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Tommasini53
06-19-2013, 08:35 AM
:help:
in comparing the head tube height of a carbon (internal headset) and a ti frame (traditional external headset)...is it as simple as adding the reported stack height of the external headset to the head tube height of the ti frame.

Example:
ti frame:
head tube: 9.5cm
Chris King headset: 3.5cm
equals 13cm total height

compare to
carbon frame:
Headtube with integrated headset: 14cm

Does my method result in an apples to apples comparison of headtube heights among frames???

I'm I missing something?? Just want to make certain my methodology to compare head tube height across frames is reasonable. :help:

oliver1850
06-19-2013, 09:59 AM
Assuming you have included the integrated top cap (some brands have options) in the measurements, the only other thing I can think of is axle to crown height of the fork(s).

rice rocket
06-19-2013, 10:09 AM
Fork axle-to-crown plays heavily into it too.

Also, integrated/zerostack doesn't mean the stack height is zero.

Mark McM
06-19-2013, 10:17 AM
As oliver1850 mentioned, the frame stack is composed of more than just the head tube length (and headset height) - you also have to take into account the fork length and the BB drop. For example, take two frames with the same fork and the same frame stack, but with different BB drops - the frame with the deeper BB drop will have a shorter head tube, even though the frame stack is the same.

If the frame stack of the a given frame isn't known, a closer approximation can be found from:

Frame stack = { Cosine( Head Angle) x [ ( Fork Length ) + ( Headset Lower Stack Height ) + ( Head Length ) ] } + ( BB drop )

Tommasini53
06-19-2013, 08:43 PM
thank you all for the information,

i know the b.b. height is different among the frames i'm comparing. i had not considered that aspect until i read your explainations. :)

Dave
06-20-2013, 09:19 AM
Mosr carbon frame geometry charts only list the head tube length, but if you know the minimum stack height of the headset top section that's supplied, be sure to add that into the comparison.

As already noted, the fork length and BB drop both need to be accounted for. That's why some brands now include the frame stack, first introduced by Cervelo. That's a measurement from the center of the BB to the top-center of the head tube. It eliminates the need to know the BB drop and fork length to make a comparison.

Comparing published reach values has it's pitfalls. You can only compare a reach value if the stack heights are the same. If not, then you need to include a correction of about 3mm of reach for each 10mm of stack height difference. For example, you may see a 54 and 56cm frame with same reach, but the stack heights differ by 20mm. In that case, the reach on the smaller frame is really about 6mm shorter, if the bars are set to the same height on both frames.