ROAD Gearing for Bogota Colombia
 

My wife is from Bogota, Colombia, so we travel there regularly to see her family. After a few trips already since we were married 2 years ago, I'm getting tired of not having a bike there (it is actually a rather bike-friendly city).

She and her family know nothing about bikes, other than sometimes someone changes the gears on the bike that the family shares and then everything goes nuts as they try to get it back into the gear they like. Really. So they're not going to be much help sourcing a bike locally, so I've begun gathering parts together for a bike to send and keep down there.

This will be for a road bike (Salsa Campeon frameset), and when picking out gearing I'm toying with the nutty idea of putting a long cage derailleur and a 9sp mountain cassette (11-32 or similar) to go with the compact crankset (34-50) for ultra-low gearing. The region is very mountainous and since we won't live there year-round, every trip down I will have to acclimatize to the high elevation. So bottom line it is steep and I'll be short of wind at the slightest climb. Hence the desire for super-low gearing (34x32).

Is this desirable? Will this work? Anyone have experience doing something like this?

A compact with a mountain cassette will work, but at that point, you may be better served with a triple. It will have a wider range and less of a gap between gears. Of course, if you prefer, you can run it with a compact and the large cassette, I did for a while on my touring bike. It's plenty low for most things, but getting it all to work together can be a bit finicky.

If you aren't used to climbing I would look at a triple with lower gear than a standard 30t triple. A 34/32 compact double as a lowest gear of 28" @ 700x25c, but a triple running like a 24-36-48 or something like that allows you to get down to a 19" gear. I know you aren't touring but it isn't like your going to have one big climb and then your through for the ride. You going to climb every time you ride, multiple times so I would look at getting something to make that easier, especially if you don't do a lot of climbing now. At least it is something to think about....

Considering your weight loss ticker I would agree with the triple, especially if you're no longer a spring chicken.

+1 I would go with a triple. Play around with the gear calculator on the Sheldon Brown site and you can see the impact of various drivetrain combinations.

An 11-32 or 11-34 9sp cassette is a fine match for this situation (and yes, it will work fine on a road bike, with a MTB derailleur). You don't need the tighter gear ratios riding solo, and it gives you lower gearing than a 12-27 with a standard triple.

If the hills are really steep and/or long, you can do this:
11-32 or 11-34 on back, long-cage derailleur, 48/36/26 in front. The 48x11 top end is still decent, and you can practically climb a cliff without getting out of the saddle.

I already have the front crank installed, which is why I'd rather not get a triple and re-engineer all that. I just wanted to see about a change of cassette, and it sounds do-able. And yeah, this is for solo riding, and I suspect a lot of up or down, but seldom nice long stretches of flats, so settling into that perfect cadence won't be an issue. If I find out on the next trip that 34x32 isn't granny enough, I may try that triple. And yes, 26x32 will let you climb cliffs :-)

The question now is, use a long-cage road or mountain derailleur? I came up with a formula for figuring out how much chain the derailleur needs to take up between big-big and small-small:

(A/2-B/2)+(C/2-D/2)=Z

where

A=Largest Rear Cog (teeth)
B=Smallest Rear Cog (teeth)
C=Largest Front Ring (teeth)
D=Smallest Front Ring (teeth)

Z=Chain Take-Up (teeth)

So in this case:
((32/2)-(11/2))+((50/2)-(34/2))=18.5T or ~9 inches of travel in the rear der. Now I just need to go look at various derailleurs. My guess is that as long as I stick with a double in front, a long cage road should do the trick with a mountain cassette.

To be absolutely sure of compatibility, use the MTB long cage (or MTB medium cage if you don't think you'll ever go to a triple). You *might* be able to get a road long cage RD to clear a 32T cog, but you might not. Clearing a 34T cog is even less likely with a road RD. Chain wrap won't matter when your cassette is chewing up the jockey wheels on the RD :)

The 9000 ft elevation will be more challenging than the hills. I have noticed that they block off some streets on weekends for bicycles, running etc. Most of the streets aren't too hilly unless you go tot he northern part of the city.

You may want durable wheels with a little wider tires. The streets are more rough than usually encountered in the US.

Thanks for the tip on that...I'll probably try a mtb derailleur.

My wife tells me they close down the streets on Sundays for walking, running, biking, and the city turns into a bike paradise. She says tons of people ride. And yeah, the northern part is hillier, but that's toward where my in-laws live, and I'd likely head out that way, maybe towards Chia.

I got to experience this in Bogota. Called 'Ciclovia' - it was very cool.

http://www.youtube.com/watch?v=ELa5CHsUepo