Originally Posted by
Russ Roth
Stack is an easily understandable thing. I've never seen a good explanation of the importance of reach vs top tube length. Care to elucidate?
Top tube length is impacted by seat tube angle. Reach is not impacted by that.
Reach helps measure how the bike will fit while standing as a result. It really helps for MTB where you stand a bunch, but as one who stands on most every hill for road/gravel, it is beneficial there too.
The top tube length of some tri bikes, mtbs, etc are totally misleading if you go just off that number. The reach measurement normalizes things. This really all started 30ish years ago with sloping top tubes and its why using just the seat tube length is also quite worthless for measuring a bike's fit as compared to another bike.
Stack and reach measurements are great because they normalize comparing bikes that are different designs.
I own a 58cm gravel bike, a 65cm road bike, a 65cm gravel/touring bike, a 63.6cm road bike and a 66cm road bike that also measures 63 depending on how its measured.
^ seat tube measurement is worthless when comparing different style bikes. So is top tube length.
Reach(and stack) also really help when comparing a bike that has a number size with a bike that has a t-shirt size. How does a size 54cm road frame with a sloping top tube from company A compare to a size medium road frame with a level top tube from company Z?