Random bikt question

[Jack Brunk]

Is a lower bottom bracket better/worse on a road bike built for long distances and lots of climbing?

Thoughts please

[chuckred]

I've wondered the same thing - for when/if I ever go the custom route.

My understanding and am also interested in what the gurus have to say - is that the lower bottom bracket is more stable due to lower center of gravity if you get your weight on the outside pedal in a turn. Since lots of climbing tends to also mean lots of high speed descending, that seemed to be a desireable trait.

Higher bottom bracket is better for pedaling through fast corners, as in a crit, high speed mountain descents don't tend to have the same need for fast acceleration out of flat corners.

Not trying to answer your question, that's better left for the framebuilders here, but just throwing my understanding out there for a "reality check".

[chrisroph]

J, i have always liked the feel of a low bb in a road bike, 75mm or so drop, they seem to climb and descend better than higher bb bikes. the confounding exception to this is my 56cm r3 whose specs say 67mm drop. its a very good stable descender, go figure.

[goonster]

It depends . . .

(but I say "yes".)

[Dave Wages]

My own experience with lowering the BB shell is that it makes you feel like you're riding in the bike rather than on top of the bike. Provided you aren't riding lots of criteriums or pedaling through corners, you'll probably like a lower BB height. I find 80mm of drop just fine with 175 cranks. It tends to feel a bit more stable as well, provided the rest of the geometry is the same.

[Keith A]

Hi Jack. I'm certainly no expert (but I play one on the Internet :rolleyes: ), but I would say that a lower bottom bracket would indeed be better suited for long distances with lots of climbing.

The compact CSi I purchased from Climb has an 8.0mm bottom bracket drop on it. It took me a while to adjust to how different this felt from the 7.0mm drop that I was used to. The problem was that it felt too stable and therefore didn't react as quickly to steering input. However, now that I have adjusted to the feel, I think this is a great bike. It is extremely stable going down hill -- at least on my short descents on the causeway and I don't notice any ill affects from the lower BB when going up.

You can certainly feel the lower center of gravity which would have to be a plus on your descents. If possible, I would suggest you try and find one to take on a test ride before you make the plunge.

[Mark35]

A lower bottom bracket also reduces the stiffness of a frame. All other things being equal.

[David Kirk]

A lower bottom bracket also reduces the stiffness of a frame. All other things being equal.

really......how is that?


dave

[victoryfactory]

another benefit of a low BB is that you can coast to a stop, unclip one foot
and place your toe on the ground to balance without dismounting.
A great thing at stoplights.

(unless you are one of those track stand guys)

VF

[Grant McLean]

A lower bottom bracket also reduces the stiffness of a frame. All other things being equal.

why, because the chainstays are a few mm's longer?



-g

[goonster]

A lower bottom bracket also reduces the stiffness of a frame. All other things being equal.

I'll buy that. The moment arms are longer.

(AOTBE bolded for emphasis)

[Ken Robb]

I think I'll beleive what Mr. Kirk has to say about frame design. :banana:

[J.Greene]

Jack,

Your current BB is holding you back man. Just think how much faster you'd be with 80mm of drop on the IF.

JG

[Pete Serotta]

general belief is that bike is more stable. (whatever that means). Serotta use to have a higher bb and then went to a little lower one (I could not tell the difference but then I am numb.)

Sach's frames were one of the the longest running having a lower bb from the general industry (I am told).

Serotta went to it in about 2002 or so. It is part of the overall design of the frame so the figure by itself does not mean that much, if anything.

Crit bikes use to have a higher bb BUT I was told that was because of corner clearance with pedals. (the newer pedals of the last 10 plus years take that need away.)

[Steve Hampsten]

For myself, I find a low BB - 80mm of drop - feels pretty stable but somewhat sluggish when sprinting or standing to climb. A 70mm drop seems to initiate a turn faster, sprints better, climbs just fine, but doesn't feel as stable on gravel or crap roads. Seated climbing feels about the same either way.

I'm looking forward to my new build with a 75mm drop... BB drop feels mostly subjective, imho.

These are just my preferences; I know lotsa guys who like an 80 drop.

[e-RICHIE]

all things being equal, more frame drop yieldsmo -

> a shorter head tube
> a shorter seat stays
> a shorter down tube
> a more elegant angle to the chainstays
> loss of power if you're a governor

there is no down side to lowering your bicycle's cog atmo.
yeah - i can hear the scraping pedals posts comingmo.

[Jack Brunk]

Jack,

Your current BB is holding you back man. Just think how much faster you'd be with 80mm of drop on the IF.

JG
JG,

I'd be much faster if I had the Ducati 1098 I saw stand on end in Malibu yesterday.

[Pete Serotta]

luckily no governors or (ex) here and the only governor I have is on my legs :confused: :confused:

all things being equal, more frame drop yieldsmo -

> a shorter head tube
> a shorter seat stays
> a shorter down tube
> a more elegant angle to the chainstays
> loss of power if you're a governor

there is no down side to lowering your bicycle's cog atmo.
yeah - i can hear the scraping pedals posts comingmo.

[sg8357]

How do you determine what BB drop to use on a frame ?

Since I ride 175mm cranks with an 8cm drop and corner OK.

Could a bike designed for 170mm or 165 mm cranks use more drop ?

[e-RICHIE]

How do you determine what BB drop to use on a frame ?


personal conviction.
corporate culture.
stuff like dat atmo.

[Steve Hampsten]

personal conviction.
corporate culture.
stuff like dat atmo.


you left out "coin toss"

[Pete Serotta]

Spokes has one of them. I see him when we start a ride and at the end. My GS just can not hang (nor can my skills)

JG,

I'd be much faster if I had the Ducati 1098 I saw stand on end in Malibu yesterday.

[J.Greene]

JG,

I'd be much faster if I had the Ducati 1098 I saw stand on end in Malibu yesterday.


What a sexy bike. I hear it has about 80mm of drop.

JG

[David Kirk]

why, because the chainstays are a few mm's longer?



-g

Chainstays are a center to center thing and don't change with drop. It's the actual length of the tube if you will. So a bike with 41.5 stays will have the same length tubes even considering a drop of 60 on one and a drop of 80 on the other.

when you lower the BB you also -

* make the head tube shorter

*make the seat stays shorter



Everything else stays the same. So if one wanted to make a statement like "a lower BB makes a stiffer bike" they probably could but I think it would be silly. The difference would be hard to test for let alone feel.

Back to the bench.

dave


edited because I didn't see sir richie's post above. He already said it all.

[e-RICHIE]

<snipped>


edited because I didn't see sir richie's post above. He already said it all.
ps bicyces with more drop are also NGS approved atmo.

[chrisroph]

JG,

I'd be much faster if I had the Ducati 1098 I saw stand on end in Malibu yesterday.

My 1098 is my only yellow bike at the moment.

I put a DP kit (full exhaust, intake, ecu) on the thing and it makes about 165hp, enough to do an accidental power wheelie at 80mph.

Its a completely ridiculous machine but I love it.

[big shanty]

ps bicyces with more drop are also NGS approved atmo.

It's true...I won't settle for anything less than 80 mm.

Arigato,

NGS

[Mark35]

Could someone explain why the downtube does not get longer when the bb is lowered?

[David Kirk]

Could someone explain why the downtube does not get longer when the bb is lowered?

The DT does get very slightly longer as the BB drops.

dave

[swoop]

you gotta look at the whole bike and how you sit on it.
a lower bb means the bb is lower. there is no big difference separate from the rest of the bike.
my favorite bike has a 6.5 drop. the bb doesn't know for how long i'm riding. its really about what you like.

i think one can look at it in terms of the analogy oversteer and understeer and which you prefer... and then think of the bb drop as one data point among many towards how one designs personality into the bike.

but i'm just a shrink between patients.... so read and flush.

go out and ride your different bikes and notice what you go through initiating a turn on a descent. notice what you have to do different on each bike to get the thing to turn...

and see if they feel different from each other.

that's what comes to mind.

what also comes to mind is that i should stick to the little area of expertise i have which happens to have nothing at all to do with bikin... yikes.

[David Kirk]

Hey Mark35,

I was curious about how much longer the DT would actually be considering BB drop. I'm in the process of building a frame that has 80 drop. I mocked it up quickly to see what the difference in DT length would be if moving to a more old school drop of 70. This frame is a 54c-c FWIW.

drop 80 70
DT length c-c 614 606
percentage change 1.4%


I also too a look at the change in front center when going from 80 to 70.

drop 80 70
front center 580 579
percentage change .002%


I don't thing the difference either way is going to affect frame stiffness in anyway really.

dave

[Grant McLean]

Chainstays are a center to center thing and don't change with drop. It's the actual length of the tube if you will. So a bike with 41.5 stays will have the same length tubes even considering a drop of 60 on one and a drop of 80 on the other.



ya, i was just speaking strickly in the Pythagorean theorem geometry sense.

But if we're talking chainstay stay tube as actual c to c, then changing the bb height
changes the wheelbase. (i was sticking to the 'change nothing else' from the
original post )

-g

[steve575]

I'm 6'4" and ride 175 cranks. I tend to like lower (80mm) bb drops better. Some manufacturers raise the bb when you get into a taller frame. I had a frame with a 65mm bb drop and in order to keep my seat to bar drop the same, my bars were higher relative to the ground. I just didn't feel as comfortable. I've never struck a pedal with my 175s an 80mm drop. Also, there is something to be said for being able to put a foot on the ground in the sadle. Some of the Euro built cross bikes are way up there. I'd be hittin my head on tree branches.

[Mark35]

Hey Mark35,

I was curious about how much longer the DT would actually be considering BB drop. I'm in the process of building a frame that has 80 drop. I mocked it up quickly to see what the difference in DT length would be if moving to a more old school drop of 70. This frame is a 54c-c FWIW.

drop 80 70
DT length c-c 614 606
percentage change 1.4%


I also too a look at the change in front center when going from 80 to 70.

drop 80 70
front center 580 579
percentage change .002%


I don't thing the difference either way is going to affect frame stiffness in anyway really.

dave

Hello Dave,

I agree with you that one probably cannot feel the change in torsional stiffness due to the longer downtube. It's there, and is measurable. But the difference in how the bike handles due to the lower bottom bracket is infinitely more noticeable.

As close as the dimensions are between the bike you built for me and my other road bike, I still find it amazing the difference in how the two bikes handle. Especially, out of the saddle and also railing through turns on mountain descents. Every time I go out to ride the Kirk is always my first choice.

Mark

[davids]

I would think that the most noticeable difference as a frame's bb gets lower would be with your overall center of gravity. What effect this would have on handling is beyond me.

My Nove has an 8cm drop, and my Love #3 has a 7cm drop. I notice the slight difference in height when I move from one bike to the other. But they both handle great, and any advantage the Peg has seems to me to have more to do with front-center than bb drop.

And, also, it can affect how far you can see down the road.

[handsomerob]

My 1098 is my only yellow bike at the moment.

I put a DP kit (full exhaust, intake, ecu) on the thing and it makes about 165hp, enough to do an accidental power wheelie at 80mph.

Its a completely ridiculous machine but I love it.

where is the point of diminishing return as far as HP on a motorcycle that weighs 400lbs. Is there any point where you can even use full throttle?

[Erik.Lazdins]

I had a bike with a higher bb than my Serotta that didn't feel as fast through a corner at speed - less stable?

I thought both bikes fit me seat tubes and top tubes saddle heights, saddle to bar reach were the same yet the Serotta feels faster in turns and inspires more confidence in descents.

The bikes I seems to be a fan of now all share lower bottom brackets - but I don't know if the bb is the sole reason.

I suck at climbing but love it much as I suck at cycling yet love it! Its the journey rather than the destination for me. Any new bike I get I wonder - how will this do on the Talimena Scenic drive? That route is the test though I probably ride only it 2-5 times per year.

Jack,
Based upon your experience in riding different bikes bikes what are your thoughts on a lower bb to a bike being suitable in climbing/descents?

Thanks for reading - E :beer: :beer:

[Jack Brunk]

I had a bike with a higher bb than my Serotta that didn't feel as fast through a corner at speed - less stable?

I thought both bikes fit me seat tubes and top tubes saddle heights, saddle to bar reach were the same yet the Serotta feels faster in turns and inspires more confidence in descents.

The bikes I seems to be a fan of now all share lower bottom brackets - but I don't know if the bb is the sole reason.

I suck at climbing but love it much as I suck at cycling yet love it! Its the journey rather than the destination for me. Any new bike I get I wonder - how will this do on the Talimena Scenic drive? That route is the test though I probably ride only it 2-5 times per year.

Jack,
Based upon your experience in riding different bikes bikes what are your thoughts on a lower bb to a bike being suitable in climbing/descents?

Thanks for reading - E :beer: :beer:
My experience is telling me that I really don't have a clue on the BB thing. More than anything what I've learned is frame geo and frame materials is key to a great frame. Most of my bikes have had either a 7-8 cm bb drop and I can't really tell much from that number. I can tell on my track bikes the BB drop because I really feel on top of the bike, alot less stand over height and the bikes really handle fast. I was more curious on the BB drop issue from an information viewpoint.

[e-RICHIE]

My experience is telling me that I really don't have a clue on the BB thing. <cut>
the truth atmo is that you really can't separate out
any details from the whole. and i'm not trying to start a
gestalt-a-thon either. if there are frame design elements
that are wacked, a low bike won't help it. if the chainstays
are too short for the drive train to work fluidly, a good
fit on it will not be a great ride. it's all connectedmo.

[chrisroph]

where is the point of diminishing return as far as HP on a motorcycle that weighs 400lbs. Is there any point where you can even use full throttle?

long before what this bike has. However, the fact that it is a big bore twin, and the dp kit, give it wonderful low rpm torque and partial throttle response. i rarely give this thing full throttle--it feels like a time warp--but its there if you want to use it.

one magazine tested a kitted 1098 at under 10 secs in the 1/4 mile trapping at around 150.

[e-RICHIE]

I was more curious on the BB drop issue from an information viewpoint.
it's fair to say that the replies here are wrt to road bikes only atmo.

[big shanty]

it's fair to say that the replies here are wrt to road bikes only atmo.

Does that include cross bikes, fixed gears, etc....or just road race bikes?

[Erik.Lazdins]

for posting this thread - its something I've wondered about out on rides, knowing that I don't know things, but still thinking about these things.

I've learned from the thread - thanks!

E :beer:

[e-RICHIE]

Does that include cross bikes, fixed gears, etc....or just road race bikes?
for me it's across the board; 'cross bicycles get their advantage from the
depth of the wheels, so the drop yields a higher bike no matter. but remove
the gears from this thread and we're at a different zeitgeist atmo.

[Ti Designs]

With tandems the captain's bottom bracket uses an offset eccentric to adjust the timing chain tension. That means there are two possible BB heights, one if the offset is above the center, the other if it's below. There are a zillion reasons for setting it up one way or the other, stability, pedal clearance, captain height, not blocking the stoker's view... It seems somewhat easy to build a test rig to see what BB height does for a single bike using the same sort of thing. One bike with just a 5mm offset would yeild a 7cm drop, an 8cm drop or a 7.5cm drop (using a centered shell). If you want to be accurate in position you could even drop out a spacer under the stem, and don't forget to lower the saddle. Given the number of bikes that some forum members have, I don't see why someone doesn't order one. It's not the lightest thing in the world, but I've also noticed there's no carbon size cycle offered...

[jerk]

With tandems the captain's bottom bracket uses an offset eccentric to adjust the timing chain tension. That means there are two possible BB heights, one if the offset is above the center, the other if it's below. There are a zillion reasons for setting it up one way or the other, stability, pedal clearance, captain height, not blocking the stoker's view... It seems somewhat easy to build a test rig to see what BB height does for a single bike using the same sort of thing. One bike with just a 5mm offset would yeild a 7cm drop, an 8cm drop or a 7.5cm drop (using a centered shell). If you want to be accurate in position you could even drop out a spacer under the stem, and don't forget to lower the saddle. Given the number of bikes that some forum members have, I don't see why someone doesn't order one. It's not the lightest thing in the world, but I've also noticed there's no carbon size cycle offered...


did you get that advice at the salon?

jerk

[swoop]

oh nevermind.

[mgm777]

The ambiguity with all this is that one rider's "agile" is another's "twitchy". Someone's "sluggish" is another's "stable". Ride what you like. Better yet, just ride. :)

[stevep]

eddie,
you could also get one of those eccentric rear hubs to go with this.
you could adjust the thing 50 different ways.
bring an allen key w/ you and you could change it in the middle of a ride.
maybe someone has an eccentric front hub to finish the project?
you could ride it in the shriners parade.but you gotta learn to juggle first.

With tandems the captain's bottom bracket uses an offset eccentric to adjust the timing chain tension. That means there are two possible BB heights, one if the offset is above the center, the other if it's below. ...

[J.Greene]

I prefer to build my wheels with hubs that are not in the center of the wheel. That way you get the Forrest Gump (life is like...) effect. Dynamic drop is where its atmo.

JG

eddie,
you could also get one of those eccentric rear hubs to go with this.
you could adjust the thing 50 different ways.
bring an allen key w/ you and you could change it in the middle of a ride.
maybe someone has an eccentric front hub to finish the project?
you could ride it in the shriners parade.but you gotta learn to juggle first.

[David Kirk]

I prefer to build my wheels with hubs that are not in the center of the wheel. That way you get the Forrest Gump (life is like...) effect. Dynamic drop is where its atmo.

JG

Built some wheels like that once for a group of Shriners for parade bikes. The had a good 2" offset to the hub. Those bikes were hard to ride.

dave

[Peter P.]

Too bad Dave Moulton doesn't participate on this forum. He could throw a wrench in the works with this discussion. Read his take on bottom bracket height/drop:

http://www.prodigalchild.net/Bicycle6.htm#BBheight

[e-RICHIE]

Too bad Dave Moulton doesn't participate on this forum. He could throw a wrench in the works with this discussion. Read his take on bottom bracket height/drop:

http://www.prodigalchild.net/Bicycle6.htm#BBheight
well if he ends with this,

"On an all-round frame like the Fuso that could be used for racing or pleasure riding; 7cm. of drop was (and still is.) a good compromise."

then the wrench wouldn't do much harm then atmo.

[roman meal]

What if you combine all three below on a fixed gear? We invented the pudding cup, peel and eat shrimp, and the glory hole. We can certainly get Jack's contact points centered over the bb.

[vaxn8r]

My two Serotta road bikes Atlanta and Legend were stock and had 7 cm drop. They both handle(d) great. I've ridden 2 other Serotta with 8 cm drop. One was stock(Attack), one was custom(Ottrott) but both were my size exactly. I can't say I cared for the bikes with 8 cm drop. I seriously doubt all things were equal because you can probably never ensure that. But for me, 7 cm of drop seems to work fine.

I truly believe you know when a bike feels right and you can tell when there is something wrong. Ride your bike a lot and it will be the one all others are compared to.

I don't know anything about frame design but I assume if I ride a stock Serotta or a Kirk or a Colnago, I'm riding the bike with the framebuilder's bias of how it ought to behave and handle. I can live with that. I don't think it's a matter of right or wrong or better.

[Steve Hampsten]

What if you combine all three below on a fixed gear? We invented the pudding cup, peel and eat shrimp, and the glory hole. We can certainly get Jack's contact points centered over the bb.

good point - i agree 100.1%. jack's in good hands, imho

but surely a 8cm drop is for shirleys? i mean, nothing wrong with that, but isn't 8cm the... you know..."jollyest" of all BB drops? which is ok, if you like that sort of thing

atmo

[Too Tall]

I paid good money to not know what the drop is. That's my story.

[saab2000]

I paid good money to not know what the drop is. That's my story.

Prolly the best advice here.