Steel, ally and alloy

[Kizibu]

I know nothing about bikes - but am hoping to learn after being out of the saddle for 40 years. But one of the many things I'm really confused about are bike descriptions and specs which talk about "alloy forks" or "alloy wheels" when I suspect they mean aluminium but can't be sure what they do mean.

An alloy used to be a mixture of metals - like brass (copper and zinc), bronze (copper and tin) and even steel which is an alloy of iron with various other things added to make it harder, stronger or springier etc. I daresay the aluminium used in bike parts has other stuff mixed in it too. So to call it an alloy may not actually be wrong. But it doesn't seem very helpful to to say some part is made of alloy as if that was a specific metal. The bloke in my local scrapyard used to call aluminium "ally" but never alloy.

 

[alecstilleyedye]

you're quite right, aluminium and alloy are often bandied around as a description of the sort of aluminium-based alloys that are used for various bits of bikes.

if a bike shop uses the term alloy to describe something, ask what metals are its constituents.

 

[mickle]

Absolutely right.

I'm as guilty as the next muppet of referring to 'alloy' rims.

 

[Yellow Fang]

Even steel's an alloy. I believe they're generally talking about aluminium though. Even aluminium and titanium are usually alloys when used for making bikes. I believe scandium is usually an alloy that is actually most aluminium. Just go for carbon, it's easier.

 

[Kizibu]

if a bike shop uses the term alloy to describe something, ask what metals are its constituents.

Its not just loose talk in bike shops. Its endemic on websites and in brochures. Here are a few random samples:

http://www.pinnaclebike.com/Compare-Bikes/?id1=348&id2=1256&id3=1255
Spacers: Pinnacle alloy 5mm
Stem: Alloy adjustable. 105mm
Brakes: Alloy linear pull brake
Rear Wheel: … sealed alloy hub

http://www.evanscycles.com/products/specialized/langster-2008-single-speed-road-bike-ec001392
Front Brake: Dual pivot forged alloy…
Rims: Alex S500 700c alloy double wall rims


http://www.cambridgecyclecompany.co.uk/index.php?main_page=product_info&products_id=270
Pedals: Nylon body w/alloy cage
Brakeset: Alloy dual pivot

http://www.ridgeback.co.uk/dl/ridgeback_brochure_2009.pdf

Double butted alloy frame

www.giant-bicycles.net/en-AU/bikes/lifestyle/2186/31870/

Giant Alloy Anatomic Bend, 26.0. stem, Giant Alloy 4-bolt.

So what are these components made of?

 

[jimboalee]

Scandium is the really light metal used to make utensils the Swedish Chef throws over his shoulders.

 

[louise]

I can not work out what difference a cro-mo fork makes in comparission to a steel one and why cro-mo is better?

 

[Over The Hill]

Having established that - get an 'Alloy' bike with lots of gears and give your self the best start point of light weight and gears for hills. Most newbies tend to go for a Hybrid as it has gearing for off road hills so can cope with a road hill OK but the majority of regular riders would still go with drop bars for road use. Lots of different hand positons available and a comfortable riding position.

Budget from £50 up for second hand perhaps dont go under £300 for new.

Best not to blow lots of cash on first bike (you may want to in a sort of commitment thing) but the best bike for you now will not be best in six months when you have settled in to it.

 

[Yellow Fang]

I can not work out what difference a cro-mo fork makes in comparission to a steel one and why cro-mo is better?

cro-mo is a type of steel. It stands for chromium molybdenum, which are two other metals used to make this alloy of steel (along with iron). I'm not sure cro-mo is considered better. It's cheaper than other grades of steel.

 

[Chris James]

I can not work out what difference a cro-mo fork makes in comparission to a steel one and why cro-mo is better?

Cr-Mo is steel, with a small amount of Chromium and Molybdenum in it. Sometimes it is also called 4130 which is an internationally recognised standard. Basically it denotes a fairly good quality low alloy steel.

As well as the alloying constituents, heat treatment and the method of manufacture make a big difference.

eg Cr-Mo tends to be a generic term for good quality steels. Reynolds 631 is also a Cr-Mo steel, but has been cold drawn for extra stength and air hardened. 853 is similar to 631 but has also been heat treated to give it extra stength. To give you an idea of the effect of these extra operations, generic 4130 has a tensile strength of around 85000 - 110000 psi whereas 853 has a tensile strength of around 210,000 psi - i.e. twice as strong. The density of both materials is the same, so theoretically your frame may be half the weight if made from 853 rather than basic 4130 Cr-Mo. Or the frame maker may choose to use some of that strength advantage to amke a frame that is only a bit lighter but is incredibly stiff and robust.

853 tubing is more expensive than 631 due to the extra heat treatment operation but also is more difficult to build into a frame as it is very hard and more difficult to cut and thinner tubes harder to weld, hence 853 frames being more expensive than 631 frames.

As far as the term 'alloy' goes, I personally have no problems with it. It invariably refers to aluminium alloys. Pure aluminium is never used in bikes as it is not strong enough unless it is alloyed. Titanium used in bikes is also in the form of alloys but they are usually quite up front about this and tell you the exact composition eg 3AL-2.5V.

So effectively, if it says alloy then it invariably refers to an alumiunium alloy. Having said that, it IS a bit vague as there are many alumium alloys, with quite different properties.

For bike frames they seem to use 6000 and 7000 series alloys

http://en.wikipedia.org/wiki/Aluminium_alloy

Scandium is an addition to an aluminium alloy.

 

[PpPete]

853 tubing is more expensive than 631 due to the extra heat treatment operation but also is more difficult to build into a frame as it is very hard and more difficult to cut and thinner tubes harder to weld, hence 853 frames being more expensive than 631 frames.

I didn't know 853 could be welded - I thought it could only be assembled into a usable frame by brazing ?

 

[jimboalee]

+ 1 Chris.

It was a widely held belief that 531 was 5% Chromium, 3% Manganese and 1% Molybdenum.

??????

Was ordinary Cr -Mo 501 ???

631, 753, 853 et al are developments on the original 531 process with, as you say, heat treatment processing.

Am I correct, Columbus Thron is equivalent to 531 ?

 

[Chris James]

I didn't know 853 could be welded - I thought it could only be assembled into a usable frame by brazing ?

853 can be tig welded, for example the Super and Ultra Galaxy are TIG welded 853.

753 had to be silver brazed.

Cycling Plus in their review of a Roberts 953 said it was weldable although I suppose lots of people will opt for a less agricultural finish if they are spending serious money on a frame.

 

[jimboalee]

I like decorative lugwork, so its brazing all the way.

 

[Chris James]

+ 1 Chris.

It was a widely held belief that 531 was 5% Chromium, 3% Manganese and 1% Molybdenum.

??????

Was ordinary Cr -Mo 501 ???

631, 753, 853 et al are developments on the original 531 process with, as you say, heat treatment processing.

Am I correct, Columbus Thron is equivalent to 531 ?

I don't know Jimboalee, I am not a not a metallurgist or an expert on bike tubing.

I am pretty sure 501 was a Cr-Mo of some sort.

531 was Mn-Mo, I don't know why it was called 531 although the ratios story (I've heard it too!) seems to be a bit of a myth. Wikipedia has it's composition as 1.5% Mn, 0.25% Mo, 0.35% C.

http://en.wikipedia.org/wiki/Reynolds_531

I don't know anything about Columbus tube sets.