Frames...

They can manipulate alloy a lot more than chromoly to tune the ride, plus your average downhill bike is ALREADY 35 lbs, make it from steel and you hit like 45. Alloy dampens a little vibration too. It isn't that hard to weld actually, just a little more involved than steel.

They are actually making downhill bikes from Carbon Fiber now. Give it time and even freestyle BMX Bikes will be made from something else. Carbon is in the race world already. I have a Carbon Fiber XC MTB for the season to ride. Super light.

dave lawrence wrote:

They can manipulate alloy a lot more than chromoly to tune the ride, plus your average downhill bike is ALREADY 35 lbs, make ...more

dave lawrence wrote:

They can manipulate alloy a lot more than chromoly to tune the ride, plus your average downhill bike is ALREADY 35 lbs, make it from steel and you hit like 45. Alloy dampens a little vibration too. It isn't that hard to weld actually, just a little more involved than steel.

They are actually making downhill bikes from Carbon Fiber now. Give it time and even freestyle BMX Bikes will be made from something else. Carbon is in the race world already. I have a Carbon Fiber XC MTB for the season to ride. Super light.

...more

What about the strength side of it? Is chromoly that much stronger than aluminium? And yeah I know, the carbon frames look mad since they don't have to stick to regular tubing.

Pretty much what Dave said, Aluminium is easier to form in to intricate shapes (Hydroforming etc), and DH Bikes are already really heavy. Also take in to consideration that you can use Larger Diameter Tubing or Thicker Tubing, to make it stronger; DH Frames have fairly large tubes. As for the Grade of Aluminium, 7075 Series Aluminium isn't suitable for such use as it is very Hard and so it it is fairly brittle and easy to Crack when used for a Frame. It is also fairly expensive for Aluminium, although cheaper than Carbon Fibre and Titanium which are often used for MTB Frames. 7005 is used for DH Frames, although 6061 is also sometimes used. 7005 and 6061 are actually quite different (By Composition), so there are Pros and Cons for both.