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Big Wheel or Bogie Wheel

barj

New member
Why and when did Snow Trac add the big wheel to the front dropping the extra set of bogie wheels? Do both styles function equally well? Thanks.
 

Melensdad

Jerk in a Hawaiian Shirt & SNOWCAT Moderator
Staff member
GOLD Site Supporter
It is generally believed that the big wheel front end was an evolutionary improvement to the design. Not sure that anyone alive can actually prove or disprove that statement.
 

teledawg

Member
1968 was generally the last year that the small bogie wheel models were produced. The small bogie wheel in the second position was prone to flats and failures because it takes most of the impact when hitting rocks or stumps in the snow. One factory solution to the problem was to install a hollow all-brass wheel in that position. This can be seen on 1968 model year Trac-Masters. I have seen 1967 Trac-Masters that do not have the all-brass wheel there. I would recommend that a solid or polyfill tire be used in the postion on all small bogie wheel snow-tracs.

Another reason for going to the big wheel design is that the front bogie wheel carrier has been known to flip over in certian conditions. This would break the suspension and springs on the carrier. One other problem with the small bogie wheel in position one is that it can contact the drive sprockets if the final-drive chains are adjusted too short. This chews up the tire quickly.
 

barj

New member
Thanks for the info. I wondered what that brass wheel was all about. Is it a difficult conversion from bogie to big wheel?
 

teledawg

Member
Thanks for the info. I wondered what that brass wheel was all about. Is it a difficult conversion from bogie to big wheel?
Yes, it would be difficult. The whole front part of the frame is different as well as the suspension.
 

Lyndon

Bronze Member
GOLD Site Supporter
When they converted to the "Big Wheel" model they did one thing that you don't find on many if any other snow cats. 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. This is probably why no other manufacturer adopted this design. The initial correction of defficiencies is as Mike said, Problems with the second tire, and tensioning problems. On one Northwest Tell machine they added additional springs for the front bogies, and this seemed to do the trick. The Snow Master is more prone to de-tracking than the Snow Trac, that is the Big Wheel models, and the old style Trac Master was next. The OLd style Snow Track vertually never detracked. A low Tire, or incorrect track tension will result in problems with any and all makes.
 

mtmogs

New member
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.....
 
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