Bicycle Mechanics - derailleur upgrade for department store bike

Hi--

Just bought a department store bike.
I'm already replacing the grip shifters with trigger shifters, and while I'm at it, seems the stock derailleur is criticized for being flimsy/cheap.
Half the reason, actually, is that I just want an excuse to mess with and learn the mechanics, and paying $30-$50 for a new derailleur(s) won't be so bad if I learn something and have fun with it too. I've spent more on a video game... So maybe I don't have to replace the low-end stock derailleur at all, but, I just want to. I'll have a lot of fun and learn something of how the system needs to be adjusted by installing a better one, anyway.

OK, I just bought a schwinn discover, which comes with a stock 7 speed cassette. I don't really see a reason to change that out. There are hills, but it's not that hilly, here in iowa.

The stock rear derailleur seems to be this:
http://www.amazon.com/Shimano-RD-TX35-Tourney-Derailleur-Regular/dp/B003ZM9RLI/ref=sr_1_1?ie=UTF8&qid=1358155528&sr=8-1&keywords=shimano+tx+35

The front derailleur simply says "sr suntour"


If you were to upgrade these, what would you upgrade to?
I'd read that shimano's alivio and deore were their better grades, and they're not that expensive really.
I was wondering which models would be correct?
The stock derailleur is for 34-43 teeth and "long" cage,

so would this derailleur then be a 'plug and play' bolt-in substitution?
http://www.amazon.com/Shimano-RD-M410-Alivio-Derailleur-8-Speed/dp/B00113HAYO
and would it be better built than the tx35 that came with the bike, which was accused of thinly stamped and cast plastic parts?
Does that fit, and even if it does, do you have any better suggestions? Is deore better than alivio: and would a '9spd' derailleur work on a 7spd bike? (as I understand it, I can't see the difference-- only that the derailer must have more range to accommodate 9spds?)

Secondly, any meaningful upgrades for a front derailer?

Finally, what's the role of the hanger --except maybe as a spacer, cause it seems some derailleurs don't need hangers?-- and would that need to be changed too?
...like I said, I'm looking forward to learning about the mechanism, by getting in and messing with it :-)

And yeah, I know this is probably money wasted and a pointless upgrade, but like I said, I'll have fun learning to install them properly-- especially while I still have a coworker who knows bikes to help me with it. I'll thank myself later when the knowledge will come in handy.
I treated my entire first car like an educational expense as well-- it didn't need a new transmission or engine but I built them for it anyway and had a lot of fun! :)

My suggestion would be to take the time to get the bicycle into the best mechanical shape possible. This would include aligning dropouts, checking the frame for proper shape, etc. Upgrading a component like a rear derailleur, without changing the quality and precision level of the chain, cassette/fw will definitely limit the advantages of a "better" derailleur.

The precision of the components you have should be adequate and should perform. I know of a business that does tours on department store level bikes. The difference is that they went through a complete and proper assembly, and are sticklers for maintenance.

I have seen many bicycles with modest heritage perform at Herculean levels. Conversely, I have seen expensive bikes, which because of many factors( mostly owners) did not perform much beyond their cheap cousins.

The Haynes book on bicycle mechanics is very complete and will give you insights into the mechanics of your bike.

Finally, what's the role of the hanger --except maybe as a spacer, cause it seems some derailleurs don't need hangers

Well, some derailleurs bolt onto a hanger that's part of the frame, and some of them have built-in hangers which are held in place by the right-hand axle nut and a bolt and specially-shaped nut that goes through the dropout. There are also hangers which attach in the same way, so you can fit a bolt-on derailleur to a frame that doesn't have a hanger built in.

Well, some derailleurs bolt onto a hanger that's part of the frame, and some of them have built-in hangers which are held in place by the right-hand axle nut and a bolt and specially-shaped nut that goes through the dropout. There are also hangers which attach in the same way, so you can fit a bolt-on derailleur to a frame that doesn't have a hanger built in.

Also, being from a department store, I doubt your bike has a cassette. It's probably a thread-on freewheel, which is technically an inferior system to a cassette and freehub, but is usually perfectly useable in practice.

I agree that your time and money is best served in other ways. First, there is nothing wrong with that derailleur. You have to be careful with random user reviews, as you have no assurance that the person had the ability to properly set up the derailleur, nor that they used/shifted it properly. The current Tourney deraillaurs are perfectly serviceable, and calling a derailleur flimsy is nonsensical - you're not using it as a hammer or wrench.

Also, there is no such thing as a "plug and play" derailleur (or any other mechanical part on a bike). The derailleur has three adjustment screws that need to be properly set and then the cable tension needs to be properly adjusted (typically readjusted a few times when the bike is new).

My suggestion is that you start learning about how to properly adjust and maintain your bike as it sits, and NOT by the "trial and error" method. As a car mechanic I'm sure you understand that there are innumerable ways to do something the wrong way - that does not tell you how to do it right. The parts of a bike are mostly visible, but that does not necessarily mean it takes little thought to work on them, as they interact with each other over distance and angles, and interact with both environment and rider.

Two of the best sites reference sites are sheldonbrown.com and parktool.com/blog. The Park site also is a resoiurce for info on the most popular line of bicycle tools, which you should acquire pretty much as you need them - to start all you need is a Phillips screwdriver and metric allen wrenches, with cone and spoke wrenches probably being the first bicycle specific tools. Videos can be helpful but are much more likely to leave out important information, so be sure to look at several, using the sites I mentioned as a starting point.

Specifically with the shift system I would start by familiarizing yourself with front and rear derailleur adjustment. Then pull the cables, making sure the housing is properly sized, and then reinstalling with oil fed onto the cable for the distance that it is enclosed by the housing, as the cables are likely not to be stainless. Don't bother with things like frame/dropout alignment until there is a problem that indicates that might be an issue.

Considering you are depending on the bike for commuting I would strongly recommend finding a good shop to properly tension, true and round your wheels. They may look in good shape but the odds are fairly high that they are not properly tensioned, and if so they will deteriate sooner rather than later.