glovoleum

I have an old beater on which I'm a regular commuter (anywhere from 8-27 miles/day). It's a Mt. Shasta
(I believe this was a KHS off-brand product) which I've retrofitted with rack, pannier, lights, handlebar extensions, body geo seat, and road tires. My son wants to bike back to college (from Texas to New Mexico), and I may accompany him for the first several hundred miles. If I go this route, should I take the opportunity to purchase a Trek 520 off Craigslist or stick with my more familiar rig ? The 520 would be a good deal (being offered below market), but I'd have to learn a new bike and new geometry and risk a few aches and pains in the process. Is it risky to 'change horses' this close (one week) to departure time, or would the more appropriate (touring) machine be worth it ?

mtnroads

Well first off, the 520 is a great bike for that and would normally be well worth it, except that the late switch presents possible problems. Two concerns - mechanical and fit. Mechanically, you run the risk of problems with an unknown bike. If you really know/trust the seller and/or can see it has recently been serviced, you should be ok as far as reliability, but you don't have much time to fix any issues that crop up. If it is 10 yrs old and hasn't been used in the last few years I would probably pass - too many things that could go wrong (dry bearings, etc.). If it is only a few years old, it should be fine. In either case, get it down to your local LBS for a service if needed, and take a good ride after that to make sure they didn't forget to tighten something.

On comfort, the 520 is very comfortable for most folks and assuming it fits you, there shouldn't be a problem. I would think it would be more comfortable than an old mtn bike, especially if you hit headwinds. If it is a fairly new or a well kept bike I would probably say go for it and have a great ride.

gobes

Though the trek 520 would probably be a better touring bike I'd be apt to stick with the old bike this close to your departure.
Unless it's my 520 that you're looking at on craigslist, https://orangecounty.craigslist.org/bik/120872278.html.

NoReg

I would go for the 520, if you are inclined in that direction. Let's say it arrives, and it sucks, OK don't take it and get it suited up later. If it arrives and seems good, what is the worst that can happen? You have to drop out. But isn't that the perfect test for a new bike?

My wife got hereself to Halifax, and bought an increadible single speed heap, then toured around the Maritimes for about 6 months. Her bike held up and it cost 50 dollars.

Yeah, if we were testing fighter planes this might not be a good proceedure. But we are talking bikes, if it looks good, it probably will be OK. Replace and lubricate the obvious, and carry a tool for everything you can fix on the bike with some probability of failure.