Buying a second hand bike is hard, especially if you don’t have a checklist and prior experience with it. I never buy assembled,complete bikes, be it second hand or brand new, in the last decade. I have lots of spare parts, including frames and forks. Funny but when I need (want) a particular bike type, I may take apart the one that I’m using most, replace the parts, and have a totally new one. Or, just put together a new one with the parts I already have, maybe buying some replacement parts or accessories on the way. This what you’ll do in time, if your passion for bikes don’t die out.
Making a bike out of parts is neither cheap or easy. It takes a lot of time, you have to stock lots of parts, hence need a decent amount of room. You have to shop a lot, because you always miss something.
Getting a complete bike is a sensible approach. Buying a second one is better, if you can buy it cheap. A used, nice bike can perform better then a brand new bike, because it is time tested, and the rider probably made it better in time. It’s also very risky and hard to understand topic for a new shopper.
It’s not gonna be easy in any way, but I’ll try to make it easier for you. It’s a hard to swallow topic.
There are 4 common(ish) frame materials: aluminium being the most common, steel, carbon fiber and titanium.
A quick word on frames: Good frames have butted tubes, either steel, aluminum or titanium. These tubes have thicker material on ends, so welds / brazes are stronger – also, easier to weld / braze. For titanium frames, it can go down to 0.5mm on center, for aluminium and steel, go all the way down to 1mm, sometimes less. Why this is important? Well, think of it as a soda can. If it has dents, structure is compromised. This is a big problem with aluminium, while important for steel and titanium, too. Check for dents. If you can, remove stickers as they may be hiding something suspicious behind them.
I wouldn’t buy a painted aluminium frame because putty makes wonders when disguising dents. It’s easier to check steel frames, as steel is magnetic: you can use a magnet. Since putty is not magnetic, it won’t stick to a place with putty under it. You have to check with a very small neomidium magnet though, as dents are generally tiny. Or, if you happen to have a paint gauge, you can spot the filler underneath the paint.
Titanium is non-magnetic, so magnet trick won’t work. But luckily, people do not paint titanium frames because they want to proudly show it.
Carbon frames are nasty. Carbon fiber can be repaired, but needs skills and an understanding of the material. The downside is, almost anybody can make a messy repair and hide it with a paint job. Without any proper X-ray checks, you cannot trust a carbon frame. Even if it’s repair-free, it may be fractured and may crack under you in the next day. I wouldn’t even buy a brand new, expensive carbon frame unless its X-rayed before my eyes. Avoid these.
Can you buy a repaired frame for cheap? I wouldn’t buy a welded aluminium frame, because in order to weld it properly, it should be annealed first, and hardened after welding. I can buy a cracked aluminium frame and fix it myself, but wouldn’t buy a repaired frame. For steel, it’s a different story. If its welded, that is risky, because tubes are very thin. Depending on the grade of steel, it may need some extra hardening/annealing after the weld. Brazing is generally safer, but not strong enough.
As a rule of thumb, stay away from repaired frames. The frame is generally the most expensive part of the bike, and good frames are not easy to come by secondhand. A badly repaired frame will make you regret your choice. It can cause death or injuries.
If everything looks right, wash the bike, and check for hairline cracks. Frames generally crack at the near bottom bracket, headtube – upper / lower tube joints, seatpost joining rear seat stays, or chainstay – seat tube joints.
Forks are risky to buy used, especially carbon fiber ones. They can be repaired, fractured internally, or cheap knockoffs. Aluminium forks are the safest bet, because it is almost impossible to fix a bent aluminium fork, if it ever bends without cracking; while steel can be bent back. Suspension forks need additional checks. You should check the rebound rate, look for worn legs or seals, and air leaks. Make sure locking works OK, because it’s a common failure. Coil forks are almost fail-proof or can be fixed easily / cheap.
If you’re buying a bike that is suspiciously old for having disc brakes, check the caliper mounts. Have they welded afterward? Do not buy a fork with added caliper tabs, because forks with disc brakes are an entirely different design. Under heavy braking, such forks will bend or even break if not reinforced properly, which is next to impossible.
Shifters are easiest to check. Just shift, and make sure they “click” consistently.
Common mishaps include bent cages, worn pulleys, worn bushes / bearings on pulleys, or bent derailleur hangers. If you’re buying a clutch derailleur (10 speeds or over) check clutch operation, as these units prone to fail. Personally, I don’t bother checking rear derailleur if they are not high-end models, as almost all derailleur problems can be fixed.
Front derailleurs are bomb proof, if the cage is not bend or badly worn out. Check 2 things: Is the front derailleur compatible with crankset? A 3 speed front derailleur won’t work with a 2 speed crankset fluidly. Also, chainring sizes matter. Most MTB front derailleurs have 14T capacity big-small chainring difference, while road derailleurs are 16T. Almost every MTB front derailleur works best with 38-44T big chainrings. That means, the curvature is important: if the bike has a 48T chainring, the front derailleur may not be compatible.
Start checking the front derailleur profile first: Ones made for 2 speed have “shallower” profile. So, if you spot a 3 speed crankset with a 2 speed front derailleur, this tells a story: either crankset or front derailleur is changed, and you may need to switch some components to make them work fluidly.
Make / model differences doesn’t make a huge difference. I have a bike with Sram X5 crankset and Shimano XT front derailluer, coupled with a Shimano XTR shifter. It works perfectly fine, because derailleur capacity and curvature matches the crankset.
Cranksets are tricky. It is the most problematic part of the groupset when buying second hand. Being (generally) the most expensive part of the groupset, people tend to repair, keep, and “upgrade” their cranksets. Sometimes with lousy ideas.
If poorly maintained, pedals are probably sticked to crankset, because pedals have steel spindles and every crank is aluminium, except the really horrible or vintage ones. Galvanic corrosion makes them stick. Try to remove the pedals. If you cannot remove them with considerable brute force, you can damage the threads die-trying. A pedal thread repair, when done properly, is quite expensive and for most cranksets won’t worth it.
Check chainrings. Chainrings are almost as expensive as a whole crankset; so if they’ re worn, add a new crankset to the price of your purchase. For premium models, you can find aftermarket parts for cheap, but do your research beforehand. Second option is to ditch the old chainrings, and go 1x.
There may be other surprises like cross-threaded chainring bolts, but I assume you’ re not crazy enough to remove the crankset and take apart the chainrings. You cannot check all. Like, a square taper fused into bottom bracket. Yes; they are hard to remove, too.
Lastly, ride the bike in smallest cog, biggest chainring, slow cadence but push hard. If it creaks, probably bottom bracket bearings busted.
Cassettes and chains
Get yourself a chain checker tool. Even you still don’t own a bike yet – because you need it afterwards.
Check the chain. If its worn, consider replacing the cassette too, because it shows bike is neglected. A dirty chain with sticky gunk on it, or rust, are sure signs of neglect. Cross your fingers and pray that the chainrings are well.
I bought a second hand bike (as a “complete bike” I mean) only once, and replaced chain and cassette first, without even checking. It was a 24 speed bike, and chain + cassette didn’t cost much.
Hydraulic disc brakes are the norm these days on MTBs and gaining traction on road bikes. You can still get some decent road or hybrid bikes with rim brakes. There is nothing wrong with rim brakes.
Hydraulic disc brakes are not my favorite, though I have to use them because it is almost getting impossible to find good frames with rim brake compatibility. There can be million things going wrong with them.
If the bike in question has disc brakes, ride the bike and listen. Can you hear a small, intermittent, rubbing noise? Congrats, you have bent rotors which is super common and almost unavoidable. If not, ride bike downhill. Don’t have to be 10% slope. Brake hard. Hear the noise? No? Great. The bike has absolutely perfect hydraulic discs.
If you hear irritating noises while you brake, there may be lots of things going wrong: lack of enough pressure, contaminated pads / rotors, or rotors worn badly. All too common.
If you’ re not after a vintage bike, and not buying disc brakes, its either V-brakes, or caliper brakes. There is almost nothing can go wrong with V-brakes: its either bad pads, or bad adjustment. That’s it. Same with caliper brakes too (like on road bikes). For caliper brakes, you may want to check if its dual pivot: dual pivot calipers are far superior, so if you have a choice, get the same bike with dual pivot brakes.
For mechanical disc brakes, it is generally worst of both worlds, except mechanical brakes are generally a bit lighter and you don’t have to deal with replacing fluids. Calipers don’t stick, and no leaking seals.
The real bad thing about mechanical disc brakes is, you need to adjust pad spacing while pads wearing out. This happens much more often then you expect. Brake pads on bikes are hopeless, they melt like candles. There is nothing to check for mechanical brakes, if they stops you, except the rotor problems as with hydraulic disc brakes.
Do not pay premium for a Brooks saddle on a second hand bike. You never know how it is cared for, and the saddle won’t be fit for you, as it is already formed for another rear end.
Saddles are highly personal items and unless you go ultra premium, they are approachable. Do not bother. Never seen anyone rejecting a good offer because the saddle is worn, anyway.
Handlebars should be without any dent, or very deep scratches. Do not worry about bar tapes or grips as most people change them, at least for hygiene. They can be found cheap.
Getting longer handlebars is always better then getting the shorter ones for your taste, because you can cut longer handlebars. I’m obviously talking about MTB or touring bars. For road bikes, there are lots of widths and geometries available, and most people like experimenting about it, including me.
If handlebars are carbon fiber, check for paint chips. Getting any carbon fiber item is a risk, but I think road bars are even riskier. It might took a heavy lateral impact, but can seem perfectly nice due to bar tapes protecting the surface. This does not mean handlebar is perfectly safe. There is no way to steer clear off trouble with a cracked handlebar.
Wheels are the most important part of the bike, next to nothing. I’d prefer an entry level bike with high-end wheels to high-end bike with medium-low wheels. Reason is simple: rotating mass. Shaving off a 1kg from a bike does not make a huge difference, but shaving off 200gr from a wheelset does.
This is why there is generally a 10x price difference between a 1500gr vs 2000gr wheelset. Still, if this is your first bike, or you’re buying a touring / hybrid / MTB, you can live without a high end wheelset. If you’ re not a competitive road cyclist, a sturdy wheelset is better than an expensive and lightweight set. As a rule of thumb, a nice wheelset with decent parts on a heavier side is much more robust then a super high end wheelset.
How do you recognise a decent wheelset? I do not recommend anything under 32 or 36 spokes if you’ re on heavier side, or buying a touring / hybrid / MTB bike. Fewer spoke count compromise durability, and in most cases, can be too fragile for certain riding conditions. Also, it’s much harder to true a wheel with low spoke count. Steer away from cheap wheelsets having low spoke count, because these wheels are generally not as strong as decent ones with 32 or 36 spokes, and in most cases, heavier: in order to compensate for “missing” spokes, these wheels have heavier rims; with beefier spokes.
My favorite hubs are Shimano, especially XT for MTB / Hybrid and touring, and Ultegra for road. These hubs are bombproof, reasonably lightweight, and cheap compared to their quality. I’m not too picky with rims, but go with DT Swiss butted spokes. These are very strong spokes, cheaper compared to Sapim, and easier to source in my country. Not to mention, they are lightweight enough. Brass nipples are nice, but overkill in most cases, and heavier then aluminium ones.
When buying a bike, inspect hubs for lateral play: turn the bike upside down, try to shake wheels sideways. If there is play, it’s a bummer. If the hubs have cup and cone bearings, they are probably shot. With cartridge bearings, it may be fixable. Now shift to the lowest cog and biggest chainring and turn the crankset like crazy. See any wobble in cassette? A slight wobble is generally normal. If it wobbles more, either the cassette is not tightened enough to the correct spec, which is generally 40nm, or hub has a bent axle. There may be some other uncommon faults, but generally unlikely. Hubs with QR axles prone to bend.
Cassettes move at crazy speeds, so certain amount of wobble is normal, because they are generally not produced to stricter tolerances that balances the weight nicely spread. Even so, even a slight bent teeth may cause out of balance. I saw perfectly true rims jumping off, because of valves causing balancing problems.
If you’ re buying a bike with rim brakes, check the sides of the rims. If they’ re badly worn, you need to replace the rims. Pricewise, rims can be bought at cheap at a decent quality, but replacing a rim is costly because you also need to replace spokes, find a good wheelbuilder and get the wheels nicely trued, even balanced. Also check the nipple area: some people tend to overtighten their spokes, causing bulges in rims, because of too much tension. For me, these rims are not rideable anymore. They are good for beater bikes, but not fit to be ridden long, or hard.
It is a good idea to get a bike that is ridden – if the bike sits stationary for too long, say longer then 4-5 months, then you should consider changing tires, even they look decent, or not worn. Tires are expensive, and getting more expensive each year. Service your tires well. If you are not riding it in winter, remove the tires altogether.
How much should I spend?
I generally buy highest end, or medium level components, because I’m heavy. I’d be pretty happy with (most) crappy Chinese components if I was 50 kilos; but I’m not. I’ve bent and break many hub axles, chainring teeth, and cassettes. These were all entry-level, but branded stuff. If you’ re 70 or under, you’ re safe with any groupset components. If you’ re 100kg with decent amount of power, you should get some high-end parts; you’ll thank me later. But still, you can save from certain parts like shifters, derailleurs, saddles. But you have to be extra careful about hubs, spokes, seat posts and cranksets. Do not try to save on them, you’ll regret it later. I used every carbon part except seatposts, because I can’t imagine what happens if it breaks. I never try to save on a seatpost.
Spending too much on a bike, be it second hand or brand new, is not a good idea for me. If you have only one bike, good luck. It’s better to have 2 cheaper bikes then an expensive bike. On one instance, I have to wait 2 weeks without riding my bike, because a trivial, stupid bolt was lost. I was living in a very small place where cargo delivery was only once a week. Having a backup bike is nice, because bikes can fail in every possible way. Or you may just crash it. It is also beneficial to take care of your bikes: you can take apart your bike, give it a proper maintenance without worrying about missing rides.
You should not spend too much, because that particular brand is popular. Almost all aluminium frames are made in China or Taiwan, in the same factory with middle-end bikes. I have a Merida bike which was over 2000$ when new, a decade ago. A bought a local brands’ frame second hand recently, probably produced at same year with my Merida. That was a bike from the cheapest brand, frame made in China, cost me 20$. Interestingly, its a stiffer frame, have larger tubes, have all the fancy stuff Merida has back end in the days like smooth welds, plus extra holes for additional water cage and racks, and weighs almost the same! Probably Merida will survive lots of high jumps, but I can’t; so who cares? There is no reason to pay premium if you’ re not exploiting the bike’s potential.
Today, you buy a Mercedes with Renault engine, and a BMW with a Peugeot engine. So, what’s the brand of your car actually? Same for bikes: Giant makes frames for Trek, Scott and Colnago. Merida owns Centurion, and half of Specialized. They also produced frames for Raleigh and Mongoose, but said to be serving many other brands, too. If you take apart a car, you’ll see a French car using German electronics like Bosch, or a German car uses French Valeo headlights. No car brand produces electronics, accessories, headlights, even engine internals like injectors, alternators, starters, pistons or valves. So, I wouldn’t pay twice the money to a Specialized bike that is having the same groupset as brand Z.
What to avoid
Make sure the bike you are buying is not stolen. Don’t know how; but at least seeing an ID of the person is helpful if you go into trouble.
Avoid bikes with proprietary junk, like “custom” seatposts. This is called vendor lock. They may sell you a seat post at a cost of the frame, or just stop producing it, or even they don’t have it as a spare part.
Also avoid dual suspension bikes unless you absolutely need it. They are heavy, expensive and have one more suspension to fail and become a money pit. Stay away from vaporware standards that will nobody know after a year later. Do not be tempted to buy a bike, judging it by “extra accessories” like pump, lights, etc – generally they’ re junk, you’ll dump and get new ones in near future. Never buy a grocery store bike because it’s cheap, which is still very expensive as its not rideable.