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mtbr remember
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Discussion Starter · #1 ·
I'm just wondering now... what is a "typical" or normal bb height on a 24" bike? This can either be taken from a 24" specific frame, or a 26" frame with 24's on it... I just want to hear some numbers that are out there being ridden.
What will a lower bb do to handling, what will a raised one do? pros, cons... manuals, etc...
preferably like to hear from those who build or have studied frame design, but that doesn't leave out any of you willing to just go to your garage and measure.
I'm running 175 cranks, and just starting to work out the final kinks out of my new ride this year, but I'm starting to think my bb is too low... ?

just glanced at some of the deathmobile specs, and it has an 11.88" height.... with what tires is this measured with? I'm assuming a super short fork as well? as in 65 or something...
what about a molly or fallguy, haven't found numbers for that... any others? quamen with 24's? even a bmx cruiser numbers?

somebody fill me in...
 

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Meh.
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Roughly 12.3" with the Pike at 95mm and DMR Moto Digger 2.35 tires.. Lower bb height makes it stable and easy to throw around. But you lose some ground clearance. I run 170s, all is well.
 

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http://www.unionstreetbikes.com/mollygeo.htm

12.3" high enough for your bb to clear when doing double peg grinds/stalls...

BMX bikes are typically 11.625" or so..

The height is really a personal preference, higher bb's have an inital easier pull in a manual but they also seem harder to stay up..

bb height also affects cornering and acceleration a lower bb will feel better cornering but with a high bb you can start pedalling out of a corner sooner...
 

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I ride a Black Market Mob with a Pike lowerd to 80mm and 24" wheels front and back... My BB height is 11.8"... It feels so nice
 

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mtbr remember
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Discussion Starter · #6 ·
thanks for the input everyone....

well, I guess mine is pretty low. Haven't held it next to my bmx bike yet, but I guess it might be just as low as a 20"er, wow...

I thought of getting shorter cranks, but that would probably feel sooo weird, since it is already kind of awkward to go from my fr bike, to my street dj 24, to my bmx, to my trials, xc, etc... they all have 175mm cranks. I like my frame, but that bb height... :skep:
 

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mtbr remember
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Discussion Starter · #8 ·
how much can you accurately assume that going from 26 to 24" wheelsets (assuming similar if not same tires are used..) will drop the frame??? :confused:

I guess I could figure that out roughly by comparing some of my bikes, but I just want to hear if someone has a more accurate way to calculate this, or already knows.

I see snaky69 put up 1", but I don't know... I'm guessing it's just under that, but I could be wrong.
 

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The difference in diameter is 2" (26-24), so the difference in radius is half that, or 1". With the same tires it'll be a 1" drop. Duh. :D
 

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mtbr remember
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Discussion Starter · #10 ·
The difference in diameter is 2" (26-24), so the difference in radius is half that, or 1". With the same tires it'll be a 1" drop. Duh.
fair enough, if same tires are used, very close to 1". But the diameter of a 24" wheel is not 24", etc. I guess I just made it much much more complicated in my head when I was writing that post.
 

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mtbr remember
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Discussion Starter · #12 ·
well, mine is about 11 1/4", somewhere around there. I'm just wondering what some of the framebuilders on this forum have to say about that... and this is with a marz 06 dj2 and a DMR Moto rt front and a Kiniption rear. pedal scrapage is an issue...
 

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That seems pretty low. 11.5" is even too low for me, I wouldn't wanna go much lower than 12".

What cranks are you running? The thing to keep in mind is many BMXers (myself included) run lower BBs w/ 180mm cranks. I'd wanna run 170s or 175s with that BB height on a 24" bike personally.
 

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mtbr remember
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Discussion Starter · #14 ·
That seems pretty low
yeah... I just remeasured on a level tile floor. It's just about 11.3 in. So, I can understand, as it is originally a 26" frame (Eastern proto), and a LOT of 26" dj/street rigs were designed on the 12.3 mark, like Snaky69's norco. so, I'm not disappoined or surprised at all, I'm fine with it, the chainstays work great for me at 15.6", the tt, wheelbase and headangle are spot on as well.
I'm running 175mm wethepeople royals (next size down is 165, too short)... and on my BMX bike I have 180mm, and it has approx. 11.5 bb height.

I guess I'm fine, since I ride mostly street with it anyway, and smooth packed dj trails, so I'm not worried about clearance. and railing berms, I'm not pedaling out to get ahead in a race or anything. I basically just crank it to get speed for a hit then coast, and i'm set.
 

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Retread soul rider
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really on the DL

I knew my BB was pretty low, but never stopped to measure 'til I read this post. I have a 2004 Specialized P.2 frame with 80mm Gold Label Series 2 fork, 26" Singletrack w/2.35" Minion DH tire on the front and a 24" SUV rear wheel with a 2.35" Arrow Racing Launch tire on the back. I run 175mm Profile cranks with Bombshell pedals - cause they're fairly narrow, they help with clearance in turns.

BB height, measured on garage floor with the bike unweighted (so no sag) and tires inflated to 42#: 9 15/16"!!!

It carves like an electric knife on Turkey Day and is very comfy on DJ, but is obviously not a very good trail bike. There's a big difference in the feeling of ease of acceleration with the 24 compared to the 26 on the rear. I'm comparing gear ratios that are very close to 55": 36x17 on the 26 and 36x16 on the 24. At the jumps I can use a shorter run up to the big set...

Anybody else have (or ever hear of) a BB under 10"??
 

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mtbr remember
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Discussion Starter · #16 ·
9 15/16"!!! Anybody else have (or ever hear of) a BB under 10"??
ouch... well, that's why I started this topic, since there is bound to be some riders out there rocking some different set-ups... get some discussion going.
but under 10"... hmmm, and just imagine how close your 36t sprocket gets to the ground with your fork at full compression?! :eekster: what was your bb height with the 26 on back? couldnt' imagine much more than like 10.5 or so... ?
if I were you, I'd look at swapping out to a microdrive! like a 28t or smaller sprocket, that is what I'm running, with a 12 in the back at the moment, with 24" atomlabs... have thought about going 13 in the back, cuz it's better for street, but right now, the dj's I've been messing around on need more speed. anyway, I would HIGHLY recommend the microdrive, especially with your low bb. and I thought mine was low at 11.3"... (but, I have a 100mm fork, so, maybe mine is getting fairly close to the ground at full compression too.)
I was at one time thinking of installing a Nemesis Project lowering kit in my 06' DJ2, but after some thought, and this thread, I decided my geometry angles are all set at 100mm, so I'll be fine until I swap out frames.
I also see that the Quamen frame, can be run either 24 or 26", and with the 24's, it has a bb height at about 11.25", and spoke with some guys running that, and they are just fine with it.
 
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