opinions are like * s, everybody has one
It seems to me that the 29er geometry should be able to eek out a little more BB height/ pedal clearance than a 26er. I may be wrong in general, but from the tiny bit of looking I've done it seems that 29er BB height is about the same as a 26er. Why's that?
... How wrong am I on this?
There isn't a right and wrong. But, IMO, there is an acceptable range of BB Height that is narrower than one might think for each application of bicycle design (high performance road, touring, X/C, DH, etc). Too tall, and the bike feels tippy, dives into corners, loses drop-off stability. Too low, pedal strikes.
From my experience, for X/C a BB Height of less than 11.75" gets a bit uncomfortable, and more than 12.5" likewise. Of course, some people have always ridden a tall BB so anything else feels funny to them. Some have always ridden a low BB, so anything else feels funny to them...
The experience of owning a Fisher Supercal29 changed my opinion of BB Height, and made me aware of how fine the difference is between 11.75" and 12". The Supercal had a whacky low BB, I measured it to be just a hair under 11.5" using the tires I used (probably Moto rear, Jonex ACX front). The bike I was coming off was a Moots YBB (26") whose BB Height was 12.125" with the biggish tires I was running back in Fall of '03.
When I first started riding that Supercal, I liked the big wheels, I liked the stability, the long top-tube but still nimble feeling, and I HATED THE LOW BB!
I thought I was going to ruin my pedals for sure. I had such a strong reaction, I sent email to modify the design of my work-in-progress custom frame, to raise the BB by God.
I think I was asking for it to be right around 12 1/8" like the Moots.
But then a funny thing happened. I started having less trouble with pedal strike because I was being more careful and adapting to the bike. Then I realized how I was exploiting the low center of gravity. I realized that I was able to rail corners on loose chunky gravel sickeningly fast, that could do drop-offs that seemed way over the top. It was fun. And, I could sit comfortably and grind along on long easy climbs, benefitting from the comfort and stability of a low BB.
So, I thought long and hard, and then asked my custom builder to tweak the design one more time, back down below 12", but not below 11.75". What I got now measures something like 11.8" or 11.85", and it's very much right. For ME.
That's how I
like to have it.
So, my opinion
, big wheels or little wheels: get the lowest BB you can stand. But that's for an XC Hardtail. Not sure what my opinion is about BB height with a fully-suspended bike. I've never owned one.
And of course, YMMV.