Spring is here and you've decided to buy a new bicycle at a big box store. Lured by the idea that prices are lower, you're visiting the nearby Canadian Tire, Walmart or whatever. Here's what to look out for and what to avoid.
Here's what I do to assess a multi-speed bike with brake levers and brakes that squeeze the wheel rims. Aside from adjusting seat height, a bicycle on display in a store should be ready to ride with everything tuned and adjusted.
First, are the tires firm. If they are not, the inner tubes may have faulty valves that leak, or else the tire pressure has not been topped up yet.
Second, grab the seat and try to rotate it on its seat post. You should not be able to. If you can, the seat's clamp has not been completely tightened or the seat post's clamp on the bike frame is still too loose.
Third, lift a wheel off of the ground and give it a spin. It should appear to be perfectly round; the tire should not appear to sway from side to side. If it does, either the tire has not been seated properly on the wheel's metal rim, or the rim itself has not been completely "true'd" when the bike was assembled.
Fourth, squeeze and release the brake levers. This action should feel smooth and the lever should return to its released position without any hesitation. Do it again and look at the brakes and brake pads.
Rim-squeezing brakes are spring-loaded. When you release the brake lever, the springs pull the brake pads away from the wheel rim. There are two kinds of rim-squeezing brakes. One looks like a horse shoe that hangs down on either side of the wheel with a brake pad at each end. This is called a calliper brake. It is bolted to the bike frame on a single axle above the wheel. The other type has separate brake arms, each with its own axle on either side of the wheel. Traditionally the brake arms are short, connected to one another with a cable that loops through a triangle attached to the end of the main brake cable that extends up to the brake lever on the handle bars. This is called a cantilever brake. A more modern type is the V-brake, which has longer arms that extend above the wheel. A single brake cable is used here which travels through a curved metal tube where it attaches to the brake.
When you squeeze the brake lever, do the brake pads touch the wheel rims at the same time? When you release and the brake arms return to their open position, are they equally far apart?
When brake pads are positioned correctly, the front of the pad touches the wheel rim first. This is called "toe-in". Also, the flat surface of the brake pad touches the rim straight-on, meaning neither the top edge or the bottom edge touches first. Lastly, when the brake pads touch the wheel rim, each pad touches the rim in exactly the same place, and not high or low.
When rim brakes are applied while the bike is moving, the pads should not squeal loudly.
Bikes with disc brakes are simpler. The disc is bolted to the wheel hub. The brake pads that squeeze the disc are contained in a block that is bolted to the bike frame and placed around the top of the disc. When you squeeze the brake lever, the brake pads should not bend the disc to one side or the other. If they do, the brake has not been completely adjusted.
Fifth, check the gear shifting. Multi-speed bikes often have indexed shifting. This means that when you use the shift control, one control click equals one gear change. To check indexed-shift gears without riding the bike, you lift the rear wheel off of the ground with one hand so it will revolve freely and hold onto the handle bar with your other hand with your fingers on the gear shift control. If there is a kick stand near the pedals, raise it first. Then you stand on one foot and use the other foot to revolve the pedal, foot on top to push down and foot beneath to pull up, and use the shift control to cycle through the gears. Or you have a companion hold the bike up while doing this. Each application of the shift control should lead to a single, satisfying clunk of the chain jumping from one gear to the next. If the chain hesitates, the shifter has not been completely adjusted.
On a bike with indexed shifting, If the rear gear-shifting derailleur doesn't have the name "Shimano" on it, I don't recommend buying the bike. There is another brand called "SRAM" which is also reliable but you won't see it on lower-priced bikes. Shimano indexed derailleurs tend to be reliable. There are a number of knock-off brands that are less so, such as Falcon (sometimes marked FIS) or Sun Race. The lower quality models are made from stamped steel plate rather than forged metal. Shimano derailleurs tend to be reliable, although not always. Two years ago I assembled a new Tim Hortons Commemorative bicycle built by Raleigh Canada that had the lowest-quality Shimano derailleur I've ever seen and it worked so badly that I replaced it with a used, better model. Again, this derailleur was made from stamped steel plate. Sometimes the derailleur works fine, sometimes it won't. When it won't, it ends up in my un-indexed derailleur box, because it is usually still fine for un-indexed applications.
Ideally, you should be able to test ride a bicycle first, but this is seldom possible at a big box store. At best, you may be able to buy it, test it in the parking lot, and bring it back inside if there is a problem.
One last thing; what are the wheel rims made of? There are three kinds. One is chrome steel, another is aluminum alloy and the third is painted steel. There have been painted aluminum rims but they are rare. If the bike has rim-squuezing brakes, I do not recommend buying it if the wheel rims are painted steel, because the paint will wear off in time and the steel will rust. Chrome is durable as long as you periodically clean it off so it doesn't rust. Aluminum rims are the best because they weigh less and provide better braking when wet.
These comments should be helpful in weeding out bad choices. I will add pictures when I get the chance.