Headtube length vs. Saddle to bar drop (Dave Kirk's take)

[firerescuefin]

The linked post is in another part of the forum....but thought that many would not come across it. I subscribe to Dave's Facebook feed or I would have missed it as well. As most things DK, really well thought through.

Enjoy.


http://forums.thepaceline.net/showpost.php?p=1781559&postcount=433

[Chris]

It's a good post and the point is taken, however, when comparing apples to apples (one race bike to another with similar bb drop) the headtube length does enter in to the picture in terms of aesthetics, if not bar drop. The fact that Trek offers two headtube lengths as does others like Parlee, speaks to this. I'm long-legged with a shorter torso. When looking at off the shelf bikes, headtube length is an issue for me simply because I don't want a stack of spacers underneath my stem.

[jtakeda]

Hmmm.

I'm the same as you, long legs, short torso.

I think a better measurement is saddle height/ how much exposed post to figure out bar drop.

Most people don't have bb drop on hand. I think daves post was more referring to custom frames.

[Chris]

No doubt, but that doesn't mean that headtube length is never relevant. When I had my Speedvagen built, Sacha and I talked about ht length because of my preference for aesthetics.

[firerescuefin]

Hmmm.

I'm the same as you, long legs, short torso.

I think a better measurement is saddle height/ how much exposed post to figure out bar drop.

Most people don't have bb drop on hand. I think daves post was more referring to custom frames.

Increasingly, people look at the measurement in isolation...which is a mistake. This is still the case with stock offerings. Certainly not isolated to the custom frame market.

[firerescuefin]

No doubt, but that doesn't mean that headtube length is never relevant. When I had my Speedvagen built, Sacha and I talked about ht length because of my preference for aesthetics.

It's a piece of the puzzle. I don't think anyone would ever say irrelevant. That was certainly not the jist of the post.

[jtakeda]

Increasingly, people look at the measurement in isolation...which is a mistake. This is still the case with stock offerings. Certainly not isolated to the custom frame market.

You're probably right.

I've never actually bought a new frame so my thoughts on the whole topic are totally skewed.

[Chris]

It's a piece of the puzzle. I don't think anyone would ever say irrelevant. That was certainly not the jist of the post.

No. I didn't take it that way. I wouldn't accuse you or Dave of thinking that.

[oliver1850]

Dave has touched on the topic several times, but that's a nice explanation of the factors involved. I do agree that when comparing similar type frames, it's nice to know the HT length. It's just one factor to consider, but important as they can vary quite a bit. I have a KHS 853 frame that's conventional in every other way, but it has a very short HT compared to other racy frames of similar vintage. I took a quick look at bikes I ride that I knew were at the extremes of the range in terms of HT length. Longest was a custom Waterford at 225 mm. Shortest was a tie between a 1990s custom SLX race frame and a Soma Double Cross at 135 mm. I'm sure they don't all have the same drop, but I can ride them all comfortably - did a solo Century on the Soma last week. What would be interesting to me is to find out if my performance was better with more or less drop. Don't know how to sort that out without some wind tunnel time.

[fogrider]

As some of us get older, we need to raise the handlebars (or the neck and arm pain is unbearable). A taller headtube helps raise the bar, with a level TT, a bunch of spacers or a long space is needed, but if too long, the steerer tube starts to flex. see the two bikes here: https://www.flickr.com/cameraroll

but a sloping toptube and longer headtube could be the solution.

[MattTuck]

Hmmm.

I'm the same as you, long legs, short torso.

I think a better measurement is saddle height/ how much exposed post to figure out bar drop.

Most people don't have bb drop on hand. I think daves post was more referring to custom frames.

Out of curiosity, is there some resource that helps one determine this?

I have all my measurements, but have no idea if my legs are longer than average, because I don't know what the average leg length is for my height.

Is there some central source of distribution data for some of these measures?

[kramnnim]

I concluded that I have short legs and a long torso based on how I'm comfortable with a low saddle height compared to my preferred top tube+stem length... I think there was a thread here where everyone posted saddle height and body height...

Anyway, I have to look at head tube lengths because of my odd proportions as a lot of frames with my top tube length will not allow me to get the bars low enough due to the HT length. (unless I go with a -17 stem)

I did wrongly assume that the R5 I recently bought would allow me to get a bit lower, based on HT length, but for some reason it uses a fork with a longer axle to crown than what seems normal/common.

[jmoore]

This exact reason is why you go custom with a guy like Dave, et al.


It's always kind of puzzling to hear about guys getting custom frames built but then telling the builder what kind of tubing to use and what BB drop they want, etc. Isn't that what you pay the builder for? To make those decisions.

[soulspinner]

Stack and reach are stack and reach. Ive seen fork spans listed on bikes for the road with 365 to 400 plus milimeters............that difference alone is the limit of spacers on some carbon forks. YMMV

[nooneline]

It's a good post and the point is taken, however, when comparing apples to apples (one race bike to another with similar bb drop) the headtube length does enter in to the picture in terms of aesthetics, if not bar drop. The fact that Trek offers two headtube lengths as does others like Parlee, speaks to this. I'm long-legged with a shorter torso. When looking at off the shelf bikes, headtube length is an issue for me simply because I don't want a stack of spacers underneath my stem.

I hear ya.

Me, I need to know that small bikes are truly small enough for me to get low - I've made the mistake in the past and I do not want to repeat it. If I'm looking at race bikes, I know certain of the variables that Dave mentions are likely not there - major differences in BB drop and fork length. If I'm looking at a race bike I know I'm looking for about a 120mm headtube length or less.

But it's one measurement that can tell me if I'm getting close.

The real measurements that matter are stack and reach, because the eliminate the noise of other variables mucking up your measurements.

Stack and reach are stack and reach. Ive seen fork spans listed on bikes for the road with 365 to 400 plus milimeters............that difference alone is the limit of spacers on some carbon forks. YMMV

stack and reach! stack and reach!
bike comparisons got a lot easier when i started looking at all my bikes in terms of stack and reach.

[bobswire]

That measurement is constant for my road bikes regardless of head tube or type of stem, quill or threadless.
http://i60.tinypic.com/wqrq82.jpg

[jzisk]

Isn't that the fundamental? That a taller head tube lessens how aggressive the drop can be made?

[guido]

Dave takes great liberty with the fork length/tire/brake clearance issue. I just don't find that very realistic. Very few folks looking for a bike these days will be comparing bikes with such a wide range of tire/brake clearances. Tire size requirement is pretty much criteria #4 after stack, reach and saddle-bar drop.

[thirdgenbird]

Dave takes great liberty with the fork length/tire/brake clearance issue. I just don't find that very realistic. Very few folks looking for a bike these days will be comparing bikes with such a wide range of tire/brake clearances. Tire size requirement is pretty much criteria #4 after stack, reach and saddle-bar drop.

I disagree. Multiple bike households often are a result of bikes with a wide range of uses/design. If you own a road bike and are shopping for a touring bike, it only makes sense to look at your existing bike as a starting point for fit.

Tire clearance also seems to be the #1 question asked in the classifieds here.

[guido]

I disagree. Multiple bike households often are a result of bikes with a wide range of uses/design. If you own a road bike and are shopping for a touring bike, it only makes sense to look at your existing bike as a starting point for fit.

Tire clearance also seems to be the #1 question asked in the classifieds here.

Hmmm... I guess I wasn't clear then. That was the point I was trying to make.

Tire size fit is fundamental to "does this bike do the things I want the bike to do".

But if stack/reach/seat-bar drop (or seat tube/top tube if you prefer) don't fit at all then it doesn't matter the type of bike or the tires it will take...

For me, at 6'1" with long arms, there are lots of bikes in the classifieds that have the correct tire clearance but at their tiny 56cm size the only place I could ride it would be the circus. Doesn't matter how great the frame is, just ain't going to work. The stack/reach/seat-bar drop of the 56cm will never match what i know works from experience/current bikes/etc. which is the real starting point.

[Mikej]

Thankfully I only care about how a bike looks- this is all too much work...

[soulspinner]

Thankfully I only care about how a bike looks- this is all too much work...

:p

[benb]

Dave's example is a great example why you need to go talk to someone like him with stack & reach #s in hand and not get worked up over the head tube length.

Say you already have a race bike that fits you well.

Now you want a Gravel bike.

If you go to him and demand the same head tube length that doesn't make any sense as it would restrict him in his ability to shape the rest of the bike correctly.

You tell him your desired saddle height, setback, stack, and reach and he'll figure the right geometry out from there.

I do wish there was some standardization in measuring saddle height. His BikeCAD examples show a bike with a zero-setback seatpost. In that case it seems to make sense to measure the seat height from the BB through the seat tube and through the clamp. But that measurement cannot be taken from bike to bike as the STA and setback on the post change.

The problem is you'd need something like the old Serotta XY tool ($$$ IIRC) to correctly measure the X & Y distance from the BB to the saddle in a way that could be transparently moved from frame to frame. Stack & Reach don't have this issue of course which is why they are such an improvement.

I seem to have been taught to measure from the BB through the center of the saddle clamp.. works fine with similar Seat Tube angles. For setback I use a plumb bob & ruler. I suppose I should be measuring seat height through the front of the saddle. That would be uniform from bike to bike assuming the same saddle.

[11.4]

I've bought custom frames for many years and there's certainly been a transition that those builders with more history are definitely seeing. I remember an Eisentraut and a Melton that barely had clearance for 21 mm tires, had steel forks (hence not a consistent axle to crown height as on carbon forks), and on the Eisentraut a really high Californian crit bottom bracket. And people really just bought road bikes back then, so they were all pretty much the same for a given rider -- cross wasn't a big thing and nobody got custom gravel bikes.

Today I might have a road bike, a crit bike, a cross bike, and maybe even a gravel bike. Plus the track bike, of course. Tire sizes, whether the bike has discs or rim calipers, and general geometry all invoke decisions are more complex and varied than in the past. If I'm trying to build a disc gravel frame with the same body position as my road bike, I have to add space for tires, potentially allow for a taller fork, and so on. In a small frame it gets a little more complicated, because one runs out of head tube (even more so with a tapered steer for which the head tube has to be longer than the tapered section) and clearance under the down tube. So the longer fork shortens the head tube to an excessive degree, plus I have to raise the bottom bracket to keep larger tire clearance under the down tube. I end up with a 3-4 cm bottom bracket drop and a 8-9 cm head tube, unless I will compromise on clearances or lengthen the wheelbase to handle the tire clearance issues. It's basic geometry on a small frame -- there's no escaping it. Which means to get a frame with good handling yet to have the drop and reach I need, I can't quite have the tire clearances. And I end up with a proportionately longer wheelbase than a taller rider would (proportionately) have. Thankfully cross is now limited to 33 mm tires, but I can't exactly use 40+ mm gravel tires that are so popular right now and expect my frame design to work well. Needless to say, on a small frame, I've already given up toe clip clearance (excuse me, shoe to front tire clearance -- I've been at this too long). I'm only talking a 50 cm or so frame, and I don't want to have to supply my own 650C tires at every race, so my builder has to design a frame around the same 700C wheels that a 6' rider would use. Unless I missed something, bike geometry didn't somehow morph to accommodate bigger tires on a small frame. The same concessions have to be made, only to a greater degree because tires are bigger. Oh yeah, and frame tubing diameters have gotten bigger as well.

I of course don't specify a head tube length without asking about other dimensions as well, and with sloping top tubes a head tube length can be pretty meaningless anyway. But I do know that even if I'm switching from a road to a gravel bike, and from short-reach rim calipers to discs, and from 25 mm road tires to 40 mm gravel tires, I'm recalculating the same relative positions of the saddle, bars, and pedals to keep the same riding position.

In short, I'm sure Dave gets lots of people who ask a simplistic question about head tube length. Especially with a small frame one can't think that way. I think some of what's being discussed here is really how people are rethinking frame design from having a consistent fork length and fairly consistent bottom bracket height to having taller forks, different tire clearances, and different bottom bracket heights. It's a learning process. Those who read this forum, or across the hall, probably have a fairly decent awareness of the issues already -- or become aware quickly as they research their next frame. I've watched fitters in good LBS's that have no idea even though they sell custom frames and charge $250-400 for a basic bike fit (not for a bike geometry, just a positional fit). I don't think one can solely consider stack and reach because those may match one's position but don't guarantee one will have a bike with good handling. Being smart while buying a custom frame is a matter of either becoming well informed, or having a builder you really trust to be informed on your behalf. Either is fine as long as you get the result you want.

[pff]

isn't this dilemma the reason why they invented the reach/stack measurements?

[stephenmarklay]

Good read -Thanks.

[weisan]

Head tube length should not be considered in isolation of other measurements.

If I do see a certain head tube number popped up, I will think to myself..."hmmm, that's interesting, let's take a closer look. "

And that's all it does.

[Anarchist]

isn't this dilemma the reason why they invented the reach/stack measurements?

"Stack" and "reach" we're dreamt up by the clowns at Cervelo to try and prove that their one size fits all, every bike should have same angles, crappy frames could and would fit everyone just fine.

[rnhood]

Pretty informative post by 11.4. I never really thought about fit from a small man's point of view, but it certainly doesn't appear to be a case of proportionally making the bike smaller in most respects. Sounds far more challenging. For most people though, component selections can go a long way in making the fit suitable. But not for everyone.

[Mark McM]

"Stack" and "reach" we're dreamt up by the clowns at Cervelo to try and prove that their one size fits all, every bike should have same angles, crappy frames could and would fit everyone just fine.

Stack & Reach were in developed and in use for a few years before Cervelo adopted it. With the advent of sloping top tube "compact" geometry bikes in the 1990s, plus some of the extreme seat tube angles being used on some triathlon bikes, standard bike measurement systems became inapplicable for describing the sizing of many frames. Stack & Reach was developed as a uniform method to describe the ultimate frame "fit" size from a fixed reference point. It may not be perfect, but Stack & Reach is the best standard frame sizing system.

[11.4]

One point I was trying to convey with regards to custom frames is that correct stack and reach don't make a good frame. They define two dimensions of a box, but the handling and other fit dimensions can still be really wonky. We've all seen custom bike geometries that looked bad, fit bad, and rode bad, even if they had the right reach and drop. In a stock frame one trusts that the manufacturer builds around a solid geometry, and usually they do. When doing a custom frame, there's a big opportunity to really mess with the frame in pursuit of either a head tube length or a stack/reach equation. A builder like Dave Kirk can protect the integrity of the design by upholding handling and fit standards in his frames. We've seen bikes where that discretion isn't applied.

[weisan]

A builder like Dave Kirk can protect the integrity of the design by upholding handling and fit standards in his frames. We've seen bikes where that discretion isn't applied.

This is a HUGE endorsement coming from 22.8/2, not that Dave pal needs more.

[ergott]

I like using stack and reach with frames I'm confident are well designed.

That said, I recently purchased a copy of BikeCAD. It's great to study the designs of different frames. I've started out getting my bike in there with the current setup. Then I see how a bike like a Specialized Tarmac would fit and see the differences. After looking a few stock bikes that are known to handle well it's nice to see what they have in common.

[Mark McM]

One point I was trying to convey with regards to custom frames is that correct stack and reach don't make a good frame. They define two dimensions of a box, but the handling and other fit dimensions can still be really wonky. We've all seen custom bike geometries that looked bad, fit bad, and rode bad, even if they had the right reach and drop. In a stock frame one trusts that the manufacturer builds around a solid geometry, and usually they do. When doing a custom frame, there's a big opportunity to really mess with the frame in pursuit of either a head tube length or a stack/reach equation. A builder like Dave Kirk can protect the integrity of the design by upholding handling and fit standards in his frames. We've seen bikes where that discretion isn't applied.

Agreed with the above. Stack & Reach weren't really intended to be the only factors for custom (or even stock) frames. It is primarily intended to be used for stock frames, and then as a first pass filter to identify the models/sizes from the vast range of available frames that might work. After the field has been narrowed down by this first pass, other frame design dimensions/features can be examined to narrow down the list further. As you say, Stack & Reach can say a lot about the potential for fit, but it says little about riding characteristics.

In the old days, frames were labeled by seat tube length. But that certainly didn't mean that every 56 cm frame fit the same as every other one. Now with sloping top tube frames, it doesn't make any sense to label frame size by seat tube length, so some other system must be used. Stack & Reach has replaced sizing by seat tube length to describe the vertical dimension of a frame, and it goes one step further by including the horizontal reach dimension, making it more precise than seat tube size alone was in the old days.

For me, Stack & Reach is just a starting point for fit. Due to my relative thigh/shin ratio, I prefer riding with a longer saddle setback than many people my size, which means that its best if my frame has a slacker seat tube angle than most frames my size. So after starting with Stack & Reach, I next look at seat tube angle. Other riders may need to filter by other criteria instead. But Stack & Reach is the best place to start, because if Stack & Reach aren't appropriate, it doesn't matter what the other dimensions are.