why do members ask how tall the HT is?

[cnighbor1]

Why do members ask how tall the HT is when considering buying a frame?
The Ht heigth is a result of how the frame was designed and is the end product of the all the other factors. Frames are not designed starting with HT length. 1st is frame size needed with TT length reguired, Standover height needed, use of frame, i.e. racing, etc.. The HT length comes after all that is factored into the frame layout
Confused
Charles

[dave thompson]

Why do members ask how tall the HT is when considering buying a frame?
The Ht heigth is a result of how the frame was designed and is the end product of the all the other factors. Frames are not designed starting with HT length. 1st is frame size needed with TT length reguired, Standover height needed, use of frame, i.e. racing, etc.. The HT length comes after all that is factored into the frame layout
Confused
Charles
Nope, not quite. Head tubes can be made any length longer than the junction between the top tube and down tube; a head tube extension. I always ask the head tube length when considering a frame purchase. That measurement allows me to see where I can put the handlebars and the amount of spacers necessary to get them to that point. For young guys head tube height is of far less importance as they go long and low. As riders (at least me) get older that dimension assumes greater importance.

[RADaines]

As riders (at least me) get older that dimension assumes greater importance.
Yep, that about sums it up for me too.

[Ozz]

Your contact points (seat, feet, and hands) determine bike fit...your feet and seat are fairly adjustable on most bikes (slide seatpost up/down, saddle back/forth) but where you place your hands depends on TT length and head tube height...there is some adjustability with spacers, but no one likes the look of a stack of spacers. ;)

Therefore, once you know TT and HT measurements, it is easy to figure out if there is a chance the frame will fit.

IMO - stand over is the least important, as it only matters when you are stopped, and not when you are riding.

:beer:

[David Kirk]

As long as you take in consideration fork length, headset type (internal or external) and BB drop you can learn a little something about where the handlebar will end up.

I don't see it as a benchmark number as there are usually too many other factors that influence it to have it give a real apples to apples comparison.

Dave

[mister]

As long as you take in consideration fork length, headset type (internal or external) and BB drop you can learn a little something about where the handlebar will end up.

I don't see it as a benchmark number as there are usually too many other factors that influence it to have it give a real apples to apples comparison.

Dave

i was just about to say this and i think this is the idea charles was trying to get across.

[bigreen505]

As long as you take in consideration fork length, headset type (internal or external) and BB drop you can learn a little something about where the handlebar will end up.

I don't see it as a benchmark number as there are usually too many other factors that influence it to have it give a real apples to apples comparison.

Dave

+1. It's a little like KOPS in that it serves as a good reference point. People want to know how bent over they will be on the bike. BB drop is relatively consistent, particularly across off the shelf frames of a given size, as is STA. That leaves top tube length and head tube length.

[93legendti]

Nope, not quite. Head tubes can be made any length longer than the junction between the top tube and down tube; a head tube extension. I always ask the head tube length when considering a frame purchase. That measurement allows me to see where I can put the handlebars and the amount of spacers necessary to get them to that point. For young guys head tube height is of far less importance as they go long and low. As riders (at least me) get older that dimension assumes greater importance.
I agree.

[David Kirk]

I think it's an OK ballpark kind of number. In my line of work though I often get folks who want to compare the new design I'm proposing to them to a current bike they own. This is all good but sometimes folks will be concerned that the head tube is 5 mm shorter than the old bike and think that it will mean that the bars will be 5 mm lower. It might mean that, and it might not and it all depends on the other stuff.

So unless the design is being looked at as a whole then the HT length isn't an accurate way to compare designs. If the two bikes in question are the same except one bike has a drop of 80 mm and one has a drop of 70 mm (both very much in the norm) then you will get headtubes that differ by that same 10 mm. 10 mm is a big difference when it comes to bar drop so the designs need to be looked at as a whole so that you don't run out of adjustment room to bring the bars up/down to your taste.

dave

[flickwet]

Results in CX bikes having much shorter head tubes for a given size

[Uncle Jam's Army]

A complete idiot question here, to see if I get this: assuming two frames are completely identical in geo (including HT length), except that one has a 70mm BB drop and one has a 80mm drop, does this mean that the frame with a 70mm BB drop has a head tube that sits 10mm higher than the one with a 80mm drop?

[e-RICHIE]

A complete idiot question here, to see if I get this: assuming two frames are completely identical in geo (including HT length), except that one has a 70mm BB drop and one has a 80mm drop, does this mean that the frame with a 70mm BB drop has a head tube that sits 10mm higher than the one with a 80mm drop?

the drop difference would only mean that everything is one cm lower OR higher (but not both) atmo.

ps

arrange disorder

:) :( :o
:o :( :D
:rolleyes: ;) :p

[Pete Serotta]

the drop difference would only mean that everything is one cm lower OR higher (but not both) atmo.

ps

arrange disorder

:) :( :o
:o :( :D
:rolleyes: ;) :p

Richard, truly appreciate it. PETE

[Mike748]

A complete idiot question here, to see if I get this: assuming two frames are completely identical in geo (including HT length), except that one has a 70mm BB drop and one has a 80mm drop, does this mean that the frame with a 70mm BB drop has a head tube that sits 10mm higher than the one with a 80mm drop?

Think of it this way... the handlebars are in the same place. Your seat and cranks are 10mm lower with an 80 drop than with 70. So the seat to bar drop is 10mm less.

[e-RICHIE]

Think of it this way... the handlebars are in the same place. Your seat and cranks are 10mm lower with an 80 drop than with 70. So the seat to bar drop is 10mm less.


eh i dunno about that atmo...

ps

arrange disorder

:) :) :)
:) :) :)
:) :) :o

[mister]

and a builder could use a different angle on the lower headlug and at the bb shell couldn't they?

there are so many variables. which is why dk keeps stressin you gotta look at the whole package...

can't just look at the ht length and say "oh, it won't fit. my bars are gonna be 10mm too high."

[DRZRM]

Wait, I'm not sure what you mean. Isn't it the higher BB height, thus higher seat, that make CX forks feel like they are lower (thus my negative stem on my road bike but positive stem on my cx bike for me to feel comfortable)? Are CX forks shorter than road forks?

Results in CX bikes having much shorter head tubes for a given size

[e-RICHIE]

what does this mean?
and a builder could use a different angle on the lower headlug and at the bb shell couldn't they?

all these (two changes) would do is deliver the down tube to different spots.
it wouldn't affect head tube length at all atmo.

ps

arrange disorder

;) ;) :D
:o :( :D
:rolleyes: :rolleyes: :D

[Ti Designs]

Much like your legs being just long enough to reach the ground, your head tube should be long enough to reach both top and bottom headset cups.

[David Kirk]

Being that a picture is worth a 1000 words here are 3000 words for you.

All three images have the same exact fit. The first one has a typical road fork and 80 mm of BB drop. The second is the same as the first with just the BB drop bring different at 70 mm. The last is the same as the second except that the fork is longer (cross fork).

All three bikes have the same fit and the head tube lengths vary from 156 mm to 170 mm.

Do the pictures make it more clear?

dave

[RPS]

Why do members ask how tall the HT is when considering buying a frame?
Mostly because it affects how a finished bike will look. Within reason IMO it doesn't make that much difference except aesthetics. Nobody wants a stem running downhill or turned up at 45 degrees and/or with 30 MM of spacers. And heaven forbid a stem extension. With the correct length HT you can avoid these unsightly options. ;)

[avalonracing]

I buy bikes using only the head tube height. Who cares about top and seat tubes? ;)

[cnighbor1]

what you really want to know is does the head tube project more than normal above top tube and how much.
Just HT length still wouldn't provide what information for how high the handles bars will be.
You could get the length but if head tube it at normal just above the top tube but good is answer?

[sean]

Other than the aesthetics of less spacers and the angle of the HT, does it REALLY matter though?

I mean, if you have a short headtube, you could run more spacers (as long as the steer tube allows) to get height.

I would think that it WOULD become an issue if the HT is too tall and you want to be lower.

I would also guess that at some point some stiffness is lost if there are too many spacers.

I guess for me, unless going for extreme discrepancies in sizes, it's something that can be dealt with. Am I missing something?

[mister]

if you have to run an insightly amount of spacers and can't get rid of them with a simple stem swap...then you probably aren't on the best fitting size frame.

[rugbysecondrow]

If I am getting a new frame via Kirk or Bedford, then I will trust what they design. If I am buying used, I need some info to help discern how the bike may or may not fit me. Is this a perfect or 100 reliable number, likely not based on what has been said. What it does is help me feel comfortable that I may or may not be ballpark. This might all be bulli*****, but it gives me the warm fuzzies.

Or, maybe they have a fork they want to use and they need to see if the HT will accommodate t.

[e-RICHIE]

what you really want to know is does the head tube project more than normal above top tube and how much.
Just HT length still wouldn't provide what information for how high the handles bars will be.
You could get the length but if head tube it at normal just above the top tube but good is answer?


charlie - there is no more normal, nor has there been a de facto standard since folks stopped using lugs atmo.

ps

arrange disorder

:rolleyes: :rolleyes: :rolleyes:
:) :) :)
;) ;) ;)

[Dave]

If you're talking about road frames, not making a completely apples and oranges comparison of road to cross frames, the the head tube length, with the headset, is quite valuable because it deteremines MOST of the handlebar height. Factory built carbon roads forks in axle to crown length vary from about 367mm to 374mm, so there is some uncertainty there.

BB drop is kind of a no brainer. If the BB is 10mm lower, the HT can be about 10mm shorter and produce the same saddle to bar drop.

Many brands are now listing reach and stack values. The stack height eliminates any error due to fork length or BB drop. It's the vertical distance from the BB center to the top-center of the head tube. With frames using integrated headsets, the head set top section varies from 8mm to 20+mm, so you still need to know what your options are. There are models with a 20mm minimum (LOOK aheadset for example).

The flaw in the reach concept is the fact that reach can only be compared (directly) when two pr more frames being compared all have the same stack height. Otherwise, corrections are needed to measure each frame reach at the same stack height. The best correction value is simply 3mm for each 10mm of stack height difference.

[jlwdm]

... Nobody wants a stem ... with 30 MM of spacers.


30mm of spacers doesn't bother me at all. My custom Serotta and Spectrum were designed with 25mm of spacers. Maybe it looks more balanced on my bikes because they are large frames. The head tubes are 225mm and 249mm.

Jeff

[Uncle Jam's Army]

Thanks Dave Kirk! I've got a grasp of it now. Like you said, a picture is worth a thousand words.

[victoryfactory]

lots of spacers or HT extension brings the bars closer to
the saddle as well as higher.

VF

[David Kirk]

Thanks Dave Kirk! I've got a grasp of it now. Like you said, a picture is worth a thousand words.


You are very welcome - it's easy to see but can be difficult to explain. Glad it helped.

dave

[54ny77]

reach for the stars!

http://2.bp.blogspot.com/_wb8bAl1P-N0/SZBLuNG3a9I/AAAAAAAAGCk/draQuMah0sQ/s400/sideheadtubecp6.jpg

[RPS]

....snipped.....

The flaw in the reach concept is the fact that reach can only be compared (directly) when two pr more frames being compared all have the same stack height. Otherwise, corrections are needed to measure each frame reach at the same stack height. The best correction value is simply 3mm for each 10mm of stack height difference.
Can you elaborate on this? How are they defining and measuring frame “reach”?

[Dave]

Can you elaborate on this? How are they defining and measuring frame “reach”?

Reach is the horizontal distance from a vertical line through the BB center to the top-center of the head tube, by Cervelo's definition. Other brands that post reach and stack values have also adopted this definition (C'dale, Trek and LOOK).

As an example of the flaw in this idea, look at the 56 and 58cm Cervelo R3. The advertised difference in reach is 9mm, but the difference in the TT length is 17mm. Both frames have the same STA, HTA and BB drop, so those dimensions do not affect the reach. The real difference in reach is 17mm, not 9mm, if the handlebars are set to the same height on each bike. When comparing frames, it's always assumed that a rider has a particular set of fit points that are not forced to change by differences in the frame. If a person bought the larger frame, assuming that he'd get rid of 25mm of spacers and only need one size shorter stem, he'd get a surprise.

The real problem with Cervelo's offerings is not enough sizes. They are using 6 sizes where at least 7 are needed.

I also have to laugh at the fact that Cervelo changed their geometry for 2011 to correct most of the complaints that I wrote about, back in 2006. I owned a 51cm (just long enough to ride it 200 miles). The HTA was too steep, the TT too short, and the chainstays too short. Now they have changed the geometry that they bragged about to about the same as other brands like LOOK.

http://www.cervelo.com/en_us/bikes/2011/R3/geometry/