At first glance, this type of fixie may seem like a paradox. Mountain bikes are built strong and heavy, with front shocks and often rear shocks too. They have a nearly overwhelming amount of components with the addition of their shocks. On the other hand, fixies are light and nimble. They are pure and simple. So what would happen if you combine the two: mountain and fixie?
Well first off, let it be said that you cannot build a fixie with a dual-shock bike frame. This simply just doesn’t work: with a rear shock system, when the shock compresses, the distance from the chainring to the cog (front to rear gears) changes a little. Not by much, but enough to cause tensioning problems with a fixie.
Since fixies have no derailleurs, there is no mechanism of ensuring that the chain is taut. Too tight, and a bike chain will not run smoothly. Too loose, and a bike chain is bound to fall off. On standard bikes, the rear derailleur takes care of this problem with a spring-loaded arm (the part that hangs downward on the rear of the bike). Without such a mechanism on a fixie, chain tension is completely regulated by moving the rear backward and forward in the drops outs.
Since the position of the rear wheel in the dropouts is fixed, there is no way to regular chain tension for a bike with a rear shock. So that is out of the question.
Front shocks, on the other hand, are fair game. In my opinion, front shocks are an extremely effective addition to any bike (that isn’t used for racing).
There are really only two disadvantages of having front shocks: 1) Added weight. Front shocks can be pretty heavy, so they definitely add a few extra pounds to the weight of the frame. 2) They can absorb energy that would otherwise be transferred into forward momentum. How much energy, it is hard to say. But as far as I can tell, not enough to make that much of a difference in everyday commuting.
While there is really only one advantage to front shocks, it is an important one: front shocks provide a much, much smoother ride on rough surfaces, including pavement, sidewalks, and dirt/gravel. With front shocks, it is also much easier to jump a curb or hop off a curb without putting as much strain on your wrists.
So I decided I wanted to make a fixie with front shocks. This is what resulted:
A diamondback frame with a standard from shock provide the core for this bike. In the front, I have a 26 in wheel with a 26 x 2.00 in tire. This is a pretty large thickness tire, which is pretty standard for mountain bikes. In the back, I was forced to use a 700c wheel with 700 x 28c tire. This is about half the thickness of the front tire. Essentially, this is a road bike tire.
Front Tire Rear Tire
The parity between the front and the rear tire dimensions definitely give this bike a somewhat strange look. However, I have found that little is lost.
On the road, this fixie yields a smooth ride on Houston’s pot-holed streets. Compared to other fixies, little to no speed is lost from the thicker front tire.
Off the road, this fixie is surprisingly able. Over the weekend, I took it out for a spin at the Memorial Park mountain bike trails. The trails consist of sections, labeled by color. I tested out the fixie on the green trail. While riding fixed and mountain biking are usually two separate realms, there is really no reason not to combine them. It definitely provides and extra challenge.
I made it through the green trails on my mountain fixie just fine. I did have to get off and walk up a few hills, as it was nearly impossible to climb while in such a high gear. But besides that, everything worked fine. Even the thin rear tire did not seem to be a problem. Ironically enough, I went out a day later on a standard mountain bike to the same trails, and ended up getting a flat in my rear tire, even with a reinforced, thorn-resistant inner tube.
The mountain fixie may not seem to be the most practical, but it is really not that bad of a setup. Its takes the best of both worlds, and forms them together into an extremely reliable bike that can take you practically anywhere!