Come Prepared: Bring a multi-tool and a small adjustable wrench. This will enable you to do some important checks on the bike.
- Check the quick release mechanisms on the wheels. They should feel loose until you close them about halfway. If a wheel is not tightened properly, you risk getting thrown from the bike.
- While off the bike, test the brakes. If non-disc brakes, make sure they are aligned with the rim. Then hop on the bike and test the brakes before picking up too much speed.
- As long as you check the wheels and the brakes, the bike should be safe to test-ride, even if it needs work in other areas.
- Pick up the front-end and bounce it on the front tire a bit, then do the whole bike on both tires. There shouldn’t be any rattling, except for maybe cables slapping the frame a bit.
- Squeeze the front brake to lock up the front wheel and then move the bike back and forth. If the fork seems to move around, then the headset is probably loose and could need replacing due to wear from poor maintenance.
Remove the seat-post. If it doesn’t move, you might want to walk away from the bike unless you want to take your chances at post removal. Even then, the bike should be seriously discounted because that post might never come out.
Test each part. Shifters, brakes, etc. Remember that each aspect of the bike that needs work will require time/money, and it all adds up. For example, a $50 bike isn’t a good value if it needs a full rebuild (usually just under/around $200) and $100 in parts. In that case, you might as well buy a $350, ready-to-ride bike.
- Brake levers should only have a bit of play in them until the pads hit the rim. Brake pads should be level to the rim and contact properly, e.g. slight toe-in, not hitting the tires, not running off the rim, etc. Don’t get on a bike with poorly functioning brakes unless you are confident you can stop the bike.
- Run through all of the gears. All gears should work and not make noise except when cross-chaining.
- Older “rapid-fire”/trigger mountain bike shifters, in particular, tend to get gummed up and need overhauling/replacement. If you are pushing the lever and it moves freely without any cable actuation, then the shifter is likely shot.
- All bearing units should spin smoothly without play. A gritty feeling means the unit is contaminated and currently has dirt acting like sandpaper to the bearings and bearing surfaces, which means an overhaul is in order. A bearing unit that is “stiff,” or hard to turn, either has old, dried up grease, or is overtightened. Be wary of overtightened bearings, as the unit may be damaged and need replacement. I find that wheels, in particular, are often maladjusted, which causes premature wear/weakened performance.
- Tires should be free of cracks or gouges and should hold air. When pumped up, they should not seriously deform when ridden. If they do, try pumping them up harder.
Alignment: Parts should be aligned properly. Bars level, stem straight, saddle straight, etc. Some of these are easy fixes, but adjusting brake lever/integrated shift lever position on a road bike can be time-consuming, particularly when you have hidden cables to deal with.
Rim Damage: Check for cracks in the rims, usually found around the eyelets. Also look for other signs of rim wear, such as the braking surface being worn down from years and years of braking use. Caution: If ridden, damaged rims should be inspected regularly.
Frame Damage and Wear: Check for dents, dings, cracks, and rust on the frame and parts. Mild rust isn’t a big deal and is often easily removed. Caution: Dents and dings, to the frame especially, can be cause for concern, particularly on the thinner-tubed lightweight frames. Keep an eye on any frame damage, and track any progression to the damage. If in doubt, take the bike to a professional.