# Explain BB Drop???



## b00001 (Dec 28, 2005)

I did some searching and I could not find a thread that explained what BB Drop actually means.

I am looking at a few different frames and some list BB height which I can understand, others list BB Drop. One frame lists a BB Drop of 2.69, and another lists a BB Drop of 2.36. What does this mean?

Thanks in advance!


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## scottzg (Sep 27, 2006)

BB drop is how far the bb is below the axle centerline. It can be more useful than BB height because it doesn't change when tires are changed, and distance below the axles influences how much the bike wants to stay upright.


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## pvd (Jan 4, 2006)

It's used to set jigs.


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## b00001 (Dec 28, 2005)

Great.

Thank you!

So the larger the number is when referring to BB Drop, the LESS clearance you would have in hitting rocks etc?


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## scottzg (Sep 27, 2006)

no, the other way around, the number is how far below the axle line the bb is. You're trading stability for clearance. The big advantage, in my opinion, of 29'ers is that they can run a TON of bb drop and still have a reasonable bb height.


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## pvd (Jan 4, 2006)

Drop is useful when making a bicycle.

Height is useful for describing how the bike rides.

Once you cross uses, you get all screwed up.


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## scottzg (Sep 27, 2006)

pvd said:


> Drop is useful when making a bicycle.
> 
> Height is useful for describing how the bike rides.
> 
> Once you cross uses, you get all screwed up.


sometimes i wonder if you take a position just because you hope to start an argument.

Not today buddy.


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## coconinocycles (Sep 23, 2006)

scottzg said:


> sometimes i wonder if you take a position just because you hope to start an argument.
> 
> Not today buddy.


no, he's actually basically correct. Steve Garro, Coconino Cycles.


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## b00001 (Dec 28, 2005)

This still is not making sense to me. Sorry. 

If one bike has a 2.7 BB drop and another has a 2.4, this means the bike with the 2.7 will have a lower bottom bracket, meaning when this bike is pedaled, the pedals will be closer to the ground. Correct?


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## shiggy (Dec 19, 1998)

b00001 said:


> This still is not making sense to me. Sorry.
> 
> If one bike has a 2.7 BB drop and another has a 2.4, this means the bike with the 2.7 will have a lower bottom bracket, meaning when this bike is pedaled, the pedals will be closer to the ground. Correct?


_*Measured*_ BB height is independent of the wheel/tire size.

When a company states a BB ht they should also include what tire size was used.

To keep the BB ht the same with different wheel/tire sizes, the BB drop needs to be adjusted. A frame designed for larger diameter wheels would have more BB drop.

In your example above, if both bikes used the same tires and wheel size, yes, you are correct. More drop = lower BB.

But if the 2.7" drop frame used 29x2.1 tires and the 2.4" drop frame used 26x2.1 tires, the first would have a higher BB by about an inch. Even if both frames use 26" tires you could reverse the BB ht with an extreme tire choice (i.e. 1.5" vs 2.8").


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## b00001 (Dec 28, 2005)

shiggy said:


> _*Measured*_ BB height is independent of the wheel/tire size.
> 
> When a company states a BB ht they should also include what tire size was used.
> 
> ...


Perfect. I am looking at 2 frames, as I will be using my current parts for build. They have the above BB Drops. If I have a problem bottoming my pedal into rocks, I would be better off going with a 2.4 drop vs a 2.7.

Thanks again!


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## scottzg (Sep 27, 2006)

coconinocycles said:


> no, he's actually basically correct. Steve Garro, Coconino Cycles.


Ehhh...?

Let's take an extreme example- you have 10 foot tall wheels with a normal 12.5" BB height. The BB drop is going to be ~4.5.' Please, tell me that this bike will be just as easy to go otb on as a 26'er.

Same with side to side motion. You have my little balance bird like the pic i posted. Those things are pretty stable, but if move the weights in his wings down a foot he will be even more stable.

BB height only sort of indicates how likely you are to smack the pedals, maybe.


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## shiggy (Dec 19, 1998)

scottzg said:


> Ehhh...?
> 
> Let's take an extreme example- you have 10 foot tall wheels with a normal 12.5" BB height. The BB drop is going to be ~4.5.' Please, tell me that this bike will be just as easy to go otb on as a 26'er.
> 
> ...


You are being way too extreme. To re-state PVD's post (and he has said it similarly before), BB drop is how a frame builder sets the bike's BB height.

Whatever the latter is (or is what to be), it is part of the overall bike design, as is the wheel size (and a lot of other factors). BB drop is what you do to achieve it.


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## shiggy (Dec 19, 1998)

b00001 said:


> Perfect. I am looking at 2 frames, as I will be using my current parts for build. They have the above BB Drops. If I have a problem bottoming my pedal into rocks, I would be better off going with a 2.4 drop vs a 2.7.
> 
> Thanks again!


You already know. Higher BB = more pedal clearance.


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## pvd (Jan 4, 2006)

scottzg said:


> Let's take an extreme example- you have 10 foot tall wheels with a normal 12.5" BB height. The BB drop is going to be ~4.5.' Please, tell me that this bike will be just as easy to go otb on as a 26'er.


Obviously, you have no idea what you are talking about.


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## themanmonkey (Nov 1, 2005)

The way I like to think about it is drop is a frame dimension and height is a bike dimension. People that use drop are designers or builders of bike frames because it's a dimension that is independent off all the other parts of the bike and refers to the frame alone. Height is what is achieved when the bike is all built up and ready to ride.


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## Schmitty (Sep 7, 2008)

Bunch of freekin old ladies. You seriously can't think of bb drop and height interchangeably and without the drama?

-Schmitty-


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## pvd (Jan 4, 2006)

Life is so funny.

I went out on a ride this afternoon. I was having a good time, trying some new lines in the same old sections. I commited 100% to a new line in some dark space. The wheel locked into a hole and I was pitched as the bike spun over in the air. As I was crashing I was watching my bike and thinking of this thread. I landed just laughing. So funny to have this happen just as it came up online. Then I looked down and my knee was not happy. I just got back from the hospital with a major laceration to the knee and a bunch of stiches. 9 days off the bike coming up.


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## scottzg (Sep 27, 2006)

pvd said:


> Life is so funny.
> 
> I went out on a ride this afternoon. I was having a good time, trying some new lines in the same old sections. I commited 100% to a new line in some dark space. The wheel locked into a hole and I was pitched as the bike spun over in the air. As I was crashing I was watching my bike and thinking of this thread. I landed just laughing. So funny to have this happen just as it came up online. Then I looked down and my knee was not happy. I just got back from the hospital with a major laceration to the knee and a bunch of stiches. 9 days off the bike coming up.


bummer


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## scottzg (Sep 27, 2006)

scottzg said:


> Let's take an extreme example- you have 10 foot tall wheels with a normal 12.5" BB height. The BB drop is going to be ~4.5.' Please, tell me that this bike will be just as easy to go otb on as a 26'er.


this is a bad example. Too many other factors.


scottzg said:


> You have my little balance bird like the pic i posted. Those things are pretty stable, but if move the weights in his wings down a foot he will be even more stable.


this is a good example.


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## b00001 (Dec 28, 2005)

pvd said:


> Life is so funny.
> 
> I went out on a ride this afternoon. I was having a good time, trying some new lines in the same old sections. I commited 100% to a new line in some dark space. The wheel locked into a hole and I was pitched as the bike spun over in the air. As I was crashing I was watching my bike and thinking of this thread. I landed just laughing. So funny to have this happen just as it came up online. Then I looked down and my knee was not happy. I just got back from the hospital with a major laceration to the knee and a bunch of stiches. 9 days off the bike coming up.


PVD-Sorry man! That has happened to me as well. That is why I wanted to be certain I understood BB Drop as I want to get a hair of extra clearance if possible. Hope you heal up quick. You will not be off the bike that long. Give it a couple days to scab up good, wrap it and go ride!!


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## NorseRider (Feb 9, 2004)

coconinocycles said:


> no, he's actually basically correct. Steve Garro, Coconino Cycles.


And I'm with Steve.

Truls


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## pvd (Jan 4, 2006)

*OTB Test #1*

I think it ended up with about 10 stitches.


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## Caisse (Jul 29, 2017)

*My explanation of BB drop and BB height.*



b00001 said:


> I did some searching and I could not find a thread that explained what BB Drop actually means.
> 
> I am looking at a few different frames and some list BB height which I can understand, others list BB Drop. One frame lists a BB Drop of 2.69, and another lists a BB Drop of 2.36. What does this mean?
> 
> Thanks in advance!


BB height is dependent on tire size, and is the space from the ground to center of BB.
BB drop is how far below the center of the wheels.

So if you take a string between the center of each tire, it would be the measurement from that line to center of BB.


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## Eric Malcolm (Dec 18, 2011)

So if you take a string between the center of each tire, it would be the measurement from that line to center of BB.[/QUOTE]

And from this measurement we set up our jigs........

Eric


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## Black Squirrel (Oct 13, 2016)

This thread is from 2009.


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## life behind bars (May 24, 2014)

Black Squirrel said:


> This thread is from 2009.


And yet still relevant.


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