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Just bought a kona nunu. nice bike but definatley on the heavy side. it's made from 7005 double butted alu. Is this lighter than the 6 series alu? i always tought it was a lighter type of aluminum alloy and was thoroughly dissapointed with the weight of this when i picked it up.
any ideas, i've checked the net already but can't find anything specific to this...
cheers peeps!
The numbers have nothing to do with the weight, it defines what the aluminium is alloyed with.
6000 series is Aluminium Magesium Silicon alloys
7000 series is Aluminium Zinc Magnesium alloys
The numbers refer to % of alloys, heat treating and finishing.
There's very little weight difference between the alloys
6061 weighs 2700Kg/M^3 whereas 7005 is 2730Kg/M^3 so 0.01% more heavy.
The big difference is down to how much of the stuff a frame maker chooses to use to make the frame.
In a nutshell. that's just how i like my replies..........cheers!
😀
The big difference is down to how much of the stuff a frame maker chooses to use to make the frame
What he said - if it's the whole bike you're weighing, the rest of the 'stuff' connected to it is going to represent >75% of the total weight, so you might want to look elsewhere for some heavy lumps rather than pointing the finger just at the frame.
Kona tend to spec some pretty low end components sometimes and they still seem to go with Marzocchi forks a lot, the cheap Marz are very lardy. OK, so the frame isn't the lightest but look to the wheels and forks first as easier places to save weight.
Pretty sure 8000 series is lighter. I don't think you'll find an 8000 series frame though.
(Mr MC former research metallurgist posting)
the weights of different alloys is irrelevant (and the difference negligible). The relative strengths and fatigue resistance will be more of a factor as they would allow a manufacturer pushing the limits of frame design to make a lighter frame by using thinner walled and/or smaller diameter tubes, more extreme butting etc.
Historically far-eastern made frames have been made of 7xxx series, US built out of 6xxx series as they were the alloys and tube-stock most readily available in those respective markets. Each would hype their alloy choice as being superior.
Laymens guides here
http://www.ibike.org/library/bike-frame.htm
and
http://www.sheldonbrown.com/frame-materials.html
Whether your Nunu was made of 6xxx or 7xxx it would be "disappointingly" heavy as its a budget frame (no offence) not a lightweight high end race frame. The reason aluminium had a reputation for making stiff frames is because manufacturers deliberately made them stiff by using large diameter tubing in order to reduce fatigue (essentially cracking due to repeated flexing), not because aluminium is innately stiff. The same alloy with a different heat treatment (the T- you see at the end) have different strengths and other properties. T6 is "peak aged" and the most often used.