Cross Country & All Mountain
Jamis XAM 1.0
This weekend, before my group ride, I got a chance to throw a leg over my friend’s brand new Jamis XAM 1.0. Jamis Bikes places this rig under the “All Mountain” category. Prior to this quick spin around the parking lot, I’ve never been on an all mountain (AM) bike before and not surprisingly some of the assumptions I originally had of the AM category were shot down and I were replaced with facts.
I originally assumed that the main difference between a Cross Country (XC) bike and an AM (you can also substitute Freeride or Downhill) bike was the amount of suspension front and rear. XC normally has between 0 – 4 inches of suspension. AM has between 4 – 6 inches of travel. But this is not the only difference and in truth, may not even be the most important difference.
Once you get on a true all mountain rig the first thing you’ll notice is not the suspension but the handling. The handling change between the XC to the AM bike is different mainly because of the head angle. I don’t want to get too technical because we’re not a highly technical site (and I don’t want to lose you), but having a basic understanding of head angles makes reading those measurements much easier to understand.
Wikipedia says that the head angle “is measured clock-wise from the horizontal when viewed from the right side.�? For me it was much easier to understand this by looking at a drawing.
Measuring Head Angle
In the case of the Jamis XAM, the head angle was designed to be 68.5 degrees. Trek uses a 68.2 degree head angle for their Remedy (their AM line) and KHS uses 69 degrees for their AM bikes. In contrast most XC bikes head angle geometry I’ve seen (Jamis, Woodstock, KHS, Trek) range between 70 and 71.5 degrees.
This 1 to 2.5 degree decrease in the head angle (or slacker head angle) between the XC and AM geometry slows down the handling of the AM rig. Slower handling means turning is slightly slower which is best when doing things that most AM rigs are meant to do: go up and down the mountain while also being able to handle jump and drops over a couple of feet high. Most XC bikes just aren’t designed to handle jumps and drops of over a couple of feet on a consistent basis while the AM finds its groove in this.
Hopefully this doesn’t appear to be a rant on AM bikes because it’s not, it’s been more of a chance to point out differences. I love my XC bikes but when I’m up in the air handling a 2+ foot jump and I twitch my handlebars right, I’ll definitely wish I had an AM to make that twitch less noticeable on the landing!