Since my trails are still closed, I decided to give Fremont Older in the Cupertino/Saratoga area a try. A lot of folks post about it in MTBR, but I've never been. From what I've seen and heard, it didn't look too crazy - so what a great opportunity to bring my re-built retro-fixed bike out. The original build is HERE.
I never really rode this bike in that form and I wanted to not let it go to waste, so a quick change out of some parts and it was very off-road worthy. I did have to spring for a new handlebar, chainring, cog, lockring and fork.
Fremont Older proved to be the perfect stomping ground for off-road fixed gear riding. I found the climbing to be more enjoyable than the descends - literally you can "spin out of control" on a fixed mountain bike. So, using the front brake to modulate your speed works very well. The super-wide 730mm handlebar helped a lot on mashing up the climbs.
This wasn't my first time riding off-road fixed - when I had my Motobecane Outcast 29'er, I had that in fixed gear fashion for a bit. If you're curious about riding off-road on a fixed gear, here is what I've discovered that may help you:
1) Use the same gearing you would for a singlespeed. There are TONS of sites and information out there regarding gearing, and it will literally make your head spin, so I won't get deep into it. Most people start out with a 2:1 ratio i.e. 32T X 16T. But this all depends on your wheel size, crank length and most importantly your fitness level. Because I'm on 700c wheels, I choose a 32T X 18T gearing which I can get up most hills with. Today posed no problems.
2) Get 'em wide. There is a lot of debate over wide handlebars, but I know, for me riding a single gear, the wide handlebar helps a lot when it's time to mash. I know this because yesterday was actually my official first ride on this bike and I had 630mm handlebars which were way too narrow. Now I have 730mm bars on there and they feel a million times better.
3) Use brakes. I use a front brake for off-road mountain riding only because my frame does not have v-brake tabs for a rear brake. If it did, I would definitely have a rear brake on there.
Brakes control your downhill speed on a fixed gear. I do not believe, for a second, that skid stopping is enough for off-road. I think it's just plain stupid on the street. Since you're not coasting on the descends, it takes a lot of energy to keep you from spinning your cranks out of control, so modulating the brakes keeps things in check. If you are only on the front brake, you end up putting a lot of pressure on your wrists, arms, shoulders and chest. Think how it is to hold yourself up in a "push-up" position. A rear brake helps balance this out and gives your legs a rest from fixed gear downhill resistance.
Don't question this. Get AT LEAST a front brake.
4) Have an open mind. Understand that this is fixed gear riding. It isn't extreme downhill - so the descends are going to suck as much, if not more, than the climbs. I actually prefer climbing over going downhill on the fixed gear. Unless you have very understanding friends who will wait for you on the downhills, it's best to leave the fixie at home if you are going on a group ride. What would be ideal is if they were also on fixed gear bikes - but that is a rarity.
If you're a strong singlespeed rider you will out climb a lot of the geared folks, however.
Off-road fixed gear riding is suitable for mountain exploration and mixing it up. If it is an all out group ride with your hammerhead friends - this won't be the bike to take. But for solo rides with exploration in mind to enjoy nature - a great choice.