Bianchi Dolomiti

[Fab Foodie]

Excuse my ignorance but is all 653, 531 etc the same thickness or are the numbers referring to the composition of the steel?

Some help here:
http://en.wikipedia.org/wiki/Reynolds_Cycle_Technology
and here:
http://www.reynoldsusa.com/english.html

 

[Baggy]

Excuse my ignorance but is all 653, 531 etc the same thickness or are the numbers referring to the composition of the steel?

Actually, my bike is 631.

Anyway, Glad Fab Foodie answered as I have no idea about composition of steel!

 

[Fab Foodie]

Actually, my bike is 631.

Anyway, Glad Fab Foodie answered as I have no idea about composition of steel!

... me neither, but I can Google ...

 

[Chris James]

Excuse my ignorance but is all 653, 531 etc the same thickness or are the numbers referring to the composition of the steel?

All steels are the same density, so if they have the same tube thicknesses they would be the same weight.

The numbers refer to differing alloys and heat treatments. The more expensive are much stronger, which allows thinner walls to be used, cutting down on weight.

I read that Thorn's 858 steel was so named because it was the thickness of the (doule) butted walls (0.5mm and 0.8mm). I think this is similar to that used on 631 frames. 953 frames can have wall thicknesses down to 0.3mm.

The builder can select tubes with diffeirng geometries and thicknesses as appropriate for the area of the frame and its final use.

 

[rich p]

All steels are the same density, so if they have the same tube thicknesses they would be the same weight.

The numbers refer to differing alloys and heat treatments. The more expensive are much stronger, which allows thinner walls to be used, cutting down on weight.

I read that Thorn's 858 steel was so named because it was the thickness of the (doule) butted walls (0.5mm and 0.8mm). I think this is similar to that used on 631 frames. 953 frames can have wall thicknesses down to 0.3mm.

The builder can select tubes with diffeirng geometries and thicknesses as appropriate for the area of the frame and its final use.

That's what I thought, so it's possible to make a lightweight frame without compromising on strength if the steel is of a certain quality. What I'm saying really is that a steel frame doesn't necessarily have to weigh more than an alloy one?

 

[Chris James]

Aluminium alloys have a strength to weight advantage over most steels, so typically aluminium alloy frames will be lighter (and cheaper for the same weight).

I wrote this

Both steel and aluminium alloys are suitable materials for frame construction. Different types of frames have different requirements. E.g.a track racing frame might be made to be extremely stiff for power transfer and an audax bike springier for long distance comfort.

As far as your comment about flexing – all materials flex. This is a function of their modulus of elasticity. Fatigue life is not directly due to flexing but due to cyclical stresses (which may come from flexing - bending but could equally come from tension / compression).

The feel of a bike is much more down to its geometry than the material it is made from. Large diameter tubing will be much stiffer than skinny tubes.

However, as User482 has already pointed out, there are distinct differences in the mechanical properties of steel – particularly modulus of elasticity, density, corrosion resistance and the fatigue limit.

Aluminium alloys have a third the density of steel alloys. So you might expect al frames to be a third the weight of steel frames. But this is not the case. Why? Because al is a much less strong material (lower modulus of elasticity) and so cannot withstand the same stresses as steel frames without failing. Also steel frames typically have very thin tube walls and al frames with this thickness tubing would dent easily.

So al frames are made with thicker walls and using oversized tubing (to limit the internal stresses in the frame). So al frames have more material in them than steel ones, hence them only being slightly lighter than good steel frames despite being made of a much lighter material.

Both al and steel frames corrode. Aluminium is actually a very reactive metal and corrodes very rapidly but it has the advantage that its oxide is very adherent so after the initial surface corrosion then rate of corrosion slows down to almost nothing. High alloys steels are less corrosion resistant for general use. However, aluminium oxide is not stable in the presence of salts and will suffer badly from localised corrosion. So it is important that you keep all bikes clean!

Finally, steel has a ‘fatigue limit’ whereas aluminium doesn’t. The springs eluded to before are operated below their fatigue limit stress and so can flex forever without breaking. The paperclips are operated above their fatigue limit stress and will fail rapidly. A properly designed steel frame will operate below its fatigue limit so will NEVER fail through fatigue. Aluminium frames will ALWAYS have the potential to fail through fatigue as they have no fatigue limit and every fatigue cycle they endure brings them closer to their final failure. However, if you design the al frame so that the stress it sees is kept to a minimum (through OS tubes, thick tubes) then it may be that you can extend the frame’s fatigue life such that it will be replaced due to fashion or crashing before it fails due to fatigue.

In summary, you can make a bike out of anything.

Steel frames will probably be slightly heavier than al frames, have thinner section tubes, probably thinner diameter tubes, be springier, corrode more easily unless looked after (eg painted and frame sealed) and will never fail due to fatigue.

Aluminium alloy frames will probably be slightly lighter than steel frames, they will be much stiffer as they need oversized tubes with thick walls for any sort of longevity, very corrosion resistant if looked after (washed regularly) and will eventually always fail due to fatigue if not replaced beforehand.

If you are interested in this sort of stuff there is quick a good chapter on it in the book Bicycling Science.
Here

http://www.cyclechat.co.uk/forums/showthread.php?t=7044&highlight=fatigue+limit&page=14

There have been quite a few threads about the advantages and disadvantages of different materials eg

http://www.cyclechat.co.uk/forums/showthread.php?t=833&highlight=fatigue+limit

http://www.cyclechat.co.uk/forums/showthread.php?t=16142&highlight=fatigue+limit

 

[Lambchop]

Some interesting stuff there Chris, cheers for posting. All this talk of aluminium frames 'failing' has gotten me slightly worried! As they have no fatigue limit, does it mean that one day my al frame bike will just snap in two? Has this ever happened to anyone on here?

 

[Chris James]

Some interesting stuff there Chris, cheers for posting. All this talk of aluminium frames 'failing' has gotten me slightly worried! As they have no fatigue limit, does it mean that one day my al frame bike will just snap in two? Has this ever happened to anyone on here?

It will eventually fail but it may take decades. In the meantime many steel frames will have rusted through!

Good frames - and bad ones - are made out of all materials. I know the lad down the road from me broke his aluminium frame. The good thing about metal frames is that they will not fail catastrophically. You should get a warning that the frame has cracked, which may not be the case with carbon fibre.

 

[Lambchop]

Update - every bike shop I've spoken to has Dolomiti's (on order or) arriving early to mid May. Will be ordering mine just after 'payday' !!! Whoop.

 

[Baggy]

<envy>
We expect pictures...