Bottom Bracket Drop question
 

Aside from the obvious increased likelihood of experiencing pedal strike, are there any handling quirks introduced by running a lower bottom bracket? Or any geometry issues that need to considered?

Thanks.

Opinions vary but I like the feel of a lower bottom bracket. My last bike I lowered mine to 85 mm (for 680 wheel/tire diameter and 175 crank arms). No handling quirks and I have yet to drag a (clipless) pedal The chainstays and down tube gets longer which allows a bit more bottom bracket sway for the same gauge tubing. If using lugs you may have to tweek the angles to fit the tubes into the sockets.

All other things being equal, a lower BB means a lower center of gravity, which most consider a good thing.

Other than the issue of changed tube lengths and angles (assuming head height is unchanged), the only potential problem is the rear wheel, seat tube clearance. If the BB is lowered along the axis of the seat tube, and chain stay lengths are adjusted accordingly, tire clearance won't be an issue, but it's something to watch.

people think they like lower bb height. I'm not sure the technical explanations really hold up. I'm pretty sure I can lower my cg by a lot just going into the drops, bike still corners the same.

Thanks for the replies.

That's because your weighting of the bike in a corner isn't dependent on your CG. Yes, it'll affect your tip-in, but beyond that, it's irrelevant. Free-body diagrams will show that how your weight (where it is) works as if that weight were applied only at the contact points. So if you're weighting your outside pedal like you should be, the bike acts as if that amount of weight were sitting on that pedal, not at your body's CG. Small changes in BB drop does have a significant affect on the height of the pedal from the ground and how weight applied there affects cornering stability.

Not sure I buy that a static analysis technique like a free body diagram has anything to do with a dynamic concept like stability. But then again, I don't know the stability criteria for a bicycle. I'm almost positive that cg and moment of inertia relative to your cg is in there, and I'm not sure about where the force is applied.

You can get a very exaggerated sense of the effect of BB/saddle/CoG height by riding a super tall circus bike.

What happens is that all "body English" movements have to be very exaggerated and you can't throw the bike into a sudden turn as fast.

That said, the difference is material at the extremes, but we're talking about a half inch or so here relative to 30-40 inches between CoG and the pavement. So, yes it does make a difference, and a lower bike may be snappier in hard corners and slaloms and the overall handling will feel more precise, but the actual difference is going to be pretty small.