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Is there a way to tell if my bike has an aluminum frame?

Huffy 26-Inch Scout Men's 21-Speed Hardtail Mountain Bike

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  • I would say first hint might be weight, but alloy now days is getting pretty light. Any more info on what sort of bike, age etc?
    – Hursey
    Oct 10, 2022 at 3:10
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    @Hursey In my opinion weight tells you nothing--some of the durability-oriented carbon bikes these days are within a few hundred grams of their aluminum counterparts. It's even worse for alu vs steel vs Ti.
    – MaplePanda
    Oct 10, 2022 at 3:15
  • @Hursey I added your requested info to my post.
    – fixit7
    Oct 10, 2022 at 3:19
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    If you stick it in a furnace, and it melts at 1,221°F, then it was aluminum. if it melts at 3,034°F, then it was titanium. :-)
    – Tihamer
    Oct 11, 2022 at 20:28
  • More seriously, dunk the frame in water to measure the volume and then weigh it. If it has a density of 1.5601 ounce per cubic inch then it's aluminum. OTOH, if it's a Huffy Scout, then (according to the manufacturer, it's steel. huffybikes.com/scout-mens-mountain-bike-56321 (See questions)
    – Tihamer
    Oct 11, 2022 at 20:40

4 Answers 4

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Stick a magnet to it. If it won't stick, it's probably aluminum. You'll be surprised at what some steel bikes look like these days...

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  • 3
    Are there not plenty of steel alloys which are not magnetic? Don’t know about alloys commonly used for bike frames though.
    – Michael
    Oct 10, 2022 at 7:35
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    Ti isn't magnetic either, but if you had a Ti bike you'd know it 😁
    – Erlkoenig
    Oct 10, 2022 at 8:51
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    @ArtGertner the OP identified the bike as a Huffy, which is a brand associated with Walmart. It won't be carbon or ti.
    – Weiwen Ng
    Oct 10, 2022 at 11:58
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    @Michael good (CrMo) and cheap ("HiTen" AKA gas pipe) steel bike frames are magnetic. Non-magnetic steels are stainless, which is used to make bikes but very rarely.
    – Chris H
    Oct 10, 2022 at 12:33
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    Also, @ArtGertner carbon is far warmer to the touch on a cold day (lower thermal conductivity) so sit it out in the cold then hold it tight and you'll feel the difference. Carbon sounds different when tapped, aluminium rings more and steel far more)
    – Chris H
    Oct 10, 2022 at 12:35
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Yes, you search for the model online which takes you to Walmart's page where they describe the bike https://www.walmart.com/ip/Huffy-26-Inch-Scout-Men-s-21-Speed-Hardtail-Mountain-Bike-Denim-Blue

There it says that your bike is made out of steel: "Frame and Fork: Hardtail steel frame and suspension fork".

The process of looking up specs online is not 100% reliable because sometimes sellers make mistakes in their descriptions. But it'll give you a fairly reliable answer before doing any tests/measurements yourself along the lines of the other answers.

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    I was thinking about this approach as well - go to the source. In addition, just mentioning Walmart as the retailer leads me to believe it would be steel as well, as that is the most common material lower-tier box store bikes are constructed with. Sure, there may be a few exceptions, but if you had to guess...
    – Ted Hohl
    Oct 10, 2022 at 17:57
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Lacking a magnet to detect if it is steel, one can look at the welds and make an "educated" guess.

When aluminum frames are welded, usually a "fat" wide weld bead is present (TIG welding), and unless the bead is smoothed out, it is a pretty obvious clue. In cases where the aluminum welding pattern is smoothed out after welding, this clue will be absent. Aluminum weld examples:

TIG Welded Aluminum

TIG Welded Aluminum

Steel on the other hand can be brazed or TIG welded. Fillet brazing will flow and smooth out some. A frame builder will usually smooth out a fillet brazed joint. If your bike has lugs, especially ornate ones, then most likely brazed steel frame. TIG welding can also be used on steel frames. It leaves a somewhat wide bead, but it "generally" is not as wide as what you see on aluminum. However, TIG on steel can be deceptive and be inferred as aluminum when it is actually steel. Steel weld/brazing examples:

TIG Welded steel headtube:

TIG Welded steel

Fillet Brazed steel after sanding smooth: Fillet Brazed steel

Ornate Lug on steel frame, brazed: Ornate Lug on brazed steel frame

Finally, beyond the welds, steel can give a tell in the form of surface rust with its distinctive tan-to-reddish/brown color. This can be obvious like the following picture, or more subtle - finding surface rust upon close inspection where paint has chipped, or in dropouts where bare metal has become exposed, or inside any of the tubes can reveal if any rust is present and identify a steel frame. One does need to be sure that the rust is actually from oxidation of the frame and not just a remnant stain transferred from a steel axle, seatpost, bolt, etc.

Yes, this is obviously steel and not aluminum:

Yep, this one is steel

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    Higher end aluminium frames have smoothed out weld seams. Oct 10, 2022 at 8:28
  • @ArtGertner true. I had mentioned that they may be smoothed out in my answer.
    – Ted Hohl
    Oct 10, 2022 at 9:43
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    Tig welded steel on cheap bikes is easy to mistake as aluminum, if you're not used to handling them. Steel is a lot heavier, though. If you're picking them up you can start to get an idea pretty quickly. Aluminum is MUCH lighter.
    – SamA
    Oct 10, 2022 at 15:22
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    @SamA sort of lighter, in that aluminium bikes have fatter tubes than steel bikes of the same weight - light steel bikes are perfectly possible. But light steel is unlikely here
    – Chris H
    Oct 10, 2022 at 15:28
  • @SamA good point. I will add that the potential to mistake a wide TIG on steel for Al.
    – Ted Hohl
    Oct 10, 2022 at 15:34
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A simple look at the frame may be enough: If you see wide, oval tubes, it's probably aluminum.

You need much more volume of aluminum to provide the same strength as steel. Also, aluminum always takes damage from flexing (steel can flex without any damage), so aluminum frames must be a lot stiffer than steel frames in order to endure any amount of riding. Steel, on the other hand, is pretty heavy, so you don't want to use unnecessary amounts of it. As such, steel frames invariably have tubes of relatively small diameter (typically cylindrical), while aluminum frames invariably have massive tubes which are typically flattened from the sides to reduce air resistance.

Put another way: If you replaced all the aluminum in an aluminum frame with steel, you wouldn't be able to lift the bike at all. Conversely, if you replaced the small amounts of steel in a steel frame with aluminum, you'd be able to destroy the frame with bare hands. And this difference shows, usually(*).


(*): I'm informed that there actually are aluminum bikes out there which are indistinguishable from steel bikes by frame design. I have my doubts concerning their long term / heavy use endurance, but they exist. (Thanks to Renaud.)

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    Certainly true for hydroformed aluminum frames that are nowadays the norm, even on entry-level bikes. However pre-hydroforming, you could also find Aluminium bikes with thin tubes. My commuter when I was student was this: sonderauktionen.net/images/full/3076.jpg (Kettler Jubilee, alu with thin tubes).
    – Rеnаud
    Oct 12, 2022 at 7:22
  • @Renaud Wow, I would not have thought this was even possible. Must have pretty hefty walls, those tubes! Oct 12, 2022 at 9:53
  • The bike was super heavy, around 18kg if I remember correctly (as pictured). It was advertised as rust-free rather than lightweight.
    – Rеnаud
    Oct 12, 2022 at 13:18
  • There are also lots of BSOs made out of Tig welded steel that look like alu frames but weigh 3x as much. Confusing until you understand the material is that much cheaper, so they figure to sell more leaden bicycles, because they have a cool look.
    – SamA
    Oct 12, 2022 at 13:42
  • Another example, similar to @Renaud's, my 2000 Koga Roadrunner (specified as 15,7 kg total bike). RE: "I have my doubts concerning their long term / heavy use endurance", the opposite turned out to be true, Kogas are generally known for their good frame quality. And this is not an outlier, many alu bikes from that era have similar tube sizes. 'Oval/wide tubes = alu' is correct, but the implication that 'thin tubes = not alu' is not.
    – BrtH
    Mar 22, 2023 at 18:46

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