Quantcast

Attn metalurgists...and nerds

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,031
5,921
borcester rhymes
What are the differences between extruded 7055 and forged 7075? Which is stiffer and stronger?

Looking at cranks, the 7055 is lighter and on the higher end crank.
 
Last edited:

Leafy

Monkey
Sep 13, 2019
542
350
Looking at matweb, 7055 extrusion has a lot higher tensile yield strength than 7075-T6 and a little bit higher ultimate. 7055 is also more resistant to fracture. I cant find a young's modulus on 7055 but it has a typical elongation at break higher than 7075 so I'd guess it would be a bit less stiff if both cranks had the same cross section. I'm also thinking that 7055 since its less common. Go with whicher cranks you think look best.
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,031
5,921
borcester rhymes
Looking at matweb, 7055 extrusion has a lot higher tensile yield strength than 7075-T6 and a little bit higher ultimate. 7055 is also more resistant to fracture. I cant find a young's modulus on 7055 but it has a typical elongation at break higher than 7075 so I'd guess it would be a bit less stiff if both cranks had the same cross section. I'm also thinking that 7055 since its less common. Go with whicher cranks you think look best.
does the forging process improve or change things? the 7055s are extruded prior to machining. The forged 7075 are not. They are virtually identical otherwise. I suspect the forged ones might be slightly stronger (7075 is no slouch) and they are like 50g heavier, which doesn't bother me much. I am pretty much willing to buy whichever look better and cost the right amount. Either should do the trick.

yunocarbon- not much reason to. I really like the rotor cranks, and I put a higher value on stiffness and strength than weight. For what I want, the only options are spec sworks, quarq/dram, or FSA. None of those appeal to me, especially not SRAM. FSA has some decent options but recently switched to a weird bolt pattern so I'd have to get one that's a few years old and 130bcd to make it work.
 

Leafy

Monkey
Sep 13, 2019
542
350
In not sure. Matweb does list the tensile strength of forged 7075 and it doesn't change much. It's hard to say since we don't know which orientation of the grain is on the cranks either, they could have put it the strong way as well.
 

Westy

the teste
Nov 22, 2002
54,232
20,015
Sleazattle
I can't remember which is which but one of those alloys will provide a transformative riding experience and the other will give you rectal EbolAIDS and curse your family for generations.