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Is the excessive weight of cheap bikes (think Walmart and Amazon) entirely down to the use of lower grade materials, or are there also compromises in design that contribute? Is it that much cheaper to manufacture heavy bikes that the additional materials used are a negligible cost?

Edit: I guess the question isn't landing. What I meant to ask is, how much does bike frame design affect weight, relative to materials choice? If it's a duplicate or off topic question feel free to close it.

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    Sheesh, I guess it is a bad question (at least how I put it!)
    – SamA
    Sep 4, 2022 at 19:06
  • What do you mean by design? For metal frames the century-old double triangle design is more or less optimal and the tradeoff is between cost and materials and manufacturing quality. Is it about gimmicky alternative frame layouts or just refining and optimizing the double triangle?
    – ojs
    Sep 5, 2022 at 9:48

2 Answers 2

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There's a common "joke" among engineers that illustrates well the point.

- Cheap
- Light
- Sturdy

Pick 2. 

Being light and sturdy requires to use more advanced techniques that you can't necessarily afford if you target the lowest price points (butted tubes, forged/machined parts, constant thickness for tubes,... - see juhist's answer for these points, but the others are either rants or misinformation).

Low quality materials are very cheap, and the cost of more advanced techniques can easily outweigh (pun intended) the price of the additional material. So it's cheaper to design a frame/component for the point with the highest constraint and overbuild the rest.

Otherwise other reasons I'm thinking about:

  • BSOs are often inspired by mountain bikes, which adds "features" that increase the weight (suspension, large tires,...)
  • typical customers in this segment are not knowledgeable about bikes (without going into clichés, I think someone knowledgeable about bikes but on a tight budget will go to the second hand market, not BSOs). If you are not knowledgeable about material science, it's common to link weight with sturdiness.
  • But I would rather suspect buyers don't care/think about weight, they are mostly looking at price and features.

Note: I do not mean however that these bikes as a whole are cheap and sturdy. They also have "cheap and light" parts that will fail fast, and make the bike unusable (because it's near impossible to find parts for these bikes).

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    According to this I should be able to pick cheap and sturdy. BSOs are frequently just cheap. Not light, not sturdy. They often have one and only one of the three - pick 2 doesn't work.
    – David D
    Sep 7, 2022 at 20:50
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Several causes:

  • Most cheap bikes are made of gas pipe steel, whereas expensive bike use high quality steel (and today increasingly commonly aluminum and even plastic -- reinforced with carbon fibers). The cheap gas pipe steel has to have thick walls because it's so weak it would fail otherwise
  • The frame tubes aren't butted, i.e. they have constant wall thickness both at the middle and at the ends near welds. Better frames are butted, having thinner walls in the middle where the walls don't have to be so thick
  • Many components on good bikes are made out of aluminum. Such as brake arms, brake levers, cranks, handlebars, stems, seatposts, rims, hubs. All of these can be cheapest possible steel on the cheapest bikes.
  • Better manufacturing methods (forging, casting, CNC machining, hydroforming, extruding) to manufacture more complex optimal load carrying shapes can be done with more expensive bikes, whereas with cheapest bikes you are restricted to stamping, making tubes and welding.
  • Handlebars and seatposts in cheap bikes have constant wall thickness, not optimized such that highest stressed handlebar sections (middle) and highest stressed wall points on seatpost (front and rear) would be thicker than other points.
  • Spokes have a constant thickness, not butted like on better bikes. Also some people con unsuspecting buyers by selling wheels with less than 36 spokes, which Sheldon Brown calls the Great Spoke Scam, and this reduces the weight of many expensive fancy bikes. Not useful, since such wheels can will break so the lightweight failed bike can't be used as a boat anchor anymore because it's so lightweight.
  • Cheaper bikes often have more components which appears to make them heavier. Generally the more you spend, the less likely you will get the useful and important parts like reflectors, bell, fenders, rack, kickstand, etc. In fact the best bikes are sold without pedals because the bike seller doesn't know what clipless system the buyer is going to use so it's better to sell them without pedals. Of course once you add those components, even the more expensive bikes would become heavier.
  • Less engineering. If you hire an experienced engineer to determine what's the minimum acceptable wall thickness at different points and what shape eliminates troublesome stress risers, you can make a component less heavy, because every part is just as strong as it has to be. For cheap bikes, there isn't enough money to pay such an engineer's salary. So they just make everything robust. Some features will be unnecessarily robust then, whereas the weakest feature limits the load carrying capacity of the entire component to be that of the weakest feature.
  • In expensive bikes, the saddle doesn't have practically any padding because that's moved to cycling shorts. Nobody weighs cycling shorts, but everybody weighs their bike and saddle weight counts when weighing bike whereas clothing weight doesn't.
  • Also possibly: most expensive bikes probably aren't so durable. For example carbon fiber can be weakened in a crash invisibly, and then subsequently fail "just riding along". Even expensive aluminum bikes also can be less durable because fancy road bikes are ridden only on good roads by lightweight athletic people, so in their intended use, they are strong enough, but when sold to a 100 kg guy using them on less than perfect roads, they would fail. Also if you sell something to a bike enthusiast, the chances it will be used 3 years from now are slim because everyone is "upgrading" their stuff continuously.
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    One thing I would take issue with is the saddle. Most cheap bikes have massive saddles with loads of padding because that's what the non-cyclists buying them think is going to be comfortable
    – Chris H
    Sep 4, 2022 at 19:07
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    Padding in cycling shorts and padding on top of saddles serve very different purposes. So to claim that you’ve moved weight from the saddle to clothing is disingenuous, at best.
    – Paul H
    Sep 4, 2022 at 21:13
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    As with other times, i found a number of points to be reasonable, but there is also some misinformation here. The obsession with 36-spoke wheels, the last paragraph.
    – Weiwen Ng
    Sep 4, 2022 at 21:19
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    The thing about spoke count can only be described as a rant. Social expectations, material engineering and design technique changes in the last four decades since the 1980's reference cannot be ignored when deciding how many spokes are appropriate for a wheel.
    – mattnz
    Sep 4, 2022 at 21:28
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    " there isn't enough money to pay such an engineer's salary." - when you are selling hundreds of thousands of BSO bikes, there absolutely is enough money to pay the engineer's salary. It's not that they can't, it's more than instead they pay the salary to push manufacturing costs down as much as possible. Sep 5, 2022 at 4:28

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