What are your thoughts on traditional BB drop figures of 60-65 mm in today’s world of progressive geometry?
As I understand it, the relatively high BB is to provide extra clearance when pedaling in deep ruts/mud/sand and provide extra clearance while bunny hopping.
For us mere mortals who arent (frequently) bunny hopping barriers, and dont have super deeply rutted courses like we see in the euro cross races, I would think that having a lower BB (and thus CG) would benefit riders more than having a more traditional high BB.
What are your thoughts on this? On one hand I think if you’re hitting your pedals in deep ruts, will the extra ~5 mm of a high BB really make the difference, but on the other will a 5 mm lower BB really be perceptible in added stability?
I may have opined once or twice on this subject in the forum…
When I got a new gravel bike this year, my primary goal was a lower BB. My last frame was a Crux with a BB drop of 68 and, for me, it was noticeable. I ended up with an Aspero with a 76 bb drop and I know I made the right choice. My cornering has improved and I fell way more stable on the bike.
Many years ago when I was doing product development in the bike biz, I did a run of prototype CX frames from 853 steel. I dropped the BB and also extended the front end in order to run a shorter stem (sound familiar?). Those bikes were universally praised by everyone who got one….including a couple of hard core CX guys at different mags.
TL:DR - I’m all in on lower BB heights for both gravel and CX, but especially gravel. A case can be made for a higher BB for dedicated CX frames, but IMO, the near-always advantages of a lower BB (lower CH, more stability, better traction) outweigh the occasional advantages (pedal strikes, bunnyhops, etc) of a higher BB.
Interesting re: the prototypes with the lower and longer geometry. Mind me asking if either that brand you were working for and/or athletes stuck with that design concept after the successful trials? If not, what were the reasons why?
With the recent trend of shorter crank arms, much of the pedal strike issues associated with lower BBs can be minimized, although I guess your seat height and CG will have to go up accordingly.
I’ve been curious about this also. I’ve only ever had my Crockett for CX and gravel, and it works great but I have nothing to compare it to. Wonder how much you would feel the difference if it was lower. I race with a guy who uses an Aspero and he really likes it. The new Cannondale CX/SE is the same frame for CX and gravel with a ~70mm drop. The 2022 Crux (which has gone more gravel) is now at 72mm.
No, we never moved forward with the project, outside of the prototypes…they were mostly done as one-offs and we never really had much intention of going into production. The CX market was still developing at the time.
Going form 68mm on my Crux to 76mm on my Aspero was definitely noticeable…significantly. Besides the stability aspect of it, I definitely don’t feel as high just sitting on the bike, riding in a straight line.
Ya, my current bike has 68 mm of drop and I’m liking the looks of the crux (except the price). Not sure how noticeable the extra 4 mm of BB drop will be or if I am better off looking at something like the Aspero or Factor LS which has 76 mm and is labelled as a gravel bike but are still plenty responsive and agile
I’ve also looked at the Aspero 5 and the Factor. They set themselves up as strong all-rounders. Like you could race some CX and then throw road tires on and do some road racing. That definitely appeals. I’m also curious to see what the new Cervelo R5-CX geometry comes out as. Looks to be very CX-specific, and aimed at the top of the market, so probably maintaining a higher BB.
The R5-CX went full traditional BB drop of 63 mm - this is actually what spurred my curiosity on this topic. In the age of long and low, CX bikes are still being created with high BBs.
There is a geometry chart near the end of this article
