When did stack & reach become a thing?

[BdaGhisallo]

Originally Posted by Mark McM

I don't understand the objections to Stack and Reach. It's just a different way to measure the same thing. If you take a given frame, and measure its size by Stack and Reach, or by Seat Tube and Top Tube, its the same size, just using different dimensions.

In a way, Stack and Reach vs. Seat Tube and Top Tube is like Metric units vs English Units.. If you have a piece of string that measures 1' 3" or 371 mm, it is the same length. The difference here is that metric units are easier to work with, because everything is decimal based. With English units, you have to use different conversions, say from inches to feet or feet to miles. So too, the Stack and Reach system requires fewer conversions. Since bike fitting nearly always starts the origin of the Bottom Bracket, the Stack and Reach system measures the position of the top of the head tube directly from the bottom tube, and not through the circuitous route up and back along the seat tube (and possibly to virtual location beyond he top of the seat tube for sloping frames), and then forward again to the head tube.

I'm used to dealing with both English and Metric measurements, and can go back and forth between them (although working with the Metric system is easier and has lots of advantages). Similarly, I can deal with Stack and Reach and with Seat Tube and Top Tube, although Stack and Reach is easier and has lots of advantages). Which makes me wonder whether those who think Stack and Reach are fundamentally different measurements really understand how to measure a frame at all.

Isn't the point of stack and reach that it provides an independent measure to get away from a lack of clarity over what seat tube length and top tube length actually mean for the size of the frame forward of the bottom bracket?

Two frames - both with 55cm seat and top tubes - will be very different if one has a 74 STA and the other a 72 STA, and their individual stack and reach numbers will reveal that.

Or am I missing what you're trying to say?

[fourflys]

Originally Posted by BdaGhisallo

Two frames - both with 55cm seat and top tubes - will be very different if one has a 74 STA and the other a 72 STA, and their individual stack and reach numbers will reveal that.

Or am I missing what you're trying to say?

I don't think so... stack and reach alone doesn't reveal anything about STA since it's a number relative to the BB and most (all?) STAs have an angle that puts the top of the seat tube behind the BB. In your example, the HTA would have to be pretty different on the two frames for both to have the same, 55cm, tt length if I understand it right... which would affect stack and reach I guess in a way... but I think one of those would have a pretty whacked out HTA...

What the poster is saying (I think) is some folks will have a difficult time getting the proper seat set-back on the 74 STA while others may have the same issue on the 72 STA, regardless if both folks require the same stack and reach... at least that's how I interpret it...

My take is that most folks looking for a bike that knows the general stack and reach they need will be within the margin of error for that stack and reach/STA relationship on that frame...

Certainly we have folks out there with "odd" measurements (I have a long torso, short arms/legs for example), but I bet most folks can fit using different seatpost set-backs, saddle rails, etc...

[Dave]

Two frames can easily have the same TT length and 72 or 74 degree STA. The head tube has nothing to do with those dimensions. Using the 55cm example, the seat tube setback would be 15.2cm for the 74 degree STA and 17cm for the 72 degree frame. Since reach is the length ahead of the BB center line, the reach on the 74 degree frame would be 1.8cm longer than the 72 degree frame. Using reach values, the fit difference would immediately be obvious.

Using reach does not eliminate the importance of the STA. I know what amount of seatpost setback I need for just about any STA. My saddle rail height is about 67cm. With a 72 degree STA, the setback is 67cm times cosine 72 or 20.7cm. With a 74 STA, the setback would be 18.5cm. The difference is 2.2cm or 22mm so I'd use a zero setback post for the 72 degree frame and a 25mm setback post on the 74 degree frame. My frame has a 74.5 degree STA, so I use a 32mm setback post to give the best centering of the saddle on the post.

[Mark McM]

Originally Posted by BdaGhisallo

Isn't the point of stack and reach that it provides an independent measure to get away from a lack of clarity over what seat tube length and top tube length actually mean for the size of the frame forward of the bottom bracket?

Two frames - both with 55cm seat and top tubes - will be very different if one has a 74 STA and the other a 72 STA, and their individual stack and reach numbers will reveal that.

Or am I missing what you're trying to say?

That's pretty much true. On the other side of the coin, you could have two frames with the same Stack and Reach, but different seat tube angles and top tubes. If you adjusted the saddle to have the same height and set back, they would fit the same.

Another thing to keep in mind is that achieving the desired contact points is not the same as fitting a bicycle. You could take a small frame and use an extra long seatpost and extra long and tall stem and achieve the correct contact points for a large rider, but the bike won't handle well.

Fitting a rider for proper handling requires locating the wheel contact points and steering axis at the right locations relative to the rider contact points. And the starting point for that is putting the top of the head tube at the right point, because the top of the head tube will determine the height and length of the steering "tiller" (stem and handlebars), and also plays a large role in the locations of the steering axis and the front wheel contact point. The location of the saddle is also important, but there is far more adjustability to setting the saddle position - you move the saddle up and down and forward and back, but you can't adjust the location of the steering axis or wheel contact points. The rider's contact points are measured relative to the bottom bracket, so shouldn't the oh so important point at the top of the head tube also be measured from the bottom bracket? Stack and Reach do exactly that.

[fourflys]

** Yes, I see now how the steeper STA angle would push the same 55cm top tube further forward (which would require a steeper HTA, no?)... I guess I was thinking that, in reality, a bike with a STA of 74 or 72 degrees would not have the same TT length assuming there was a complimentary (acceptable) HTA...

Dave,
Maybe we are thinking of reach from two different definitions... When I think of stack and reach on the context of this thread (new way to determine size), I think of the picture below as that's the stack and reach measurements in geo charts... in this picture, I don't see how STA could have anything to do with reach as discussed... now a steeper HTA would certainly lengthen the reach or a taller HT extension would shorten it... what am I missing? (and I could certainly be missing something here).

[tommyrod74]

Originally Posted by fourflys

** Yes, I see now how the steeper STA angle would push the same 55cm top tube further forward (which would require a steeper HTA, no?)... I guess I was thinking that, in reality, a bike with a STA of 74 or 72 degrees would not have the same TT length assuming there was a complimentary (acceptable) HTA...

Dave,
Maybe we are thinking of reach from two different definitions... When I think of stack and reach on the context of this thread (new way to determine size), I think of the picture below as that's the stack and reach measurements in geo charts... in this picture, I don't see how STA could have anything to do with reach as discussed... now a steeper HTA would certainly lengthen the reach or a taller HT extension would shorten it... what am I missing? (and I could certainly be missing something here).

If you want to make understanding Stack and Reach as simple as it can be, think of it this way: it’s simply a way to take seat tube angle out of the equation, by always using 90° as the effective seat tube angle. Done.

[fourflys]

Originally Posted by tommyrod74

If you want to make understanding Stack and Reach as simple as it can be, think of it this way: it’s simply a way to take seat tube angle out of the equation, by always using 90° as the effective seat tube angle. Done.

Totally agree! That's why I said my thoughts are most of us humans will be able to fit any bike with "normal" geos if we know the stack and reach works for us as I trust the designers have built in the proper STA relative to the other numbers...

[Mark McM]

Originally Posted by Dave

Using reach does not eliminate the importance of the STA. I know what amount of seatpost setback I need for just about any STA. My saddle rail height is about 67cm. With a 72 degree STA, the setback is 67cm times cosine 72 or 20.7cm. With a 74 STA, the setback would be 18.5cm. The difference is 2.2cm or 22mm so I'd use a zero setback post for the 72 degree frame and a 25mm setback post on the 74 degree frame. My frame has a 74.5 degree STA, so I use a 32mm setback post to give the best centering of the saddle on the post.

Your argument actually shows that STA is far less important than frame reach. As you show in your example, you can achieve the same saddle setback with a variety of different seat tube angles, by using a different seat post. This is exactly why seatposts are interchangeable and available in a variety of different setbacks. In contrast, you can't adjust the Reach dimension (horizontal distance from BB to head tube) of the frame. So getting the correct Reach dimension of the bike is of utmost importance, and from there you just select a seatpost with the necessary setback.

From your example, you could have two frames with the same Reach, but one has a 72 degree STA and the other has a 74 degree STA. These frames might have a difference in top tube length of 2cm. After adjusting the saddle setback to the same position (which might require different seatposts), the bikes will fit and handle the same. But what if you had 2 frames with the same STA but one had a top tube 2cm longer than the other? You could use different length stems to achieve the same fit, but the two frames would never handle the same, due to differences in the lengths of the stem and front center.

So, the primary dimensions for proper frame fit are Stack and Reach, and STA is just a secondary consideration.

[Dave]

[QUOTE=fourflys;3015388]** Yes, I see now how the steeper STA angle would push the same 55cm top tube further forward (which would require a steeper HTA, no?)... I guess I was thinking that, in reality, a bike with a STA of 74 or 72 degrees would not have the same TT length assuming there was a complimentary (acceptable) HTA...

Dave,
Maybe we are thinking of reach from two different definitions... When I think of stack and reach on the context of this thread (new way to determine size), I think of the picture below as that's the stack and reach measurements in geo charts... in this picture, I don't see how STA could have anything to do with reach as discussed... now a steeper HTA would certainly lengthen the reach or a taller HT extension would shorten it... what am I missing? (and I could certainly be missing something here). [QUOTE]

The HTA is not part of the fit, period. Reach and stack have one definition. One brand can have the same reach and stack as another, but significantly different HTA, fork offset and trail. Compare a Cinelli superstar to a specialized atheos. They have both models with nearly identical reach, but the Cinelli will have a slack HTA and more trail. STA is also about the same.

[fourflys]

Originally Posted by Dave

The HTA is not part of the fit, period. Reach and stack have one definition. One brand can have the same reach and stack as another, but significantly different HTA, fork offset and trail. Compare a Cinelli superstar to a specialized atheos. They have both models with nearly identical reach, but the Cinelli will have a slack HTA and more trail. STA is also about the same.

** maybe what I'm trying to say is a taller stack will effectively shorten reach... while HTA doesn't change much, it does rotate on an axis, which would move the top or bottom further away or closer... (thus requiring a different TT length assuming a constant STA) obviously, that would affect trail, etc...

again, this is why stack and reach are useful metrics for the average person IMHO... assuming the other numbers are not whacked out, you should know if you can get a fit you like...

[e-RICHIE]

Originally Posted by fourflys

Yeah, not so sure on all that... While I agree HTA by itself is not a definitive fit paramter, are you telling me a steeper HTA would NOT result in a longer reach when the STA remains constant? (imagine the center of the head tube on an axis, you rotate it and the top and bottom gets farther or closer) If the TT length (either literal or effective) is measured from the middle of the seat tube (either c-c or c-t) to the headtube (either c-c or c-t), you would HAVE to have a longer TT with the same STA... now, does BB drop, trail, etc come into play? for sure... but the TT runs from the seat tube to the head tube if I'm not mistaken... so if you start out with parallel STA/HTA for a given TT length and then change the HTA for some reason, the tt length must change... right? At least that's what makes sense in my mind...

again, this is why stack and reach are useful metrics for the average person IMHO... assuming the other numbers are whacked out, you should know if you can get a fit you like...

We’ve had these same conversations 15-20 years ago here.

Yes, if all dims are constant (sic) and the head tube angle increases, reach will be lengthened.

I’m agreeing with your reply.

[tuscanyswe]

Originally Posted by fourflys

Totally agree! That's why I said my thoughts are most of us humans will be able to fit any bike with "normal" geos if we know the stack and reach works for us as I trust the designers have built in the proper STA relative to the other numbers...

That would hold true for toptube measurement and headtube length as well. Well for most things that usually are in relation to each other i guess .)

[jimoots]

Originally Posted by Mark McM

Your argument actually shows that STA is far less important than frame reach. As you show in your example, you can achieve the same saddle setback with a variety of different seat tube angles, by using a different seat post. This is exactly why seatposts are interchangeable and available in a variety of different setbacks. In contrast, you can't adjust the Reach dimension (horizontal distance from BB to head tube) of the frame. So getting the correct Reach dimension of the bike is of utmost importance, and from there you just select a seatpost with the necessary setback.

From your example, you could have two frames with the same Reach, but one has a 72 degree STA and the other has a 74 degree STA. These frames might have a difference in top tube length of 2cm. After adjusting the saddle setback to the same position (which might require different seatposts), the bikes will fit and handle the same. But what if you had 2 frames with the same STA but one had a top tube 2cm longer than the other? You could use different length stems to achieve the same fit, but the two frames would never handle the same, due to differences in the lengths of the stem and front center.

So, the primary dimensions for proper frame fit are Stack and Reach, and STA is just a secondary consideration.

100%.

And if we are talking frames of a similar 'size' (i.e. the S/M/L 52/54/56 measurement), the STA's are usually within 0.5-1 degree, which is tends to be easily handled by moving the saddle on the rails to get the same saddle to BB relationship. Worst case you can change the post as required.

So for the vast majority of people they are comparing frames of similar size between manufacturers - stack and reach does a great job of summarising the size chart.

I just don't get the cynicism.

[dolface]

Originally Posted by jimmy-moots

100%.
...

I just don't get the cynicism.

Seconded. If you don't like/understand stack and reach go with ST/TT, no biggie.

To paraphrase a joke from the MTB world when 29" wheels came out: "Pick a measuring system and be a dick about it"*

*not that anyone has been particularly rude here**

**Original joke/line: Pick a wheel size and be a dick about about it (attribution unknown).

[jimoots]

Originally Posted by dolface

Seconded. If you don't like/understand stack and reach go with ST/TT, no biggie.

But then also pay attention to the STA, HT length, BB drop, HTA, fork length and fork rake.

Which is surely way more confusing than looking at stack/reach and considering STA hahahahhaa

Hence my confusion about being cynical about stack/reach