What Are The Different Between Fat Tire Bike VS Mountain Bike
Last Updated on
There are a few simple things to know the difference between a fat tire bike vs mountain bike. A fat bike has wider tires than a standard mountain bike and has geometry changes to make this possible. A fat bike will generally have a tire over 3” wide and up to 5” on some newer fat bikes. If you want to know more about these differences then read on.
Fat bikes are snow joke
There is more to fat bikes than just some manufacturer fitting tractor style tires to their mountain bikes. Fat bikes were designed to cross Alaskan snowfields. Standard mountain bikes could not handle the snow of Alaska.
Your standard mountain bike will have a tire that is about 2.25”. Now think of this as your foot. What happens when you stand in snow? You sink. Now pop on some snowshoes or a set of tennis rackets and what happens? You stand on the surface of the snow. Flotation is the essential reason why fat bikes have fat tires.
You cannot though squeeze a big fat tire into a standard mountain bike frame. You need to change the geometry of the frame and fork to be able to fit these tires.
Fat bike wheels are huge
Looking at fat bike wheels and tires and you instantly see that the tires are much fatter. What you probably did not notice is that your hubs are wider as well as the tires. Hubs have become wider to allow bigger and stiffer wheels to be built. Originally fat bikes were built with asymmetrical frames to allow standard width hubs to fit frames and allow tire clearance.
As fat bikes became more popular, it became possible to sell fat bike specific parts. More sales led to frames becoming symmetrical again, but hub width has become wider. Originally fat bikes started on a 135mm standard mountain bike rear hub. Now you will mostly see 170mm or 197mm rear fat bike hubs.
By going wider with the hubs, wheel manufacturers have been able to go wider with rims. Mountain bikes used to come with 21mm internal width rims. Fat bikes now run 100mm wide rims. 100mm rims mean that you can safely fit 5” wide tires on these rims. 5” wide tires mean that frames need a lot of clearance.
Longer backends on fat bikes
To help fit fat bike tire to the back of fat bikes, you will see that they have longer chainstay lengths than standard mountain bikes. The longer chainstays also help the bike to stay upright and feel stable when you are traversing less than ideal terrain.
To help supplement these long stays, manufacturers have increased bottom bracket width. Your bottom bracket is the area where your cranks go through. Standard mountain bikes have a 73mm wide bottom bracket shell. Fat bikes jumped up to shells that are 100mm wide. This has over time been driven up to 120mm wide.
This change might seem hard to see, but if you want smooth gear changes, you need these changes. The 120mm wide bottom and 197mm wide rear hub mean that you will be able to run gears without your chain fouling. It also means that you will have mud clearance when you run 5” wide tires. This means the back end of a fat bike is much wider than that of a standard mountain bike.
These changes have also had to be made at the front of the bike as well. Your bike would look silly with a 2.25” front tire and a rear 5” tire. Your front fork will have a wider spacing, and you will again find wider hubs on your wheels. You can be looking at 150mm hubs over the standard mountain bike size of 100mm.
Fat bike head angle
The next major area of difference between a trail style mountain bike and a fat bike is that a fat bike does not have as slack a head angle. Slack head angles are all about speed. If you are on snow, sand, or in a bog, you will more than likely not be speeding along. You will be carefully navigating treacherous terrain so you will be going slowly. For this reason, you will want a steeper head angle to avoid slow speed self-steer that you get with slack angles.
So as you can see you have some very visible differences between fat bikes and mountain bikes and you also have some very invisible ones. One thing is for sure you cannot easily confuse a fat bike with a mountain bike.