# Stack and Sizing Chart Recommendations



## jeremy3220 (Jul 5, 2017)

Reach and stack are often said to be the most important factors in sizing. Some recommend taking the hypotenuse (aka "pythag")of the reach and stack as the best way to determine sizing. Which theoretically makes sense because it should work across different categories (XC, Trail, Enduro). However, after looking at manufactures' sizing recommendations and comparing numbers there isn't much consistency. 

Examples:

Giant Trance in XL (recommended for riders up to 6'4")
Reach: 18.5"
Stack: 24.7"
Hypotenuse: 30.86"

Santa Cruz Bronson in XL (recommended for riders up to 6'6")
Reach: 18.7"
Stack: 24.17"
Hyp: 30.56

Ibis Mojo HD4 in XL (recommended for riders up to 6'6")
Reach: 18.9"
Stack: 24.4"
Hyp: 30.86 (same as the Trance)

Giant Anthem in XL (recommended for riders up to 6'4")
Reach: 18.5"
Stack: 23.3
Hyp: 29.75"

Santa Cruz Hightower LT in XL (recommended for riders up to 6'3")
Reach: 18.43"
Stack: 24.72"
Hyp: 30.83"

Santa Cruz Hightower LT in XXL (recommended for riders 6'3"-6'7")
Reach: 19.61"
Stack: 25.43
Hyp: 32.11"

For the 27.5" bikes the bike with the longest hypotenuse and tallest stack (Trance) has the shortest max height recommendation. Giant also makes the same size recommendations for the Anthem with a way shorter stack and hypotenuse. 

Santa Cruz recommends the Bronson XL (hyp=30.56") for riders up to 6'6" but the Hightower XL (hyp=30.83") for only up to 6'3".

Based on reach, these recommendations make a bit of sense but no sense at all for stack or hypotenuse. For someone 6'4", you're recommended bike sizes that have stack and hypotenuse numbers all over the place (even by the same manufacturer). Are manufacturer recommendations useless or is stack/hypotenuse really not that important?


----------



## Ray Lee (Aug 17, 2007)

Somewhat off topic but I tested a bikes that I really wanted but had to rule it out because it felt so low (stack) so I am keep to figure this out. Isn't stack measured to the top of the head tube?, so it would not take into account the length of the fork steerer.

Seems like manufactures come up with some crazy hight range recommendations for the largest bikes... LARGE 5'.8"-6'.1" and XL 6'-8'.3" feet LOL. 

I am only 6'3" but more leg than arm so I end up with the seat 4 inches higher than the grip height (time trials bike ridding position) 

I really dont get why manufactures cut the steerer... its easy for the end user and/or bike shop to do with a $30 tool but pretty much impossible to replace with a longer one (replacing the whole crown and stanchions)


----------



## *OneSpeed* (Oct 18, 2013)

jeremy3220 said:


> Are manufacturer recommendations useless or *is stack/hypotenuse really not that important?*


I've not heard of your formula before. I does not sound like a good method of comparing sizes at all. An XC bike isn't supposed to fit like an AM bike. It's a different animal.



Ray Lee said:


> Seems like manufactures come up with some crazy hight range recommendations for the largest bikes... LARGE 5'.8"-6'.1" and* XL 6'-8'.3" feet LOL.*


I agree, the upper range of XL bikes (from most manufacturers) is not accurate. They just do that to avoid offering another size, aka XXL.

I'm also 6'3" and run 80-110mm stems on most XL frames I've owned (mostly 21" frames) along with offset seatposts. So realistically anyone taller than me would need a pretty long stem on these size bikes. How long of a stem would a 6'8" guy need on my bike? Ginormous.


----------



## jeremy3220 (Jul 5, 2017)

*OneSpeed* said:


> I've not heard of your formula before.


It's not my formula.

The Earth Remains - Journal - Bikes for the Very Tall

http://www.leelikesbikes.com/sizing-down-when-you-get-a-new-bike.html

Reach: Bike geometry tables haven't done the math for us - WheelSizeAgnostic



*OneSpeed* said:


> I does not sound like a good method of comparing sizes at all. An XC bike isn't supposed to fit like an AM bike. It's a different animal.


The idea is that the 'rider area distance' aka 'pythag' is a number that gives you an idea of fit consistent across different style geometries. That's the theory anyway. The reason I made this post is I'm not sure if it's valid.


----------



## NWA_Tre (Sep 30, 2021)

jeremy3220 said:


> It's not my formula.
> 
> The Earth Remains - Journal - Bikes for the Very Tall
> 
> ...


I may be reviving this topic  a few bikes I like have much lower stack than anything else I’m looking at. I find it odd, or perhaps there is not a good standard for how stack is measured across manufacturers. One told me it was from tire contact patch to top of stem cap…🤨


----------



## jonshonda (Apr 21, 2011)

Reach is really tough now because the sta is changing so much on bikes, that a 76 and 72sta bike with the same reach will have a much different fit. So the ett might be a better indicator of fitment?


----------



## socalrider77 (Sep 1, 2012)

jonshonda said:


> Reach is really tough now because the sta is changing so much on bikes, that a 76 and 72sta bike with the same reach will have a much different fit. So the ett might be a better indicator of fitment?


For seated riding yes, but for everything else a longer reach will ride different than a shorter reach regardless of seat angle 


Sent from my iPhone using Tapatalk


----------



## NWA_Tre (Sep 30, 2021)

socalrider77 said:


> For seated riding yes, but for everything else a longer reach will ride different than a shorter reach regardless of seat angle
> 
> 
> Sent from my iPhone using Tapatalk


This is my take as well. I DO think ETT is being ignored by people who are just looking at reach and HTA/STA. Yes, you can adjust seated position a little, but I do think finding a bike that fits you is a better approach...if possible, lol


----------



## jeremy3220 (Jul 5, 2017)

NWA_Tre said:


> This is my take as well. I DO think ETT is being ignored by people who are just looking at reach and HTA/STA. Yes, you can adjust seated position a little, but I do think finding a bike that fits you is a better approach...if possible, lol


It makes sense to look at ETT if you're moving to a steeper STA and not sure what works for you. Personally seated position is secondary so reach and stack are the most important for me.


----------



## NWA_Tre (Sep 30, 2021)

jeremy3220 said:


> It makes sense to look at ETT if you're moving to a steeper STA and not sure what works for you. Personally seated position is secondary so reach and stack are the most important for me.


exactly my situation and yes, unless ETT is off by like 50mm, I'm prioritizing R and SH


----------



## Fuse6F (Jul 5, 2017)

The size chart recommendations are wrong.

ive reached out to multiple manufacturers to bring their attention to the need for a tall clyde bike fit.

none are interested.

Having the same rear center across the entire size line from xs to xxl should clarify the point

Xxl bikes sizes are out of touch with xxl rider needs. It isnt just reach and stack that need to be addressed.


----------



## brawlo (Mar 13, 2012)

The geo charts, particularly stack and chainstay length, should be a fairly clear indication that manufacturers are catering more to the smaller riders going long and sizing up than catering to the small percentage of riders who genuinely need a monster size bike


----------



## jonshonda (Apr 21, 2011)

socalrider77 said:


> For seated riding yes, but for everything else a longer reach will ride different than a shorter reach regardless of seat angle
> 
> 
> Sent from my iPhone using Tapatalk


Seated riding is the majority of riding that the majority of riders do. It's how a bike fitter would fit you to a bike, while you are pedaling the bike. 

This is what makes posts that are asking questions to riders on a national level so difficult. Local trails should dictate what bikes riders buy, not trends. Lots of these big bike companies are on the west coast, making bikes that work well for their local trails. But if you aren't always going up or going down, and pedal your bike in a seated position, is a long bike that has a super slack hta and steep sta right for you? doubt it

Where I ride, we pedal a LOT, likely more then 80% of the time. So pedal efficiency is important, and being comfortable and able to be in a neutral position while pedaling is important, because we pedal on flat ground, up hills with seated and out of the saddle climbing, down hills while seated and out of the saddle. 

Granted this is me interjecting my opinion based on the trails I ride, which is what I should be doing. I shouldn't be telling someone who rides completely different types of trails what to ride, because I have not a clue.


----------



## NWA_Tre (Sep 30, 2021)

jonshonda said:


> Seated riding is the majority of riding that the majority of riders do.


If this is statistical, then cool...but it reads like most of "us" are pedaling in the saddle most of the time. I think many of us are the opposite. Short punchy climbs favor standing or being on the tip of the seat and last maybe 10 seconds. The rest of the time on flow, downhill, technical sections, etc. it wouldn't make much (any) sense to be in the saddle. Maybe I'm wrong...


----------



## Fuse6F (Jul 5, 2017)

NWA_Tre said:


> If this is statistical, then cool...but it reads like most of "us" are pedaling in the saddle most of the time. I think many of us are the opposite. Short punchy climbs favor standing or being on the tip of the seat and last maybe 10 seconds. The rest of the time on flow, downhill, technical sections, etc. it wouldn't make much (any) sense to be in the saddle. Maybe I'm wrong...


i dont know about you, but i find that i spend most of my time grinding my way up the mountain. this invloves plenty of seat time due to the low climbing speed vs my descent.


ett determines seated fit. imo. 

sta determines a bikes intention for climb or flat trails (adjusted for travel *at least until flight control affects designs)

reach/stack to me is a factor more for the attack position.

trying to get them all optimized is the difficult problem due to variances in body proportions.


----------



## NWA_Tre (Sep 30, 2021)

Fuse6F said:


> i dont know about you, but i find that i spend most of my time grinding my way up the mountain. this invloves plenty of seat time due to the low climbing speed vs my descent.


Regional differences I guess. We have elevation gain here but there are few long sustained climbs. I DO value seated fit, though. Even our short climbs can be steep, loose, and require good lines. You’re right that dialing it all in is tough but necessary


----------



## jonshonda (Apr 21, 2011)

NWA_Tre said:


> If this is statistical, then cool...but it reads like most of "us" are pedaling in the saddle most of the time. I think many of us are the opposite. Short punchy climbs favor standing or being on the tip of the seat and last maybe 10 seconds. The rest of the time on flow, downhill, technical sections, etc. it wouldn't make much (any) sense to be in the saddle. Maybe I'm wrong...


You totally ignored my comments about asking questions on a national level. For almost every trail within 180 miles of me, you will have your ass planted the majority of the time. So why would anyone pick a 76deg sta bike that must pedal differently then a typical 74deg bike?


----------



## NWA_Tre (Sep 30, 2021)

jonshonda said:


> You totally ignored my comments about asking questions on a national level. For almost every trail within 180 miles of me, you will have your ass planted the majority of the time. So why would anyone pick a 76deg sta bike that must pedal differently then a typical 74deg bike?


Oh, sorry, wasn't ignoring that part of the comment, rather just addressing one portion of it. I'm sure it was just a misunderstanding.


----------



## jonshonda (Apr 21, 2011)

NWA_Tre said:


> Oh, sorry, wasn't ignoring that part of the comment, rather just addressing one portion of it. I'm sure it was just a misunderstanding.


 No worries! 

I am pretty confident that the modern geo is great for out of saddle descending, standing and possibly tip or the saddle climbing. But I really question seated pedaling and climbing, and also with how the wheelbase is growing, how much fun the bike is whilst not blasting 100%. Also with so much of your body over the front of the bike and the front wheel being that much further forward, right switchbacks and overall low speed steering. 

I know there is a review of the new tallboy where the rider pretty much doesn't understand the point of the new geo, until speeds reach top and or they are bombing down a hill. Which makes me wonder if it will be a boring bike for everything under 9/10ths.


----------



## NWA_Tre (Sep 30, 2021)

jonshonda said:


> I know there is a review of the new tallboy where the rider pretty much doesn't understand the point of the new geo, until speeds reach top and or they are bombing down a hill. Which makes me wonder if it will be a boring bike for everything under 9/10ths.


Could be rose colored glasses, but I've read some glowing reviews of the Honzo ESD, for instance, and it was in all situations or...most


----------

