Beater bike tuning?
 

Right now I'm using two different bikes. A Trek 7.1fx as my main commuter and then a Mongoose(pre-Walmart) single-speed as my beater bike. however, the bottom bracket on the Mongoose is worn and the cranks have a slight wobble due to it. The rear wheel is also a bit out of true. Despite that, it still rides fine. So I'm wondering, would it be a good idea to get those things fixed? It would cost about $60. Since it's just a beater bike, would it be a good idea to invest money into? Or should I wait til it gets worse to a certain point? Any help would be appreciated. What would you do?

Sounds like the perfect time to learn how to fix bikes. Depending on your bottom bracket style (cartridge or cup and cone) it could just need a repack and adjustment or a new ~$20 cartridge BB. The balance of the $60 you would have spent can be spent on tools which you can use over and over. That's what I did.

Do you have a coop in your area? If so you can pickup a new cartridge style bottom bracket (UN26) for about $13 and learn how to true a wheel as well.

+1

Might be a good time to add some bike repair books to Your Library ,
or get ones that circulate from the Public Library.

+2

Even if it ended up costing you more to fix it yourself than to have the LBS do it, the knowledge gained alone would be worth the cost. I don't think I would pay to have the LBS fix it because even working that kind of bike is worth approximately nothing (which is not to say it's not worth riding). If you try to fix it yourself and you screw it up badly you've still gained experience and haven't really lost much. If you fix it successfully (which is much more likely), you'll have properly functioning bike and the skills to keep it that way.

Start here...

http://www.parktool.com/blog/repair-help

I've slowly bought tools as needed and learned to repair along the way. It's been well worth it.

What they said.