 1981-1985. At Killington we had some rollers that we pulled for packing snow. That year we really didn't have much snow to deal with, we mainly pulled powdermakers trying to loosen the snow up. We did have a tiller that we used some, but it was slow going compared to the powdermakers.
When I went to work at Alta the grooming requirements were quite different and the equipment was more advanced. We had to be able to climb in deep soft snow, so we had to be able to pull anything we used as a drag up into the air when the climbing got tough. We had compactor bars instead of rollers, and we used tillers both to work loose snow to get it to set up harder, and the more traditional use of breaking up really hard snow. A tiller has a bar with teeth on it that is lowered into the snow, and then a hydraulic motor turns the bar which chops up the snow.
Tiller on the back of a Pisten-Bully.
The people that made the tiller found that the crumbs of snow left a rough surface when flattened with just a smooth surface. They attached the comb which moves the snow around laterally and vertically and has the pressure points under the ridges. All of this helps pack the just tilled snow particles into a smooth corduroy surface. At the time our compactor bars just had a smooth surface, and if the snow was a little wet you would end up with a very hard smooth surface that was hard to set an edge in with a ski. So a homemade toothed edge was added to the back of the bar which leaves the same looking finish as the tiller. The toothed edge would also move the snow around enough to fill in low spots. Unless the snow was very soft a smooth bar would usually leave spots where you could see cat tracks.
The advantages of the ridges are a little more important to a skier, it is way easier to set an edge if there are ridges. But I still think that the ridges would help with a tire. The ridges also collect blown snow and extra base on the trail is always good at some point. If you have a drag that is easy to pull then you have the option to go with a metal comb. If you would rather buy one or if your drag is hard to pull, then you would need to go with a plastic comb. With a snowcat the snowcat tracks do most of the actually compacting so their isn't much difference between a metal or plastic comb, but depending on your drag and what you are pulling it with, the metal comb might do a more thorough job.
When you groom at a downhill resort, you try to get on the hill as early as you can, and the steeper slopes and the ones with big moguls where you are going to have to really mix the snow up you try to do first. The longer the time the snow has to set up before people get on it the better off you are. Grooming a trail late in the day so it can set up all night when it is cold is much better than grooming something where people are going to be on it right away.
Putting in a good base at the start of the season works well. This is something that could be done on a bike. At Alta after the first big snow in the fall someone would go out in the oldest snowcat and groom the main runs without a drag, and if it was a bad year we could tell that we had that hard layer through the whole year.
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Thread: Corduroy grooming