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It's hard to opine, methinks, while trying to stay divorced from wheel size (since the industry moved to BB drop instead of BB height) but I think it's still worth a discussion. Too low is obvious, pedal strikes become a serious problem.

But how high is too high for BB height, in your opinion?
 

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When the bike feels tippy/unstable and you feel you're to high from the ground? That's how it felt for me the last time. I got used to it after a couple of rides though (borrowed bike).

A long wheelbase bike can afford a higher bb as it's already extra stable due the the length.
 

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Too many variables. It depends.

Generally speaking if you're having a hard time keeping the front wheel down on a steep climb the BB is too high, or the chainstays are too short, or the front end is too short, or the wheelbase is too short, or the STA is too slack. Not to mention frame size, saddle height, and bar height.

See what I mean? Bike geometry is not a singled out number, you have to consider the complete package.

I have a full suspension bike with a relatively high BB height (for modern geometry) and I had to go to shorter cranks because of pedal strikes. I have multiple hardtails that have very different BB heights and they all handle great. The higher BB bike I notice it's easier to lift the front wheel despite having longer chainstays than the low BB bike with short chainstays.

This is still a contentious topic in the cyclocross race world too. There seems to be two schools of thought, low BB's are better or high BB's are better.

I've recently been thinking about the down side of having a higher BB. (comparing old school XC geo to very modern aggressive geo) Since I stand on most climbs I'm not worried about the front end being light on climbs. But that bike doesn't feel as planted as my more modern geo hardtail, and it's definitely less confident in steep terrain or when things get rowdy. This also has a lot to do with FC and wheelbase, not just BB height.

Personally I like modern geo so long as the BB is not too low, but ideal BB height depends on the bike, terrain, and rider.
 

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Generally speaking if you're having a hard time keeping the front wheel down on a steep climb the BB is too high, or the chainstays are too short, or the front end is too short, or the wheelbase is too short, or the STA is too slack. Not to mention frame size, saddle height, and bar height.
I have hard time imagine things, can you explain this
"chainstays are too short, or the front end is too short " ?

I understand that chain stay too short make weight rear-bias. So the front wheel doesn't have enough weight.
But front end too short also cause it to lift? Short front end is more under the rider, and it should get more weight on it, right?
 

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I've got a bike with a little over 14 inches of BB height. It's a mullet (29/27.5), but older geo (and a short wheelbase). It's harder than my Process to maneuver the downhills, but the higher BB gives me confidence when traveling fast over chunk. I've wondered how a high BB with new geo would ride. Most riders I've spoken to on this subject would like to see bikes with slightly higher BBs than we are seeing today.

Edit: The bike climbs very well.
 
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