BB Height VS HT Angle for stability

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3/18/2020 5:28 PM

Hello everyone!

Hope you are all safe and healthy!

So, I'm in the market for a new frame that resembles my old frame and found a cult hawk that has it all except the BB height, which is 11.8 as opposed of 11.5
But it has the HT angle of 74.5 which is very close to 74 that I currently have

What I'm asking is: is HT angle more important for stability than bb height?
Should I get the frame or should I keep looking and get a frame with 11.5 but an angle of 75?

Cheers!

For stability what's more important

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3/18/2020 5:34 PM

Chances are, it won’t make a HUGE diffference. I’m not saying your reasoning is unclear, it’s just that sometimes the numbers game is all in the head. From 11.5 to 11.8, I can’t imagine the difference will be very noticeable. That being said, I think HT angle makes a bigger difference. Just my opinion.

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3/18/2020 5:37 PM
Edited Date/Time: 3/18/2020 5:37 PM

The lower number for HT angle or BB height will create a more stable feeling. If your current frame is 74HT/11.5BB that will feel a bit different than 74.5HT/11.8BB.

Personally I've found HT to make a bigger difference in how quickly or not I can get comfortable with a frame. Differences in BB height is something I can adjust to very quickly. I never could get used to 75HT. Always felt twitchy.

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3/18/2020 5:42 PM

I’d wait and get a frame with the geometry you’re looking for. If you know what you like why ride anything different?

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3/18/2020 9:06 PM

As a rider, I'd s say you won't notice either, or at least you'll get used to it quick. If I had to guess, I'd say BB because HT angle is overrated.

As an engineer though, it's an interesting question... All else being equal:

1 degree HT angle changes wheelbase by about 1/4", which changes turning radius by about the same amount with the bars at 45 degrees.

HT angle also affects self-straightening due to gravity, by transferring some of your weight in the horizontal direction. There are studies, but my math says 1 degree transfers about 1.1% more weight to the horizontal, at least near the 75 degree typical angles.

BB height changes your center of gravity, which changes horizontal leverage. For example, assuming a 13" chainstay, 1/4" higher BB gives about 6.6% more leverage when pulling into a manual, or about 6.6% "more loopy" and "less stable".

They both do other stuff too, and I'm not sure the numbers mean much because any other differences in geometry would change the results at least as much, but at least it gives you something for comparison.

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Remember when you could ride all day and not be sore for a week?

3/18/2020 11:05 PM

HTA and BB brings a different kind of stability, as said before, you’ll hardly feel the change upfront, just a really really tiny difference on how your bike turns.
But the lower BB will be felt A LOT, you’ll feel sticked to the ground, more stable at speeds, and manuals will be way less twitchy and easier to hold, you’ll also feel like you “lose some pop” compared to a higher BB, in reality, you don’t, but i feels that way when you try to hop super high on flat.

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3/19/2020 12:24 AM

Francky is onto it, you'll notice BB height more assuming the same cranks and pedals are being used.

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3/19/2020 3:48 AM

Many thanks guys!
Great answers here!

I'll keep searching for a more suitable frame.

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3/19/2020 10:38 AM

Francky wrote:

HTA and BB brings a different kind of stability, as said before, you’ll hardly feel the change upfront, just a really really tiny difference on how your bike turns.
But the lower BB will be felt A LOT, you’ll feel sticked to the ground, more stable at speeds, and manuals will be way less twitchy and easier to hold, you’ll also feel like you “lose some pop” compared to a higher BB, in reality, you don’t, but i feels that way when you try to hop super high on flat.

I'm curious about this cuz when I switched from my 20.6/11.5 hangover to a 21/11.6 dagger with the same backend length and setup and everything.. it was a lot harder to hop over stuff with the Dagger and I cant tell if it's because of the longer tt or the higher bb but it was remarkably more difficult to jump on to the stuff that felt easy on my hangover.

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3/19/2020 11:05 AM

Francky wrote:

HTA and BB brings a different kind of stability, as said before, you’ll hardly feel the change upfront, just a really really tiny difference on how your bike turns.
But the lower BB will be felt A LOT, you’ll feel sticked to the ground, more stable at speeds, and manuals will be way less twitchy and easier to hold, you’ll also feel like you “lose some pop” compared to a higher BB, in reality, you don’t, but i feels that way when you try to hop super high on flat.

Sean_Goff wrote:

I'm curious about this cuz when I switched from my 20.6/11.5 hangover to a 21/11.6 dagger with the same backend length and setup and everything.. it was a lot harder to hop over stuff with the Dagger and I cant tell if it's because of the longer tt or the higher bb but it was remarkably more difficult to jump on to the stuff that felt easy on my hangover.

I guess it is because you aren’t quite used to your new top tube, might be a little harder to lift the bike, but theorically you should even be able to go higher because you have more leverage, even if it takes a little more effort.

It’s just like if the longer tube added “1 harder point” and the higher BB bringed “0,5 easier point”
It the end, one doesn’t quite compensate for the other and it just rides different.

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3/19/2020 12:09 PM
Edited Date/Time: 3/19/2020 12:10 PM

Francky wrote:

HTA and BB brings a different kind of stability, as said before, you’ll hardly feel the change upfront, just a really really tiny difference on how your bike turns.
But the lower BB will be felt A LOT, you’ll feel sticked to the ground, more stable at speeds, and manuals will be way less twitchy and easier to hold, you’ll also feel like you “lose some pop” compared to a higher BB, in reality, you don’t, but i feels that way when you try to hop super high on flat.

Sean_Goff wrote:

I'm curious about this cuz when I switched from my 20.6/11.5 hangover to a 21/11.6 dagger with the same backend length and setup and everything.. it was a lot harder to hop over stuff with the Dagger and I cant tell if it's because of the longer tt or the higher bb but it was remarkably more difficult to jump on to the stuff that felt easy on my hangover.

Francky wrote:

I guess it is because you aren’t quite used to your new top tube, might be a little harder to lift the bike, but theorically you should even be able to go higher because you have more leverage, even if it takes a little more effort.

It’s just like if the longer tube added “1 harder point” and the higher BB bringed “0,5 easier point”
It the end, one doesn’t quite compensate for the other and it just rides different.

Flex and balance can be different.
---------------------------

The easiest way I can think of putting HT vs BB is.

Out of the two. HT is primarily the only one that has to do with the bike's own stability.
BB is primarily A rider input/ feal.

Think of stability as, The bike's ability to keep upright and track straight when ghost riding.

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3/19/2020 12:32 PM

Wayne S wrote:

Flex and balance can be different.
---------------------------

The easiest way I can think of putting HT vs BB is.

Out of the two. HT is primarily the only one that has to do with the bike's own stability.
BB is primarily A rider input/ feal.

Think of stability as, The bike's ability to keep upright and track straight when ghost riding.

I was noticing that exact same thing..

Whether ghost riding or trying to ride no handed, these modern geometry frames are nothing like the BMXs of the 1980s. 80s bikes could ghost ride an 8th of a mile.. I used to have a bike, in the big school parking lot, I could pedal really fast and ghost ride it and it ran slightly to the left, I could stand there and it would eventually ride itself back to me and I would catch it without it crashing lol. Same thing riding no handed, 1980s bikes you could ride no handed all day..

My 2020 Kink Williams is impossible to ride no handed..

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3/19/2020 5:39 PM

Francky wrote:

I guess it is because you aren’t quite used to your new top tube, might be a little harder to lift the bike, but theorically you should even be able to go higher because you have more leverage, even if it takes a little more effort.

It’s just like if the longer tube added “1 harder point” and the higher BB bringed “0,5 easier point”
It the end, one doesn’t quite compensate for the other and it just rides different.

Wayne S wrote:

Flex and balance can be different.
---------------------------

The easiest way I can think of putting HT vs BB is.

Out of the two. HT is primarily the only one that has to do with the bike's own stability.
BB is primarily A rider input/ feal.

Think of stability as, The bike's ability to keep upright and track straight when ghost riding.

Black Swamp Ghost wrote:

I was noticing that exact same thing..

Whether ghost riding or trying to ride no handed, these modern geometry frames are nothing like the BMXs of the 1980s. 80s bikes could ghost ride an 8th of a mile.. I used to have a bike, in the big school parking lot, I could pedal really fast and ghost ride it and it ran slightly to the left, I could stand there and it would eventually ride itself back to me and I would catch it without it crashing lol. Same thing riding no handed, 1980s bikes you could ride no handed all day..

My 2020 Kink Williams is impossible to ride no handed..

Exactly. This is why in my opinion HT is more important than BB height when it comes to feeling stable. A slacker HT angle feels more stable because it actually is.

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3/19/2020 7:47 PM

Francky wrote:

HTA and BB brings a different kind of stability, as said before, you’ll hardly feel the change upfront, just a really really tiny difference on how your bike turns.
But the lower BB will be felt A LOT, you’ll feel sticked to the ground, more stable at speeds, and manuals will be way less twitchy and easier to hold, you’ll also feel like you “lose some pop” compared to a higher BB, in reality, you don’t, but i feels that way when you try to hop super high on flat.

Sean_Goff wrote:

I'm curious about this cuz when I switched from my 20.6/11.5 hangover to a 21/11.6 dagger with the same backend length and setup and everything.. it was a lot harder to hop over stuff with the Dagger and I cant tell if it's because of the longer tt or the higher bb but it was remarkably more difficult to jump on to the stuff that felt easy on my hangover.

That is a fair jump, people will say oh "only 0.4" blah blah" but it makes a difference. Longer TT will take more effort to lift the front end, but if you went to say an 11.8 or higher BB with the same 21 geo that would likely help as well.

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3/20/2020 11:11 AM

@am-shaegar have you checked out the black magic frame? That's about as stable as it gets unless you go to a race frame.

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