Steel vs Aluminium vs Carbon vs Ti vs Scandium

Shaggy_Dog

I once read in an article by the great Sheldon Brown that vertical compliance of various seatstay designs is just a load of marketing guff, and that a slack seat tube angle offers more comfort than the various types of metals used in the construction, especially if a lot of seatpost is sticking out of the frame.

I have heard that it's also possible to have a very rigid steel frame and a whippy alloy one, contrary to the generalisations about the comfort factor of each material

I've had a few alloy HT's over the years and a couple of nice Cromo frames, mostly by Gary Fisher. Last year I had a Ferrous (True Temper Platinum OX) and a Paragon (hydroformed Aluminium) and I can't say I noticed any more comfort in one material over the other. The steel bike was a smaller size so had more seatpost sticking out of it and my colleage said he could literally see it flexing under my body weight but I couldn't feel any difference. That said I rode a Kona King Kahuna scandium hardtail and that really felt special, the handling wasn't quite as dialled as the Fishers but it was comfy and very, very fast.

My carbon full suss is a different story altogether. Last summer I had a HiFi Pro (aluminium) and now I have a HiFi Pro Carbon, the difference in comfort is astonishing! It's more noticeable descending out of the saddle, where the imperfections in the trail are muted by the carbon (anything that doesn't get through the stiction in the rear shock, bigger hits feel the same) I compare it to having the wheels hovering a couple of millimetres from the ground or having big wooly socks and gloves. It's a very strange sensation, you can still communicate what the tyres are doing but it just feels so much smoother and faster. Unfortunately it's a very flexy platform tortionally when compared against the newer alloy frame so tends to ghost shift and requires serious commitment to push it hard

I've had a Dedacciai steel track bike that was as rigid as anything I've ever ridden so that throws another spanner into the works.

I haven't put a lot of time into titanium in any form or carbon in hardtails but I have ridden Trek Madone road bikes and it's the same feeling. I've heard that Ti feels the same as steel but lighter.

Any thoughts guys and girls?

supersonic

I think to a large extent Sheldon is right. The modulus of steel is THREE times that of aluminium, and twice that of titanium. But how the tubes are formed has an impact on the the actual tube and frame stiffness. Double a tubes diameter (but keep the wall thickness the same) and the stiffness of the tube TRIPLES! As aluminium is much less dense, and doesn't like been flexed due to fatigue, they are often oversized hence why they generally feel stiffer.

But many alu frames with careful butting can seem to flex a bit more, and heavy steel frames can feel stiff. The same for titanium and carbon. There is another factor and that is high frequency buzz absorption. Carbon layup can reduce this, and different metals absorb differently.

Scandium is aluminium - with upto 2% scandium added to increase fatigue and strength chararcteristics. All bike alus feel exactly the same as have exactly the same stiffness. This is true for all steel alloys. So this again reinforces that the tube dimensions and profile is a huge factor.

Recently we have seen frames with vertical compliance built in. But as shedldon says, seatposts, angles, tyres, saddles and many other things influence comfort.

Steel can be very stiff, alu very whippy. The generalisations just aren't really there any more as new techniques and tube formings make things different.

Shaggy_Dog

I was under the impression that scandium doesn't increase the strength of the tubing but allows it to be more weldable, therefore giving thinner tubes and a whippy feel

supersonic

It does do that too - but also increases tensile strength. Easton says it doesn't, but it does. There are also other effects as metallurgy is a vast subject, and too much to go into much detail here really!

http://www.scandium.org/Sc-Al.html