A Ghetto Guide to Fitting Yourself on a Mountain Bike

Adjusting my bike's fit

I originally wrote most of this article as a part of my series on buying your first mountain bike almost a year ago in March. Somehow, this post just languished in my drafts section all of that time, until finally I got a tweet the other day asking for advice on just this topic. I've added a section in order to complete the article, so here it is, about 10 months late!



Please note this is intended for use by a Cross Country/Trail/All Mountain user.

When shopping for a mountain bike, one of the single most important aspects to consider is fit. Fit is crucial if you are buying a $5,000 race horse, or you are looking at one of the $300 hardtails I mentioned (close to a year ago). If your bike doesn't fit correctly, it won't ride well and will make your experience with mountain biking unenjoyable. It could be exceedingly futile due to lack of horsepower from a bike too small, or exquisitely painfull due to a bike too large (and kissing the top tube with your man (or woman) parts). Yes, bike fit is important!

Again, here is another very big reason why shopping at a local bike shop is far superior to shopping at Wally World. Not only are there more bike sizes to choose from to find a better fit (like I mentioned previously), but the people employed at an authentic bike shop know what they are doing. They will help you find the bike that fits you best, and (if it's a good shop) cater to your every need.

I do realize that many people like to go the Craigslist route, and try to find a bike for cheap from a private party. (I'll talk more about that later.) If so,  

Here is Greg's step-by-step ghetto bike sizing guide:

Frame Size:

1. While standing on flat ground, throw your leg over the bicycle.  You are now standing over the top tube.
2. Slide as far back along the top tube as possible, until your butt is touching the seat post.
3. Then, grabbing the bike in front of you and behind you, lift it up as far as you can until it presses into your junk.
4. Judge how high you lifted your bike/the amount of room between the top tube and your parts. This is important to know, as odds are there will be a time when you have to hop off on a tough trail.  You don't want to make your voice squeak every time you dismount (or any time that you dismount for that matter).
5. When standing over your bike in the position mentioned in number 2, you want there to be MINIMUM one inch of space before the top tube touches your pants.  It would be ideal to have several inches of room there. 
6. If there is not enough room, try a size smaller. (Or if shopping used, don't buy that bike.) If there is roughly 4+ inches of room, try a size larger and see how that feels.

The second major thing to consider with fit is saddle height.

1. When seated and clipped in (or the ball of your foot is on the pedal), there should still be some slight bend in your knee. 
2. When the center/arch of your foot is on the pedal, your leg should be completely straight.  Having a saddle at this height will give you maximum horsepower while riding
3. If your hips are rocking off of your saddle when you pedal, it's too high.  Bring it down a notch.
4. Your seatpost shouldn't be out of the bike past the line labeled "Minimum insertion."  I could give you a metaphor, but I think the words "minimum insertion are pretty clear: make sure it's sticking in that much.
5. If the seatpost has to stick out past the minimum insertion mark to achieve optimum saddle height, either the frame is simply too small, or you just need a longer seatpost.  In order to determine if the frame is too small, please see the steps above.

Saddle Fore/Aft Position: 

If you are riding a road bike or a cross-country race machine, you want to have your saddle positioned so that when you have the cranks set horizontal your knee is directly above the ball of your foot, which as you'll see below should be directly above the axle of your pedal.

However, if you're just an average Joe trail rider or are riding aggressive all-mountain, you might want to consider sliding the saddle back. Some people think that this provides a better angle for better leverage when climbing a very steep slope and puts your weight further back for more aggressive descending.

Personally, I like my saddle back a little from the roadie position, but I'm generally not too hung up on saddle position. As a trail/AM rider, I spend a lot of time out of the saddle putting some body English on the bike in order to negotiate a technical sections of trail, or to simply descending aggressively. Once you get of the saddle, the point is moot.

So while this is a point to consider as you set your mountain bike up, don't get too worried about this detail. Frame size is much more crucial

Minor Concerns
 
In my mind, those are the major concerns as relate to bike fit.  Very quickly, here are a few other minor ones:

• Cleat position: Should be right under the ball of your foot.
• Angle of the saddle: For mountain biking (Cross Country/Trail/All Mountain) the saddle should be either perfectly flat, or have the front angled down.  I prefer mine angled down just a hair.
• Handlebars, stems, and etc: From my experience, most of the choices you make in this category depend on your riding style
• Saddle Fore/Aft Position: I don't know a whole lot about this, but I'm currently riding with mine as far back as possible.

Achieving a good bike fit is crucial to enjoying your riding experience.  Again, if you shop at a reputable bike shop, they can help you out with all of this.

Your Turn: What do you think about bike fit? Do YOU know more about any of this sizing stuff than I do? Then please comment!