Relationship between reach and stack?- Mtbr.com

# Thread: Relationship between reach and stack?

1. ## Relationship between reach and stack?

I've heard people discussing how stack relates to reach, but never heard an explanation. When people say reach is connected to stack, what exactly do they mean? When I think about that, it seems like a lower stack would pull you forward more, therefore feeling like a longer reach, whereas a higher stack would do the opposite, feeling like a shorter reach. Is that accurate or am I off track? Does that mean that a bike with the same reach but higher stack will feel shorter and vice versa?

2. Reach is X and stack is Y in Cartesian coordinates. It can't get much simpler than that.

3. Originally Posted by Lone Rager
Reach is X and stack is Y in Cartesian coordinates. It can't get much simpler than that.
I understand that, but Cartesian coordinates don't answer the decreased or increased reach question.

4. stack and reach just give you a point in space, in referanceto you're frame or where you start, assuming your seat.
You can't change the stack or the reach if yu are talking about the frame, which people often are. If you know what works for you, then it makes looking at frame geo easier to match what you like.
But then there is stack and reach of your bars, this you can change. As mentioned above it's all to do wit geometry (not geometry of the frame) or s it trigiometry, whatever.
Because your headtube is at an angle, putting spacers or a higher rise stem, not only raises the bars (stack) it also due to the angle brings them back closer to you (reach). Putting a longer stem on increase the reach, but also increases the stack (assuming positive angle stem)... going shorter does the opposite.

or some crap like that.

5. I think I get what you're asking.

I've come to think that the thing that matters the most is the position of my torso. Whether my hands move further away or down with respect to the saddle, I'm going to have to lean forward more. So yeah, you can make fine adjustments to how roomy your cockpit feels and how your bike balances by moving your stem up or down.

I do think there are some independent effects of reach and stack as well. Too long a reach feels crappy rolling off rocks and things, even if I'm using a high stack. Too tall a stack feels really weird when I'm really putting out the power on a smooth surface, like the road.

Basically, think of your torso in your preferred riding position and your arms comfortably bent. You can swing your arms through an arc and your hands will trace a bunch of positions where your handlebars can be. But since most of us do put a little weight on our hands when we ride and ride from a few different positions, the number of good places for one's handlebars is a lot smaller.

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6. They are related but I don't think you can effectively substitute one for the other. You have to dial each to fit you personally.

Fwiw, a higher stack with a given reach, means a longer bike because of the HTA.

7. Stack height hasn't been much of an issue until long travel 29ers came about. If you're like me and have short legs, you'll struggle with bikes that have a high stack height.

8. OP, as said Reach and Stack are idependant, as long as you run your stem slammed right ontop of the headset or the same number of spacers below it/rise stem/rise bar, but once you start messing with spacers under the stem, stem/bar rise then you can start altering the effective Reach. Effectively if you add spacers under your stem because your frames Stack is too low for you, you then effectively shorten the Reach because the HA is sloping backwards and therefor moving your ste/bar combo anywhere up, also effectively moves it back.
So say you were looking at 2 "identical" geo frames Reach wise, but one had a lower stack, but you needed the higher stack, then you would need to add spacers under your stem and/or a rise stem and/or bar on the lower stack frame, which would then have lesser reach thereby making them not really equal geo wise for you, only someone who would run the bar in the same place on either.

9. Originally Posted by 06HokieMTB
Stack height hasn't been much of an issue until long travel 29ers came about. If you're like me and have short legs, you'll struggle with bikes that have a high stack height.
I think a lot of people struggled to get their handlebars high enough in the past. Now too, though I think it's less bad.

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10. At 5'9.5" and a short inseam too much stack and not enough reach is a big issue when it comes to choosing a bike. In my next bike I want at least 450mm reach and 605mm or less stack. 450mm or less seat tube so I can fit a decent dropper as well. I general I still think reach is too short, stack too high, and seat tubes too long on a majority of frames. Tall riders are going to have other fit issues.

11. I tend to think of the upper body in terms of the triangle formed by the handlebar/seat/shoulders. The bottom side of the triangle is tilted at some angle (hands higher or lower than the seat). While reach and stack are related, they're really issues that should be considered separately (i.e. figure out how stretched out you need to be and then how upright you would like to be). You can compensate for stack and reach with a little trig and a stem (within limits). What works best is almost entirely individual to you and your style of riding.

12. Originally Posted by LyNx
OP, as said Reach and Stack are idependant, as long as you run your stem slammed right ontop of the headset or the same number of spacers below it/rise stem/rise bar, but once you start messing with spacers under the stem, stem/bar rise then you can start altering the effective Reach. Effectively if you add spacers under your stem because your frames Stack is too low for you, you then effectively shorten the Reach because the HA is sloping backwards and therefor moving your ste/bar combo anywhere up, also effectively moves it back.
So say you were looking at 2 "identical" geo frames Reach wise, but one had a lower stack, but you needed the higher stack, then you would need to add spacers under your stem and/or a rise stem and/or bar on the lower stack frame, which would then have lesser reach thereby making them not really equal geo wise for you, only someone who would run the bar in the same place on either.
Finally, someone who gets it!

To put it another way, here's why stack is not the same as adding or subtracting spacers under a stem:

Adding stack to a frame's geometry moves the front end directly upward, but spacers move along the steerer, which isn't vertical - it's on the axis of the head-tube angle. If you have a 66° head-tube angle, for example, raising the stem 10 mm will also shorten the reach by 4.1 mm.

As LyNx said, a frame with a "long" reach with a low stack is a lot shorter than you think, while a frame with a modest reach and a towering stack is probably a very long bike.

13. Originally Posted by AndrwSwitch
I think a lot of people struggled to get their handlebars high enough in the past. Now too, though I think it's less bad.

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As a tall guy with long arms it can still be a struggle. For reference, I'm running my bars on my Hightower about a 1/4" from fully slammed but I would like to go higher. The problem is that's what feels comfortable from a reach perspective.

There's another thread where bar width is being discussed to help with the feeling but for those with long arms and really wide shoulders that does less to eat up some reach than one might think.

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14. Originally Posted by R-M-R
As LyNx said, a frame with a "long" reach with a low stack is a lot shorter than you think, while a frame with a modest reach and a towering stack is probably a very long bike.
ins't it the opposite? as you increase the stack you shorten the reach?

15. Originally Posted by mik_git
ins't it the opposite? as you increase the stack you shorten the reach?
I think he's referring to the overall bike but not sure.

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16. Originally Posted by mik_git
ins't it the opposite? as you increase the stack you shorten the reach?
Nope. If you increase handlebar height with spacers, you shorten the reach to the bar, but if we're looking at frame dimensions, a larger stack with the same reach (and HT°) gives a longer front-centre.

Here's a way to picture it: Imagine a bike with a generous reach number, but zero stack (the head-tube is level with the BB). Impossible, I know, but it's a thought exercise. Long reach, therefore big bike, right? Well, once you add a couple feet of spacers along the 65° head angle, the bar is in your lap. It also means the front-centre is essentially equal to the "long" reach, which makes the front half of the bike just over half as long as normal.

Reach alone doesn't make a big bike, you also need generous stack! This is the main reason why a 29er with modest frame reach numbers and high frame stack usually feels larger than the reach would suggest - because it is!

17. ah yeah, I see what you're saying, thought you meant if you had the reach, then added the stack to the frame (essentially the same as adding spacers).. so yeah I was thinking backwards r maybe sideways.

18. Originally Posted by mik_git
[...] then added the stack to the frame (essentially the same as adding spacers) [...]
I think we're on the same page now, but just to be sure, adding stack to the frame means - to me - a frame designer modifying a design to have higher stack. This is different from adding spacers: the former creates a larger bike with a longer wheelbase, while the latter simply moves your hands higher (and closer).

19. yeah I was thinking say if you had the frames side by side, one with shorter reach, and with stack of A,then the one with longer reach, starting at stack A and increasing from the same stack to B hence making shorter... but thats not right the short one has stack A and reach X and the long one has stack B and reach Y, two completely different points.

20. Originally Posted by mik_git
yeah I was thinking say if you had the frames side by side, one with shorter reach, and with stack of A,then the one with longer reach, starting at stack A and increasing from the same stack to B hence making shorter... but thats not right the short one has stack A and reach X and the long one has stack B and reach Y, two completely different points.
Yikes, that's not the easiest description to follow.

Whenever this comes up, I recommend to draw it on paper. Draw the head tube region of a frame using a ruler and pen. Using a pencil over the pen drawing, extend the top tube (this maintains the same stack) and draw a parallel head tube, fork, and down tube. Notice how the fork is now farther forward. Same stack + more reach = longer bike by the exact difference in reach.

Now erase the pencil and experiment with stack. Draw another top tube slightly above the pen drawing. Stop the line directly above the end of the original head tube. This maintains the reach at a different stack. As before, draw a parallel head tube and fork from your pencil top tube. Notice how the fork is again farther forward, but not quite as much. Same reach + more stack = longer bike by about 40% of the difference in stack.

21. Reach and stack has everything to do with how your body position and weight will be distributed on the bike.

22. Originally Posted by R-M-R
Finally, someone who gets it!

To put it another way, here's why stack is not the same as adding or subtracting spacers under a stem:

Adding stack to a frame's geometry moves the front end directly upward, but spacers move along the steerer, which isn't vertical - it's on the axis of the head-tube angle. If you have a 66° head-tube angle, for example, raising the stem 10 mm will also shorten the reach by 4.1 mm.

As LyNx said, a frame with a "long" reach with a low stack is a lot shorter than you think, while a frame with a modest reach and a towering stack is probably a very long bike.
Originally Posted by R-M-R
Yikes, that's not the easiest description to follow.

Whenever this comes up, I recommend to draw it on paper. Draw the head tube region of a frame using a ruler and pen. Using a pencil over the pen drawing, extend the top tube (this maintains the same stack) and draw a parallel head tube, fork, and down tube. Notice how the fork is now farther forward. Same stack + more reach = longer bike by the exact difference in reach.

Now erase the pencil and experiment with stack. Draw another top tube slightly above the pen drawing. Stop the line directly above the end of the original head tube. This maintains the reach at a different stack. As before, draw a parallel head tube and fork from your pencil top tube. Notice how the fork is again farther forward, but not quite as much. Same reach + more stack = longer bike by about 40% of the difference in stack.
Originally Posted by aliikane
Reach and stack has everything to do with how your body position and weight will be distributed on the bike.
Does this mean it'd be a wash to add a 10mm spacer under the stem on a 66* HA ?
And that adding spacers to bikes with HAs steeper than 66* will slightly lengthen the effective reach and adding spacer to bikes with HAs less than 66* slightly shorten the effective reach?

23. Originally Posted by dimitrin
Does this mean it'd be a wash to add a 10mm spacer under the stem on a 66* HA ?
And that adding spacers to bikes with HAs steeper than 66* will slightly lengthen the effective reach and adding spacer to bikes with HAs less than 66* slightly shorten the effective reach?
No, I was referring to the actual frame dimensions. Comparing two bikes with the same reach, but 10 mm different stack, your hands will end up in different locations if you simply add 10 mm of spacers to the bike with lower stack. The point is that spacers or stem rise are not equivalent to an equal change in frame stack.

66° is not a magic number. The exact implications to geometry will change slightly, but the principles remain the same for a head angle of 70° or 60°.

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