A disclaimer: if you already have nagging knee problems you will find that this style of riding either helps correct the issue or puts you in a wheelchair. This article is not science and I am not Adam Craig. I am an average midwestern mountain biker with access to a blog that needs some articles.
Onto the glory of fixed fun . . .
Fixed gear bikes have been around for as long as bikes have existed. They are not the first bike you usually pick up when going out the door for a ride. Why is that?
For starters, you can't coast. Oh, and you have to pedal backwards to slow down because you only have a front brake. They can also tire you out faster since there's no such thing as coasting. Also, they will always, always be a singlespeed hardtail one at that.
Most people think fixed gear riding is foolish and stupid. It's slows you down they say and it wrecks your knees. Surely you must hit every single rock on the trail and skid all over the place.
Nah, not really.
My first ride on a fixxxie was at Greensfelder two years ago. I had the winter blues and bikes sucked. I felt slow. It wasn't as fun as it used to be. I had read about these Boone ti cogs that bolted onto a disc-brake hub where the disc would normally be. So I ordered one up and put it on my single speed at the time, a Surly Karate Monkey.
Took off the rear brake, flipped the wheel around and bolted the cog on. Done. I now owned a fixie. A genuine 32x16 fixed gear bike meant for trail use.
Nervously, I rode it on Dogwood. About 30 feet in I almost snapped my knees off when I tried to coast. Can't do that, when you think about it for a second, you know? The trail felt new, felt hard and tried to kill me. Many times. Logs wanted my pedals, rocks begged to shred my crankarms.
It was great training to say the least and way fun. Fixed riding demands that you focus entirely on the trail, your bike and speed. Obstacles must be avoided, threaded, hopped, whatever. You learn to rock out on just a front brake. No, you don't want to skid - that wrecks the trail and your speed. Timing log hops is the hardest. Rock ledges come a close second. You have to lift up the rear wheel and kick back just enough to get the cranks up and over the obstacle. Sometimes the logs will stop you in your tracks. The situation just didn't work out. It happens.
Sometimes that works, sometimes the cranks get a bit crappier looking. Generally speaking, I've never wiped out from making crank contact with a rock or log. The bike will shudder or go off line but recovery is almost immediate. Learning to feather the front brake is crucial because only so much leg force can stop you when you're traveling 18mph.
I slowly built up enough rides to confidently tackle the DeClue trail, Berryman, and Chubb. I don't ride fixed on every ride but it helps to stay in tune with it at least 3 times a month over winter. If you stray too long without a fixed ride under you, don't be surprised to find that you want to coast and tear your feet off your pedals.
When starting out, I suggest using a low gear, like a 32x19 or so. This lets your cranks spin much faster and gives your more options to get over obstacles. Plus, you're not killing yourself on the trail. Always remember, coasting is crashing.
I usually only run fixed over the winter months. It gets too hot in St. Louis to constantly spin but I'm not saying you can't do it. Summer is when you want to be railing gulley berms on your favorite bike.
Whatever you do, remember to watch out for obstacles, slow down on the downhills and REMEMBER YOU CAN'T COAST. Your kneecaps will explode if you forget this rule while jamming on a descent. Your front brake is your friend. Don't be the Hulk and backpedal when your legs are wasted - you risk injury. Use your hand brake when nature is attempting to feed you tree bark. You will be amazed at how much power one brake has and how hard it is to really wash out the front wheel. Be smart through rock gardens and loose gravel - physics still apply.
Oh yeah . . . and don't listen to naysayers. With practice you can keep up with other bikers. You may not be able to outrun them on a descent but with the gear/chain/rear wheel throwing you uphill, you can assure yourself that you have the best momentum generator going.
Do enough fixed rides and you will improve in several areas; handling, speed, cadence and endurance. When you get back to your standard rig you'll find yourself not coasting as much, but instead rocketing through tech gardens, flowing over roots, logs, rocks with mucho endurance to boot.
I just finished up a ride out at Chubb and it was unreal. It felt as fast as on the traditional single speed. See you on the trail.