Fat Bike Geometry

Feb 15, 2013

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In the current issue of Adventure Cyclist, I brought up compact frame geometry in my Fine Tuned column. One benefit of compact geometry that I failed to bring up in that article is in the case of fat bikes, where it seems to be heavily favored.

When you're hopping on and off a fat bike while standing in a couple inches of snow, you want as much stand over clearance as you can get. Because of this, I've seen a few people drop down a size when purchasing a fat bike. For instance, if they rode an 18-inch mountain bike, they would opt for a 16-inch fat bike. The problem with this approach is that while you may get a better fit as far as stand over height is concerned, you sacrifice a good seat position relative to your bottom bracket, and you may find yourself swapping out for a longer stem, which can cause your already sluggish handling to become even more so.

If you're into comparing geometries from one fat bike to another, there are a lot of other features to keep an eye on. Before you get too deep into comparing spec charts, it's best to determine the style of riding you're interested in. Two things I tend to look at closely are head tube angle, and bottom bracket drop.

Looking at the bottom bracket, fat bikes tend to have a 100 mm bottom bracket shell, which is wider than what you would see on most mountain or road bikes. With a wider stance on the bike, you are more likely to clip a pedal when cornering unless you raise the bottom bracket. If you think you'll be riding your fat bike on trails at higher speeds, this can be an issue. However, if you plan on mostly riding wide open snowmobile trails and roads, this doesn't come into play as much.

Head tube angle is a little trickier to judge. In general, a steeper head tube angle (closer to 90 degrees) can give you more responsive handling. This can be attractive for people looking at more technical trails that demand quicker handling, but it's not the only way to tweak handling. A shorter stem, shallow fork rake, or even higher tire pressure can create more responsive handling.

These are good things to have in mind, but in the end, your best bet is to just get out and test ride a few bikes and decide for yourself what you like. Otherwise you'll end up spending an exorbitant amount of time reading forums, and checking out geometry calculators, when you could spend your time out riding.

Photo by Josh Tack.

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TOURING GEAR & TIPS is written by Joshua Tack of Adventure Cycling's  member services department. It appears weekly, highlighting technical aspects of bicycle touring and advice to help better prepare you for the journey ahead. Look for Josh's  Fine Tuned column in  Adventure Cyclist magazine as well.

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