Cheap Singlespeeds. SS $100 bike, $200 bike. Walmart thruster. 6KU fixie. Bikesdirect Dawes Streetfighter SST

Singlespeed bikes.  The simplest type of bike.  If you live somewhere flat, hate maintenance, and like to pedal hard on hills, these are for you.

DON'T get a $129 walmart Thruster!!!

It's a pile.

The cheapest, decent quality singlespeed  is the $200 6KU.

The frame and fork are high tensile steel, which is a bit heavy, but is quite durable.  The wheels are nice, with super strong deep V rims, and good hubs.  The fork is threadless.  It fits fatter tires and fenders.  The cranks are pretty nice.  This is a good bike for $200.

There are even are a ton of frame and wheel color combinations to choose from, too.

http://www.citygrounds.com/fixed-gear-single-speed-bikes#brand=6ku

The main crappy things on this bike, things to upgrade to make it a more durable commuter.  Are the freewheel, it has junky chinese one that will fail.  The freewheel is the gear on the back wheel, that coasts and makes the clickity noise.  Good quality  ACS, Shimano, or GT ones are $15-25 dollars.

And the tires.  Good quality, flat resistant tires are key to a bike you ride everyday.  Continental gatorskins, Schwalbe Marathons, and Panaracer Paselas are all good tires, between $30-40.

At $230, you get the Bikesdirect Dawes Streetfighter.

This bike has a cromoly steel frame and fork, which is lighter and stronger, better quality.  Realistically, most people won't bend the hi-ten 6ku frame, and it is maybe 2 pound difference.  But the streetfighter is definitely the better frame. 

The tires and freewheel still need urgent replacement.  The seat, seatpost, bars are a bit junkier than the 6ku.  Not a huge deal, as these are parts many bike riders will replace anyways to make their bike fit better and more comfortably.

The $230 Dawes SST is similar bike, except with drop bars

26" Schwinn Sidewinder $149 26" mtb, shimano 3X7 gears.

This is the best bike you can get at walmart for $150, if you are a medium sized person.  Every magna, roadmaster, mgx, huffy, next bike that is cheaper than this is a total piece of garbage.  This bike is actually serviceable, functional, and worth fixing.

The Schwinn Sidewinder is a 26" wheel mtb, with 3X7 shimano parts for 21 gears.

It's parts are pretty decent:

Shimano tourney 3X7, derailleurs and grip shift shifters.

Alloy linear pull brakes and levers.

Wheels with alloy double wall rims and alloy hubs.

It compares pretty favorably to a Trek 820, $380 bike shop quality bike.

http://www.trekbikes.com/us/en_US/bikes/mountain/sport/820/820/p/1008600-2016

The gears, wheels, brakes are the same.  The trek does have better tires, thread-less fork, nicer bars, seat, post.  And it comes in many sizes.

This gets to the main thorn with the walmart bike.  It only comes in one size, 17", or medium, good for people 5'7"-5'10" about. If you are shorter or taller, you are out of luck

The bike shop bike has 5 sizes, XS, S, M, L, XL.

Also, the bike shop bike is put together by someone that knows how to assemble and adjust a bike.  This makes a huge difference!  If you took the Walmart schwinn to a bike shop to have them assemble/tune the bike so it works right, labor would likely be $50-75, and worth it.  That said, bicycles are not rocket ships, and someone with good mechanical aptitude, and willingness to do some research and buy $25-50 of tools and lube can do a good job.

The main crappier parts about the Schwinn is the threaded fork and stem.  And crappy suspension fork.

The handlebars and seatpost are also heavy, cheap steel, where the trek are aluminum.  

Neither of these are that noticible to basic commuter bike rider.

The tires are a weakness.  The stock tires get flat easily, and wear out fast.  Replacing them with flat resistant tires would be a huge upgrade for someone using the bike to get to work.  The knobby tires roll slow on the road.

$13 Panaracer 2" touring tires are a good choice

http://www.niagaracycle.com/categories/tires-pan-tour-26x2-0-wire-bk-bk

Otherwise, just use the bike til stuff breaks.  Most likely things you are likely to run into issues with are the chain. $7 KMC Z50 chain http://www.niagaracycle.com/categories/kmc-z50-chain-6-7-8-speed-1-2-x-3-32-x-116l-silver-brown

Seatpost.  Check the stamp at bottom of post, likely 27.2mm, and get alloy Kalloy seatpost, around $20.  

For people that are not medium sized, or people that live in areas that have good used bike markets, a used 90's MTB from Trek, Giant, Specialized, Cannondale, etc, for less than $150, is a better deal.

Mongoose Stat 29" disc, $219

http://www.walmart.com/ip/29-Mongoose-Stat-Men-s-Mountain-Bike/21191093

Mongoose Stat
-Aluminum frame, size 18"
-29" wheels, fast rolling, comfortable, good selection of tires
-disc brakes.  More consistent in wet weather.  The brakes don't wear out your rims, like rim brakes do.  Brake pads and rims last longer with disc brakes.

Is the stat a decent bike?  It sells for $220, and has been on sale for as low as $160.

The aluminum frame is pretty good quality, and has some nice details, especially for the price.  It has a common 1 1/8" headtube, 68mm euro bb shell, 27.2mm seatpost.  It comes in one size, 18".  Good for 5'8"-5'11" riders.

The fork is a very heavy, cheap, steel suspension forks.  This is one of the worst parts of the bike.  The good news is that it is 1 1/8" threadless steerer tube, the most common size.

A chromoly steel rigid fork would be a good replacement.  This is simpler, lighter, no maintenance, easier to fit fenders.  You don't want shocks on a commuter bike.
This $50 Nashbar fork is a good choice.  Axle to crown: 453mm.

The Stat uses 1 1/8" stem, with 25.4mm handlebar.  These are the most common sizes.  Easy to swap out different styles of handlebars, or different length stems.
Stems are <$20
Bars are $15-35 depending on style.

The wheels use Quando aluminum quick release hubs, F&R.  It uses a freewheel in the rear.  Double wall 29" aluminum rims.  These are pretty nice wheels.
The tires are cheap, knobby tires.  They roll slow, and get flats easily.  Faster rolling, more flat resistant commuter tires are the best change you can make to this bike.  Continental, Michelin, Vittoria, Rubena make nice 29x2.0" fatty city tires for around $20-30 per wheel

29" rims and 700c rims are the same diameter, and their tires are usually interchangeable.  Both 29" and 700c rims have the same 622mm ERTO diameter.  29" rims tend to be wider to work with fatter tires.  700c tend to be narrower to work with skinnier tires.
29" tires are measured width in inches, for example 2.0".
700c is by "c", bacially mm's.  23c= 23mm very skinny.  You can fit fatter 35c and up tires on 29" rims.

These Schwalbe 700 X 40c tires are a bit narrower and faster rolling.  40mm is about 1.6" wide, so they still have some cush.
$25 for the pair is a great deal.

Fenders are another thing to think about when choosing tires.  There are not that many fenders available for fatty 29X2+" tires.  The Planet Bike Cascadia fenders are an excellent choice, but pricey at $45.

More common sizes are 700X45mm fenders, $23.  These only fit smaller width 700c tires, 44c or lower.
Going this route, you are under $50 for good tires and fenders.

The Promax cable disc brake calipers are not terrible.  One bad thing is their brake pads are not commonly stocked at bike shops.

Replacement Cheap brake pads on ebay

Better brake calipers, that take commonly stocked brake pads would be a good upgrade for this bike.
Avid BB-5., $33  These are good brakes and brake pads are readily available for them.  The are better constructed, and easier to adjust.  The promax's are not bad, though.

The brake levers have a plastic body, with an aluminum lever blade.  They work, but they are flexier than levers with an aluminum lever body.  The cables and housing on the bike are poor quality.  Better levers and cables would really improve this bike.
Shimano Acera levers, including cables & housing, $14

The 3 X 7 speed SRAM grip shifters are good.  The shift cables & housing on the bike are poor quality.  Shimano, SRAM, Jagwire make good shift cables & housings.

Shimano Tourney derailleur.
7 speed freewheel & chain.  Drivetrains usually last about 3000 miles.  The replacement parts for this bike are very inexpensive.  The chain and freewheel on the bike are cheap chinese.
The 7 speed freewheel costs $12 to replace with good quality shimano one.
Better quality SRAM chain is $8.
This bike has one of the most affordable drivetrains to replace.

The cranks are chinese, aluminum arms, with stamped steel rings.  They are not light, but they are durable.  The bottom bracket is euro threaded adjustable loose ball.  Replacement shimano cranks are around $40, and bottom brackets around $20.  Though I would expect the cranks to last awhile.

The pedals are pretty nice aluminum BMX pedals.  Most walmart bikes have janky plastic pedals, these ones are good.

The seat and post.  The quality of the seat is not terrible, but it is heavy and has a really tacky cover.  It is one of the cheapest looking things on the bike.

The seatpost is a cheap "seat guts" style post.  These are heavy and prone to creaking and slipping.

 A 2 bolt Kalloy 27.2mm seatpost would be a good upgrade for <$20.

Kalloy 2 bolt aluminum seatpost $14

Singleworks city limit, leather, $20

Overall, the bike is not a bad choice for a commuter.  The worst parts are the tires and fork.  The brakes would be better with quality levers and cables.  Decent seat and post would save weight, look better.
Tires= $25
Fenders= $22
-------------------
Fork= $50
Levers= $13
Seat & post= $34
$144 total.