View Full Version : bb height
MadRocketSci
01-14-2004, 02:52 PM
Hi alls,
I've seen a lot of people talk about the advantages of having a lower 8 cm drop, and I'm curious to know if there are any disadvantages. I ride out here in the San Francisco Bay Area, specifically the hills west of Palo Alto, where we have some long, twisty, turny descents (love the west side of alpine rd). Would a 7 cm drop have some advantages here? I've heard some west coast builders like Della Santa and Fuso build with a higher bottom bracket, so I'm wondering if the terrain is part of the reason. Or are there other reasons?
I've just built up my '97 7 cm bb-drop stock Atlanta, so I'm just curious to know...
Thanks!
Ben
BigMac
01-14-2004, 03:52 PM
No disadvantages, only advantages. Lower BB will actually make for a more stable high speed descender as well as a more adept climber.
Where did you hear or read Roland Della Santa or Dave Moulton (Fuso builder/designer) preferred high bb's. Dave had a brief run of so-called early 80's "Americanized-crit" inspired geo frames complete with steep, fast front ends and high bb's Fortunately most builders, American and foreign, have since dropped this style of offerings. Most Dave Moulton designs, including his great "John Howard" labeled customs during the late 80's have around 7.4-7.5cm drop. Similarly every Della Santa I've seen is built around similar bb drop unless for some reason a rider absolutely insisted on a higher bb, all Della Santa's are custom afterall. I still see some of the newer builders employing 7cm drops, occasionally even less but most experienced builders, particularly those with racing backgrounds either as a builder or rider, are employing 75-80mm drop.
Ride on!
MadRocketSci
01-14-2004, 04:07 PM
BigMac, thanks for the reply.
About Della Santa and Fuso...Della Santa I can't back up besides saying I remember someone telling me. What they said was the opposite of what you said, ie, 'he likes to design with a higher 7 cm bb drop but will do 8 if you ask for it'. But, like I said, that's just something I thought I remembered hearing. Maybe someone with a Della Santa could chime in.
Fuso statement comes from the Shaw's cycles webpage, in regards to Russel Denny...
"The Fuso road is the perfect American all round frame. With a high bottom bracket and stiff backbone the Fuso is at home sprinting through corners in a criterium while it’s balance, compliance and Dave Moulton design allows the rider to negotiate with confidence the twisting washboard descents found here in the San Francisco Bay Area. Built and painted in Southern California Pricing is moderate with delivery usually under 6 weeks. "
http://www.shawscycles.com/frame.html
If there are no advantages, why did Serotta use the higher drop until recently?
Thanks again.
hypnos
01-14-2004, 04:14 PM
Will be finalizing the order for a fixed gear road frame. Would like to use 170mm cranks. Are there any opinions regarding optimal BB drop for this application.
Jeff
BigMac
01-14-2004, 04:40 PM
I can't honestly say why Serotta used 7cm drop up until '01 or '02. I do recall the owner at my local shop indicating the request for lower BB's was among the most commonly requested items on Serotta's custom order sheet, that and HT extensions. Apparently, Ben & Co listened to consumer demand and made these items standard fare at the same time.
I know Roland a little bit, he is among the many Eisentraut influenced builders from 60's/70's, Albert builds 8cm drop as standard and has for many decades with very few exceptions. I also have several friends with Della Santa's, his largest dealer was located in nearby Orinda, CA for many years, they all have low-ish bb's.
The Fuso frames I referred to were the original creations of Dave Moulton. I in fact was unaware somebody had resurrected the name or design. Unfortunately, this new Fuso seems to have followed short-lived 80's version. Are they all painted frost white with the neat HT badge depicting a finery pot pouring moulton steel into a casting? This were GREAT looking frames, even if they did handle like a junkie on withdrawl.
The geometry Dave employed on his John Howard frames as well as the beautiful frames he constructed during his tenure under Masi in SanMarcos is a far better riding and handling bike, usually with moderately slack STA's, low-ish BB's and lovely handling front-ends (57-59mm trail depending on frame size). Faleiro Masi had a great deal of influence on much of Dave's work noted by very clean and simple lug lines along with smooth and relaxed geometry. Frankly the idea of a high BB needed for crit racing is a bad 80's joke. If you're racing fast enough, you're not going to pedal into a turn, only accelerating out of it. Guys like BigMig never had a problem using his 180mm cranks on a low (74mm) BB frame.
It's your dime but I'd never recommend a 7cm or less BB frame, nor one of those ultra short trail frames which it appears this latest Fuso replica is based upon.
Ride on!
Keith A
01-14-2004, 05:06 PM
Here's a question for everyone...
Is there an industry-standard wheel radius used when a company gives a bottom bracket height in a geometry table? It makes it difficult to compare the bottom bracket location when two different measuring schemes are used.
Another thought, I noticed that Waterford uses a 7cm BB drop on all their frames. If lower is better, then I wonder why they are using 7cm instead?
the 7cm bb drop is nice for a bike which is not going to be raced or ridden hard. all the biikes the jerk has ever ridden had between 7.4-8.3 drop.(the latter were for specific dirt road paris roubaix style races where fatter taller tubulars were used) in any case, theres this tought among many builders that pedal clearance is a design parameter. even serotta stated that their new lower bb was the result of newer lower profile pedals like the speedplay. in reality if you are taking a corner as hhard as you can a low bb bike is going to be able to take an inside line faster and harder....the '80s ameriican crit geometry is a joke....a typical kermesse bike for example has an 8cm drop...short tight chainstays and a trail of around 5.9-6.0 acheived with a tight rake and a steep head angle. methinks someone who isn't going balls out around corners but wants a bike which "feels" fast might prefer a high bb. the jerk just thinks they feel twitchy and poorley designed.
the jerk
SBash
01-14-2004, 07:40 PM
My personal opinion is most people with a highend ride probably could not tell the difference between 7cm and 8cm bb drop Unless they're speedracer. Many frame builders are closer to the 7cm than 8cm such as Merlin, Moots , Calfee, Independent Fabrications, just to name a few and usually the larger the frame the lower the bb-cm drop. For most of us (Not Racers), you are going notice a bigger difference in other angles such as headtube, fork rake, chainstay length, and tires than bb drop. Remember this is my personal opinion!
SB
slowgoing
01-14-2004, 07:53 PM
Cannondale was less than 7 for years and years and only rose above 7 a tad bit with its CAAD7 frame. Because Cannondales have been the cheap, disposable bikes of choice for many, at least for crits in the US, I don't think it's accurate to say that a 7 cm drop is no good for racing. My own personal observation has been that higher bbs seem to help my climbing on extremely steep grades. Or, said better, the frames on which I seem to climb the best have higher bottom brackets. Whether that's a factor or not I couldn't tell you.
SBash
01-14-2004, 08:02 PM
slowgoing
I think this 8cm bb drop is hyped up and I doubt most people are going to notice on head to head road test or even notice at all. There are so many other factors, like I said in my previous post that factor in more than bb drop. Good point on the Cannondale, probably the most used crit frame out there.
SB
slowgoing
01-14-2004, 08:29 PM
SB - I'm not sure if it is hype or not because I have also noticed that frames with lower BBs do seem more stable on the flats and while descending. It's just the going up part that I haven't observed, particularly on really steep grades.
SBash
01-14-2004, 09:18 PM
Now on the otherhand, if I do have a frame built custom for myself, which I may have done later in the year by Dave Kirk, than probably will go with the 8cm bb drop. I'am just saying that not that big of a deal for most riders.
SB
MadRocketSci
01-14-2004, 10:55 PM
Hey, thanks for all the great responses...
Yeah, bb height is just one component of the bike's handling...I was thinking there should be a reason why they still build higher-bb bikes. I'm trying to figure out a set of frame characteristics that would suit the particular type of terrain and riding i do, i.e., lots of climbing and fast, twisty descending, for my own curiosity. Tradeoffs for bb-drop were a bit hazy...
I wonder if dbrk has opinion on this, since he's got serotta's of many vintages?
-B
Keith A
01-15-2004, 08:24 AM
Does anyone know the answer to my question?
Is there an industry-standard wheel radius used when a company gives a bottom bracket height in a geometry table?
Marron
01-15-2004, 09:59 AM
I may be the princess and the pea type, but I can definitely tell the difference between a high and low BB. Back in '97 I bought a Marinoni Sport Tourer as an alternative to a Heron Road. In theory it should have been a great choice; it had long chainstays, plenty of tire clearence and relatively slack angles. Unfortuantely I disliked in from the first ride. It turned out that either through design or error the BB drop was only about 6.5. The result was that I always felt like I was on stilts. After two years of trying to like it I replaced it. Now I think the highest BB I'm riding is on one of my Merckx, around 7.5.
Keith A
01-15-2004, 10:25 AM
Out of curiosity, I checked out Pegoretti's website and see they his standard geometry also uses a BB drop of 7cm.
My one and only road bike is a Bianchi San Remo, with a 65mm
bb drop. I have assumed it was given a high bb for extra clearance on unpaved roads. My next bike will have a 75 or so bb drop so I can compare the difference.
MadRocketSci
01-15-2004, 11:29 AM
yeah, i've noticed that many modern off the peg italian bikes have the higher bb's and shorter chain stays. Cinelli Super Corsa is an example. Maybe pedal clearance is the intention behind this, but it'd seem that these bikes would be made with the kind of riding i'm describing x 5 - going up and down alpine roads with steep sharp switch-back curves.
weren't the older italian bikes (derosa, masi, etc) more the low, long type?
this shouldn't be rocket science :)
I have two bikes with an 8cm drop, one with 7.7, one with 7.4, one with 6.5, and a mountain bike with godknowswhat. I've owned and ridden plenty of others in the 6.5-7.5 range. My finding is that I can imagine I feel a difference between 8.0 and 7.5 - I don't like one more than the other, but it feels a little bit different. Once I get down to 7.0 or, particularly 6.5, there's a very notable difference and I pretty clearly don't like the feel of these bikes as much. I know there are plenty of other variables that effect the feel of a frame, but there's been enough consistency between my likes and dislikes (some of which I didn't know the measurement of until after I'd ridden it for a while) that I think there's something to this and the differences can be felt.
That said, I can't really explain the differences as much as feel them. The bikes with 8cm drop feel funny when I haven't been on them a while, like I'm always leaning back and forth, but are sublime once I adjust, particularly on fast and twisty descents. The bikes with about 7.4 or 7.5 feel just fine right away and stay feeling fine, but never reach the level of truly amazing that the lower bb frames do. Nothing to EVER complain about though. The frames with 6.5 to 7.0 just feel funny to me, like there's an abruptness to the leaning side to side that doesn't feel natural or seamless, it's like its indexed with specific settings at various points in the lean, but you can't be in between these points.
I guess I tried to explain it even after acknowledging my inability to do so.
Sorry :)
-Ray
MadRocketSci
01-15-2004, 07:21 PM
Here's something off of Bill Boston's web page. He sells fitting software, used to build bikes, and from the tribute to him on the Spectrum website, it sounds like he's a biking Yoda:
http://www.billbostoncycles.com/bottom_bracket_height.htm
no mentions of stability in descents, just talk about pedal clearance and the ability to pedal into a turn with a higher bb. i wouldn't think this was written in the 80's because it's a web article, but at the same time it talks about typical crank lengths of 165mm.
i guess like many things biking it's as much opinion as anything else. but i like collecting the data points anyway!
Too Tall
01-16-2004, 06:35 AM
Hypnos, I built a custom track bike (for the road and TTs) last yr. with a 7.5 drop and running 180 cranks. Folks reviewing the spec. ALL said I'd have problems with hitting cranks. Me thinks they read alot and ride a little! Bottom line is I don't hit the cranks and never looked back. With ANY fixed bike on the road you will have to either hold the bike up some or Walden it through tight turns. Enjoy.
hypnos
01-16-2004, 08:34 AM
Too Tall,
I'm showing my ignorance here, but how does one Walden a bike through tight turns?
Jeff
Too Tall
01-16-2004, 10:32 AM
Rock the bike semi-upright as the inside pedal comes down and past 180....repeat through the turn. The bike rocks under you, see?
hypnos
01-16-2004, 11:28 AM
Thanks. Will give it a go.
Ken Robb
01-16-2004, 02:22 PM
I think I read somewhere that complete bikes sold in the USA were required for "safety" reasons to have a minimum BB height and that the minimum was actually quite high. Frames sold alone were not subject to this rule. Somebody out there must know if this is true???
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