HT length, What may be an ignorant question

[Clancy]

Will some framebuilders out there or members steeped in the knowledge of frame building please explain to me what considerations go into the decision for a HT length and why HT lengths seem to vary so much.

Example, the new Flannimal in a 54 has a 132 HT while the new Ritchey Outback has a 140, the Surly Cross Check w an ETT of ~ 54 has a 91mm HT. Yes I realize there's other differences in the geometries of these bikes but my point is for pretty similar bikes the HT's can be very different in length.

I've seen stock frames in 54 range with 102-140 HT's.

I'm not referring to endurance geometry. What I'm looking at is the big differences in HT lengths for a given size of frame across different manufacturers.

Why?

[weisan]

http://www.scienceclarified.com/photos/geometry-3146.jpg

[NoMoreParagon]

Will some framebuilders out there or members steeped in the knowledge of frame building please explain to me what considerations go into the decision for a HT length and why HT lengths seem to vary so much.

Example, the new Flannimal in a 54 has a 132 HT while the new Ritchey Outback has a 140, the Surly Cross Check w an ETT of ~ 54 has a 91mm HT. Yes I realize there's other differences in the geometries of these bikes but my point is for pretty similar bikes the HT's can be very different in length.

I've seen stock frames in 54 range with 102-140 HT's.

I'm not referring to endurance geometry. What I'm looking at is the big differences in HT lengths for a given size of frame across different manufacturers.

Why?

Thats a good question. I think there are 3 points to bear in mind:
1) is the HT built for press fit headset cups or integrated? If you use, say, the Chris King Inset, the HT will be, ceteris paribus, shorter in order to account for the headset stack which can be as high as 25mm.
2) fork crown to axle measurement...road fork is 367mm vs CX for at 390ish...once again a CX/Gravel frame will have shorter HT compared to road for a given handlebar stack
3) sloping vs traditional geo...sloping tends to have a taller HT for a given reach/stack combo

hope that helps!

[jtbadge]

This comes up every once in a while, another factor is BB drop.

David Kirk and Richard Sachs, among others, had some nice input here:

https://forums.thepaceline.net/showthread.php?t=214239

[bigbill]

Thats a good question. I think there are 3 points to bear in mind:
1) is the HT built for press fit headset cups or integrated? If you use, say, the Chris King Inset, the HT will be, ceteris paribus, shorter in order to account for the headset stuck which can be as high as 25mm.
2) fork crown to axle measurement...road fork is 367mm vs CX for at 390ish...once again a CX/Gravel frame will have shorter HT compared to road for a given handlebar stack
3) sloping vs traditional geo...sloping tends to have a taller HT for a given reach/stack combo

hope that helps!

My custom gravel was roughly based on my Serotta road bike. The Serotta is a 60 with a 58 top tube and 210 headtube. The gravel bike has similar measurements but with a 160 headtube because axle to crown is 50mm more on the gravel bike.