specifically in seatposts? I'm in the market for something a bit longer than my current 350mm, and in my price range there are a lot of posts made of different types of aluminium. I figured I might as well try to find out which one has the best strength to weight, or whatever. They seem to be either 7005, 7075, 6061 or there was even a 20-something.

6061 <<Cheap
2014
7075 <<Pricey

from cheapest/heaviest, to lightest/priciest, if they've used the material properly.

heavier posts (if they have sort of similar clamp types) will have a stiffer ride (if you can be bothered to measure these things).

The reason why a 6061 post is cheaper than a 7075 post is not because the 6061 alloy is cheaper (it is a bit), but because the material is easier to machine, form and process.

Thanks for explaining that. I guess my initial choice looks good then, and in the next few weeks I'll have a new post that you might have had a hand in designing 🙂

I reckon (please correct me Brant) that in reality what material is used will not affect user choice. As in "I'll buy that bike because its made of 7075, which is better cos its more expensive".

The designer makes the decisions as to how light/stiff/durable the bike will be using the materials and processes at this disposal. So for the end user ignore the material type and ask yourself if the frame/component provides you with what you want and use that as your buying guide not material…

I wouldn't get too hung up about it. There's more to seatposts than the alloy from which they're made. I like Thomson posts for two reasons; they're well made and the anodising is better than most, and they have a 'bending fuse' – designed to bend rather than fail catastrophically.

As with frame design it's as much the design as it is the material.

Ideally I probably would buy Thomson if I had the funds. I've had them before and they did what they should. Unfortunately funds are a little tight just now so I'm pretty much set on the Nuke Proof Warhead. It gets a lot of nice comparisons to Thomson for a chunk less money.

Anything to put me off the Warhead?

Anything to put me off the Warhead?

I'm currently overhauling the Nukeproof line for 2011.

However, the seatpost is very lovely and likely to stay largely unchanged 🙂

If 6061 is cheapest, how come most of the £50 alloy bikes are 7000 series? Is 7005 cheaper still?

Most 7000 series alloys can revert to a pretty good state after welding, i.e. you can get away without doing post weld heat treatment. Armed with that knowledge I have always suspected that the cheapo bikes use 7000 series alloys so that they don't have to heat treat them after welding, saves a wedge of cash…

You are confusing 7075 and 7005.

First isn't weldable, second is.

7005 is much easier to heat treat than 6061.

The bigger number doesn't automatically mean a better alloy.
We make our alloy frames out of 7046 though.

You can weld 7075, its just crapola structurally afterwards. Widely used in the injection moulding industry to make mould tools of and then fill in the gaps by welding when they make a tooling change.

IADS International Alloy Designation System

http://aluminium.matter.org.uk/content/html/eng/default.asp?catid=214&pageid=2144417046

http://materials.open.ac.uk/mem/mem_ccf7.htm