Since Tredecillion was pondering using feedwater flow and enthalpies directly in calculations of turbine balance, I thought I’d help “lower the bar” by spewing some pent-up biking geekspeak. Really, I just need to get this out of my system. I’ll cook something later this week. Promise.
One of the things I disliked about the original configuration of my Bike Friday was the shifting. Switching among front chainrings was clunky, sometimes evoking profanity if the chain slurped down past the small ring and wedged itself between the hinge and the bottom bracket. The sloppiness is a result of some compromises made related to the small wheels and the limited range of gears I can push without knee pain.
It’s often convenient to refer to quantify the drivetrain in “gear inches,” the distance moved for each full rotation of the pedals. It’s defined by the simple formula:
# teeth in front chainring circumference distance traveled
X of = per revolution # teeth on rear freewheel the wheel of the pedals
A low number means pedaling is easy, but I don’t go as far. A high number means I go farther, but it takes more effort. It’s just like the low gear on your car’s transmission. If the number is too large, I’ll need ice and ibuprofin for the rest of the week.
In the original setup, I had front chainrings of 39-48-60 and rear freewheel of 11-34. Sparing my gentle readers the tricky math, this is a gear-inch range of 22.9″ to 109.1″, or 6.1 to 29.2 miles per hour. It’s a comfortable range.
Unfortunately, there are three engineering problems with this setup. The first one you can sort of see in the picture. The arc of the front derailleur is tighter than the arc of the biggest chainring. The front derailleur was designed for a 52-tooth ring. To make it work with a larger, 60-tooth ring, the derailleur has to be positioned much further than it should normally be, creating extra slop in the way it kicks over.
Second, there’s some manic handwaving necessary because (as my mechanic explained, I don’t quite see it) the Vuelta chainrings don’t have the little grooves on every fourth tooth that kick the chain up to the larger ring easier. Finally, a lot of extra chain needed to handle the shifting possibilities — 21 teeth up front (60 – 39) and 23 (34 – 11) in the back.
An extra bonus feature, only available on the overpriced DVD version, and which you can easily see in the photo, is the rear derailleur hangs very low to the ground. This sucks up leaves and other organic debris. In the morning, the noise freaks me out.
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Ideally, what I need to do is reduce the rear freewheel’s size, which would also let me reduce the front chainrings’ size. It just so happens that Shimano makes, but doesn’t advertise well, a component group for small-wheeled bikes under the “Capreo” label. The upshot is there’s a 9-26 freewheel available. Plugging the numbers back into the formula above, thereby sparing you all mind-numbing boredom, this means I can use a standard Ultegra triple: 30-42-52. Shifting problem solved!
Sort of… it turns out my original bike was made with an Ultegra double crank with spacers to add a third ring. I managed to barter with someone for a triple crank (and the rings). The next road block was having to get a wheel built because the Capreo freewheel only works with the Capreo hub. It has something to do with crossing the streams – cats and dogs, living together.
The final stumbling block came when Tom (of Issaquah Ski and Cycle), my mechanic, discovered the braze-on (the little bolt hole that I use to secure my fender and pump) was right where the front derailleur ideally should hang. This, it turns out, was simple to resolve thanks to some photos from the folks at Bike Friday: grind off a small, braze-on-sized semi-circle from the front derailleur clamp.
The results are amazing. The bike shifts well, and I haven’t picked up any large pieces of decaying, organic matter. The new setup has a gearing range of 23.1 – 115.6″, or 6.2 – 30.9 miles per hour.
With that settled, the next thing I’m fiddling with is tires. I originally had Schwalbe Stelvios. These were great, up until they started wearing out. Any aerodynamic/friction advantage they had was furiously negated by the time I spent changing flats. It… wasn’t… fun.
I’ve had a pair of Primo Comet Kevlars on since just before STP last year. They’ve fared better, but the rear tire is worn out. Schwalbe’s Marathon Slick is supposed to be “Road Touring,” which is mostly what I do. The tire has a slick tread, reinforced with a kevlar layer. It feels somewhere between the thin Stelvios and the heavy Comets. I plan to put a few hundred miles on it before passing judgement and adding another on the front. I also picked up a Continental Top Touring tire, which is legendary for longevity. If the Marathons work out, I should be due for a replacement just before Ride Around Washington in August. If it doesn’t work out, I’ll try the Continental.
August 2005 update: I’ve had a lot of problems with rim wear and think this is a symptom of overheating as I have a gnarly, serpentine downhill on the way to work. I put my old wheel with the 11-34 cassette back on. Meanwhile, I’ve been shopping for replacements.
None of the local bike shops — Il Vecchio, Sammamish Valley Cycle, Issaquah Ski and Cycle, Gregg’s — can build 406 wheels. Three mail order places I contacted who can make 406 wheels do not have access to Capreo parts or even the proprietary tool to extract the cassette. Bike Friday is the only option, and while their prices are reasonable, they’re quoting me 3 weeks for new wheels.
After some more thinking on this, I’m going back to a non-proprietary hub and cassette. I’m having a set of wheels built at Hostel Shoppe with the SRAM 11-34 cassette.
Forget the cooking man, keep spewing out the bike geek goodness! 🙂
Coolness. Congrats on finding the right gearing. If you still have trouble with the chain jumping off into oblivion, they make these little “chain deflectors” you can get that prevent this unwanted behavior. The “dog fang” by a company called Deda is the one I have on my bike. Tom down at Issaquah Ski and Cycle sells what appears to be a better one. Spew on, brother!
I have a bike friday that came with the same set up as your original. I too have switched to a capreo and more normal triple front chainrings.
My mechanic was unhappy about how high the front derailleur sits because of the braze-on. It seems to work, but the clearance is too high.
So, was it easy to get the braze-on ground off? I wonder if I should do?
rob
I kept the braze-on, but ground down the front derailleur. See picture:
here
Hey! I found your site when I was searching on the Capreo system.
I have a KHS folder I’m kitting out for touring. I was thinking of the Capreo system too but had some concern about the non-standard nature of the hub and cogs. Thanks for the straight-dope on that…sounds like something that could cause a small problem to turn into a big problem – especially in a remote area.
Some other folks have suggested a Schlumpf speed-drive to bump up the gearing – any thoughts on that?
http://www.ncf.ca/~af895/bike/KHS.html
I build 406 wheels and would be interested in building purchasing your old one. I will then locate the needed tool and toy around with this gearing on my sons 24″ mountain bike that because of the smaller wheel size, has extreamly low gearing.
Hi!
I just wonder if it would be advisable to change the lower gear cogwheels on the Capreo to e.g. 17–21–25–29 to get a gear range of approx. 26–119 inches with 20″ wheels and a double chainwheel? Personally I think the 20% steps in the low range would be OK to be able to cope with steep parts when touring, while keeping the possibility for high speed. (This set-up is planned for a Moulton NS Double Pylon)
Best regards,
Paer Jansson
Hi Paer, as long as your derailleurs are set up to handle the size differences in the chainrings, this should be OK on the low end, though it won’t shift as crisply.
Jim/et al:
I am dithering. Capreo or standard?
I’m buying a BF, which I will be using mostly for commuting, and for the occasional fast group ride. The bike’s top gear with an 11-tooth cassette will be in the 96″-97″ range. A Capreo set-up would get me up into the ‘teens, say 115-6 gear inches.
Indecisice as I am, I am afraid of committing to a proprietary hub/cassette format like Capreo–don’t want to get betamaxed; not keen on buying yet another lockring tool (matter of principle, not the $11); definitely don’t want to be SOL if I decide I want or need a cassette with a lower low than 26t.
But, of course, I am equally afraid of shelling out for a performance bike like the Friday that lacks adequate top-end capability…
What’s your take on this dilemma? Assuming a 53t big chainring (18 sp), will the difference between Capreo’s 115-ish gear inches and the standard 11t cassette’s 97-ish gear inches be substantial, or would it splitting hairs, say on the order of 1-2mph? (nb: I seldom hammer 53×11 on the flats, but sometimes do going down hills).
Thank you,
-Jamey
Hi Jamey,
It really depends on how much you want the top range of gears and whether you’re a spinner or masher. I’m a spinner, meaning I prefer pedaling in the higher RPMs to pedaling slower with more power per stroke. With my standard Ultegra setup, it tops out at the 97-ish gear inch range, which is fine for maintaining the main 20s on the flats. On downhills, I hit the mid 30s. I enjoy having the low-low gear for the ultra-steep hills and when I’m just tired and need to keep moving at a snail’s pace.
The Capreo worked well for me, and from what I can tell, Bike Friday keeps it adequately stocked. The charge $75, which is on par with a standard quality Shimano one, though twice what I pay for the 11-32 9-speed SRAM from Performance or eBay. The special lock-ring remover was an annoyance; even Hostel Shoppe didn’t have them in stock.
So, were it me, I’d look at using more standard parts and forgo the Capreo. (However, if you do go that route, and are interested, I will sell you my used Capreo hub and cassette so you have spares.)
Another option, if you don’t have the indexed shifting, is to use a larger front ring. My original bike had a 61T up front, but its arc wasn’t as compatible with the arc of the derailleur, leading to clunky shifty.
Jim
Jim,
Are you still interested in selling your used Capreo hub and cassette?
Still have that Capreo wheel and would consider selling? If so, I’m near you in Sammamish.