# Stack height... a discussion on it's affects that isn't just "It affects reach"



## shredjesse (Oct 18, 2017)

*Stack height... a discussion on it's affects that isn't just "It affects reach"*

*Backstory: *I recently purchased a 2019 Norco Sight demo bike after demoing it, as I really enjoyed how it rode compared to my regular bike. I was surprised to discover that despite the longer reach, the bike was easier to manual, as it would seem to me being more in the bike would make getting your weight back over the rear wheel a bit more of a chore.

Reviewing the bike afterwards, not only is the stack height higher than on my previous bike (2017 Trek Fuel EX 8) I noticed there are a ton of spacers under the stem raising it even higher.

Playing around now with a variety of bikes, I am finding that a higher stack height tends to allow me to manual significantly easier, and this improves onwards to more consistency over drops, better consistency hitting jumps, etc etc.

So go ahead and google "stack" for bike geometry, and all you'll see are articles telling you how much more important reach is, and that stack affects reach. Even at the most recent demo I hit I mentioned how much I liked stack and the guy goes "Yeah, that will reduce reach, I can see that as you may be on the short side of a large frame". Except the reach is still longer than my previous bike.

Looking at some other bicycle sports bikes, stack really affects body position, and offers a variety of different affects. Look at trials bikes for example with their massive riser bars.

*The discussion: What exactly does stack do for bike control, fit and all that, other than a minor affect on reach.*


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## mack_turtle (Jan 6, 2009)

Reach and stack form a right triangle. The hypotenuse is the effective downtube length. I use that more than anything to determine how my body will fit on a bike. Handling is how that fit applies to the wheelbase, front-/ rear-center, BB drop, etc. It's possible for a bike to fit well and handle horribly.

Stack is a product of BB drop, headtube angle, and fork length.

FWIW, I have my handlebar low because of the way it balances me on the bike, I think. The grips are close to level with the saddle, but that's mostly a coincidence. I 
ignored saddle/grip drop when I set it up because I am usually not sitting down when handling counts. I have my hands in a position where I can keep weight on the front end without forcing it, but high enough that I can hop and manual when needed. For the way I ride my local trails, I would not want the choppered-out tall handlebar setup I see on a lot of bikes. Too much rearward bias for climbing and tech for my taste.

My experience: when I had to jack my bar way up high because it's comfortable for my back (not applicable if you have a legitimate, diagnosed irreversible back injury), handling suffered. I started getting better results when I started working out, strengthening my core so I can ride in an aggressive position more often without straining my back.


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## shredjesse (Oct 18, 2017)

Thanks for sharing. Did you find a higher stack helped with manuals or any other aspects?

Also how does stack relate to BB drop and headtube angle? Fork Length I get as it increases the height. I would also include stem spacers and handlebar rise as factors for stack... or is there some other term for actual final handlebar position?


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## Lone Rager (Dec 13, 2013)

It's where the grips are that matters, not the combination of stack-height, stem, or bar bend that gets them there.


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## mack_turtle (Jan 6, 2009)

Look up Lee McCormack's RAD theory.

Don't get _too_ caught up on the numbers. Every bike is going to be different so you have to experiment. Reach, stack, and EDT will give you a good idea though.

Yes, getting the handlebar higher and closer to you definitely makes manuals and hops easier, but it also makes it harder to keep the bike stable. I would be more likely to loop out and have to work harder while riding in "tyanarasuarus rex arms" position if the bar is too high.


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## shredjesse (Oct 18, 2017)

Lone Rager said:


> It's where the grips are that matters, not the combination of stack-height, stem, or bar bend that gets them there.


I'm sorry, but don't all of those things contribute to where your grips actually wind up? Reach being a factor, and stack-height, and stem spacers/risers, etc etc.


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## shredjesse (Oct 18, 2017)

I googled "Lee McCormack's RAD theory" and got a pretty brief Pinkbike article that mostly told you to buy his book, heh.


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## Lone Rager (Dec 13, 2013)

shredjesse said:


> I'm sorry, but don't all of those things contribute to where your grips actually wind up? Reach being a factor, and stack-height, and stem spacers/risers, etc etc.


Yes, any combination of those factors that get the grips to the same position will work the same assuming the geo of the bike remains the same. Geo in this case means where the lower head set bearing is wrt the BB and the head tube angle.


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## shredjesse (Oct 18, 2017)

Okay, and so this is a discussion on just what adjusting a single variable does. Care to comment?

Adding height to the final bar position generally does _____________________ to how the bike rides, although too much causes ___________________________.


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## Fleas (Jan 19, 2006)

I can't vouch for this 100%, but as much as high stack makes manualling easier, it also provides increased leverage in the _wrong_ direction -> OTB. On a raked out bike this is less of an issue, but there's still a balance point over which you never want to be.

I have played with high hands, just to see what it's like. It was bad.... and weird. Steering felt unstable and I rode very upright instead of more flat-backed. Being high up felt uncomfortable on rough and steep (down) terrain - it felt like my hands were moving forward and back with the bike instead of up and down with the terrain. It was a weird, disconnected feeling. ..._and_ unstable.

-F


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## shredjesse (Oct 18, 2017)

Huh, why would high stack contribute to OTB? I feel like a low stack puts me way more over the front.

So that's a too high stack. What does a too low stack do?


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## Cerberus75 (Oct 20, 2015)

shredjesse said:


> Huh, why would high stack contribute to OTB? I feel like a low stack puts me way more over the front.
> 
> So that's a too high stack. What does a too low stack do?


Low stack means that if you're putting spacers under the stem to get the bars high enough you loose reach, the slacker the head tube the worse it is. They make rise bars only so high.


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## shredjesse (Oct 18, 2017)

I meant what does it do for riding to have a low stack or low final bar position...

I also really want someone to actually measure how much reach you lose with even a large amount of spacers under the stem and a very slack headtube angle (64degrees, 90mm rise). I'd bet good money that it is minor, and easily offset by a small adjustment in stem length.


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## Shayne (Jan 14, 2004)

shredjesse said:


> What does a too low stack do?


Not possible IMHO

Stack is so high (industry wide) currently that I can't get bars low enough to ride comfortably. Pretty much all the bikes I've tried out had a beach cruiser feel.


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## shredjesse (Oct 18, 2017)

See where I said "or too low a bar position"? Humor me. Pretend you put drop bars on that **** or something like that.


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## Carl Mega (Jan 17, 2004)

Shayne said:


> Stack is so high (industry wide) currently that I can't get bars low enough to ride comfortably. .


I share your opinion but sometimes I feel like an outlier. Long travel forks and bigger wheels have jacked up stack quite a bit over the years. Luckily head-tube-angles being slack helps some (slacker = lower front respectively) but I find that having a low stack keeps me in touch with pressuring the front wheel during cornering.

Not everyone likes that feel - it does put more weight on the hands and unweighting the front will require more of a deliberate effort.

A major differentiator in selecting a frame in my latest bike build was the stack - literally 2.75" difference between frames with same travel. Completely different feel.


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## Cerberus75 (Oct 20, 2015)

shredjesse said:


> I meant what does it do for riding to have a low stack or low final bar position...
> 
> I also really want someone to actually measure how much reach you lose with even a large amount of spacers under the stem and a very slack headtube angle (64degrees, 90mm rise). I'd bet good money that it is minor, and easily offset by a small adjustment in stem length.


There are stem reach calculators that can show you. The issue is you should only use so many spacers with a 100mm head tube. There are plenty of people who like a certain bar/stem combo that this is all part of the buying process.


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## Le Duke (Mar 23, 2009)

Stack is a pretty major consideration for me, being relatively short, relatively leggy, and having wide-ish shoulders for a person my height.

Here's a comparison of two bikes I'm considering for my next bike, with my current bike in the third column. I also added in the size small of one bike up for consideration. Note how the small Sniper Trail has a nearly identical reach as my Yeti, the same head tube length, yet has a stack height an entire inch (25mm) lower. While I have my current bike set up with a Syntace FlatForce 77mm stem, which is about as low as you can go, I can't imagine a bike where the stem clamp itself is an entire inch lower than that.

https://geometrygeeks.bike/compare/...dium,orbea-oiz-tr-2019-m-tr,yeti-asr-2017-md/


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## Le Duke (Mar 23, 2009)

Stack is a pretty major consideration for me, being relatively short, relatively leggy, and having wide-ish shoulders for a person my height.

Here's a comparison of two bikes I'm considering for my next bike, with my current bike in the third column. I also added in the size small of one bike up for consideration. Note how the small Sniper Trail has a nearly identical reach as my Yeti, the same head tube length, yet has a stack height an entire inch (25mm) lower. While I have my current bike set up with a Syntace FlatForce 77mm stem, which is about as low as you can go, I can't imagine a bike where the stem clamp itself is an entire inch lower than that. As someone who can tell if my saddle is pointed a couple of degrees up or down, left or right, or a couple of millimeters to low, this would be a huge change for me. Massive.

https://geometrygeeks.bike/compare/...dium,orbea-oiz-tr-2019-m-tr,yeti-asr-2017-md/


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## mountainbiker24 (Feb 5, 2007)

Shayne said:


> Not possible IMHO
> 
> Stack is so high (industry wide) currently that I can't get bars low enough to ride comfortably. Pretty much all the bikes I've tried out had a beach cruiser feel.


I'm going to assume you are on a size small or medium bike and are under 6' tall. Large bikes have relatively short head tubes for taller people. I don't understand why somebody 6' 3" tall has a head tube 10mm longer than a bike designed for somebody 5' 8" tall.


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## attaboy (Apr 4, 2008)

mountainbiker24 said:


> I'm going to assume you are on a size small or medium bike and are under 6' tall. Large bikes have relatively short head tubes for taller people. I don't understand why somebody 6' 3" tall has a head tube 10mm longer than a bike designed for somebody 5' 8" tall.


yep, have the opposite problem that stack height is too low on most bikes. At 6'2" and leggy it was challenge to get my new bike's grips high enough. Have many spacers and 30mm riser bar. used Lee McCormicks RAD and its right where he suggests.


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## Fleas (Jan 19, 2006)

shredjesse said:


> Huh, why would high stack contribute to OTB? I feel like a low stack puts me way more over the front.
> 
> So that's a too high stack. What does a too low stack do?


Maybe I'm crossing up terms here...

If we're just talking about the stack dimension of the frame, most bikes put the rider in a favorable (neutral) position.
If we're talking about unusual hand locations via bar/stem combinations, then it all only works within a fairly small margin before the compromises rear their ugly heads.

Just being higher raises your center of gravity.

If you consider slow speed rock crawling, when your front wheel falls in a hole, your reaction against the handlebar is to push so you can remain upright. If you have enough momentum, no matter how low you drop your a$$, your hands are still high and you're pushing forward -> OTB

By the same token, if your stack is somehow really low (and/or forward), your arms aren't long enough to keep your COG behind the handlebar.

In the "goldilocks zone", you have both the ability to adjust your COG relative to the handlebar AND follow the terrain without upsetting your balance.

I think seat tube angle affects reach more than anything now. I moved from a L frame to an XL frame and I still can't use below an 80mm stem because the saddle is more forward even when it's all the way back on the rails.

-F


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## Devilla27 (Feb 7, 2021)

Fleas said:


> Maybe I'm crossing up terms here...
> 
> If we're just talking about the stack dimension of the frame, most bikes put the rider in a favorable (neutral) position.
> If we're talking about unusual hand locations via bar/stem combinations, then it all only works within a fairly small margin before the compromises rear their ugly heads.
> ...


That doesn't make sense though. Your center of gravity is not going to change much just because your hand position is an inch or two higher. Your pedals and butt are still in the same location and last I checked that's where most of your weight is. Reach of course is going to affect the weight on the front wheel but the influence of stack on weighting the front wheel is much smaller. 25mm of reach will do way more than 25mm of stack.

I have the same issue as the Guy who is 6'2". I'm not leggy, but my torso is really long with shorter than average arms at 6'0" So as a result I feel like I have a lot of weight on my hands when gripping. Yeah It doesn't make that much sense that there is only a 10mm difference in headtube length between a medium and large frame. I have all my spacers under (20mm) with 25mm riser bars and and I still feel too much pressure on my shoulders/hands from hinging down to reach my bars.


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