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Discussion Starter · #1 ·
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?

If the wheelbase is longer and the rotating mass higher with all the other 29er goodness, then why not sneak in a little extra pedal clearance too? It seems like this might just be accomplished without giving up too much in 29er stability and what-not.

With the constant talk about rolling (coasting) over larger obstacles it would be nice to also hear.. and pedal over larger obstacles too. How wrong am I on this?
 

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Many people are super-concerned with standover height.
The range in BB drops between 29" frames is quite wide. Niner uses some 70mm, as does Orbea. Fisher uses 50mm. Pick what you prefer!
 

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opinions are like * s, everybody has one

cheepnis said:
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.
 

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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.
BB height on my rigid forked HT WaltWorks is 10.75-11.25" depending on tires. Took little or no time to adjust to it, don't hit a pedal more than once every 10 rides. Of course a lot depends on where you are riding. I can imagine hitting pedals riding through baby head rock gardens, but I'd usually be going up hill slowly, and a pedal strike there doesn't bother me. Going down through the same area I would have the pedals horizontal anyway. The benefit for me of a low center of gravity on fast downhill corners and less lofting of the front end on steep uphill steps is a good trade off for the occaisional pedal strike. Personal choice however, YMMV. :)
 

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Discussion Starter · #5 ·
Relatively speaking

won't a 12" BB height on a 26er feel more awkward than a 12" height on a 29er? Or does BB height have the same effect on both geometries? Without a study on the cycling mechanics of BB height it just seems like the BB could be raised a little bit without affecting the feel relative to a 26er. Wheelbase is longer, wheels are bigger, seems like an extra 1/2" or so of clearance would do no harm.

Of course everyone will have their own preference in general. But what I'm wondering is what increase in BB height can occur when moving from 26er to 29er before a real change of feel is noticed?
 

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cheepnis said:
won't a 12" BB height on a 26er feel more awkward than a 12" height on a 29er? Or does BB height have the same effect on both geometries? Without a study on the cycling mechanics of BB height it just seems like the BB could be raised a little bit without affecting the feel relative to a 26er. Wheelbase is longer, wheels are bigger, seems like an extra 1/2" or so of clearance would do no harm.

Of course everyone will have their own preference in general. But what I'm wondering is what increase in BB height can occur when moving from 26er to 29er before a real change of feel is noticed?
It is the overall geometry that matters. The wheel size is not really much of a factor. With a longer wheelbase a higher BB may be necessary to maintain pedal on rough terrain.

I tend to prefer a higher BB mostly because I like to use long cranks. I also like the extra chain ring clearance and the way the bike reacts in the corners and technical terrain.

That said, I ride bikes with BB heights ranging from ~11.6 to 14.5", plus I can change the BB height by nearly 3/4" just by changing tires. Any change in handling I adapt to quickly, other than banging pedals. That is harder to adjust to and I have had a few crashes on the low BB bike because of it.
 

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team_bfd said:
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.
Below 12in, but not below 11.75in - ie: you're zooming in on something that's within a range of 6mm - you think you could tell the difference in 3mm either way - on BB height?

Oh my.

 

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Below 12in, but not below 11.75in - ie: you're zooming in on something that's within a range of 6mm - you think you could tell the difference in 3mm either way - on BB height?

Oh my.

My thoughts, too. Using a Klaw 29" tire vs a Spec Fast Trak 29" will change the BB height by ~6mm.
 

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And if you have a calculator come up with your ideal crank length, you're probably 5mm off at least, too short :)
 

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team_bfd said:
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.
And if we're sticking to fairy stories, this phenomena is what I call "Emperors new clothes" Syndrome, where you're trying to convince yourself that something you found a negative, is a positive.

https://www.totil.com/images/keis_38_39-489_640x480.jpg

I really don't see, how on a mountainbike, with the same crank length, a lower BB is better (within the limits of production bikes).

Steve Peat (UK Downhiller) does very well on his DH race bike, which is specced with 165mm cranks - to keep things low - he's 6'4"!
 

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I know a semi-pro DH'er that likes his bikes super-low. Lower than I like XC bikes.

For stability's sake (a good sake) as long as I don't have pedal strikes, low BB's are fine by me. My SuperCal was too low, an XL simply deserves 180mm cranks after all.
As long as the BB is just high enough to not have to think about pedal strikes, good enough!
 

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This is an interesting a timely thread.

I just completed my first week of riding my new Orbea 29er and I have an observation to make. I bash the heck out of my chain ring over logs that I normally clear with my 26.

I have to admit that at age 59+ I have no technique when it comes to XC. So take my comment for what it is worth. I don’t bunny hop, I just “pop” my front tire over the log and hope the rear tire makes it over with the rest of the bike. To make matters worse the advantages of the 29er Orbea allow me to approach these logs much faster than I would on the 26, only to bash these logs even harder.

But on the bright side it is satisfying to run down my biking buddy after he has pulled away by him clearing the log on his 26er.

I guess this old dog will have to learn new tricks (and practice proper technique).

P.S. My GF Rig 29er clears these logs with ease, for obvious reasons.
 

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Oh my, what a jerk

Below 12in, but not below 11.75in - ie: you're zooming in on something that's within a range of 6mm - you think you could tell the difference in 3mm either way - on BB height?

Oh my.
Oh my, what a jerk.

I can feel a 5mm change in bar position, probably a 2mm change in seat height. Instantly. Why shouldn't I be sensitive to BB height?

I like a low BB. As I mentioned earlier, YMMV. (Maybe y'all should look up what that means)

What do you care anyway? I certainly wouldn't ever bother you for one of your shite bikes.
 

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Memphisrider, at age 59+, do you ever really use the 44x11 gear? ;-)

I ask because if not, you may just as well get a 36t or 34t middle and replace the outer with a bashguard. Hurt those logs! The bashguard being smaller than a 44t will already help clearing the logs, but if you hit, it just help make the hit softer for the rear wheel.

29" offers 10% more mechanical advantage over 26" drivetrains anyway, so the need for the 44t and 11t is much much smaller. Although I'll admit hitting extra high top speeds on the 29", because it still feels safe hitting braking bumps at 40mph, is fun.
 

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shiggy said:
My thoughts, too. Using a Klaw 29" tire vs a Spec Fast Trak 29" will change the BB height by ~6mm.
I was talking about BB height in the context of designing a custom. So, I was saying (to my builder), using a motoraptor rear and a jones ACX front, and a White BW.8 fork, I want my BB height to be right here (more than 11.75, less than 12).

I understand that BB height changes relative to tires. Thanks for the clarification though. Helpful.
 

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bb height/ tires

I am having a hard time seeing this tire change=change BB logic. Certainly the BB is higher off the ground, aiding the pedal strike problem. But, doesn't the "feel and handling" of the bike remain pretty much the same since the hubs, frame, seat, etc all move up by exactly the same amount? What am I missing?
 

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Memphisrider said:
I bash the heck out of my chain ring over logs that I normally clear with my 26.
Memphisrider- Put the chain int he big rig for crossing the big logs, even if it means having to cross-chain a bit. With the chain on the big rig it will slide right over the log instead of the chainring biting in :cool:
 

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team_bfd said:
Oh my, what a jerk.

I can feel a 5mm change in bar position, probably a 2mm change in seat height. Instantly. Why shouldn't I be sensitive to BB height?

I like a low BB. As I mentioned earlier, YMMV. (Maybe y'all should look up what that means)

What do you care anyway? I certainly wouldn't ever bother you for one of your shite bikes.
I have to agree with you bfd... I notice small changes in my set up... millimeters. By their logic, you wouldn't notice the difference between a 175mm crank and 180, but they all claim that they need 180mm cranks...

I notice a difference between a 170 and 172.5mm crank, a 2mm increase in saddle height, or any other change that I make to my bike. The logic about tires increasing BB height is plain stupid. Taller tires raise the whole bike, not just the bb. And what if you run the taller tires at lower air pressure, can that not drop the bike back down the 6mm?
 

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I went from a 26" Merlin with a 12.5" bb to a KM with about 11.5" bb. Since both were singlespeed, and I was used to the high bb, I hit my pedals all the time on the KM. I refused to ride it fixed offroad, which was part of the reason I wanted the KM (I mean, It's a Surly, after all), so I sold it. I would have bashed my pedals all the time riding it fixed.

I never really felf comfortable on a bb that low. My Rig, on the other hand, has about a 12.5" bb with the bb rotated to the bottom of the rotation, so I could get way up in the air if I wanted to. I'm currently working on the design of a new 29"er for myself, and I'm putting the bb between the Rig and the KM so that I can put it up to about 12.5" or down to about 12" or just below, depending if I'm fixed or free, technical or non-technical, etc. I think I settled on 61mm drop, if I remember correctly.

And Brant, I like your bikes.
 
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