Head Tube Size
 

Larger points where tubes meet allows for stiffer frames. Stiffer frames generally sprint and climb better. Since you're looking at a new bike with a 1" headtube, I'm betting it's steel- if you're looking at steel, then stiffness is kind of out the window anyway- great material, very strong- but flexy by nature.

Actually - it is a carbon bike. I found it odd that they still use 1" head tubes, but was wondering if the stiffness from the head tube size is a perceptable differnece.

1-1/8" to 1-1/2" headset design have been used by Ridley and others for quite a while already. But it's starting to turn into a trend this year.

this is on my Time as well. i think there's something to it. the front end is rock solid. on full speed descents there isn't the slightest hint of movement. i don't know if this is due to the head tube, the fork that's on the bike, or a combination of the two (which is what i suspect). conversely, i have an Orbea Orca with a standard 1-1/8" head tube that is a bit longer than most, and it flexes like a noodle. it's flat scary to get up to speed, the thing wobbles so much. i don't think i'd even look at a 1" head tube. but that's just me

Seems like the trade off would be in aerodynamics for the added stiffness you would get. C'dale does their research so perhaps it is a good design?

There is a material characteristic knows as the Modulus of Elasticity which defines how stiff a material is. Steel is twice as stiff as Ti and three times aluminum so basically it should be said that steel is "stiff by nature".

The stiffness of a frame tube is a combined factor where the Modulus of Elasticity of the material is multiplied by a shape factor known as the Moment of Inertia. The stiffness goes up greatly as the diameter increases. Bottom line is that steel frames can be either stiff or flexi - depends on the Moment of Inertia of the tubes the builder chooses.

The reason many steel frames on on the compliant side of the equation is because a) they can be (unlike aluminum) and b) the material is density challenged which drives builders to use the thinnest and lightest tubes available thus making the frame more flexible.

Nothing inherently flexible about steel.

The diameter of a head tube is a meaningless concept, except when it limits your ability to use the headset and fork of your choice. A company can build a high quality product in any of the standard diameters (and the Chino-crap companies have proven they can build cr#%p products in any standard size).

A more meaningful concept is the HEIGHT of the head tube. "Cycling Plus" was comparing entry-level road bikes from Trek and Specialized that were both about size 56. The head tube on the Trek was shorter than average for a medium sized bike. The Specialized head tube was taller than average for a medium sized height. "Cycling Plus" editors found it much easier to get the bars up to the correct height with the taller head tube...no need for a huge stack of spacers, or a goofy looking "giraffe" stem.