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For the past few months I've been planning to buy my first mountain bike. I'm struggling with buying an aluminum bike or a steel one. I recently read that aluminum bikes are as heavy as steel bikes: Builders usually make the aluminum tubes larger and thicker to make it stronger, which adds extra weight and makes it heavier just like the steel ones. Aluminum bikes break easily, it breaks before it bends but the steel on the other hand bends before it breaks and could last a lifetime.

So my question is which one should I get?

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  • "I recently read that aluminum bikes are as heavy as steel bikes:" - (aside BSO's) Most cheap bikes are aluminum, most steel bikes are higher cost. Higher costs bikes are lighter. At the same price point, aluminum will almost always be lighter. (But weight is not everything, so its not a concern anyway.)
    – mattnz
    Oct 23, 2021 at 20:23
  • @zahraa what's your experiences with riding? have you ridden a a bike before? Or a MTB ?
    – Criggie
    Oct 23, 2021 at 21:50
  • I've never had a MTB and I personally like it so much.
    – Zahraa
    Oct 24, 2021 at 4:29

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There's a lot more to unpack in the materials used for bikes. The terms steel, aluminum and alloy are all vague names that don't actually describe the material being used.

"Steel" frames can either mean hi-tens steel that you'll find in big box stores or a steel alloy that you read about on mtb websites such as chromoly (chromium-molybdenum) or Reynolds 531 (manganese-molybdenum).

"Aluminum" could mean any of the aluminum alloy series including 2024, 6061, 6011, 7005 or other aluminum alloys. Each has different characteristics like cost, strength, weight and ease of welding.

There are other alloys, that also can be called either steel or alloy by some people, with compositions of Beryllium, Magnesium, Titanium and Scandium.

There is also a lot to understand about tube manufacturing including pipe shape, if it's single, double or triple-butted, thickness used and welding technique used.

Going down the material rabbit hole won't make it any easier to buy a mountain bike. The best place to start is to determine the type of riding you want to do and your price range and then go visit a bike store (not a big box store). They will help you find a bike that suits what you need and that won't break easily. You may also get a choice of material if you're price range is high enough!

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I recently read that aluminum bikes are as heavy as steel bikes: Builders usually make the aluminum tubes larger and thicker to make it stronger, which adds extra weight and makes it heavier just like the steel ones.

This is not generally true in my experience. A identical frame with the same stiffness will be lighter in aluminum. Steel does damp more vibrations, but modern aluminum drop bar bikes are surprisingly comfortable, and you will be using even wider tires and at least front suspension. In any case, small amounts of weight make surprisingly little difference to your cycling performance.

You're likely to be up against a lot of faster cyclists on fancy bikes. The secret is this: endurance athletes take time to develop to their full potential. The folks who stick with serious cycling long enough to develop that potential will often buy fancy bikes. It's fine, it's their money. They are not fast because they own fancy bikes. They own fancy bikes because they've been in the sport a long time. They're fast because of the same reason - although probably many of them will still get beat by a fit and less experienced rider on a cheap bike, and probably a lot of them were that fit younger rider on a cheap bike at some time.

Aluminum bikes break easily, it breaks before it bends but the steel on the other hand bends before it breaks and could last a lifetime.

It's completely untrue that aluminum bikes break easily, as is the contention in juhist's answer that threads in aluminum bikes strip easily. All bikes can break. It's true that aluminum has a finite fatigue life and steel doesn't, but bicycles are likely to be retired well before an aluminum bike would break. Additionally, if the welds weren't perfectly done, it's possible for any material to eventually fail at the weld, including steel.

Juhist's assertion that steel is more repairable than aluminum is true.

Criggie asserts that any entry level bike is probably aluminum. I'm not 100% sure that's true for drop bar bikes, as there are lower-end steel bikes available. I have a feeling it's accurate in MTBs. Regardless, I'd agree that for a first bicycle, it doesn’t really matter what material you get, even if you’re almost certainly getting aluminum.

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I think the key word here is "First mountain bike"

You've not said what kind of riding you want to do - a MTB for cross country riding, or around a flat dirt path with the kids. Could be commuting on poor roads where you think you need suspension.

I suggest you focus on something that costs well below your maximum budget. Whether that is steel or aluminium doesn't really matter, either will last plenty-long enough for you to form opinions about what you like and what you want to fix/change.

In reality, any new entry-level bike will be aluminium. If you end up with a second hand bike (and that's totally okay) you could get either steel or aluminium.

The most important thing is to be comfortable - a bike that hurts is a bike you won't want to ride. Get 6-12 months of time on your first bike, and you'll know what you want out of cycling. That may be a second bike, an upgrade/replacement to your first bike, or just small changes.

ANSWER: Either's fine as a first bike. Be comfortable, just ride and enjoy your bike.

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    First mountian bike, not first bike. This could be an experienced road rider, potentially. Or maybe not!
    – JoeK
    Oct 23, 2021 at 13:51
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    I kind of disagree with this advice. It very much depends on how much OP is planning to spend, how much it “hurts” to “waste” money on a too-good bike etc.
    – Michael
    Oct 24, 2021 at 17:26
  • @Michael fair enough - feel free to downvote and/or post your own answer. I tried to stay away from specific values to stay on topic.
    – Criggie
    Oct 24, 2021 at 20:05
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For mountain bikes, I'm not really sure there's a choice, for a new bike at least: from a quick search from some manufacturers, the offer in steel is really marginal, and most of the offering is about bikepacking bikes (niche products then, that I wouldn't recommend for a first bike).

Another way to answer the question is to look at the manufacturer's warranty, if fatigue is your primary concern to choose one material or the other. Generally speaking, warranties are longer for steel frames than aluminum ...but some manufacturers (Trek, Giant and Decathlon - possibly more, I didn't search) offer a lifetime warranty on their frames.

So choose a price point and look a the available options. If there's a steel bike among the possibilities, then you can consider it, but given they are more expensive, you probably have a trade-off on the other components. No need to consider a steel frame as first criteria, and if you worry about fatigue, take the bike from a manufacturer that offers a longer warranty.

Note: it is possible that the brands I gave as example don't offer the lifetime warranty in your location, so better to check. Some are also limited to the original owner, so they may not apply if you buy the bike second-hand

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  • There are plenty of steel options, but it's dependent on your price point and the type of MTB you want. If you're after a (very) entry level mtb <$1,000, Trek's 820 would be a consideration. If you're after an aggressive trail hardtail, like a lot of people re-entering the sport or coming with some experience and knowledge, and not looking to go into +$5,000 then you'll have a few options. At the $3,000 - $4,000 mark there's at least the Norco Torrent and Kona Honzo ST to consider. Good information on warranties, people often forget about those!
    – DWGKNZ
    Oct 25, 2021 at 12:30
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Usually aluminum frames of equivalent quality are slightly lighter weight. Not much, but you can measure the weight difference. Also today, due to economies of scale, aluminum frames are usually somewhat cheaper.

Sure, you could compare a butted thin-wall high-strength steel frame and the cheapest aluminum frame you can find that doesn't have butted tubes. In thus case, the steel frame could be even lighter. But that's not an apples-to-apples comparison.

The main benefits of steel are:

  • Practically infinite fatigue life. If you subject an aluminum frame to a heavy load repeatedly, it will eventually break due to fatigue. Steel has a fatigue limit so if the load is below that limit, it will never fail.
  • You don't have to worry about stripping threads. All threads in a frame have been designed for steel. When those same threads are reimplemented on aluminum, they are very weak and stripping is a major concern.
  • The measurements of frames such as head tube size have been optimized for steel. Aluminum frames should optimally have larger head tube, which they usually don't (except today there are tapered tubes that have larger size where needed, specifically in the headset lower cup). Similarly for very heavy riders, cantilever brake post sizes might be a concern on aluminum forks.
  • Ability to be cold set. If the rear hub over locknut dimension that is in fashion currently increases, you can bend a steel frame to the wider over locknut dimension.
  • Repairability. If a steel frame fails, you can remove paint from a small area, weld it and repaint. Aluminum would require you to heat-treat, requiring stripping all components and paint, and then putting it to a heat treating oven that would destroy all components and paint if not removed, then refitting all components and repainting the entire frame.

I'd say if you expect a 30-year or longer life from your frame, get a steel frame, but do consider carefully what hub axle standards (thru-axle / QR, if thru-axle which from the many dozen competing standards), brake attachment standards (cantilever / one of many disc brake standards), bottom bracket standards (you should really get threaded BSA), seatpost standards (get the most common 27.2mm!), headset standards (you should really get external cup 28.6mm), rear over locknut dimension (130mm / 135mm) and eyelets (choose full for fenders, rear rack, front rack and headlight on fork crown) you get. Choosing unwisely can lead to a shorter than 30-year useful life. If you are happy about 10-year life, then aluminum is probably a better deal because aluminum frames are today more common, cheaper and lighter.

Also remember that on the low end of the market "steel" can mean gas pipe steel. Sometimes called "hi ten steel" where "hi ten" means "high-tensile" because there's a rumor someone could in theory build a bike from even weaker steel. Those gas pipe / hi-ten steel frames should be avoided at all costs, because they are practically never butted and also a lot of the steel is needed to make the bike durable which makes the bike very heavy. If buying a steel frame, the keyword to look for is the type of steel: it should be chromoly i.e. chromium molybdenum steel such as 4130, or a brand name steel like Reynolds, Columbus, Tange or Vitus.

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    If a steel frame fails, you can remove paint from a small area, weld it and repaint. That's not likely to be cost-effective, though. And for a bicycle not built out of gas-pipe steel, the welding isn't likely something that can be done sitting on your garage floor using an arc welder from a big-box store. Oct 23, 2021 at 12:31
  • True, welding is something that needs to be done professionally and finding a good welder can be tricky. Still, I disagree about the cost effectiveness. If you do the paint removal and repainting yourself, the cost of a welding job is probably far less than the cost of ordering a new frame and the value of your time you spend moving all your components to the new frame.
    – juhist
    Oct 23, 2021 at 12:37
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    Also I think it's misleading to say "many disc mount options". There are only 3 in general use and the newer ones will take the older calipers (eg flat mount easily takes a post mount caliper with an easy to find cheap adaptor).
    – JoeK
    Oct 23, 2021 at 13:48
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    I do not think the seat post diameter matters at all as long as dropper posts are available for that size. And without a dropper post it is a non-issue. The other sizes are not uncommon at all. I have no problens with 31.6 (almost the same 31.8 handlebars). Oct 23, 2021 at 14:36
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    The question is for a mountain bike, the recommendation of specs doesn't seem to be appropriate. OLD of 130mm are road only, 135mm is only found on entry level bikes, through axles of 148mm are the norms for MTBs. 27.2mm seatposts are used in road, 31.6mm is more common in MTB. I wouldn't also consider non disc brakes for a MTB: MTB tires need to be wide to provide grip, which is more to achieve with cantilever or v-brake,...
    – Renaud
    Oct 23, 2021 at 19:43

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