jambon

Friends,

Being tall and long of leg I always felt that my correct seat height put my center of gravity up high enough that I felt a little unstable on my bikes and meant that I had to do all sorts of tricks(riser stems , steerer extenders etc) to get my bars upwards to the point where they were comfortable for me and the saddle to bar drop was not so severe.

I am looking for a new bike and with this issue in mind my attention has swung toward BB drop.

Now lets say a bike A is marked as 73mm BB Drop and another bike B in the same wheelsize is marked at BB drop 80mm.So with saddle height as constants on both bikes would I be correct in assuming that my butt would be 7mm closer to the ground on bike B and that my saddle to bar drop would will have diminshed by roughly 7mm?

also part 2 I am curious to know , what are the BB drops like on most road orientated bikes? I have found a frame with an 80mm BB drop and that seems the lowest out there.

Iride01 

I tend to ignore BB drop. But I can maybe see where you might be thinking a lower BB means you'll be lower overall and maybe more stable. I don't know. Sounds plausible. How much difference I guess we'll have to hope someone else knows. Stability is also obtained from the amount of trail your front wheel has. More is better for that aspect in general.

Getting back to bikes with more BB drop and assuming we are talking about bikes with the same size wheels, then keep in mind the more drop the more chance of hitting the ground with a pedal when in a turn. The longer the crank the more chance you have. I recently road a frame with 175 mm cranks and pedaling through a turn I hit the pavement with a pedal. Not so bad that it caused a wreck, but I did clinch the saddle more between my cheeks. <grin>

Good question though, I'll be interested in the thoughts of others on this too.

tyrion

Yes (if by "saddle height" you mean height from crank axle).

Not necessarily, but that might be possible.

79pmooney

I ride 175s. I like pedaling turns and hate hitting pedals. I pay attention to BB height. Also pedal design and "Q" factor (the distance outboard of the pedals; a factor of bottom bracket and cranks. Foot and shoe width can come into play.

Once you have a frame, there is little you can do there besides ride skinnier tires. "Q" factor can be played. Some of the high end racing level offerings of the bike companies are considerably narrower "Q" than the more common cranksets. (I suspect this is because wide "Q" cranks fit any bike, narrow ones hit some bikes' chainstays and riders can have heel contact issues. I ride the lowest "Q" I can achieve on my bikes - for my knees. That it helps pedal strike is a bonus.

Pedals vary a lot, both in how far below the axle they extend and how wide they are. I like pedals where the outboard bottom corner is removed (a lot of racing pedals). My LOOK compatible FORTE clipless are pretty reasonable in corners. My double sided MTB SPDs hit easily.

I prefer my bikes to have BB heights of 10 3/4" for the "faster" bikes and fix gears. 10 5/8" is OK I have one with less than 10 1/2" (with the SPD pedals). I call it the "slinky". I hit those very sturdy pedals on a regular basis. (The heights measured with the tires I use pumped up. Not a useful number for frame design but all that matters as we ride.) NOw I a

Carbonfiberboy 

Bottom bracket height is all about ground clearance. On a road bike, that speaks to the amount of lean one can have while pedaling without the pedal striking the ground. Now the thing is that most bikes come with cranks which are really too short for you. The standard formula for crank length in mm is 5.5 * inseam in inches. Do the calculation and you might get a crank length which isn't even made. Longer cranks will want a higher BB. So there's that. Longer cranks + a higher BB doesn't move your butt up any higher as long as the smaller BB drop and extra crank length are the same. In fact, you probably want a road bike with a higher BB so you can use longer cranks at the same saddle height. I don't think there's a noticeable handling difference. Look at endurance bikes to get a taller head tube and thus less available drop.

If you're way over 6', you probably won't be comfortable on a stock bike. I have a 6'5" buddy who has a custom Ti bike with a head tube that looks like it's a foot long.

79pmooney

Not all vary their seat height as they change crank length. Some do it as a lessor fraction of the crank length difference. And others just live with pedal strike. I do not alter crank length for BB height. All my bikes are 175 and my BB heights are mostly high but not all.

tyrion

Or you just learn to what degree of lean angle you can and can't pedal through.

63rickert

This will be about an outlier. I know it is an outlier

Lowest BB I have ever seen was on the bike Ron Boi campaigned his last couple years in Category 1. He built it himself. Had a bottom bracket drop of 101mm. This would also be in the era of wide and thick Campy 1037 pedals. No, he could not pedal through the corners. Didn’t matter, he was always first out of the corner. Being lower he was more stable and could push the bike hard. Bike got through the corner fast even if he didn’t push. Other benefits were he got a better draft off other riders and other riders got less draft off him. Ron could not handle a bike like Roger Young could, he could not push to the limit like John Howard could. He could beat them in every corner every time on that low bike.

If, as a matter of personal preference, you just don’t like pedal strike, fine, get a bike without. Pedal strike is not that big a deal. When pedals were wide, Campagnolo 1037 again, everyone hit the pedal in every corner. Most of the time it was not even noticed. Only way most even knew what had happened was the pedal body was ground down on bottom outside corner. When it was ground down so far the bearings showed it was time for new pedals. One hundred guys going through criterium corner, presumably every one of them striking pedal. No one flinches, no one moves off their line. Maybe one guy even notices. It is not the end of the world.

Again, if you don’t like it you don’t have to have it. But bikes that have strike can be real good bikes.

Cyclist0100

If you're in the market for a new bike and know you've had previous issues with fit because of your height and long legs, I definitely would not rely on advice from an internet forum to guide you through that selection/purchase process. A good, independent, professional bike fitter will (IMO) be a much better option. The best time to be fitted for a new bike is before you buy.

mack_turtle

I pay a lot of attention to BB drop as it has a pretty big affect on how the bike handles. for my riding style on my mountain bike, I don't want to too low for the sake of ground clearance on trails, but moreso because of how the bike handles with a higher BB. for bikes that are ridden fast on downhill terrain, a lower bottom bracket lowers the center of gravity, making the bike more stable at speed. that's critical in some situations. on the trails I prefer to ride (which is great because it's what most trails the area are like), there's a demand for a nimble, maneuverable bike that I can wrangle up and over obstacles. there is a lot of bunnyhopping, manuals, small drops, etc that require a lot of body english to maintain momentum. more BB drop would put my cranks lower between the axles and therefore make it more difficult to throw the bike around in these situations. this is most likely part of the reason why CX and trials bikes have a high BB less BB drop.

more BB drop makes a bike more stable, which is why you see a lower BB more drop on bikes designed for loaded touring. it makes the bike very stable, something you want in some applications.

Moisture

BB drop and your centre of gravity is obviously dependent on which size crank arms you use.

In your case, Bb height is only part of the equation. Assuming you are using the correct length arms according to inseam, you need to find a bike with a shorter top tube and a taller stack. Then, adjusting your stem and handlebars will make more sense.

If you need crank arms which are 180mm and you currently use 170, a 10mm higher BB with the 10mm linger cranks obviously won't have any change with centre of gravity