Questions about purchasing bicycles and parts
16 posts • Page 1 of 1
Looking at MTBs and I guess roadies etc, I sometimes see different types of aluminium used. For example Felt refer to 6061 aluminium, Giant refer to "ALUXX FluidFormed" and I think I have seen a 7 series aluminium amongst others.
So my question is which is better if any? Is there some sort of rating or guide online?
Also what sort of specs should one be looking for in a frame (e.g., in terms of butting, welding etc)?
FluidFormed is the technique they use to shape & butt the tubes. It lets them get the funky bendy and odd shaped tubing. Butted tubes are better because the tubing is thinner where it can be and thicker where it needs to be, so the frame is lighter and often stronger too.
"ALUXX" and "Alpha Aluminium" are Giant and Trek trademarks referring to the alloys they use - I don't know what the numbers for those are but they are probably some form of 6061 or 7005 which are the most common Al. alloys.
Digging into old memories here....
The first digit refers to the "family" of alloys, the other three being different variants of the basic mix. 6061 is bog stock, cheap as chips stuff. 7 series, particularly 7075 is sooo much better.
Many makers specify their own mix, and so you end up with Giants' ALUXX and similar.
Fluidforming is a process first used by Giant to create integral frame gussets for MTBs which has spread far and wide, basically the cut and mitred tube is placed into a sealed mould and high temp oil is pumped into the tube which forces it into the shape of the mould, supposedly altering the grain of the alloy at the same time.
I'd still rather have a craftsman create something for me in the finest British steel....
...whatever the road rules, self-preservation is the absolute priority for a cyclist when mixing it with motorised traffic.
London Boy 29/12/2011
You need to be sure that they've recycled Australian beer cans. Many overseas beer cans carry impurities that can cause uneasiness in the way your bike reacts and has been knowb to make it shy away from fluttering handkerchiefs or sudden noises.
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Second that (the steel part), although I have a fondness for light weight Japanese steel (Tange Prestige or Ultimate). We dont want to start another materials debate but have a look here http://spokesmanbicycles.com/page.cfm?pageID=157
Check this out
Amongst other things:
"...7005 aluminum is actually the stronger aluminum alloy. This begs the next question, which is the better material? 6061 is of course, or at least that is the opinion of most bike manufacturers..."
"...The difference between the two is that 7005, because of its high alloy content (over 6%), is harder to manipulate the material and to weld it. This means that with 6061 it is much easier to add strength adding tubing features like triple butting, ovalized tubing, and tapered walls that reduce the weight and improve the strength of the tubing..."
I think if you get a good quality touring bike you will be fine with what ever alloy it has.6061 will be fine,7005 is lighter/stronger but this is also relative.I had a 7005 alloy Gary Fisher (read trek) and it broke at the bottom bracket 3 times before I gave up and sold the warranty frame.(to a mate who built a beautiful racebike with it the drove into his garage with it on the roof).So I suppose I am saying dont read too much into the alloy type as a 7005 might be a stronger alloy but if it is a way lighter frame it actually might also be a weaker frame.Especially as us on the bigger size stress bikes a wee bit more than the chicken legs .
From what I recall, 70xx series alloys are significantly stiffer than 60xx, but they are more brittle. This makes them harder to work, and also means they have to designed carefully to avoid stress failures.
It can be done, though, as the use of 70xx is common in aircraft manufacture - that's why you'll sometimes see it referred to as 'aviation grade'.
i was under the impression that 7005 (7 thousand?) series aluminium doesn't need to be heat treated - thus more cost effective
and 6061 is heated treated to get its strength, which means more production costs, which leads to higher price to pay for a 6061 alum frame...
hmmm.... might go investigate more....
So would I be correct to assume 7005 in a MTB [Avanti Ridge Rider] would be okay. I would be using it as tourer with possibly a Xtracycle fitted. A 2007 model has come up for $550 and it may be in the right size.
Should be okay.
Has hydraulic brakes but low spec shifters and FD. You'll probably have to fit a cable disc calliper on the rear if you Xtracycle it as I don't think there is an easy way to get a hydraulic tube to work that far from the bars.
Cheaper frames aren't normally less strong, they're normally just heavier.
Note also the specs say 8 speed, which it seems is being phased out of most bike models these days. Nothing wrong with 8 speed, but you may eventually hit problems with parts and need to upgrade shifters, cassette, chain and R derailleur. That need is still probably a couple of years away though, so you'll see a few kms before then anyway.
Okay, back to hunting.
CORRECTION: The Xtracycle comes with a 8 speed chain but a nine speed is available at extra cost.
The 2008 model is $899 RRP but I am not sure what the specs are. Avanti haven't updated their website yet. Mind you if I go new I would get the Montari I think.
Was hoping to save a few bucks on the bike so if go BOB or Xtracycle the whole package is more reasonable.
There can be huge variations in material properties between the various families, and merely specifying the 4 didgits makes it an incomplete material reference.
The various stages of hardening (be it heat treating, ageing, cold working etc) need to be specified as part of the material, e.g. 7075-O, 2014-H14 etc etc.
7075 is a common aerospace grade, but then their is varying qualities of that grade as well. The purity of the base alloy also has a significant effect. You can get industrial 7075 which may be 99% pure alloy, but the true aero grade is 99.999% pure. That last 0.999 can make a HUGE difference.
7075 also has a great affinity to stress corrosion cracking - not a good thing at all.
To get a really good understanding of the relative material properties, you would need to look up a good Engineering book. I could scan something, but then would need someone to host it.
Either way, the different materials used would have different x-sections and wall thickness to account for that, soo they'd all be pretty much on par in strength, but the weighht and quality will differ.
To be different, the LeMond uses 6066 Alloy to be different
Bloody hard to find a suitable second hand MTB it seems. Turns out this is a XL frame which will be too big for me. Maybe a blessing in disguise.
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