@Wile_E To answer your stack question:
One needs to remember that the rise in the bars raises the grips/ hands without necessarily affecting the effective reach (unless you are doing something weird with bar roll) but allowing a tiny reach adjustment if required. Increasing stack/ rise with spacers also reduces reach (it is a right angle triangle with a 64º angle) - not much but when you are after the perfect fit and overall balance on a bike those 2-3 mm increments all add up.
In exactly the same way that 10mm does not appear to be much on paper (re chain stay lengths) but those of us who are taller riders (XL frame size) really notice the difference between the Norco at 445 mm and other brands who insist that 433-5 mm is the perfect chain stay length.
I can feel the difference between my 2020 Sight (445 mm and 78º seat post angle) and my 2020 Optic (440 mm and 76º seat post angle) whilst in theory they should feel almost the same at sag given the same rider weight and the difference in rear travel (150 mm vs 125 mm). Overall I feel that Norco made a mistake by not going for the 78º seat post angle on the XL Optic. And as a result, other than the slight difference imposed as a result of having more travel the Sight is actually the better natural climber.
You can also micro adjust effective reach 3-5 mm with the position of saddle rails but in reality if you need a bigger adjustment one should go to a shorter or longer stem (despite a longer stem being "not cool").
Bar back sweep can also affect reach (at the grip) as 1º over 400 mm is 6.9 mm (working on the average XL rider having a 760 - 800 mm bar).
It is interesting that there are brands who will tell you how they carefully tested and developed their new hard tail and decided on the 'perfect' chain stay length of 435 mm (which is about the effective length of a 2020 Sight chain stay at sag).
Also the final effective stack is affected by the overall stack height of the stem as well (which generally vary between 30 mm and 60 mm).
It is the main reason that there is not a good cockpit comparison calculator for mountain bikes as the maths gets really complicated when one considers all the little triangles and how changing the length or angle of one affects another.
Most riders don't have the inclination or the budget to spend the money and valuable ride time experimenting with their set up (it actually only has to be done properly once and then one has a mathematical base line that one can calculate changes from).
Aug. 9, 2020, 4:45 p.m. - AndrewR
@Wile_E To answer your stack question: One needs to remember that the rise in the bars raises the grips/ hands without necessarily affecting the effective reach (unless you are doing something weird with bar roll) but allowing a tiny reach adjustment if required. Increasing stack/ rise with spacers also reduces reach (it is a right angle triangle with a 64º angle) - not much but when you are after the perfect fit and overall balance on a bike those 2-3 mm increments all add up. In exactly the same way that 10mm does not appear to be much on paper (re chain stay lengths) but those of us who are taller riders (XL frame size) really notice the difference between the Norco at 445 mm and other brands who insist that 433-5 mm is the perfect chain stay length. I can feel the difference between my 2020 Sight (445 mm and 78º seat post angle) and my 2020 Optic (440 mm and 76º seat post angle) whilst in theory they should feel almost the same at sag given the same rider weight and the difference in rear travel (150 mm vs 125 mm). Overall I feel that Norco made a mistake by not going for the 78º seat post angle on the XL Optic. And as a result, other than the slight difference imposed as a result of having more travel the Sight is actually the better natural climber. You can also micro adjust effective reach 3-5 mm with the position of saddle rails but in reality if you need a bigger adjustment one should go to a shorter or longer stem (despite a longer stem being "not cool"). Bar back sweep can also affect reach (at the grip) as 1º over 400 mm is 6.9 mm (working on the average XL rider having a 760 - 800 mm bar). It is interesting that there are brands who will tell you how they carefully tested and developed their new hard tail and decided on the 'perfect' chain stay length of 435 mm (which is about the effective length of a 2020 Sight chain stay at sag). Also the final effective stack is affected by the overall stack height of the stem as well (which generally vary between 30 mm and 60 mm). It is the main reason that there is not a good cockpit comparison calculator for mountain bikes as the maths gets really complicated when one considers all the little triangles and how changing the length or angle of one affects another. Most riders don't have the inclination or the budget to spend the money and valuable ride time experimenting with their set up (it actually only has to be done properly once and then one has a mathematical base line that one can calculate changes from).