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www.dirtrider.com

Building High-Performance Snow Bikes

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Unless you’re a sunbelt resident, motorsports tend to be a seasonal thing. The arrival of pumpkin-spice everything each fall signals that it’s time to winterize all the summer toys—the wakeboard boat, the UTVs and quads, and even your convertible. That’s when the salt car with the snow tires comes out, and if you’ve got the wherewithal, the snowmobiles get tuned up and ready to rock.

Over the last few years, though, the popularity of “snow bikes,” motocross-style cycles with ski and track conversions, has soared. It certainly didn’t hurt that Snow Bike competition made its X Games debut in 2017 at Aspen, and now these nimble, powerful winter rides are showing up everywhere there’s powder.

To get a closer look at this burgeoning powersport, we talked to Junior Jackson at Junior Jackson Racing, and he gave us a full education on the machines that make year-round roosting a reality. “It basically starts with a 450 you buy out of the dealership, and then you get what’s called a Timbersled, which is a kit that comes with a ski and a track with suspension, so you basically eliminate your swingarm and front wheel, and the track system has its own suspension,” Jackson explains.

There are actually several companies making snow-bike conversion parts. Timbersled is an industry leader, and is so strong in the market that Polaris bought the brand in 2015. But the conversions all follow a similar pattern: Start with a big-displacement four-stroke off-road bike—per Jackson, “Yamaha, KTM, Honda, and Husky are the main ones”—then add the kit. Up front, the wheel is replaced with a ski, and in back a track drive assembly substitutes for the swingarm and rear wheel.

Driven by a chain just like the donor bike’s rear tire, the track typically features deep paddles for traction and its own suspension, designed to keep the entire length of the track parallel and in contact with the surface of the snow. “The race version is called a 120, and it has a shorter track,” Jackson explains. “Now they have other setups for mountain riding—129 or 137 depending on what you like. It’s relative to the length of the track.”

Timbersled claims it’s possible to convert a dirt bike from tires to tracks (or vice versa) in less than three hours, and the total cost of a kit is just a fraction of what a new snowmobile will run. Combine that with the nimble nature of a dirt bike, and there’s a whole new world of winter recreational possibilities.

“Guys are finding out you can go a lot more places with these than you can with snowmobiles,” Jackson says. “You can ride in and out of the timber and stay on top of the snow, so people really enjoy riding them. It’s also great for places that don’t get a lot of snow; you can turn your dirt bike into something that you can ride in the winter as well, instead of buying a $15,000 to $20,000 snowmobile. It’s pretty neat that you can cross over from the summer to winter like that.”

Of course, in the entire recorded history of internal combustion, nobody has ever said, “Yeah, that’s good enough. Don’t add any more power.” While it’s certainly possible to enjoy a stock 450 with a snow-bike conversion, Jackson specializes in building bikes for competition and high-performance recreational use.

“When I build motors, I do it for both the mountain guys and the race guys,” he explains. “If you take a stock bike and go ride it in the mountains, you’re going to need to change the thermostat to regulate the water temperature, and we’ll use an Athena GET ECU so that we can tune it properly for the cold conditions. On the stock ECU, when the water temperature is too low, it will start dumping fuel and keep the bike from running well. That’s why we use the GET ECU.”

Because you’re dealing with colder, denser air and much more efficient engine cooling, it’s advantageous to internally modify the donor bike’s engine to take advantage of the winter conditions as well. Per Jackson, “One thing that you can do with these bikes that you can’t do with motocross is that you can build them to the hilt because you can run a lot of compression and do things you can’t do with a motocross bike since they will never see the heat. You can make a lot of power and still hold up, because they always run cool.

"We’ll run higher compression, do head porting, and use different intakes to accommodate the snow, plus a different exhaust and different cams… We are full-on building these motors,” Jackson adds. One big factor is the choice of pistons, and for that, Jackson relies on Wiseco for custom slugs designed to his specifications for compression ratio, compatibility with high-lift camshafts, and general durability.

What specific factors go into Jackson’s custom piston requirements? “Tighter tolerances on the wrist pin, and deeper valve pockets based off of my application,” he explains. “I am also making the bottom where the rod connects stronger so that at high rpm and high horsepower when you hold it there for a long time, it doesn’t pull the rod out of the piston. Instead of going lighter, we’re not worried about that; we want to keep them alive.

“Basically we are making big power on engines that are being run wide open all the time in deep snow so they need to be able to last,” Jackson continues. Unlike the typical motocross environment where throttle modulation to maintain traction loads and unloads the engine, a high-performance snow bike spends much more of its life at high load and high revs. “It has to be durable but still make the power,” he explains.

Whether for competition or recreation, snow bikes are poised to outpace traditional snowmobiles in terms of sales, and while the cost of entry is relatively low, like any motorsport the sky is really the limit if you want a built-to-the-hilt bike. Per Jackson, “It’s really been going on for about five years, but only became mainstream last year with the X Games. It seems to be really taking off, and I have been getting a lot of calls and interest. You have the cost of the bike and the ski conversion, but once you have all that, you are good to go. But you can spend as much as you want once you start chasing high performance.”

The good news is the same manufacturers who have supported the robust off-road and motocross market with affordable off-the-shelf and custom parts are also in the game for snow bikes. “Obviously power is a big thing—whether you are a mountain guy or a race guy, whether you are 20, or 70 years old, it’s important,” Jackson concludes. “You have that big track on there, and often you’re between 5,000 and 10,000 feet in the air in the mountains. That means power is significantly lower. It’s a full mod, and you need to have good parts to make the motor last and run hard.”