Why low bottom brackets on Serottas?

[jckid]

I didn't realize how low the bottom bracket is on my Fierte until I got a new Bike Friday. The difference is dramatic--like almost an inch! I always feel like I'm going to whack my crankarm when I pedal through corners on my Serotta. With my Friday, I don't have to worry about it. I like the feel of the higher bottom bracket better.

This has me wondering, what is the point of a low bottom bracket? I'm assuming there must be some reason why some bikes have an 8cm drop, while others have a 10cm drop, but I have no idea what the reason would be.

[Fixed]

bro get used to it it rides better
cheers.... bro I don't think your bike has a 10 b. b.d.

[KevinK]

I think its more the case that your Bike Friday has a higher than normal BB. My understanding is that because the smaller wheels on a Friday require much larger chainrings, a higher BB height keeps the large chainring from hitting curbs and other obstacles when you go up and/or over them.

Kevin

[Ozz]

... I always feel like I'm going to whack my crankarm when I pedal through corners on my Serotta. ...
If you're pedalling thru corners, you're going too slow! ;) :p

BTW - you only have 8cm BB drop on your Fierte....unless you have a 60 or 62 frame....then you 7.5CM

[dgauthier]

This has me wondering, what is the point of a low bottom bracket?

Based on the info I've absorbed over the years from this forum, a lower bottom bracket is supposed to make the bike feel more stable, especially during technical descents. Pedalling through corners is supposed to be bad technique on such a bike. On the other hand, some bikes are specifically designed with higher bottom brackets to allow for pedalling through corners, as one might do during a short, fast street race. This is achieved at the expense of stability, however. It all depends on what you want.

Perhaps one of the handsome and talented frame builders that frequent this forum could provide more detail.

[Ray]

I'm assuming there must be some reason why some bikes have an 8cm drop, while others have a 10cm drop, but I have no idea what the reason would be.
I'll leave it to others to sing the praises of low bottom brackets (I tend to like 'em but can't isolate the variables well enough to tell you why), but to correct your math slightly. 8cm of bb drop is considered a LOT. Serottas have it, Rivendells have it, I'm sure the custom builders do it on some of their bikes, but I've never seen a production bike with any more drop than that. 10 cm of drop is pretty much unheard of unless you're using wheels larger than 700c, which I'm not aware of. Bike Fridays do have high bbs, by the way, which may be one of the reasons I never got comfortable on a friday for longer rides. I've had two of these bikes and 40-45 miles was about my limit on either of 'em.

-Ray

[atmo]

what road bikes have a 10cm drop atmo!?

[MartyE]

perhaps what we have here (is a failure to communicate? . . .wait wrong
movie) is a mix of terms and we are confusing Bottom Bracket Drop with
Bottom Bracket Height?
My Reus is a dutch criterium geometry, very high bottom bracket it's close
to that of my track bike, is that what OP is talking about? I know I'd have
to seriously lean this bike over in a corner to get any pedalstrike.

marty

[jckid]

Yes, I guess I was a bit confused. I do know that my Fierte has an 8cm bb drop. Prior to my Serotta, I had a Litespeed Firenze that had a higher bottom bracket. I was thinking that a higher bottom bracket meant a larger number, but I guess the reverse is true. I looked up the geometry of the Firenze and found that it had a 6.7cm bottom bracket drop.

As far as me being slow, well yes, I am probably slow compared to many of you. I don't worry about speed as much as I did when I was younger. I just ride, because I love to ride. And I ride alone most of the time anyway, so I don't have to worry about keeping up with a group.

[ken]

I've got a quick question for you geometry gurus.

Some companies list "Bottom Bracket Drop" while others (a minority) list "Bottom Bracket Height" in their geometry tables. I'm having trouble trying to compare these two. In simple math, my guess is that if you add these two, you end up with the radius of the wheel.

My question is this: What is considered the standard radius of a 700c or 27in wheel, considering variability in wheel/rim and tire height?

Thanks for your collective expert insights.

Ken

[Jason E]

Good question, Ken. I was noticing that after reading this thread and comparing geometries from different sites and catalogs...

It seems a lot of cross specific geometry from Felt or IF are around 5.5 or 6 for BBD and then others are using closer to Road bike heights, 8 cm +/-.

Is the Lower BB on 'Cross bikes (Specialized for example), as opposed to the older idea of a higher BB (the aforementioned IF), to go along with the faster courses being put up with less barriers, or just a case of some people like peanut Butter and others do not?

I was mentioning to someone that I like the higher BB because it allows me the rare opportunity to have decent seatpost showing and still have a level TT. Something my little stumps do not often allow for, though, that's ruly just a useless aesthetic reason.

[atmo]

Good question, Ken. I was noticing that after reading this thread and comparing geometries from different sites and catalogs...

It seems a lot of cross specific geometry from Felt or IF are around 5.5 or 6 for BBD and then others are using closer to Road bike heights, 8 cm +/-.

Is the Lower BB on 'Cross bikes (Specialized for example), as opposed to the older idea of a higher BB (the aforementioned IF), to go along with the faster courses being put up with less barriers, or just a case of some people like peanut Butter and others do not?

I was mentioning to someone that I like the higher BB because it allows me the rare opportunity to have decent seatpost showing and still have a level TT. Something my little stumps do not often allow for, though, that's ruly just a useless aesthetic reason.


1) center of gravity heights on 'cross frames were higher in
the old days to allow toe clips to dangle during dismounts
and re mounts atmo.
2) the higher bb won't affect your seatpost amount at all. unless
i misunderstand your point, how do you reconcile seatpost
height amounts unless a seat tube length differs? bb height
and frame drop won't rearrange your leg extension adios.

[Jason E]

1) center of gravity heights on 'cross frames were higher in
the old days to allow toe clips to dangle during dismounts
and re mounts atmo.
2) the higher bb won't affect your seatpost amount at all. unless
i misunderstand your point, how do you reconcile seatpost
height amounts unless a seat tube length differs? bb height
and frame drop won't rearrange your leg extension adios.


To Part 1: Ahhhh.... Clever....

To Part 2: The Key was the "and still have a level TT" part.

48cm c-t-c is always 48cm c-t-c, but with the higher BB, the TT is level if the HT is i n the same spot. The Lower BB makes my little tiny elfin frames into slopers. :rolleyes:

That's all I meant.

[atmo]

To Part 1: Ahhhh.... Clever....

To Part 2: The Key was the "and still have a level TT" part.

48cm c-t-c is always 48cm c-t-c, but with the higher BB, the TT is level if the HT is i n the same spot. The Lower BB makes my little tiny elfin frames into slopers. :rolleyes:

That's all I meant.


hmm
if both frames are 48cm seat tubes, one has more post showing atmo?

[Jason E]

No, the tt is closer to Level which makes me feel like a tall boy.....

[insert artist formerly known as Manet's internet link of a tall boy here]

[atmo]

No, the tt is closer to Level which makes me feel like a tall boy.....

[insert artist formerly known as Manet's internet link of a tall boy here]

ah - i feel ya' atmo.
thanks.

[Grant McLean]

. Pedalling through corners is supposed to be bad technique on such a bike. On the other hand, some bikes are specifically designed with higher bottom brackets to allow for pedalling through corners, as one might do during a short, fast street race...

Just to expand on this point a bit, it's very possible to pedal through corners
on a low bb bike, it just depends on your technique, speed, and where you
define the "corner" to start and end. Look at these different lines....

I don't think anyone means to pedal the whole way through the corner.
If that happens, you're going so slow, it's not going to matter.
It's about at what point you start your pedals turning after the apex. The
point is to carry as much speed at the apex as possible, and keep your
momentum going. The bike is leaned over furthest at the apex, and there's
no reason you can't "straighten up" and start peddling after this point.
In a group, if you're in the middle, boxed in, the people around you are
going to determine your line and speed. One or two revolutions isn't going
to get you dropped.

g

[Fixed]

bro
nice grant
cheers