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What is Good Fat-Bike Trail Grooming?

Ed: One of the main topics at the Global Fatbike Summit happening in Ogden, Utah this weekend, as well as the just concluded Midwest Fatbike Summit in Cable, WI, is the topic of Grooming Trails for Fatbikes. We are fortunate to have Ken Blakey-Shell’s experience grooming snow trails for various uses to give us a primer. So, Ken, Take us away…

What is Good Fat-Bike Trail Grooming?

This seems like such an obvious question but in reality there is a lot more to it than just compacting fresh snow. How wide is optimal? How firm does the trail need to be? How much fresh powder is too much? What are the different things groomers are doing out there to the trail?

Width

There is a lot of debate out there about what is the perfect width for trail grooming. Some people love the challenge of riding a 6″ wide strip while others want more width so they don’t have to worry about falling off the trail all the time. Most dedicated fat-bike trails are being groomed somewhere in the range of 18″-40″ wide. There are a ton of factors that go into this but the width of the trail corridor (distance between the trees or other features that border the trail) and how tight corners are greatly determines what type of vehicle can be used to groom. For instance, a tracked ATV is close to 40″ wide and can’t get down a lot of singletrack trails but a Rokon 2-wheel drive motorcycle can do down most any trail a bike can. The width of the groomed trail is largely going to be determined by the vehicle pulling the grooming implement. Regardless of if you are pulling a groomer under your own power or using a motorized vehicle, you typically want to mostly cover up the tracks made by the vehicle, leaving a consistent tread behind.

Puck riding the narrow, groomed single track at Sunny Vale in Wausa, WI. Usable trail width is 20" to 24" or so.

Puck riding the narrow, groomed single track at Sunny Vale in Wausa, WI. Usable trail width is 20″ to 24″ or so.

The width you groom at isn’t the actual width of rideable trail. If the trail is in a high snowfall area, over time the compacted snow builds up and you ride down a “wall” of compacted snow, surrounded by powder. Even though the snow is compacted across its full width, the snow will start to collapse when you get near the edge of the groomed trail, spitting you off into the powder. Another factor is that the groomer most likely isn’t going to be able to go down the same exact path every single time so there will be some variability side-to-side with how things are packed resulting in softer trail edges. Lastly, the line that the groomer takes isn’t necessarily the line that riders will want to take because of momentum and flow on the bike. Having some trail width to select a line can be nice.  Depending on your snow conditions and packed depth, all of these factors add up so that your 30″ groomed trail may only produce a 20″ wide strip of nice ridable trail. Groom wider than you think is necessary and a line will develop with fatty traffic.

Firmness

Another big factor in good grooming is how firm the trail is. Firm is fast and fun. For a lot of snow conditions, getting a firm trail takes a lot more than just compacting the snow. Anyone that has tried to climb a hill in compacted snow that isn’t bonding well will be familiar with the “buzzsaw” effect where your tire just spins and digs a hole into trail.  Well groomed trail will be both densely compacted and the snow will hold together enough for good traction.

Snowflake close-upTypically fresh snow consists of a bunch of crystals that are fairly sharp and large. Because of this crystalline structure, the snow won’t compact well and the crystals won’t bond together because there isn’t much contact area between crystals. It is similar to a container of rocks with a bunch of space in between the rocks. Big snow crystals will still have a large amount of air in them. If you can break apart the snow crystals or “knock the air out” using groomer speak, you get better compaction and bonding, improving the firmness of the trail. 

Beyond just breaking down snow crystals, another way to improve the firmness of snow is to mix fresh (big crystals) and old snow (broken up crystals). Going back to the container of rocks analogy, this is like mixing sand in with the bigger rocks thereby filling some of the airspace. Having a mixture of big and small snow crystals not only increases density, but also is a great environment for snow crystals to bond.

There are a variety of ways to knock air out of snow. Just compacting snow will break down snow crystals somewhat but most grooming implements also try to move the snow around and thereby break up the crystals before compacting it.

http://mud-sweat-gears.com/blogs/news/10675437-fat-bike-trail-groomer-update

This is a drag used on the Traverse City trails. Note the surfaces to move snow outboard, then inboard before compaction.

There are tons of ways to do this through “tillers,” teeth/knives and different surfaces that move the snow around can be used. How much the snow gets “worked” needs to be controlled depending on snow type. If you have snow that bonds easily (aka good snowball conditions), it may pack up on these working surfaces and gunk up the groomer instead of getting laid down on the trail tread. This is part of the reason why a lot of groomers use different grooming implements based upon snow conditions.

This is what it looks like as the drag moves over the snow processing it before compaction.

This is what it looks like as the drag moves over the snow processing it before compaction. Photo courtesy of the Keweenaw Nordic Club who allow fat bikes on their trails!

Lastly, firmness improves over time because snow crystals have time to bond together. Freshly groomed trail will be a lot firmer if it sits for an hour (minimally) or overnight.

Trail Texture and Fixing the Trail

fresh trailThe last major component to well groomed fat-bike trail is the smoothness and flow of the trail. Anyone that has ridden a trail after a thaw/freeze cycle and the trail is bumpy and rutted knows the importance of a smooth trail. Ideally a groomer will be able to fix these icy bumps, divots and ruts. All of those ways described above that snow can be worked to break down crystals can also help to fix bumpy trail by breaking up the snow/ice and laying it back down. Some grooming implements are really good at removing the tops of bumps and depositing snow in depressions. Other implements specialize in breaking up or scouring an icy trail so there is some traction.

Ed: In the coming weeks we will be getting into more specific discussions with trail club members and land managers about how they create great rides in their local areas through land use initiatives and trail grooming techniques. Stay tuned, you’ll probably learn something you can apply in your neck of the woods!

8 Responses to What is Good Fat-Bike Trail Grooming?

  1. Bob Dunahee January 22, 2014 at 2:37 pm #

    Great idea for a series, thank you!!

    • Rick January 22, 2014 at 3:03 pm #

      great work Ken!

  2. FatBike Mike January 23, 2014 at 9:27 pm #

    Great read, I live in the Albertan Rocky Mountains, and have been on a fatbike in the winter months for a couple years now. The entire last winter I was the only fatbiker around, I rode what I could, walked the rest, and groomed via biking. On big snow days I’d snowshoe my loop, and found that was a good width for riding. I also would poach the occasional snowmobile trail and found they were great, except really straight and boring. Last week I finally bought a beater sled and a touring toboggan and plan to groom with it now. Two passes and done like dinner, plus I can carry home a load of firewood each trip. Life is good.

  3. Sean Ralph January 24, 2014 at 8:47 am #

    Great story – thank you. Very helpful as I am working on a proposal to a Land Manager to gain fat bike access to a Park that is only open to snowshoes and skiers at the moment. Great material here for our discussion on what is required to groom a fat bike trail.

    Keep the material coming. Another useful story might be sharing material used for making proposals and negotiating fat bike access with land managers.

    -Sean

  4. Robert Hood February 3, 2014 at 11:17 am #

    I’ve been using a wooden pallet pulled behind a snowmobile to groom a track on the neighboring farmland. I use it right-side-up so the larger gaps between boards are on the bottom. The pallet loads up with snow and is quite heavy. two passes and some cold weather results in a smooth firm trail that is about 40″ wide.

  5. Hehner November 3, 2014 at 12:40 pm #

    Has anyone looked at or have experience using powerboard or powered track type equipment as a Fatbike trail groomer. I just came across several options that look like they might allow for mechanical grooming assistance in areas too tight for snowmobiles.
    Mattracks powerboard: http://www.mattracks.com/tracks/powerboard/
    BPG Werks DTV Shredder: http://bpgwerks.com/products/
    Scarpar: http://www.scarpar.com/index.php/news/talking-about-us
    Skizee: http://skizee.ca/other%20assets/WEB/Ataglance.html
    MTT-136: http://www.gizmag.com/mtt-136-personal-electric-sled/30932/

    • Ken Blakey-Shell November 5, 2014 at 5:59 am #

      I have never heard of a trail system using anything like that but if someone out there is trying something like that I would love to hear about it. The idea does look intriguing.

  6. Jesse September 27, 2016 at 1:50 pm #

    I have been grooming for FAT bike 2 seasons, about 25+ years xc ski before that. What we have found is the West Yellowstone track Systems compaction drag works best with the least amount of time on the terrain we choose. We can get a fairly tight trail a bit over 20″ wide with the 30″ groomer.
    Grooming over dirt MTB trails is not a good idea for many reasons. Too tight for the most part and makes them muddy longer into spring.
    Our trails we get snow every couple days in small amounts of 2-5 inches of dry powder, with occasional larger snows and temps that range from balmy 60’s to artic cold any week of the winter. A ROKON or Big Wheel bike wouldnt make it 10 ft. A 24″ wide tracked sled works. We can groom at about 8 miles an hour with good results, and for 12 miles of trail it takes 2 passes to be firm enough the next day with 200+ lbs added the 230lb compaction drags 2nd pass.
    Another thing I might add is grooming is a night time job, sun hits dry powder and it gunks up big time. Just drop the groomer where it sticks and get it after sunset. Also if you groom in the daytime when overcast people will try to ride it and mush it up before its firm, bikers are not snow savy for the most part.
    Snowmobiles overheat in the daytime much easier too.
    If you live in where the snow has lots of moisture and it is cold I suppose the ROKON and other things work well, in dry powder if you want to cover much ground the above mentioned is the ticket so far.
    This year we are going to use a tracked ATV with a blade to shape the trail a bit to fill in little gulches and level side hills after the first deep snows and groom with a Ski Doo 24″ tracked snowmobile.
    People always ask of other ways to get the job done, and the answer for our conditions is not really, if you want to ride the trails the day or two after the snow stops falling with good consistent conditions bikers will actually enjoy riding on a consistent basis.

    Jesse
    Rushmore Mountain Sports
    Spearfish, SD