Touring - Shopping for a new crankset for Trek 520

I put a 24T on my Trek 520 to give me a granny gear since I am hauling more weight for self supported touring. Now my chain jumps off and twice on a 60 mile ride this past weekend I was having to stop and put the chain back on. Why is that happening?
I would like to put a new crankset on there that would give me the best gearing for touring with a load of 30-45 pounds or more.
I'm embarassed to admit that I really don't even understand how all that gearing stuff works. I just know that I want something that will allow me pedal reasonably comfortably up the steep hills I am anticipating tackling later this Fall.
What do I need to buy and where do I order it? This is going to be part of my birthday gift from my husband (along with my new Go Lite Hex 3 tent) so I am willing to spend a bit more for quality and be really happy with it. Advice??

did you edit your chain-length at all? or adjust your derail?

did you edit your chain-length at all? or adjust your derail?
My LBS did the work for me, so I really couldn't say. I really wish I was not so mechanically challenged. I need to learn all this stuff but just don't know how to start.

My older 520 has an LX crank which is Shimano's mid-upper grade mtn bike setup, but with moderate overall gearing. I have 24-36-46 chainrings in front, and 13-30 on the rear (7spd). It is fine overall, and the few times I've toured I did not go too heavily loaded. If I did, I might want a 32 or 34 on the rear. That said, some are using mtn cranks with low gears (22-32-42) on their 520's, and in fact my local LBS will do that swap if you buy a new 520 from him. That would give you VERY low gearing, especially if combined with a 32 or 34t low gear on the cassette. With the newer wide-range cassettes, you would still have adequate high gears. I recommend you have a bike shop do it because the chain will likely need adjusting in length, and the front derailleur may need to be adjusted down slightly as the chainrings are a smaller diameter.

... some are using mtn cranks with low gears (22-32-42) on their 520's, and in fact my local LBS will do that swap if you buy a new 520 from him. That would give you VERY low gearing, especially if combined with a 32 or 34t low gear on the cassette. With the newer wide-range cassettes, you would still have adequate high gears. I recommend you have a bike shop do it because the chain will likely need adjusting in length, and the front derailleur may need to be adjusted down slightly as the chainrings are a smaller diameter.
That sounds like a plan, but what exactly do I order to take to my LBS and from where do I order it? Or should I just tell my LBS to order the parts and do the labor?

I must have been hit with the stupid stick! I just did a search of this forum and found scads of great answers on my topic. I'm still learning the boards and the features. Sorry for bothering everyone on an already covered topic.

What happened? Did the chain fall off when you shifted to the small ring?

If so, something like that http://n-gear.com/ should be useful.

My LBS did the work for me, so I really couldn't say. I really wish I was not so mechanically challenged. I need to learn all this stuff but just don't know how to start.

Hit the garage sales, get an old bike for no more than $20, take it apart and put it back together. Lube it and replace bearings and cables. Use sheldonbrown.com and parktool.com as references.

Do that once, and you'll have a basic understanding of how bikes work.

I just switched out the whole drive train on my Trek 520.

I replaced the stock "105" crankset with a mountain bike Deore LX crankset (26, 36, 48). Sometimes I wished I had gone a bit smaller on the small chainring, but 90% of the time it's just fine (plus, I feel like I'm doing some strengthening). I also replaced my rear casette (12-32) with a slightly lower one (12-34).
That allowed me to hit my goal of my lowest gear being at or below 20 "gear inches".

I only recently learned about gear inches myself, and it's not worth learning too much about, but it is a helpful way to be sure that you're going to get as low as you want. This website: http://www.sheldonbrown.com/gears/ has a gear inches calculator. For example, if you got a front chainring as low as 22teeth and back cog as big as 34 teeth, then you'd be at 17.5 gear inches, which is phenomenally low, and maybe what you want. (I don't know if you rear derailleur will be able to "eat up" enough chain so that you can get into all your gears successfully, however).

As for the chain, when I put my new drive train on, I also put on a new chain, which just happened to be the exactly right length right out of the box.

I just did this about 2 weeks ago, so feel free to write to me outside of this public dialogue if you want some more explanations. I'm not a mechanic, but I understand a lot of it and I'm a good teacher. (dvsabban@drizzle.com).

Good luck!

Hit the garage sales, get an old bike for no more than $20, take it apart and put it back together. Lube it and replace bearings and cables. Use sheldonbrown.com and parktool.com as references.

Do that once, and you'll have a basic understanding of how bikes work.
That is an awesome idea. Can I really do that? I mean, the most I have ever done is put on the kid's training wheels, repair Tonka trucks, and tease Oreos out of the VCR.
Is there one book that would clearly help me without assuming that I am already a greasemonkey? Is there an "Idiot's Guide to Bicycles"? Those web sites look great, but I am truly starting from scratch.
I think I will have my 16yo son do this with me as a project for school. I home educate so perhaps he can incorporate his love of physics and math into helping me with the gearing and I will give him a credit. I wish I had taken apart and rebuilt a bike when I was 16. Please recommend a book.
Thanks!

I really like The Bicycling Guide to Complete Bicycle Maintenance and Repair for Road & Mountain Bikes by Todd Downs (http://www.amazon.com/exec/obidos/tg/detail/-/1579548830/qid=1123734115/sr=8-1/ref=sr_8_xs_ap_i1_xgl14/104-3713825-4027958?v=glance&s=books&n=507846)

It has lots of good pictures and repeats all the stuff that needs repeating for road versus mountain bikes. It also spends some time on recumbents specifically. I found it a really good way to learn my way around a bike.

As for the gear inches thing, I think it's less important to actually understand the math of it and just use it as a way to compare various setups. 20 gear inches is pretty low (easy to pedal)...17.5 is VERY LOW, 100 is respectably high, and 125-140 is VERY HIGH.

The other thing that I found tremendously helpful with doing my own bike work is having some sort of stand. There are the bigger, expensive ones that hold the bike nicely by the seat post like in bike shops....there are the less expensive stands like the Performance brand stands that hold the bike by the downtube, and there are the amazingly inexpensive stands ($10-$30) that are more like a double-prong kick stand, but they hold the bike up and do their job well.
All my bike maintenance just became so much more enjoyable once I had a stand, since I could concentrate on the work and didn't have to worry about fighting with the bike to keep it up.

Good luck

I've got a Sugino XD on mine. I already had the square taper crank puller and didn't want to buy a new tool one day for the splined, plus it's got the gears you're looking for. Check it out: http://store.somafab.com/suxd600cr.html

I've got a Sugino XD on mine. I already had the square taper crank puller and didn't want to buy a new tool one day for the splined, plus it's got the gears you're looking for. Check it out: http://store.somafab.com/suxd600cr.html

I can vouch for the Sugino XD. Since I wanted to keep my beloved STI shifters, I purchased and installed one of these cranks through my LBS ($60 OTD) just before a recent tour of Michigan's Eastern Upper Peninsula.

My gearing setup is the Sugino 26-36-46 and a Schram 11-34 cassette which brings it pretty close to a MTB crank setup you can get with bar-end shifters (a la Trek 520). In addition to the lower gearing this setup provides, I also find the ratios on the 36-tooth middle ring to be better cruising gears for me--when loaded, I rarely find myself shifting off the middle ring, except for steep climbs or thrilling downhills.

Have fun and enjoy your bike!

B.