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  #136  
Old 11-24-2021, 07:27 PM
HenryA HenryA is offline
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If everything outside the white box is of no concern, then stack and reach is perfect for you.
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  #137  
Old 11-24-2021, 07:53 PM
Dave Dave is online now
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Quote:
Originally Posted by HenryA View Post

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If everything outside the white box is of no concern, then stack and reach is perfect for you.
You haven't been reading my posts about the importance of the STA. Stack, reach and STA will determine the fit. I also have my steering geometry preferences - more than 58mm of trail, which some brands think is appropriate for the smallest and largest frames. My current Cinelli Superstar disc is one of the best frames I've owned. I ride the smallest size with a 72-73cm saddle height and a 10cm saddle to bar drop. The 415mm stays are the longest I've ever owned.
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  #138  
Old 11-24-2021, 08:39 PM
tommyrod74 tommyrod74 is offline
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Originally Posted by jimmy-moots View Post
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.
Yep. What’s interesting is that it is being used by some people to compare their road fit with their mountain bikes fit, or to compare an older mountain bike with modern geometry. That’s where it falls apart – once head tube angles get slack enough, all of a sudden you don’t really have a choice but to be sitting further forward relative to the bottom bracket to be able to weight the front wheel in turns (and thus the steep seat tube angles you see on these bikes), and then all comparisons using stack and reach or a little more difficult to make, because you’re no longer using the BB as a reference point for where your saddle will go.
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  #139  
Old 11-24-2021, 09:58 PM
jimmy-moots's Avatar
jimmy-moots jimmy-moots is offline
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Originally Posted by tommyrod74 View Post
Yep. What’s interesting is that it is being used by some people to compare their road fit with their mountain bikes fit, or to compare an older mountain bike with modern geometry. That’s where it falls apart – once head tube angles get slack enough, all of a sudden you don’t really have a choice but to be sitting further forward relative to the bottom bracket to be able to weight the front wheel in turns (and thus the steep seat tube angles you see on these bikes), and then all comparisons using stack and reach or a little more difficult to make, because you’re no longer using the BB as a reference point for where your saddle will go.
MTB is an interesting use case, the 'fit' is much more dynamic and overall, less critical. When I got a trail bike I fully relied on my buddy in the shop to size me for a bike, I had no idea - my inclinations as someone who predominantly rides road were at odds with the handling demands of a trail bike.

Agree with the point though, and it's the same with say a TT bike. You can't take your road fit and expect it to work on some other platform that has other demands and compromises.

But again, this is edge case stuff. If you're a punter in a bike shop comparing a Specialized Tarmac with a Giant TCR with a Cervelo R-something with a Cannondale Supersix... Stack/reach is absolutely brilliant for that purpose.
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  #140  
Old 11-25-2021, 09:04 AM
HenryA HenryA is offline
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Originally Posted by Dave View Post
You haven't been reading my posts about the importance of the STA. Stack, reach and STA will determine the fit. I also have my steering geometry preferences - more than 58mm of trail, which some brands think is appropriate for the smallest and largest frames. My current Cinelli Superstar disc is one of the best frames I've owned. I ride the smallest size with a 72-73cm saddle height and a 10cm saddle to bar drop. The 415mm stays are the longest I've ever owned.
Not aimed at you, as you obviously are concerned with things outside the white box. As you should.
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  #141  
Old 11-25-2021, 09:28 AM
Mark McM Mark McM is offline
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Originally Posted by HenryA View Post

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If everything outside the white box is of no concern, then stack and reach is perfect for you.
If everything outside the box is a concern, then Stack and Reach is also perfect for you. Stack and Reach is used to measure the basic frame "cockpit" size using he center of the BB shell as a reference point. Likewise, the other dimensions outside the box (saddle setback, chainstay length, front center, BB height, etc.) also use the center of the BB shell as their reference point. Stack and Reach is simply a more consistent frame measuring system.
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  #142  
Old 11-25-2021, 11:11 AM
marciero marciero is offline
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Originally Posted by Mark McM View Post

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.
The front center may or may not change, depending on HTA and rake. True, those would also effect handling. But even in the first example, whether the two bikes handled similarly or not would depend on HTA and fork rake, and consequently, wheel flop, trail, and front center (not to mention chainstay length, though maybe not discernable). It's true that in the first example if the front end geo were the same on the two bikes you would have the same or similar handling, where in the second example either front end geo or front center would be have to be different. But only in the fringe cases could you have some likelihood of knowing what the effects on handling might be. Aside from that, from the perspective of fit alone, adjusting via stem length is a wash with adjusting via saddle/seatpost setback. You cant make honest comparisons in handling without additional assumptions.
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  #143  
Old 11-25-2021, 05:56 PM
soulspinner soulspinner is offline
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Quote:
Originally Posted by Mark McM View Post
If everything outside the box is a concern, then Stack and Reach is also perfect for you. Stack and Reach is used to measure the basic frame "cockpit" size using he center of the BB shell as a reference point. Likewise, the other dimensions outside the box (saddle setback, chainstay length, front center, BB height, etc.) also use the center of the BB shell as their reference point. Stack and Reach is simply a more consistent frame measuring system.
You said it better than I could.
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  #144  
Old 11-25-2021, 10:04 PM
tommyrod74 tommyrod74 is offline
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Quote:
Originally Posted by jimmy-moots View Post
MTB is an interesting use case, the 'fit' is much more dynamic and overall, less critical. When I got a trail bike I fully relied on my buddy in the shop to size me for a bike, I had no idea - my inclinations as someone who predominantly rides road were at odds with the handling demands of a trail bike.

Agree with the point though, and it's the same with say a TT bike. You can't take your road fit and expect it to work on some other platform that has other demands and compromises.

But again, this is edge case stuff. If you're a punter in a bike shop comparing a Specialized Tarmac with a Giant TCR with a Cervelo R-something with a Cannondale Supersix... Stack/reach is absolutely brilliant for that purpose.
I don’t know that I would say that mountain bike fit is less critical than road bike fit. I just think they have different primary objectives.

Having ridden and raced both for years, on the road bike my primary fit objective is power output, with handling being secondary. That’s not to say that handling isn’t very important; it’s just to say that as long as I can put out power comfortably, and handling is in the ballpark, I can make it work. Ideally, I’d optimize both. I have a lot more margin for error on the handling of the road bike, as a little more or less weight on the front wheel doesn’t mean I can’t get through turns at high speed, because traction on the road bike is more readily available than on dirt.

On the mountain bike, it’s much more of a fine balance between the two, as it doesn’t really matter if I can sit at threshold comfortably for long periods of time if I keep blowing through returns at high speed because I can’t wait the front wheel enough, or I can’t make uphill switchback turns happen.
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