Kind of like shoe size.

Not to mention that there isn't even a consistent way to measure a seat tube. Is it center-to-center, or center-to-top? Depending on seat lug design, there could by a few centimeters difference in the measurements of the same seat tube. Which means that even on frames with horizontal top tubes, seat tube length isn't always a good way to determine what the minimum/maximum stem height. But Stack will tell you the min/max stem height directly.

Stack and reach became a thing when I turned 56

it's what you do when that item you need at home depot isn't on the shelf where it should be, but you see a case of 'em 15' above you.

:p

Yeah stack and reach was a construct created by a bloke on Slow Twitch many moons ago. Cervelo were an early adopter and it seems to have caught on more broadly early 2010's.

You can basically take stack and reach as a good guide for whether a frame will fit - the only thing you need to take into account is the seat tube angle and whether or not you can get your saddle in the right position with respect to the bottom bracket.

With frames of 'comparable size', STA's tend to be within a range that allows you to adjust... but if you're slammed on the rails one way or another then it comes into focus.

The other point that has been noted is that as you increase stack, reach decreases. So if you have a frame that has the right reach but not enough stack and you plan to add spacers to increase the stack, then reach will need to be corrected for with a longer stem. Usually no big deal, but if you are already running a long stem then it may be a concern.

But yeah. As a rule of thumb. Very handy. Allows you to quickly ascertain if something might be a good fit, then you can drill down into the specifics.

As an example, my preferred Colnago size is 52s, which has comparable reach to a 50s and 54s (the three sizes are within a few mm). The 50s needs spacers, a longer stem and I go back on the saddle rails. And a 54s is possible, on paper, but I would need a straight post and likely be quite forward on the saddle rails.

Yep and folks thought people repping bigger tires/lower pressures where just talking smack as well... or electric shifting, or wider rims, or... you get the point.

Anything new will often feel like marketing BS, I'm certain disc brakes on Mtn Bikes were thought of that way as well many years ago... and sometimes it is just marketing BS, but it's often a great way to move forward with something that many are prepared to ride out the status quo with...

Is stack and reach the end all, be all? I wasn't that sold on it either, to be honest, but after reading the links posted above from Slow Twitch, pretty sure I'm sold...

just my .02 anyway, not to call you out specifically...

I'm pretty sure it was a sarcastic comment

I keep seeing folks mention stack and reach is a good metric, as long as the STA is correct...

Is there really that many production road, cross, or gravel bikes that have a whacked out STA for the given stack and reach? I mean I've been looking at frame geos a LOT lately and there doesn't seem to be much difference in STA at all, outside of .5-1 degree... and you do account for most STAs being in a good range above, I've just seen a lot of folks mentioning this...

I gotta assume a given stack and reach will have a suitable STA/HTA for the intent of the bike function... now if you'r talking custom, who knows...

could me and I totally missed it... :D

I retract my rant :banana:

One thing I’ve not seen mentioned in this thread is how much headset type affects this. With S&R we are measuring to the top center of the headtube and on top of this head tube we are placing a headset. A traditional press-in threadless headset will have an upper stack of about 18 mm (depends on brand and steerer diameter but 18 mm is a good rough number) so the headset will end and the stem spacers will start at about 18 mm above the head tube.

On the other hand the bike might use something like a King Inset headset. These have a stack of just 8 mm…so the spacers would start at just 8 mm above the head tube. This of course gives a full 10 mm of difference from where headset ends and the spacers start. Maybe that’s no big deal to some. It could mean that you can’t get the stem low enough or that you have too many spacers and this is with a frame that has the desired S&R. If headset isn’t factored in it can lead to frustration.

As a slight aside - Richard said some time back in this thread head tube length is overrated spec. Headtube length depends on so many different things as he mentioned (fork span, fork rake, head angle, BB drop…etc) and I’d add the above to that….if you don’t know the headset type the headtube length is even less relevant. On occasion I design a bike for a client and they ask about the head tube length and when I give it to them they are sure that the bike won’t fit because their existing bike fits just right and the head tube length is different. It’s a confusing moment to be sure when I tell them that the headtube length isn’t a “thing" and that we need to look at the relationship between the three contact points and not the all too many ways those dots can be connected.

Interesting as usual.

dave

A perfect example of what Dave is saying above can be seen in the numbers on this Parlee, if I understand Dave correctly (more headset, less reach)... the short, medium, tall is due to headset flex fit top cap I think.

https://www.theproscloset.com/produc...lee-chebacco-m

Ya agreed. It’s not a thing. Contact points are a thing.

Someone above mentioned “all this” was a way to ascertain if a frame will fit. Fit is only a part of the recipe. It (the design) has to work (deliver) too. The two ingredients don’t live in isolation.

Stack is normally measured to the top-center of the headset bearing. Even then, there's always more height added by the top bearing cover. Buyers just need to be aware of the stack reference point and what must be added, at the minimum.

My current Cinelli Superstar and previous 2017 Colnagoframes have the same top bearing as my old 2004 look KG461, but the 2004 frame was made before stack and reach were used. Same for my look 585 frames.

Understand what you're buying.

There is one class of bike that often does have out-of-whack seat tube angles - 700c bikes in very small sizes. It's fairly obvious that smaller people need smaller bikes, with a shorter reach. But wheel size limits how short the reach can be before there is too much toe overlap Sure, a certain amount of toe overlap can be tolerated, but there is actually a CPCS regulation on how close the wheel can be to the pedals, so there is a regulatory limit on how short the front center can be.

Many people see the top tube length as a gauge of the reach of a bike. So in order to produce small bikes with short top tubes, which therefore "sound" like they have short reaches, many bike makers would use exceptionally steep seat tube angles on their smallest size frames. With a steep seat tube, you can shorten the top tube, yet still maintain the required front center. It used to be not unusual to see in the geometry charts that the actual Reach dimension of some bikes stopped decreasing below a certain size, and the only reason the smaller sizes had shorter top tubes was because the seat tube angles would increase.


The problem of course is that a steep seat tube angle means that often a rider can't adjust their saddles to the proper set back, and even if they could get the saddle far enough back, that would effectively increase the reach to the handlebar. With the Stack and Reach system, the Reach dimension is decoupled from the seat tube angle. This makes it harder for bike makers to "cheat", and make it seem like their frames are smaller than they really are.