Carbon Strenght VS Metal?

[Guest coenie]

I was chatting to a friend who is keen on getting the Scott Scale carbon. The frame only weighs 950g. ish.

 

I always thought and have been told that you want a stiff BB and and headset area for power transfer, now with the Scott scale, it is ONLY carbon.

 

What do you hubbers think, would this be able to give you the same stiffness as a heavier frame, where they have used some metal in the BB, will this carbon only frame not be more like a wet noodle when you ride it?

 

I told him that the Niner, although heavier should be stiffer...and I am not sure if one can trust the carbon only version when you jump on the pedals.

 

Does anyone know if there is there a weight limit on those frames?

 

Look at the pics and give me an opinion

Edited February 15, 2011 by coenie

[Top Fuel]

I am not expert but I think carbon bikes are very strong. However I saw a guy snap his bike 2 weeks ago, so make sure his warranty is very good. The last thing one needs is to claim for a frame and they come up with excuses not to pay the poor fellow. I am sure they stress test these frames before they sell them. Be good to see what other peeps say on this. Does the Scott come with the metal insert or not?

Edited February 15, 2011 by Top Fuel

[The Drongo]

coenie

 

Whilst I can't comment on the flexing, if the Scott is the BB on the right then it looks like it takes the Truvativ Pressfit 30 BB???

They fit a 46mm ID BB shell, 73mm wide.

Nylon cups are pressed in, supposed to increase bearing life, but need a 30mm spindle crankset.

 

The integrity of the headtube and BB strength will rely on the carbon lay-up.

 

SCOTT are tops with carbon. Up to your mate, but that thing is a wippet!

[Guest coenie]

I am not expert but I think carbon bikes are very strong. However I saw a guy snap his bike 2 weeks ago, so make sure his warranty is very good. The last thing one needs is to claim for a frame and they come up with excuses not to pay the poor fellow. I am sure they stress test these frames before they sell them. Be good to see what other peeps say on this. Does the Scott come with the metal insert or not?

No the Scott comes as in the picture, no metal inserts at all and I am thinking that it will flex...

[Minion]

I reckon the carbon-only frame will be stiff and strong enough. The main reason for the metal BB shell is that the resin matrix for the carbon fibre isn't strong enough to hold a thread for threaded BB cups. It should, however, be OK with press fit cups.

 

Edit: Also, if you look at the tubes on the right, their outside diameter is much larger than those on the left. This adds significantly to the stiffness and allows them to use thinner walls.

Edited February 15, 2011 by Edam

[AndreZA]

If the headtube and BB areas are stiff enough for riders like Cavendish and Horshovd then it is strong enough for us plebs. But I'll be weary in the cheap carbon frames where they do not get that much testing/quality control.

[kennyg]

Got to agree with Mampara...

 

Carbon, is like 6 - 12 times stiffer than mild steel and in the region of 3-6 that of our best Aluminium. Thats based on equivalent weights.

 

The carbon shell if layered correctly, in a BB 30 style will provide a really stiff light weight setup. In my opinion, the lay up of the integrated system is stronger and less likely to fail, than the inserted BB.

 

I am not up to speed on who is doing what at the moment ito manufacturing, but Scott has a reputation for pushing the envelope weight vs reliabilty being my question, however, a company like Niner, will sacrifice a few grams and lean on reliability, as they are smaller and far more in a niche, where reliability could hurt there market share.

[Johan Bornman]

The only way to get rid of the metal in the BB is to go pressfit. Like Edman says, threads in carbon isn't a good idea, although that hasn't stopped DT Swiss from making some ridiculously stupid rear shocks with carbon air cannisters with fine thread. That has to be the de-facto lesson in how not to do things in carbon.

 

Trek Madone went metal-free in its BB and used pressfit bearings. However these are known to work themselves loose. I've inspected such a problem bike up close and I cannot figure out what happened. The carbon press-fit socket doesn't show any sign of scuffing or fretting, yet, enlarged enough to make the bearing fit loosely.

 

I am not too sure that a long-life press-fit BB is possible in carbon.

 

On the other hand, alu shells in carbon are known to give problems when water enters the interface.

 

But since you only asked about strength and stiffness, I suppose you're OK for the metal-free frame.

[Guest coenie]

Thanks for the info, you also answered some questions I did not post.

 

Long term I thought that something might give