Buyer Beware! Things to Watch Out For When Shopping For Used Bikes

If you're looking for a bike on a budget, it's hard to go wrong with a good-quality used bike. A bike that's a bit old and out-of-date to the eye of the weekend racer or gear junkie might be the perfect choice for a commuter, and with a little searching, you my be able to find your next ride for next to nothing.

While the internet can be helpful in finding a good used bike, it's still best if you can take a look at it in person to make sure it lives up to your expectations.

Low mileage! Runs great!

With that in mind, here's what you should be looking for when checking out a potential bike purchase, what's not a big deal and what is a total dealbreaker.

Wheels and Tires

• The tires are flat/soft: This is probably no big deal. Because rubber does bleed air over time, the bike may have just been sitting too long and the tires simply need to be pumped up. Even if you need to replace the inner tubes, they usually only cost about $5 each. 
• Dry rot: If the surface of the tire is cracked or rotted looking, you'll probably have to replace the tire itself. If the rubber is coming off in chunks or the inner tube is starting to bulge through the tire, you definitely have to replace the tire to be safe. This is not difficult, but expect to pay at least $15-25 a tire. 
• Bent rims: if the rim of the wheel is a few millimeters out of shape from left to right, it may be possible to "true" the wheel by adjusting spoke tension. However, if the wheel is noticeably bent (so much so that the tire hits the frame of the bike), has a large dent in it, is cracked in any way or is otherwise seriously damaged, you'll likely have to replace it, which could cost anywhere from about $40 up to over $100 each wheel. Road bike wheels and mountain bike wheels made for disc brakes are the most expensive. Also, wheels made from carbon fiber are less than ideal for commuting, and if they have any sign of damage at all are best not trusted. 
• Loose hubs: if there is a small bit of wobble at the axle, you can usually eliminate it with some minor adjustments (which may, however, require some special wrenches to fit into the tight space between axle nuts), the same goes for wheels that are a bit too tight and don't spin freely. If the wheel is spinning unevenly and making clicking or popping noises, it's probably suffering from bad bearings. At best, this means replacing the axle bearings, which requires less than $10 in parts and some know-how. At worst, the hub of the wheel itself may be damaged, which will require replacing the whole thing. If the wheel flops around really loosely, or appears to be missing parts, assume it's damaged beyond hope. 
• Broken spokes: if a single spoke is broken, it can usually be fixed by a bike shop or a home mechanic with some know-how. If two spokes or broken the wheel should be checked over carefully. If three or more spokes are broken, assume the wheel is shot. 

A severely dry-rotted tire with the tread falling off. Note also the cracked sidewall and exposed threads. 

This carbon-fiber wheels has a crack running from the bottom of the S all the way around. It's easy to miss upon a casual inspection, but could potentially lead to wheel failure and a serious crash. 

Brakes

• Brake pads are worn: Brake pads are easy to replace, and can usually be found for less than $10 a pair. Make sure to get the type of pad designed for the brakes on the bike (bring an old one into the shop with you to compare if you're not sure). 
• Brake pads are hard: sometimes the brakes on bikes that sit for a long time oxidize and harden. This can lead to noise and poor braking, as the hardened pads won't grip as well as good pads. Often you can use a nail file or sandpaper to scrape away the hardened surface of the pads and restore their grip, otherwise, just replace them before riding.
• Brakes squeal: This can be due to hardened pads, a dirty rim or from poor adjustment. As long as the brakes actually stop the bike noise can be adjusted out or ignored
• Brakes are out of adjustment: Brake adjustments can usually be performed with basic hand tools, and in most cases are very simple. If the bike has caliper brakes or linear pull brakes this may involve only one or two points of adjustment. If the bike features traditional cantilever brakes, this may be somewhat more complicated.
• Broken brakes: Many low-to-mid-level mountain bikes from the 1990s had Shimano Altus cantilever brakes. These brakes had a gray plastic piece between the brake body and where it attached to the frame of the bike that housed the return springs. Over time these spring housings almost always split. Replacement parts aren't made anymore, and you'll have to get whole new brake sets. Figure on a cost of $12-20 a wheel for basic replacement. Also, if you decide to replace the original cantilevers with modern linear-pull brakes, you'll also need to replace the brake levers, they're not compatible. 
• Broken/rusted cables: Brake cables are about $5 each. If a cable looks worn or frayed expect to replace it. If the cable is slightly rusted, it's probably OK, but if it's severely rusted or binds in the cable housing, you'll have to replace it and possibly the housing as well. Road Bike and Mountain Bike style brakes use different ends on their brake cables, so make sure you get the right kind.

It's a bit hard to see from this angle, but the plastic housing is cracked right under the brake arm. 

Shifters and Derailleurs 

• Broken/rusted cables: cables easily replaceable in MOST cases. In older SRAM grip shifters it can be hard to get the old cable out without damaging the shifter, and you may want to trust it to a bike shop (which will cost more). Most bikes use the same types of shift cables, with the exception of some old ten-speeds and modern Campagnolo shifters. Look carefully at the end of the cable and make sure you get one that matches. 
• Broken shifters: shift levers on modern bikes can be the most complicated part of the whole thing, and therefore the most failure prone. Check the shifter to make sure it clicks through each gear and back. If it slips, jams or misses gears, assume you're going to have to replace it. In the case of a road bike with combination shift/brake levers, this could easily set you back $200 and could be a deal breaker. If it's an old-school friction shifter (no clicks), then it's probably indestructible and you won't have much to worry about. 
• Bad adjustment: shift adjustments can be very easy and may not even require tools for minor problems. If the shifting is slow or seems to get caught between gears, you may just have to turn the adjusting barrel located on either the shifter or derailleur itself to fine tune it. Major shifting adjustments require tightening or loosening cables at the anchor bolts. 
• Stuck derailleur: sometimes a derailleur will become so corroded it jams in place. If this is the case, it's probably dead and should be replaced (anywhere from $20-50 for basic stuff, much more for higher-end parts). However, first make sure the problem is the derailleur itself, not a rusted cable, which is easy to replace, or overtightened limit screws. Limit screws are a pair of small screws on each derailleur that control far it is able to move. If a poorly-informed mechanic overtightens these screws, the derailleur won't be able to move at all (if they're too loose, the chain will fall off the cogs). 
• Bent derailleur hanger: The rear derailleur attaches to the frame near the rear axle. Sometimes this attachment point is part of the derailleur itself, other times it's a part of the frame. If it's part of the frame and somehow damaged, it can sometimes be bent back into place. If it's too badly bent, but is designed to be replaceable, expect to spend about $25-30 on a replacement part. If it's badly bent and non-replaceable (welded on) you're out of luck. 

Chain, cranks and gears

• Rusted chain: if it's a little cosmetic rust, but the chain moves freely, you can lube it up and ride on. If the chain is binding or has stuck links, you'll need to replace it ($20-40)
• Worn chain: this can be hard to spot, but if the chain is worn out, it will cause poor shifting. If it stretches badly enough, it can also cause wear on the gear teeth, especially the rear cogs, which can result in slipping and thrown cogs. This is only a concern on high-mileage bikes, as most chains will last for thousands of miles before showing ANY wear. 
• Stripped gears/broken teeth: replacing the rear gear cluster (the cassette or freewheel, depending on what type) requires special tools and will cost anywhere from $20 on up. Most better-quality cranksets have removable chainrings, so you can replace worn out rings without having to replace the whole crank assembly, but cheaper ones are riveted, so it's all or nothing. Note that most newer cranks and cog sets have some teeth smaller than others, or oddly shaped, to make shifting smoother, so be sure the "broken" teeth you see are really not meant to be that way. 
• Loose cranks: This can be a major hassle, especially on some older bikes. Sometimes the crank bearing assembly (aka bottom bracket) is adjustable, but often if there's more than a slight wobble, you'll end up replacing bearings in very least. Some older Italian or British bicycles use oddball threading that can make it hard to find replacement parts at an affordable price. If the bottom bracket is fine, but the cranks themselves are loose, expect to have to replace them, which can be pricey. 

Frame and Fork 

• Scratched paint: not a big deal. On steel bicycle frames, it's good to cover chips and scratches with paint or even clear nail polish to prevent rust
• Rust: surface rust on steel or corrosion on aluminum is usually harmless, and can be cleared up with steel wool and touch-up paint. However,  rust can weaken and ruin a steel frame if it's more than "skin deep." 
• Dents: small dings on a steel frame can usually be ignored. Sharp dents or creases on aluminum may eventually turn into cracks, although it may take a long time. Major dents in any frame are bad news, and any sort of ding or chip in carbon fiber can lead to a crack down the road. 
• Bent frames or forks: If it's a steel frame, and it's not bent bad, you can sometimes have it re-aligned, but not always. If it's aluminum, no. If it's badly bent, it's probably not fixable. Bent forks are bad news. 
• Cracks: Cracks anywhere are a dealbreaker. 
• Wrong size: if the frame is a bit smaller than is ideal you can get a longer seatpost and stem and make it work OK. It'll never be perfect, but it'll be OK. If it's way too small, forget it. If it's too big, there's nothing to be done, no matter how good of a deal it seems to be.