Following is a post I made on mtbr.com in July 2002 after doing an initial conversion (along with my Bianchi Volpe) to singlespeed using a derailer as a tensioner. For a report on its eventual conversion to singlespeed without a tensioner, see my Cutthroat Pass ride report.
In January 2003, after nearly 10 years of faithful service, the Sundance died of an ovalized headtube. It was replaced by my KHS as a budget interim replacement until I could get the funds together to buy a Surly Karate Monkey (which I did later that year).
I just spent a weekend in Central Oregon with my two bikes, a boxful of cogs and several PC-58 chains. I am pleased to report that both of my bikes are now SS off-road capable.
First off, the mountain bike. It's a '92 Fuji Sundance, still going strong after all these years. Fully rigid, of course, and vertical dropouts so it needs a tensioner. I'm not thrilled about using my derailleur for this, because my Volpe project taught me how much energy is wasted by all that chain wrap.
But wait a minute ... if all I need is chain tension, not chain wrap, why not use just ONE of the jockey pulleys of my derailleur?! It IS spring-loaded, after all! Now that means I'm operating in pull-down mode, not push-up, but guess what ...
IT WORKS! It seems very solid - I used it to do the Cultus and Swampy Lakes loops, and also rode partway around Waldo Lake today with it, and didn't drop the chain once. The one concern would be that the chain is now turning the jockey wheel in the "wrong" dire?tion, which could eventually back the screw out. I'm not too worried though, so far no problems, and if the screw does come out I'll Loctite it back in. Here's a close-up of the drivetrain:
I'm using the middle (36t) chainring on my old "standard" crankset with a 21t cog in back, for a ratio of 1.71 -- basically the same as the 34x20 that is so popular. After riding it for a while, I can see why, too -- it's just tall enough so you can get some speed, but low enough that you can still power up the climbs.
Here's the bike (pic was taken at the Swampy Lakes shelter near Mt. Bachelor):
Why, thanks for asking ... yes, that IS an unusual stem/handlebar setup! The original stem and bars were too low for me (pre-suspension geometry), but the threadless adapter and riser stem put them a bit too high. But with my recently purchased Salsa CrMo big-sweep bar angled mostly down, I've got the bars at the right height and at an angle that is MUCH more comfortable for me than the traditional orientation. Not quite like drop bars, but a bit of the same idea ... and I can use my MTB levers.
OK, this SS setup was working great. Even better, by using my existing derailleur I can swap out cogs, rewrap the chain the "normal" way and run in geared mode (which for me is currently a 1x5 setup: 24x11,15,19,24,30) whenever I want.
But I wasn't quite satisfied. I was inspired by Sheldon Brown's "double-singlespeed" idea of having two chainrings and two rear cogs, sized so that the same length of chain would work for either combination. You have to get off the bike to shift, of course, so maybe it's not cheating? I don't care, I wanted to see if I could make it work, so I slapped a 30t cog on next to the 21t. (If you look at the pic below closely, BTW, you will see a smaller third cog in between the 21t and the 30t ... in the unlikely event the chain slipped off the 21t cog to the left, it would fall down onto this useless cog instead of catching on the 30t and jamming everything up).
Jeezus, it works! Now in addition to my 1.71 gear (which I still anticipate using most of the time), I have a 0.80. This is a VERY low gear. But I don't use it for tackling super-steep, technical climbs ... that still requires the old "24-inch" gear. What it IS nice for is LONG moderate climbs that are just too exhausting (at least for me) in the taller "normal" gear.
My only concern with this arrangement is that the jockey wheel is VERY close (about 2mm) to the 30t cog when it's in the low gear. I'll have to keep an eye on that. Anyway, here are pics (taken at the South Waldo Lake shelter) of the "double-singlespeed" setup in the climbing gear:
and in the "regular" cruising gear:
and one of the bike with this setup (yes, there's still some mud at Waldo): ... and here are pics/description of the 'cross bike OK, here's what I did to the Volpe cyclocross bike. As you may recall from last week's post, for commuting I had alrady set this bike up in a 48:18 (2.67) gear using the large chainring and a DX cog in back. With the DX sprocket it is totally bombproof (as opposed to the ramped cog I used at first), and I completely trust it to stand up to my hammering in traffic. I leave the derailleur on the bike - just shifted out of the way - because this is my road bike too. As if my weekend wasn't busy enough, I spent Friday morning doing my annual road ride around Crater Lake. That would be WITH gears.
Anyway, off-road riding with this bike was going to call for some VERY different gearing than I was using for commuting. As you might have guessed, I wanted to do the same kind of "double-single" thing that I did on the mountain bike. I ended up pairing the 38t middle ring with a 23t cog (22 would have been closer to the "standard" 1.7 ratio, but 22s are fairly rare and I don't have one), and the 28t small ring with a 32t cog. This gives me ratios of 1.65 for the ordinary gear and 0.88 for the climbing gear. Here's a pic of the drivetrain:
A close eye will note the rubber band drawn across the jockey wheels of the derailleur. Whassupwithat? Well, I noticed on my commute that with no chain tension across them, the pulleys rattled around, making a horrible racket. The rubber band solved the problem cheaply and effectively.
and the bike:
(by the way, that front tire IS as fat as it looks in the pic: it's a 700x45 Panaracer Smoke. Good God!)
Oh boy, big problem: ramped cogs. On the SS'ed mountain bike they work just fine, but that's because I'm using a tensioner. On this bike there is no tensioner, and I threw the chain a couple of times attempting to climb the very difficult Windy Lakes trail (Crescent Ranger District). This setup is just NOT suitable for honking my way up steep, technical climbs. If I do, I will get hurt. Bad. I've done my best to center the chainrings, which has helped, but I still can't hammer.
I've seen descriptions on this board of various methods (pie plates next to the cog, etc.) to keep the chain on, and I may have to experiment with this. But even without that, maybe that's gonna be OK. Mostly I'm going to leave the really rough stuff to the mountain bike, and use this bike on mellower trails. As it is, I rode the Oldenberg Lake trail (same trailhead), using the climbing gear for the ascent and the "regular" gear for the descent. Even though there was LOTS of fencepost-sized deadfall to hop over, I never threw the chain once.
It may be that I'll decide I don't need the low gear on this bike since I'll probably take the mountain bike if I know I'll be facing a long, grinding climb. In that case, I'll go back to a single gear using a DX sprocket in back. I experimented with that setup too this morning (busy weekend!), using the 18t DX that I alread have. 28:18 is a bit low, with a ratio of 1.55, but it works fine and is rock-solid, so I may have to invest in a 17t or 16t. No pic of this setup?for off-road, but it looks pretty much the same as the commuting arrangement shown here:
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