Alan Farroll
Well-Known Member
Going to buy my first mountain bike. I notice some are aluminium and others alloy. Is aluminium heavier? what about an alloy frame rusting? What's it an alloy of?
Thanks in advance
Alan
Thanks in advance
Alan
Alloy or aluminium?
- Thread starter Alan Farroll
- Start date
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D
Deleted member 23692
Guest
'Aluminium' bike are in fact aluminium alloy. Pure aluminium would be too soft to make a bike frame out of, so it's alloyed with various other stuff to make it fit for purpose. Zinc, magnesium and silicone are the usual suspects but many other elements are used. It won't rust (like ferrous metals), but the bare alu-alloy will oxidise - which forms aprotective skin, but it wont corrode.
Cycleops
Legendary Member
- Location
- Accra, Ghana
An aluminium alloy frame cannot rust, but it may oxidize if it doesn't have a protective coating. "Butting" where the tubes are varied internally in thickness throughout its length will affect it's weight.
raleighnut
Legendary Member
- Location
- One of the 'Elite'
Some 'alloy' frames are prefixed CrMo Alloy this is a steel frame and superior to a basic steel frame and will normally be lighter than an aluminium frame at the same price level. Quality Aluminium frames tend to cost a lot.
Alan Farroll
Well-Known Member
Okay. Thanks this is becoming clearer. So if a manufacturer says the frame is for instance "ALUXX-Grade Aluminium" or they simply state in the specifications of a £600 mountain bike that it is Aluminium, then it is not really pure aluminium but an aluminium alloy!!?? And also, if the specifications state that the frame is an "Alloy" then it also is an aluminium alloy??!! Is this correct?
Cubist
Still wavin'
- Location
- Ovver 'thill
Yes. You'll see a couple of different aluminium alloys in today's market, 7005 and 6061. 6061 is an older type of alloy, and needs a particular hardening process to finish it. It contains magnesium and silicon. 7005 is newer, and can be air cooled. It's denser than 6061 which means stronger for a given tube wall thickness. 7005 tends to be found on more expensive bike frames and can be butted (material removed from the middle where it isn't needed, and left in at the ends where it's welded to other tubes. ) Butted tubes tend to be lighter than non-butted. 7005 can be hardened in air, and tubes tend to have sculpted or swoopy shapes allowing the tubes to flex more than straight tubes whilst still retaining strength where it's needed. Straight tubes can be very stiff, fine for transferring power through the frame, but aluminium alloys are stiff to the point of harshness, so shaped tubes give a more comfortable, compliant ride.
Steel varies massively in quality and weight, depending on alloy and metallurgy. As @raleighnut says, chromoly steel is used for more expensive bike frames. Cheaper ones are made of high tensile steel, very, very heavy. Chromoly has several variants, all mostly given a Reynolds number, and this denotes the metallurgy used, and the tubing properties all differ depending on that. Mountain bike frames in chromoly are very popular, with some niche and boutique brands leading the market. However, the type of alloy used varies (as does the price) Steel MTB frames can be strong and bombproof, with neater, slimmer tubes than aluminium, but are rarely lighter (they need different geometries and strengths in different areas to road bikes) The On One 456 is a prime example, as is the Ragley Blue Pig. Stiff, strong and relatively inexpensive, (given the market) with chromoly frames. More exotic and expensive steel alloys, the prime example being Reynolds 853, are quoted as being the "perfect material" for a MTB frame. 853 tubes can be made to the same strength as chromoly for a given tube diameter, but the tube walls can be extruded thinner, and therefore lighter for the same strength. Cotic makes two identical frames, the BFe and the Soul. Their geometry is identical, their intended use is identical, as the framebuilder is at pains to point out, but because the 853 used in the Soul can be made thinner for the same strength, it is lighter, and gives a more compliant, springy ride. What's more, unlike other chromolys, 853 can be air hardened and becomes stronger as it is welded, so doesn't need reinforcing gussets in MTB applications. The heavier, less compliant chromoly BFe is significantly cheaper. To date, steel alloy development stops with the 853. More recent Reynolds variants have proved to be too light. Still as strong for the same tube size, but too flexible, meaning that wider diameter tubes would be needed to prevent the tubes becoming too flexible (or noodley), and this would mean more material would have to be used, thus defeating the weight advantage.
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Cycleops
Legendary Member
- Location
- Accra, Ghana
Well, if @Alan Farroll wasn't confused before he sure must be now!
raleighnut
Legendary Member
- Location
- One of the 'Elite'
No, a steel alloy is a different material to an aluminium alloy. All metals can be Alloyed even Gold to give 9ct. 18ct and 22ct versions.
Cubist
Still wavin'
- Location
- Ovver 'thill
However, in bike marketing terms, a steel alloy frame would be billed as steel or chromoly. Alloy is generally used to denote an aluminium alloy. So if @Alan Farroll is in the market for a new bike, he can be reassured that an "alloy frame " is going to be an alu alloy. Very few entry level MTBs are made of steel alloy, and if they are, the marketing will,make sure you know it.
D
Deleted member 23692
Guest
Just to compound the confusion... steel is an alloy of iron, so cro-mo is just a different blend of 'steel'
Alan Farroll
Well-Known Member
Thank you all for your feedback. This helps a lot
jack smith
Veteran
- Location
- Durham
Basically without going too technical they are all pretty similar so just buy which bike you like!
Drago
Legendary Member
- Location
- Suburban Poshshire
What about the Woodelo?
