Cycle Geometry

[Orange]

Can someone please explain - in layman's terms - the pros & cons etc of differently angled frames? Which angles are we talking about and when the knowledgable talk of a bike's geometry, what exactly are they talking about?

 

[HLaB]

At a very basic level, a tighter geometry puts the cyclist in a lower position and is in theory more aerodynamic, whereas a loser geometry put the rider more upright, which may be more comfortable but less aerodynamic.

 

[Orange]

Thanks HLaB.

Does that relate to frame length? Would a longer frame stretch you out more, putting you in a lower, more aerodynamic position? If so, wouldn't that increase the inside angles?

Or am I still not getting it?

 

[Norm]

I don't think it's about "geometry" as you see it, Orange.

Geometry, in bike terms, relates to the BB height, the head tube length, the offset of the seat post, the wheelbase, the stem length and the shape of the bars.

It could also cover stem angles, down tube angles, rake and offset of the forks and relative lengths of top tube to seat tube but it's not, generally, a specific number of degrees or the measurement of any particular component, it's about the way that the whole bike is set up and used.

 

[Norm]

Does that relate to frame length? Would a longer frame stretch you out more, putting you in a lower, more aerodynamic position? If so, wouldn't that increase the inside angles?

Frame size is certainly one of the factors.

My Secteur (road bike) has a medium frame as the more hunched position is not only more aerodynamic but it also means you have to use "core" body muscles.

My Tricross (general use and off road) has a large frame which has an inherently more "relaxed" geometry, IMO. The saddle is the same height on both but the extra length and extra head tube height on the larger frame means that the bars are higher on the Tricross so I have more room and I'm sitting more upright.

 

[Orange]

Ah, OK, maybe that's why I was having trouble visualising it. Thanks Norm.

 

[Norm]

If you are anywhere near Windsor, you would not be the first to try the two of them back-to-back to see how each feels and how much difference the "geometry" makes.

 

[HLaB]

Thanks HLaB.

Does that relate to frame length? Would a longer frame stretch you out more, putting you in a lower, more aerodynamic position? If so, wouldn't that increase the inside angles?

Or am I still not getting it?

In someways the geometry will relate to the frame length but because a frame is triangular, if you lengthen it the overall angle stays the same but the top tube to down tube angle actually become tighter.