do u have advice for buying a bike for the first time on a budget, like facebook marketplace has so many bikes but idk what to look for
Ok, so bikes are simple looking machines but they have a complicated history and nuance, so there's still a lot to look out for. It is really hard to cover concisely. I will try to put the really important condensed parts in bold.
Firstly avoid getting ripped off. Secondly try to get the right bike the first time. If you get a good deal on something that doesn't end up being exactly what you want, you can probably offload it for little to no loss later.
In order to avoid getting ripped off on a bike that needs a ton of expensive maintenance, or worse one that cannot be made safe or pleasant to ride for less than the cost of another bike, it's important to know what to look for in terms of the condition of its components and the states of their adjustments. To really understand what to look for you have to understand how the whole machine goes together and how it's ideally supposed to work. I'm going to write this response assuming that you know nothing about bikes or even about the machine elements that make them up, forgive me if I explain too much.
So that this is more useful to anyone who is not already familiar with bicycle anatomy/terminology, I'm going to stick some images here for reference going forward.
Check the frame for any cracks or non-original dents or bends to the tubes. Noticeable bends or cracks are an instant no. Dents can be a total non issue depending highly on the bike and the location and severity of the dent, but it's best to just avoid them. Significantly worn-away material that ends up looking like a dent can actually be less problematic than a similar dent, but is probably best to just avoid as well for our purposes. For example I have an aluminum cyclocross bike with really severe cable rub on the head tube and have been riding it pretty hard for several years with no issues, though I do monitor for cracking. I would also stay away from anything carbon fiber just because it's possible that it could be damaged in a way that's difficult or impossible to discern for a layperson, but will lead to catastrophic failure under load. Early-mid 2010s Cannondale CAADX bikes come to mind - Cannondale is still honoring a recall on the stock forks for these frames. From what I understand, many people were injured, or in at least one case even killed, due to unexpected catastrophic failure on forks that had never been crashed or damaged in any way during their use. I actually bought one of these bikes used a few years ago without knowing about the recall, learned about it after owning the bike for a few weeks and had the fork replaced with a much nicer one at a licensed dealer.
Moving on from frames, to simplify it as much as I can, some of the moving parts of the bike are bearings and some are cables pulling against springs. For example there is a set of two ball bearings in the head tube of the bike which allow the fork to rotate in the head tube and steer the bike, a similar set of two bearings inside the bottom bracket shell of the frame which allow the crank arms to spin smoothly, another similar set of two bearings inside of each hub that allow the wheel to spin, etcetera. All of these bearings exist to permit the smoothest and most quiet motion possible, typically rotation on one axis, given cost, engineering and manufacturing constraints. If there's any play in one of these bearings off the axis of its intended movement, it's misadjusted and is likely damaged if it's been ridden much in that condition. Bottom bracket bearing play can feel like a side to side freedom of motion in the crank arms, off of the axis of their normal rotation around the bottom bracket spindle, for example. A rim may produce a clicking sound or feel loose side-to-side, indicating play in the hub bearings. The handlebars and fork might move forward and backward or side to side a little with respect to the head tube, off from the normal rotating motion of steering, which usually suggests play in the headset bearings. Call a local independent shop and ask what they charge, parts and labor, to replace a cheap threadless headset and this should give you some idea of how much you might be able to haggle someone down if you find this kind of bearing play on a bike. It's possible that it's just an adjustment issue and it'll work like new after being adjusted, but you should be prepared for the possibility that whatever has play will need replaced to feel good again. Besides feeling bad to ride, loose bearings long term typically lead to safety issues involving the components whose forces they bear.
Bearings that make a whispy dry sound are running dry and ideally need to be greased, which is non trivial service. Bearings that sound rough or rumble when rolling are hopefully just over tightened, not a big deal, but may be correctly adjusted and just rolling over previous damage meaning they can't be adjusted to achieve smoother less resistive rolling.
Basically you want to make sure that any rotating assembly on the bike operates smoothly, relatively quietly and without excessive resistance or play off axis.
Brakes on most of the budget bikes you'll find will be simple mechanisms where a lever on the handlebar pulls on a cable, which actuates some arm or caliper clamping the rim of the wheel or a drum or disc rotor on the hub. The wheel end of the brake will have at least one spring involved that pulls the pads back out into their resting position where they should never contact the braking surface. Sometimes you can get a hydraulic disc brake on a cheaper bike, similar rules apply for assessing their condition. In general for cheaper/more budget bikes it's probably best to avoid disc and drum brakes. Look for V brakes or dual pivot side pull caliper brakes. Cantilever brakes are also fine when set up correctly but I personally strongly prefer adjusting and otherwise maintaining V brakes.
I'm going to devote some extra attention to brakes because they're so important for a bike to be safe for most people, ironic given that I usually ride a brakeless bike I know. Brakes should stop hard without painfully difficult lever input, and the lever should feel firm and never be able to actuate so far that it touches the handlebar it's mounted to. A little bit of wiggle or play in the pivot of a cheaper brake lever is normal and not cause for concern. When I build a bike, one of the standards that I almost always hold it to is that if I squeeze the front brake lever hard, I should be able to stop the wheel so quickly that the rear wheel comes off the ground at least a little; if you're reckless with it you should be able to throw yourself off the bike over the handlebars by grabbing the front brake too hard. You should also be able to completely lock up the rear wheel with your body weight in a normal seated position. Otherwise your brakes are at least out of adjustment, and potentially using components that are too ineffective to be adjusted into proper function for some reason or another - avoid. Some bikes need major work to get decent brakes, e.x. a lot of vintage road and cruiser bikes used steel rims which become useless as a braking surface with moisture, and you would need a new set of wheels to fix this.
Try to make sure there's a decent amount of material left on the pads, and for rim brake wheels check that the brake track isn't super concave which usually indicates a level of wear warranting a wheel replacement, although some vintage rims were manufactured with intentionally concave brake tracks, so this is usually but not always a cause for concern. While we're talking about worn out wheels, inspect the spoke holes in the rims for cracks, very common failure point especially on wheels with worn out brake tracks.
Basically make sure the brakes stop hard and without making crazy noises, and that the pads or any other wear components aren't worn down to nothing.
For our purposes anything with gears is also just a shift lever or levers that pull and release tension on a cable. The cable tension is in opposition to a spring in the derailleur. If one click of the shifter gets you one gear shifted, every time, all the way up and down all of the available gears on the bike, you're in good shape. You should be practically unable to cause the chain to come off of the gears completely on either the front or rear, otherwise at best something needs adjusted. For bikes with both front and rear derailleurs, a little bit of noise from derailleur cage rub is normal when the gear combination is cross chained. Other than that if it's clean and lubricated the chain should be quiet and smooth. If the pedals feel like they jump forward when you pedal really hard, then the chain, one of the cogs, or both are worn enough that they should have been replaced quite a while ago. If the chain seems to hesitate a lot in shifting, jumps back and forth between two gears with no shifter input, or won't go in or out of a gear, something is misadjusted, worn, or both.
Basically make sure all of the gear combinations on the bike are accessible and work reasonably smoothly, keeping in mind that caveat about cross chaining.
Ok, that's about it for not getting ripped off, without talking about what appropriate prices are for different bikes. This is really hard to explain and depends on your budget, where you live and stuff, so I'll leave it to your research to decide. Feel free to reach out if you have any questions about any particular bike.
The bike also has to fit you reasonably well. This is also really complicated but easier to boil down. Standing over the bike, not seated, feet flat on the ground, you should have somewhere between 1 and 3 inches between the top tube and your body. Seated in the saddle with the pedal at the very bottom of its rotation, with your foot flat and the ball of your foot over the center line of the pedal, you should be able to adjust the saddle height such that your leg is almost fully extended, slight bend in the knee but not locked out straight. Try to get a longer test ride in than just going around the block, do a couple of miles or more on it and see if you feel super stretched out or unstable/uncomfortable with the size of the bike. A bike that's too big feels hard to move around on and cumbersome to steer and ride over bumps and stuff. A bike that's too small feels twitchy and out of control, and like your weight is too far over the front. A lot of this can be tweaked significantly with handlebar, stem, and seatpost changes, but that can be expensive to dial in so best to start with something that already feels decent to get around on.
Finally try to get something that makes sense for your use case the first time around. Tires are super important, particularly their width. If you're racing on smooth tarmac skinny tires are great, but if you're commuting on normal streets, rough pavement, loose gravel, leaf litter etc, for general use I would try to get at least a 32 mm wide tire and lean toward a larger tire up to 42 or 45 mm, maybe more depending on how much you value comfort over speed or efficiency. For riding dirt 45 mm or ~1.8" is more of a minimum. You can get away with less tire for sure but it will suck significantly more for most people. I ride a 35 mm semi slick tire on almost everything, excluding technical mountain bike stuff at which point I much prefer to ride 2.25" or wider tires with at least a little bit of knobs. If you can only have one bike for general use and you're not going mountain biking, somewhere between 35 and 42 mm width is probably the sweet spot. Tire compound and tread pattern or lack thereof matter a lot too - look up reviews of whatever tires are on the bike and try to guess if you'll want to replace them.
Gearing/gear range is also really important. If you plan on riding a lot of hills, especially steep ones, you want something that has a low gear where the number of teeth on the largest cog is the same or greater than the number of teeth on the smallest chainring, a "1.0" gear ratio. On my mountain bike I have a ~0.73 bottom gear, 34 teeth up front and 46 teeth in the back. Because there's only one chainring on my mountain bike, this severely limits the top end of the gear range. On the bikes you'll be looking at the hardest gear in the back, the smallest cog, will have 11 teeth, maybe as many as 14 teeth for older bikes. On my bike that top gear of 34x11 is a hair over a 3.0, which often feels too spinny in lively riding on flat ground or down a hill. The bike is specialized for being able to climb steep, loose terrain for long periods of time and for descending difficult terrain where my top speed is much more limited by my ability to pick a good line and handle the bike as opposed to pedaling hard, so this is a great trade off, but if I try to commute on my mountain bike it kind of sucks. That being said, the bike I get around town on is a single speed (brakeless fixed gear but I won't get into that here) with a ~2.53 gear ratio, and I love it very much. For a single speed in my area and with my particular preference for cadence on flat ground and my fitness level, this is great gear ratio. I can get up any hill I need to with significant effort, I almost never spin out downhill, and I can cruise at any speeds that I'm aerobically capable of comfortably on flat ground. Try to do a test ride up the steepest hill you expect to encounter often and assess whether you're going to be comfortable with the gearing that's available, but understand that you will get stronger and be able to handle the same hill on a much harder gear eventually.
Feel free to reach out if you have any specific questions! I love thinking and talking about this stuff. Bikes r fun.
