How much difference is there in weight between frame sizes?

[Thursday guy]

Typically how much difference is there in weight between frame sizes of the same bike?

Say for a bike which is quoted for weight 13kg, how much would this difference translate to?

 

[Citius]

A few grammes either way - not noticeable and not worth worrying about.

 

[biggs682]

steel,alloy or carbon ?

 

[Fab Foodie]

A few grammes either way - not noticeable and not worth worrying about.

This ^^^^
It's not significant on a 13kg bike plus a 70+ kg rider.

 

[Drago]

Any tiny weight difference is more than offset by the performance efficiencies that a properly fitting frame brings.

 

[Thursday guy]

steel,alloy or carbon ?

the frame is aluminum

 

[biggs682]

the frame is aluminum

as mentioned before then very little indeed

 

[accountantpete]

If you changed the alloy steerer of the bigger bike to carbon they would probably weigh the same.

 

[MichaelW2]

More significant is the difference in stiffness. Frames are designed around M size. If XS and XL size is made withe the same profile of tubing, the XS will be much stiffer and XL less stiff than M.
This is the complete opposite of requirements, where smaller, lighter, less powerful riders need less stiffness, not more, and bigger, heavier, stronger riders need more stiffness.
Specialized recently designed the Roubaix saying:
"With size-specific engineering and a frame that delivers the best balance of vertical compliance, low weight, and torsional stiffness, riders of all sizes can experience the same ride quality and performance as Boonen."

ie this is a special feature, not a standard method of designing frames.

 

[Citius]

Who says that smaller, less powerful riders need 'less stiff' frames - and why?

 

[KneesUp]

Who says that smaller, less powerful riders need 'less stiff' frames - and why?

It sound logical - if you generate less power, the frames doesn't have as much force to resist and thus doesn't need to be as stiff, ergo it can be made of less material, thus making it lighter and therefore going some way to improving the power/weight ratio.

I'm not sure you can say that smaller riders always produce less power though - I had a friend at school who was (is - I still see him occasionally) 6 inches shorter than me, but he had thighs like tree trunks (compared to my drainpipes) and he was always wrecking bike parts through sheer force (and bad technique, probably).

 

[MichaelW2]

Who says that smaller, less powerful riders need 'less stiff' frames - and why?

Once your frame is stiff enough to resist bending forces, any extra stiffness is not needed. It takes extra material to make the frame too stiff and detracts from a comfortable ride.
Smaller , less powerful riders exert smaller forces on the frame than larger, heavier, more powerful riders.

 

[MichaelW2]

I'm not sure you can say that smaller riders always produce less power though - I had a friend at school who was (is - I still see him occasionally) 6 inches shorter than me, but he had thighs like tree trunks (compared to my drainpipes) and he was always wrecking bike parts through sheer force (and bad technique, probably).

Did your friend ever wreck a frame?
On average, it is true. If you add in the use of shorter cranks for short riders(ie levers on the bottom bracket), this magnifies the effect. And visa-versa
Mostly, XS and XL riders don't know what a well designed frame should feel like since they rarely experience one. A few custom builders may get it right, but sourcing tubes of the correct profile is not easy. Carbon maestro Parlee build each frame with specially selected tube of the correct diameter and stiffness.

 

[Sittingduck]

What about smaller but heavier riders?

 

[Citius]

Exactly - or even taller, lighter ones. I think some people have been reading too much promotional literature.