The short story on what is the perfect winter bike is whatever bike allows you to pull a bicycle snow plow. Bare pavement will make any bicycle work quite well as a winter bike.
If that is not an option, consider two different kinds of bicycles for winter conditions. I’m assuming you are using studded tires, which in my experience, is essential for winter cycling.
Narrow tires tend to slide into any grooves, bike or car tracks. Narrow tires do better at digging through snow to grip pavement underneath. As snow depth increases over 4″, narrow studded tires may be the only way to keep moving!
The wider the tire, the less sliding around in ruts there is because a wider tire has a flatter surface. Although fatbikes are touted as the best winter bikes, even fatbikes can slide in icy ruts under certain conditions, especially if there is water or snow on top of ice (but much less likely than other kinds of bicycles).
Many cyclists get through winters on 2-3″ wide tires by dropping tire pressure to about half. Fatbikes are particularly good at handling extremely low tire pressures but expect the pedalling effort to increase exponentially with lower tire pressures. At 5 psi, the effort seems about 5X higher and speed goes down to about 1/4 of normal. A typical 20kph effort then deteriorates to a high effort 5 kph ride, barely adequate to maintain balance.
Electric fatbikes have the benefit of helping you run low pressure by providing more power to overcome some of the resistance from tire flexing. However, even fatbikes have their limits and are not always the best winter bike.
Fatbikes do make decent road bikes if your tires can run higher pressure (say 20-25psi) and have no tread in the center (flexing tread creates more resistance). Some tires will have a solid strip of rubber in the middle of the tire to reduce rolling resistance (A.K.A. beach tires). Acceleration will be slower due to heavier wheels but they can still keep a good pace with commuter bikes if you are considering using one kind of bike for everything including off road riding and climbing extremely steep grades. In fact, a fatbike may be one of the few bikes with a heavy enough front end that you can keep the front wheel on the ground climbing some insanely steep hills! The heavier wheels also make riding on tricky terrain easier because they just roll over everything.
Icy conditions require really good studded tires. Think of knobby tires with lots of studs. Tires with road tread tend to clog up more quickly with snow, reducing their effectiveness. On bare ice, pretty much any studded tire will work well. Chains are very effective on ice and are particularly good in deep snow where studs and tires become ineffective.
Despite the growing popularity, fatbikes do not work well in deep snow. The wide tires push a lot of snow and after 3″ of snow they begin to act as if you are riding on steel bearings with the front brake dragging.
Where fatbikes excel above other kinds of bicycles is on packed snow which is icy. The wider tires offer better grip in conditions where narrower tires become tricky to ride, especially if there is water or snow on top of ice. Consider combinations of packed and loose patches of snow for example.
On hard packed snow, narrow tires work quite well. But hit a patch of loose snow, wheel tracks, or semi patched snow that breaks apart under the weight of the tires and it quickly becomes very stressful as the narrow tires quickly lurch sideways.
Wider fatbike tires won’t sink in to these patches of loose snow to the same extent and therefore provide a more consistent stability. When those big tires do slide, it happens much slower, allowing time to compensate without freaking out. When you have to ride through furrows of deep packed snow from snowplows, just pedalling hard and crashing through it is usually all it takes. I wouldn’t dare try this on narrow tires because they’ll often dig in and could launch you off the bike.
With all this talk about how good fatbikes are, you’d think they’d make the best winter bikes in all conditions. While this is generally true, fatbikes fail quickly in deep snow. The solution then is to install tire chains which will grip the loose snow better. When snow is mushy, even tire chains can plug up with snow making them ineffective. What tire chains do, is increase how much slush and deep snow you can safely ride through. They provide a significant increase in traction.
When snow gets deep enough to make riding a fatbike impossible (in my experience 4″ of snow), What can you do?
Think narrow. If wide tires don’t work, try narrower knobby tires with studs and tire chains. It has allowed me to ride in snow 6″ of snow vs the fatbike becoming useless in 4″ of snow. Using 2″ wide tires (half the width of some fatbike tires), can work well enough to allow riding sometimes in up to 12″ of snow. The more snow the front wheel pushes, the more likely the back wheel will spin out as it tries to force the front wheel through the snow.
And what if this doesn’t work?
Think ebike. If you can add a little power to turn the front wheel against the resistance of the snow, the rear wheel won’t use up all of the available traction. If you use too much power driving the front wheel, it will spin out because there is less weight on the front tire to get enough traction. In fact, adding weight to the back wheel helps improve traction. Riding a heavier bike or adding weight to both wheels will help improve traction overall.
And what if this doesn’t work?
The last option, in my opinion, is the K-track (a snowmobile like track that replaces the rear wheel). They provide more traction in snow than a fatbike without tire chains, and in doing so, require more effort.
Any kind of riding in deep snow requires more effort for that matter. The laws of physics haven’t changed. All we are doing is looking for the best compromise under widely differing winter conditions. No one bike can do perform best under all winter conditions but several different kinds of bicycles can provide a wide margin of safety and traction when commuting by bike all winter.
The best winter bicycle is a compromise. Having different kinds of bicycles is like having different tools for different jobs (weather conditions).
Having the right kind of winter bicycle is how winter cyclists have fun when they’re not supposed to.