crank length/bb height

i was browsing the internet on this 110 degree day here in the midwest and saw the website for Zinn Custom Cycles. i took note of the 220mm cranks and was just thinking about what those would be like. i also saw the picture of the bike on this page that is built for someone 6'7''...

http://www.zinncycles.com/bikes.aspx?bike=road

i guess im just curious to know if cranks that long would require a custom frame such as the one above in order to keep the pedals from scraping the ground on every turn? i ride 175mm cranks and it seems like with my bb height 220s would be a serious problem. does bb height change much with frame size?

No doubt, that with your bike you might have a problem with 220mm crankarms ... but, you don't need to buy a "custom" bike to have a higher BB.

The bike in question has a taller BB similar to what you would find on a TRACK bike OR some older frames (observe the almost horizontal chainstay), to name two possibilities (there is at least one other off-the-shelf option for tall riders) [BTW. The pics will undoubtedly "vanish" if/when Zinn changes his webpage's content]):


Compare the "normal" chainstay angle on the smaller ZINN bike:


Some pedals have more pedal clearance when leaning the bike over than others -- you can check how far you can lean your bike if you lean your bike over while standing next to it ... you can/will see that you can probably lean your bike over much than you might think EVEN IF you clip your shoe into the pedal on your 175mm cranks ... maybe, not!?!

While I fall into the camp that believes that longer cranks are better ... there is a reasonable, maximum-and-minimum length to use for each person ...

How tall are you (and, specifically, what are the dimensions of your femur & lower leg + shoe size)?

What is the size of your current frame (seat tube & top tube)?

Why are you considering such a long crankarm OR are you just musing?

i am definitely not in need of any 220s. the 175s are my fit. this is purely an interest bug.

FWIW. If you look at the geometry "charts" for most frames, the "drop" varies minimally from frame size to frame size for a given model/style ...

The attached chart & schematic are Colnago's ... 'G' represents the drop which you apparently have to interpret because whoever drew the schematic figures you want to know the ground clearance with an unknown tire size (let's presume 700x23).

The reason the smaller frames often have MORE ground clearance is because the headtube can only be "so short" if you are building a frame with a HORIZONTAL top tube ...

On the other side of the coin, my vintage 60cm Gitane had a slightly lower BB than all of my current frames because to undoubtedly minimize the headtube length AND (mostly) to keep the rider from being unnecessarily higher AND because 170mm cranks were the norm.

So, it could be suggested that what is true for Colnago is probably true for other frame makers with regard to maintaining the same-or-almost-the-same BB drop for a given model of off-the-shelf frames.

And, if someone were to get a custom frame from ZINN/anyone, then Zinn (in particular) would probably NOT spec the taller BB unless he also convinced the buyer/rider to use longer cranks (presuming you/someone are/is a taller rider, that is) ... which he would if your height allowed/warranted.

BTW. Cyclocross frames are one of the OTHER off-the-shelf frames a person can buy which will usually have a higher BB shell.

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I'm 'only' 6ft, and I used 180s a few years ago without any problems on standard bikes (sizes 56, 57 and 58), although I only have size 43/44 (9/10) feet. I only ever remember hitting the ground once.

If guys have bigger feet, and/or ride with their heels in (toes out), big cranks can present problems with heels whacking into the seat-stays and/or the rear derailleur. Toe clearance is also an issue, but not as big, coz it can be gotten used to.

Anyway, I was obsessed with the long cranks thing for about a year, but gave them up as a bad joke, and I now ride 172.5s and 175. I do think bigger guys should (or, can easily) use bigger cranks, but some of the 'formulas', like 21.6% of inseam (or whatever it is) are ridiculous, especially for anyone over about 5'8". Some shorter guys use relatively very long cranks (and I dunno how the hell they do it), but I reckon they shouldn't, and I suspect they only do so coz they're used to it, coz the first crappy bike they bought when they were young probably (and incorrectly) came with 170s as standard!! It's a farkin joke that 6ft3"+ guys ride 175 to 180, and 5ft4" guys ride 170 to 175!!

One of my two-bit theories why shorter guys tend to be not so good on the flats is that they're using cranks which are too long, and they can't "get on top of the pedals" at the top of the stroke to pound them properly!

I reckon give 180s a shot, coz they're a standard-ish size, and relatively easy to get.

I'm 6'1'' (6'1.5'' on a good day), use a 58-60-XL frame depending on the company and have used my 175s for the last year and a half. My first bike was a hand me down from my dad who is 5'10'' and it had 170s. I never even considered crank length as a problem because i was new to the sport and had never tried anything else to provide a first-hand comparison, not that I would have known what to look for then if I had. That bike has become a trainer-only bike, and when I come inside on a bad day I have trouble pushing the 52-19 because I simply can't get any torque. My knees barely feel as if they've extended. That's the reason I've been doing some research on crank length.

I would however be curious to try some 180s sometime just for the comparison. I really notice a difference when I push myself back in the saddle to get set in for a good climb, but I think that 180s might be too much.

To deviate further from the original topic, I have heard of people using the same frame as I currently am (Cinelli Xperience) run into problems with heels clipping the chain stays, but tend to ride heels out so there shouldn't be any issues there.

Funny you should say that, because I sold my Cinelli Proxima (which is what the Xperience used to be called) because my heels hit the stays, but I ride with my heels in (toes out).

My right heel always hit the stay, just at the back of the 'C' on the Cinelli sticker

FWIW. I know some people obsess about a crank's Q-factor when they are shopping for a new crank, but I think many riders will not be adversely affected by setting up their crank with a slightly wider Q-factor ... what worked for Obree may not be the optimum for someone else.

Unless a person walks with their heel in-or-out, I think a skewed foot position on the pedal may be aggravated by the narrow Q-factor.

Consider that on a MTB, the Q-factor's crank is usually about 15mm MORE than on a road crank ... a Q-factor that people have lived with as "standard" for more than a decade.

To mitigate the likelihood of anyone hitting his/her heel on the frame OR crankarm (which I've seen evidence of on several cranks), I would suggest a BB with a longer spindle may mitigate the problem ...

With cranks which use an external BB, you would need to get the "triple" version of the crank & set it up without the granny ... yes, triple cranksets have a wider Q-factor that riders manage to live with!

177.5?

Crank length IS definitely a matter of rider preference ... some acclimation is often necessary when changing lengths, but sometimes you only need to adjust the saddle height & fore-aft position ...

I concur that the formula for crankarm length is too arbitrary and therefore a questionable methodology to use when fitting a bike ... the formula is, IMO, a crutch for the shop or frame fitter to use.

BTW. I would be classified as a shorter rider (5'9") who uses a long crank ... I switched to 177.5mm this year (from 175mm ... I have other bikes with different length cranks [i.e., 170mm & 172.5mm]) ... most of my riding involves a lot of climbing ...

I have been planning to set up a bike with a 180mm crank to try, too!?!

Tentatively, with a bike briefly-and-NOT-optimally set up on a trainer with a 180mm crank, I would say that 180mm seems doable for me ... but, the proof will be on the road.