Maybe you’ve never been tempted to buy a bike at Walmart or from another department store, but you almost certainly know someone who did—or might. So-called “big-box” or mass-merchant stores, like Sam’s Club or Costco, sell 75 percent of all bikes in the US, according to the National Bicycle Dealers Association.

People are drawn to department store bike deals by convenience and price—particularly for children’s bike, which are quickly outgrown and replaced. But there are several very good reasons to buy bikes from one of the approximately 4,000 specialty bike stores in the country instead. As holiday season—a prime bike-buying time—approaches, here’s what to know about big-box bikes that could save you, or a friend or family member, some trouble.

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They’re sometimes sloppily assembled.

The people building bikes in the warehouse area of your local Walmart are often the same employees who are unboxing floor-sample items and assembling flat-pack furniture for display. There’s nothing wrong with those jobs, or with the people who do them. But bike assembly should be done by a trained specialist with proper tools, and it’s rare to find a qualified bike mechanic at a big-box store.

All bikes, whether destined for Walmart or an independent bike dealer, are shipped to the dealer partially assembled: Even bikes from mainstream cycling brands sometimes aren’t properly built at the factory and need to be thoroughly checked during assembly. A trained bike mechanic knows what to look for and can spot factory-assembly problems that need to be fixed, as well as ensure proper final assembly.

Last winter, a reporter for Orlando’s News6 bought four bikes at area mass-merchant retailers and took them to a local bike shop for a safety check. Three of the four failed the inspection due to assembly errors. The stem wasn’t tightened on one; another had a rear brake cable so loose the brake never contacted the rim. On the third, the bike shop mechanic inspecting the assembly quality was able to loosen a front wheel axle nut with a single tap of a wrench handle. If you buy a bike online and have it shipped directly to you, you’ll get the bike in a box and have to assemble it yourself. You can argue that assembling a bike is no more complex than building a dining room set from Ikea, but an unstable table likely won’t lead to serious injury.

Even if there aren’t outright safety issues, poor assembly can mean mis-shifting drivetrains, underinflated tires, loose headsets, wheels that are improperly tensioned and prone to damage, and other problems that will shorten a bike’s lifespan.

No knowledgeable bike salespeople.

As with the assemblers, the floor employees at most department stores are generalists who have to do everything from price-checking items to cleaning up the pile of shirts in boys’ clothing to putting together an aisle endcap display. Most don’t really know about bikes. Much of the time, they won’t be able to help a buyer select the right bike for their needs or answer questions about bikes.

They’re not that much cheaper.

Yes, you can still get a department store bike for not much more than $100, and adult bikes for $200 abound. You can even buy a fat bike . But Consumer Reports, not historically a fan of expensive cycling equipment, points out that cheap bikes are heavy and often made with inferior parts. Why spend $200 on junk?

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You might also notice that prices for mass-merchant models are starting to approach those of bikes you’ll find at a local bike shop. Target sells a Titan Dark Knight men’s hardtail mountain bike for $380. That’s the same price as Trek’s 820 model or Giant’s Revel 2, both of which are sold at specialty bike shops only. They have better parts and benefit from professional assembly. You’d even be better off buying a used bike.

One size does not fit all.

Every bike we’ve seen for sale in a department store comes in one size only, and some size in a way that makes us cringe. (Target’s idea of how to size bikes: by wheel diameter.) That Trek 820? It comes in five sizes, down to a 13-inch model that’s perfect for shorter riders. The idea that bikes should come in rider-specific frame sizes is not a controversial notion—at least, not any more than the idea that, oh, televisions should come in various sizes to fit your entertainment space.

Forget about getting service.

All bikes break in slightly with initial use, or need a quick drivetrain or brake tune-up. Pretty much all bike shops offer at least one free adjustment for new bikes sold there (some offer longer service plans, for free or for a premium payment). But no department store has a service department for its bikes, so you’ll end up taking it to a shop for repair anyway, where you’ll pay market rate for labor to fix anything that slipped or was misadjusted to begin with.

Finding replacement parts for mass-market bikes may be incredibly difficult, as they aren’t designed with serviceability in mind. Most shops base repair prices on labor rates of at least $50 an hour—often higher—plus parts. Particularly if the bike wasn’t properly assembled to begin with, you might pay more in repair costs at a bike shop than you did for the bike itself.

The warranty sucks.

Even big-box bike brands sometimes offer warranties, but they’re often much less comprehensive than those of brands available in bike shops; typically, warranties are a year on the frame and less, if any, on the parts. Schwinn, which formerly sold bikes in independent stores and now sells in big-box stores, has a separate warranty for bikes sold at mass retail than those sold at bike stores. The mass-retailer warranty is generous, but includes two significant drawbacks not found in a bike store’s version of the warranty. All warranty claims must be shipped pre-paid to Schwinn’s parent company, Pacific Cycle, which will cost you almost as much as one of those cheap bikes to begin with. And the mass retailer warranty doesn’t cover items broken accidentally, which leads us to wonder what exactly is covered.

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By contrast, Trek and Giant both offer a limited lifetime warranty on almost all frames, which is standard for bikes sold through independent retailers. All licensed retailers are designated warranty service centers, which means they will handle claims for you. And with the move to house-branded parts, bike brands are offering stronger warranties on components. For example, Bontrager-brand parts, except for normal wear-and-tear items like tires, are covered by a two-year warranty. On that Trek 820, the handlebar, stem, seat, seatpost, and rims are all covered. Giant covers Giant-brand parts and accessories for a year.

Joe Lindsey Joe Lindsey is a longtime freelance journalist who writes about sports and outdoors, health and fitness, and science and tech, especially where the three elements in that Venn diagram overlap.

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