Back in the day, mountain bike sizing was based on seat tube length, and if you could straddle the frame without the top tube crashing into your important items, you were good to go. This is obviously no longer the case, and with all the numbers and opinions floating around, it can be quite a difficult landscape to navigate.
Let’s first look at the size charts of these manufacturers. These charts are a good starting point, but it’s important to keep in mind that these are suggestions, not hard and fast rules. You’re trying to find the bike that’s best for you, and you alone – deviating from the recommendations is no reason to worry. Now, if you told me that at 6’3″ you were planning on buying a size small, well, that might be something you’re worried about, but it doesn’t seem to be.
The fact that you have found a litter number that works for you is a great place to start. Reach is useful for determining what a bike will look like when you get out of the saddle – your descent position. Too much reach can make it hard to put weight on the front wheel, while too little reach can make a bike feel cramped, like you’re going over the handlebars. Personally I’ve found it to be about 20mm to suit my height, although it’s very possible to go even further either way – it’s amazing how much the human body can be adaptable.
However, range is only part of the equation. The effective length of the top tube is another useful number to consider. This one gives you an idea of how the bike will feel when you’re seated, which is important because that’s what you’ll be doing for much of every ride. The angle of a bicycle’s seat tube has a big influence on the effective length of the top tube. For example, take the Mondraker Superfoxy. The size wide has a reach of 490mm and a seat tube angle of 75.5 degrees, resulting in a fairly long top tube length of 651mm. Compare that to the Canyon Torque, which also has a 490mm reach. It has a shorter top tube length of 636mm due to its steeper 77.5-degree seat tube angle. 15 millimeters might not seem like a lot, but if you’ve ever tried a 35mm stem versus a 50mm stem, you’ll know that’s a noticeable amount.
Reach and top tube length are the two numbers I refer to the most. The third number that is good to know, especially for taller runners, is the stack. This number gives you an idea of how tall or tall the front of the bike is. Taller bars can be used to give you a more upright position, but there are limitations – comparing the stack height of the bike you’re on to the one you’re considering can help you get an idea of this that you will feel. For a deeper dive into the importance of stack, reach and handlebar height, be sure to check out Seb Stott’s great article on the subject.
Confused yet? Let’s hope not, but there’s no denying that all the numbers can be overwhelming. If possible, I highly recommend that you test drive the bike or bikes you are considering. In fact, riding a bike, even if it’s just for a short loop, can make the decision-making process much easier.