In comparing frames of equal stack and reach, what does BB drop effect. Lets say frame x has a BB drop of 60 and frame y has a BB drop of 65 and both have same stack and reach…
Let me also throw head tube angle into the mix. 72.5 vs 73. If they both have the same stack and reach, does it make a difference?
BB drop = vertical distance between the center of the BB and a line running between your two wheel skewers.
Big BB drop (i.e. a lower BB) = lower center of gravity and arguably better aerodynamics although I’ve never really bought that.
Low BB drop (i.e. a higher BB) = higher center of gravity and more corner clearance (if you’re one of the 0.1% of triathletes who rides in a way that makes that an issue)
What BJL said. It doesn’t effect much, though it affects clearance (hence why most cross bikes have a higher BB) and as a side effect toe overlap.
cool thanks, and what about a head tube angle?
Head tube angle largely affects handling, although in conjunction with lots of other factors. For the most part you do best when letting the frame designer worry about these things.
BB drop can be an issue if you are a “long crank” sort of person and pedal through corners.
If people keep going with shorter cranks you may see frames with more BB drop to help handling and aerodynamics.
Styrrell
but neither of these factors effect stack and reach? I have large ridley dean, and am trying to get the same exact position on a 58 p3 just to compare the handling characteristics and ride quality between the two. Both frames have nearly then same stack and reach. They only differ in bottom bracket drop and head tube angle. I use an 80mm stem for the ridley, Im assuming I can use that same 80mm stem on the p3 and be good to go?
Yep. If the BB drop and head tube angle are wildly different the bikes may “feel” different but it’ll be in a “twitchy vs lazy” way or a “I’m sat on the bike vs I’m sat in the bike” way - your position will translate and which you prefer will be personal.
the ridley has a 65 for BB drop and the p3 has a 60. The ridley has a head tube angle of 73 and the cervelo has a head tube angle of 72.5. Im guessing they will feel similar then…
but neither of these factors effect stack and reach? I have large ridley dean, and am trying to get the same exact position on a 58 p3 just to compare the handling characteristics and ride quality between the two. Both frames have nearly then same stack and reach. They only differ in bottom bracket drop and head tube angle. I use an 80mm stem for the ridley, Im assuming I can use that same 80mm stem on the p3 and be good to go?
Yes, the different head tube angles will mean that out at the end of the stem, the handlebars will be a mm or two higher or lower but not enough to worry about it. Identical as far as you can feel.
Stack and Reach are values relative to the BB, so bottom bracket drop has no affect on a stack/reach measurement. This makes sense since you touch the bike relative to the pedals (bb) anyway.
A lower BB means you have less ground clearance when pedalling around a corner.
And yes, all those handling things already mentioned.