Carbon stays in frames.

The addition of carbon fibre seat stays and chain stay tubes to race frames is an old idea I first noticed surface briefly by some manufactures in steel frames about 1980.
IT IS NOT NEW TECHNOLOGY, frames and parts have been made from carbon since the mid nineteen seventies. It has become popular in the last couple of years. I see and hear many comments about carbon stays in aluminium frames but I think some thought should be applied to their virtues.

Comments like "It is like riding on a flat tyre it is so soft"
"The carbon dampens road shock." There may well be some merit to this but,show me some data on the vertical compliancy of carbon stays compared to aluminium stays or steel stays that have the same rigidity and weight or resistance to flexing under the stress of pedalling etc (carbon seat and chain stays weigh more than using aluminium tubes!).

How much does the stay flex when the rear wheel rides over a bump in the road for your backside to notice the difference? First the tyre encounters the bump and by far the greatest shock dissipation is encountered here. This can measure from millimetres to as much as 2 centimetres from serve thumps. The type of tyre and its profile from 20mm to 23mm for example and its construction will influence this amount, not to forget tyre pressure. Ten PSI in the tyre can make a difference. The age of the tyre also affects its elasticity. Then the rim and spokes is next to encounter the bump on its way to your bum, the difference between rim profiles, spoke number, gauge and tension. The hub then transfers this to the frame. The frame encounters the stress and the stays and other tubes send this to the seat post and saddle (we are disregarding the handle bars).

How much does the stay flex from the bump? No one really knows, if they do they are keeping quiet as it is impossible to get data from manufactures of carbon stays.

It could not be possibly more than one millimetre, perhaps 2 at most or there will be some serious frame damage occurring (wheels will be a right off by now!). Then lets not forget the saddle. The saddle shape, flexing of saddle rails, rubber inserts, padding and gel to dissipate the shock. Then the chamois and the rider's bum which we know is a considerable place of shock absorption.

OK, we know carbon has slow rebound effects etc but the way I see it in the whole scheme of things it is a very small factor in the equation. What is really happening? Perhaps that slow rebound effect is also sapping energy in the transmission of pedal force to the chain. It wasn't long ago that overly rigid frames were being pushed as being better for going faster. Maybe the "riding on a flat tyre feeling " is true. Perhaps it is like riding on a flat tyre due to the loss of crisp pedal force reactions or is there other factors as mentioned before coming into play?

I am sure there could be an effect happening but considering all the other factors one may need NASA equipment to detect the differences. Carbon frames were heralded in the mid eighties to become the norm for high performance frames but today 95% of frames are still metal. The ride qualities of carbon have not been popular. Also reliable construction problems. Hi tensile materials may be better. Is this a fashion trend publicised by the pro team bike suppliers to keep sales buoyant.

I have doubts about the positive benefits of carbon stays especially when some are concerned with extra weight. I myself cannot notice any difference that could not be attributed to other factors when riding different frames with or without carbon stays.

Yes I will build a frame with carbon stays but I am not convinced at this time of its merits against the weight penalty it brings.