Cross country mountain bike racing has the longest list of variables riders must face out of any genre of racing. This is because not only are you going down the hills, you are also going up them. Efficiency on the climb is just as important as maximum speed on the descent. This creates somewhat of a balancing act when it comes to preparing a bike for XC racing. A bike set up to fly through the rocks and technical corners of a descent is going to be a terrible burden when you reach the uphill. Similarly, a feather-light bike that is stiff and rigid to pedal up the climbs with ease, is going to fall apart on the downhill.
Here are a few setup tips for the perfect XC bike that I've learned over the years:
1. Never sacrifice strength to shave grams
The lighter the bike, the easier it will go up hills. This is true, but only with a bike that isn't broken. Most times, the lightest, most advanced parts are the first to break when you hit the first technical descent. Things like racing wheelsets with low rider weight limits, or all-carbon seats that weigh 15g may seem like a good idea on paper, but they are a gamble on the trail. The truth is, the small weight penalty for components that offer some protection against the obstacles you're sure to run into after the climb is insignificant. A couple hundred grams will never prevent you from winning a race, but a bike that won't roll will always lead to a DNF.
2. Tire pressure
Even with tubeless tires, I prefer relatively higher pressures than most people would expect. I weigh 135 lbs and depending on how technical the course is, I'll run 25-30 psi in my front tire, and 28-35 in the rear. This is for two reasons: the first is protection of the rim and tire. XC tires are thin, so when you are going over rocks and roots at high speeds, the tire can fold all the way in and hit the rim. This can damage the rim and slice the tire. So the minimum pressure I'll run at a race is determined by how low I can go (within the range I listed above) without hitting my rims.
The next thing is rolling resistance. More pressure means less tire in contact with the dirt, which means you are going to roll faster. This is very important in XC racing, but it's a double edged sword – less rolling resistance means less traction. If a course is filled with fast, loose corners, I aim for lower pressure so I can carry more speed through the turns. However, if a course has few corners or has many big ruts or berms to do the cornering for you, I'll side with higher pressures in my tires.
Much like tire pressure, I side with higher pressure here as well. Soft/slow suspension is inefficient while pedaling. Because of this, I will usually run fast rebound and 15-30 psi higher than the OEM pressure chart for my weight recommends.
While racing, the most important thing you want your suspension to do is to help you save energy. The best way to do this is to set it up to keep you safe and in control in the high speed sections and on the big hits. I've found that putting a bit more air in than the charts recommend and keeping the rebound fast, allows me climb efficiently without even needing to mess with locking anything out, while also providing plenty of confidence to hit any rock gardens, drops, or jumps as fast as the course allows on the descents.
To me, brakes that work too good are a much bigger problem than brakes that don't work good enough. The truth is, skidding is slow. Any time a tire locks up on the trail, you are losing time. Because of this, brakes that are incredibly sensitive and touchy are a disadvantage. Massive, overly powerful brakes are unnecessary in XC racing. For me, I like small rotors and small levers that require a strong pull before either wheel locks up.
If you've got an XC race coming up, try a few of these setup tips out. Remember, the key is always to find a balance between efficiency and control. As you go farther in either direction, you begin to lose the other. Finding the balance that works best for you is the secret to the perfect bike setup.