Minimum acceptable BB height/max. BB drop?

[satanas]

It seems like few current production bikes have BBs much less than 270mm high, maybe due to CPSC regulations. I noticed though that one of Dave Moulton's early bikes mentioned on his blog had a 9.25"/235mm BB height, maybe with 165mm cranks - that's 30mm or more lower than is common these days. And one of the bikes tested in BQ at the construcreur contest in France had ~90mm drop IIRC, whereas most production 650b bikes are ~65mm.

I personally find 270 is more than enough for anything except mountain biking, and ~260 gives better handling (IMHO); around 264mm (10.375") seems about ideal. Less than 260mm means needing to be careful pedalling in sweepers - I don't pedal around tight corners anyway. I'm inclined to think less than ~255mm might be a pain pretty often, but I've never had anything lower than that.

The real question is what minimum tyre size might be usable with ~75mm drop, and this will be limited by the BB height. There are some nice light 650b tyres from 25mm upwards, like Schwalbe's Pro One, and there's always 700c.

Comments? If anyone has ridden anything with sub 250mm BB heights, how did this work out, and what crank length did you use?

Thanks,
Stephen

[Justin Hughes]

I spec'd my bike with 75mm BB drop. With Switchback Hills measuring exactly 2" (50-51mm) BB height is 268mm measuring imprecisely with a tape measure (didn't put a level against the bike and the basement floor is decidedly imperfect). I ride 170mm cranks with one sided SPD pedals. If I had it to do over again I would choose 80-85mm BB drop depending on builder input as I do not intend to run a smaller diameter tire. I will build up a 700c wheelset at some point soon. I certainly would not want anything less than 70mm drop. 

I've caught a pedal in a turn on a fixed gear twice and managed to stay upright. I understand the importance of a higher BB on a road race bike, but I don't race so it's "go low" for me. 

Justin

[David Parsons]

I've a machine with ~70mm BB drop, 170mm cranks, & Confreries/Schwalbe Ones (~250mm BB<->ground with the Schwalbes), and in the ~4000 miles it's been a 650b machine I've had 1 (or 2?) pedal strikes accelerating around sharp curves -- I /try/ to not pedal on sharp curves, but occasionally I forget.   

-david parsons

[Stephen Poole]

Thanks David, that's reassuring! I might get a bit more drop after all. BTW, how do you like the Schwalbes?

[Mark Bulgier]

Back when we all used Campy quill (toke lip) pedals, it was easy to cut a bit of beercan and insert it under the threaded dustcap, facing down.  Then we'd race around tying to get the beercan material to scrape the ground.  After enough of this we got good at predicting the lean angle that would make it rub.  Then we trimmed the beercan shorter, so we had to lean more to get it to scrape.

After enough of that, it was possible to remove the beercan and reliably scrape the actual dustcap just a smidge without crashing.  That gave a nice advantage in criterium racing, even if it was just a psych boost.  Confidence does add speed.

That was 35 years ago and it's definitely one of those "use it or lose it" skills.  I didn't, so I did, respectively.  Now I never ever hit a pedal on the road, despite using 180 cranks, because I scrupulously avoid pedaling through corners.

Liking low BB is one of the reasons I hate riding a fixed gear on the road.  We used to do it in the winter, which might be another reason I don't like it -- I associate it with being wet and freezing.  Classical Pavlovian conditioning -- I shiver at the thought of riding fixed on the road.

Freewheels were invented for a reason yo!

Mark Bulgier
Seattle

[David Parsons]

The Schwalbes are pretty nice.  I've not ridden them on anything long (only <=30 mile loops) but on those they're super-fast and ride as nicely as Pari-Motos on pavement.  They don't have nearly the float that a Pari-Moto or Confrerie has, though, so they slither around more on gravel.

-david parsons

[Stephen Poole]

On 26 May 2017 3:10 am, "Justin Hughes" <justin...@me.com> wrote:
>
> I spec'd my bike with 75mm BB drop. With Switchback Hills measuring exactly 2" (50-51mm) BB height is 268mm measuring imprecisely with a tape measure (didn't put a level against the bike and the basement floor is decidedly imperfect). I ride 170mm cranks with one sided SPD pedals. If I had it to do over again I would choose 80-85mm BB drop depending on builder input as I do not intend to run a smaller diameter tire. I will build up a 700c wheelset at some point soon. I certainly would not want anything less than 70mm drop. 

The GR allegedly had 65mm drop, but measured BB height was ~272mm with Hetres so I suspect it was a little less. This always seemed a bit too high to me, and I never once looked like clipping a pedal.

I'm inclined to think 75mm drop is likely to work for me (YMMV) with tyres down to at least 38mm, but it might be a bit tall for 700c, for which I agree 80-85mm would be better.

> I've caught a pedal in a turn on a fixed gear twice and managed to stay upright. I understand the importance of a higher BB on a road race bike, but I don't race so it's "go low" for me.

When I last rode fixed I had 170mm NR track cranks and Frog pedals. With 275mm BBH I never felt clipping a pedal was likely, while with 270mm it always felt like it was going to happen but never did. I've clipped pedals hard a couple of times in the past with no ill effects other than surprise and scratching the pedals; hitting pedals isn't usually a big deal but could get annoying if it happened frequently. Unless you're regularly riding crits and feel you must pedal around corners I see no advantage to a higher BB except for pedalling over obstacles on fire trails, especially since few people now use toeclips, so crushing them is a non-issue these days for most.

I've owned a number of bikes where I wished the BB was lower, but few if any where it was too low.

Later,
Stephen

[Stephen Poole]

I've never heard of anyone doing this, but it's a great idea.  :-)

I'm inclined to agree about riding fixed on road, and always tended to find it a bit nerve wracking. However, it's quite hilly here and so it's hard to find an acceptable gear, given one needs to go both uphill and downhill. I found hill starts and downhills were the limiting factors. Too high and it's almost impossible to start at uphill traffic lights, and too low feels like one's legs are going to break off on downhills. Freewheels definitely have their good points as do multiple gears - as indeed does fixed.

[Ben Van Dyke]

I have a 650b wheelset on a Salsa Vaya with 75mm drop. Running 2.2 WTB wolverine tires and 170 mm cranks. No issues thus far. 

On Thursday, May 25, 2017 at 8:32:28 AM UTC-7, satanas wrote:

[Eric Nichols]

I have a GR v2 with reported 65 mm drop. It seems lower to me though I've never measured it. I use 180 mm cranks, and use the bike as an all-road explorer (which it excels at, IMO).

With 42 mm BSP tires, I tend to strike the pedal on rocks and trail debris. The bike works better off-road with the 48 mm SBH tires: higher BB, more tire, slightly less trail. Just those few mm makes the difference for me in terms of judging/avoiding pedal strike.

I can't imagine running a shorter tire on that bike. I like low BB, but with the GR I've found my functional limit for all-road riding. I could go a little lower on a road-only bike.

Eric "lucky strike" Nichols

[Stephen Poole]

On 26 May 2017 11:48 pm, "Eric Nichols" <ericni...@gmail.com> wrote:
>
> I have a GR v2 with reported 65 mm drop. It seems lower to me though I've never measured it.  I use 180 mm cranks, and use the bike as an all-road explorer (which it excels at, IMO).
>
> With 42 mm BSP tires, I tend to strike the pedal on rocks and trail debris. The bike works better off-road with the 48 mm SBH tires: higher BB, more tire, slightly less trail. Just those few mm makes the difference for me in terms of judging/avoiding pedal strike.

The BSPs have been reported as being ~40mm wide, while SBHs seem to come in between 48-51 mm, depending on the rim. Reported radii are about 335 versus 345, so the difference isn't all that small. As trail increases with tyre radius, there's more trail with the SBH than the BSP, not less, plus more gyroscopic force, pneumatic trail, etc.

> I can't imagine running a shorter tire on that bike. I like low BB, but with the GR I've found my functional limit for all-road riding. I could go a little lower on a road-only bike.

One big difference here is your crank length. Many in this thread have been using somewhat shorter cranks, i.e., David was on 170mm, I use 172.5, etc.

With the SBH @ 345 radius -65 drop -180 cranks that gives 100mm from pedal axle to ground and 280mm BBH, while I was okay with a similar amount of clearance on very rough back toads in India and Pakistan (318-42-172.5=102.5/276), and would have been happier with `5mm less.

Plus riding on fire trails, as opposed to roads, paved or not, probably accounts for ~10mm of extra clearance being needed, and very likely a lot more than that if things get technical. I'm fine with ~260 on bitumen or smooth dirt and 265-270 is okay for unpaved back roads, but fire trails reallly need *at least* 280mm for me, and 290-295mm is better. Over 300 starts to feel stilt-like to me, as does 270+ on the road, but this is personal preference;.

Pedals also matter as taller or wider pedals hit the deck sooner than something like Frogs -  switching between Frogs and platforms can make a huge difference to clearance.

Later,
Stephen

[njh...@gmail.com]

On Friday, 26 May 2017 01:32:28 UTC+10, satanas wrote:

[snip...]

The real question is what minimum tyre size might be usable with ~75mm drop, and this will be limited by the BB height. There are some nice light 650b tyres from 25mm upwards, like Schwalbe's Pro One, and there's always 700c.

Comments? If anyone has ridden anything with sub 250mm BB heights, how did this work out, and what crank length did you use?

My old Litespeed road race machine had 76mm BB drop - I converted it to 650b, and rode it for a couple of years using Michelin Megamium 650bx32 tyres and 170mm cranks. With that setup it was possible to ground a pedal (Crank Bros Eggbeaters) if I continued pedalling while cornering rapidly, but after doing that once or twice I learned when not to pedal through corners and it wasn't a problem thereafter. Photo of the bike when setup as described.