Touring - 520 with smaller cranks

hey,

it seems that all people with the 520 change the cranks to a 48t. i don't get it why? if you think 52tx11t is too large why not just use a 52tx17t or something like that? i meen wouldn't it be good to have the 52tx11t for downhills??

Originally posted by Turbonium
hey,

it seems that all people with the 520 change the cranks to a 48t. i don't get it why? if you think 52tx11t is too large why not just use a 52tx17t or something like that? i meen wouldn't it be good to have the 52tx11t for downhills??

The point isn't the size of the big ring. It's the size of the small one, and the tooth-differential between big ring and small ring that a derailleur will handle.

If you need at 24 or 26t small ring -- and most people do, for getting up real hills with real loads -- no FD will let you also use a 52t big ring.

And after ascending a grade with a full load, you're generally going to want to use the descent for recovery, not for going as fast as possible. Besides which, going as fast as possible in a descent with 50 pounds of panniers and stuff is not really recommended.

RichC

what is FD? front deraileur?

Originally posted by Turbonium
what is FD? front deraileur?

Yep.

R

In U.S. units, good useful gearing for touring is considered to top at 100 gear-inches (see http://www.sheldonbrown.com/gears for a gear calculator). As it comes, the Trek 520 has gearing up to 127 gear-inches. And the low gear, being at 25 gear-inches, is good either for a young person with good knees, or someone who never climb hills steeper than 8-10%, or someone who doesn't load too much the bike... but not when two or more of these factors are combined!

If you mostly commute or tour with light loads, you could "improve" the gearing with something like Sheldon's Cyclotouriste 13 or 14 -- http://www.sheldonbrown.com/k7.html --. It gives you closer ratios near the top (good on the flats) by getting rid of those "useless" high gears. However, you can't go much lower than you have, except by changing chainrings. BTW, you can mount your own cassette with cogs taken from 2 or more cassettes.

For your information, I have 44-34-22 chainrings and a 12-14-15-16-17-19-21-25-32 cassette on mine. It gives me a high gear of 99 gear-inches... whcih I rarely use. Even my next highest gear, at 85 gear-inches, is rarely used. And while it might seem low in regard to what's commonly available these days, if I spin pedals at 80 rpm, it allows me to pedal at 33 km/h (top gear at 80 rpm would go to 38 km/h).

Regards,

When I had a 50t ring, I only ever used it once, on a 15 mile ride with a heavy tail wind. I found that the smallest gear was too high for my style of riding, which includes very teel (20%) hills, and riding tracks and trails. Swapping the road triple to an MTB triple was one of the best moves I made.
With low gears, a standard touring bike can go anywhere a mountainbike can.