Chain Stay Length and BB height
- Thread starter iksmudge
- Start date
Shorter chain stay makes the bike easier to whip around and more "twitchy". Also, it makes the bike easier to manual.
Higher BB makes it easier to pop off of jumps and bunny hop higher.
Higher BB makes it easier to pop off of jumps and bunny hop higher.
Quicker handling and easier to pull up. Not sure about higher hops though.
the short cs trend started in the mid-90's with people grinding the dropout slots further up in bikes such as S&M Holmes, Hoffman TAJ, Standard STA, etc. the '95/96 HOMELESS Mack came with a 14" cs slammed, which was considered very short for the time.
cs's hung out in the mid 14"s for several years until a few street riders started going with the ultra-short cs that was only then seen on flatland bikes. i'm not positive but i think steven hamilton may have had one of the early under-14" cs street/park/dirt frames.
however, the demand for a stable trails 20" is still there. and you will see companies like DELUXE still making cs's in the mid 14"s.
with 24" an 26" the story's a little different. Union Street, Tonic, NS and Superco revolutionized short cs for 24" mtbmx. Greg Melms' prototypes and Liquid's Feedback 24" bmx are the first 24" bmx cruisers to have ultra short cs's that i can think of (although HOMELESS did a cruiser in the mid 90's called the FATTY which i want to get my hands on where they based the geo on their MACK). with 26" MTBMX, several companies--Blackmarket, Transition, Superco, Atomlab, Doberman, NS, Eastern, . . . etc. have made awesome handling bikes by getting that big 26" wheel further up in the dropout.
i personally don't think it has to be ultra-slammed. 15.75" feels pretty damn good to me with 26" wheels. if you're trying to do manual to 180 or manual to bunnyhop tailwhip or something, i can see going shorter, but the MOB has the geometry nailed for 26" MTBMX trails and racing.
high bottom bracket i'll save for another time.........
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lower bb lowers your center of gravity and provides a more stable ride, better for corning berms ect. a higher bb raises your center of gravity alowing for more powerfull bunny hops and more pop off of jumps. trails frames (atleast with 26" wheels) tend to have a lower bb and longer chainstays, while more street oriented frames have higher bb's and shorter chainstays. personall for me bb height makes the biggest difference to me in a frame. i absolutly despise negetive bb's on my hardtails, i like it high and with short chainstays
Or, more technically, "reach". (bb center to headtube center on the horizontal)
generally speaking,high bb feels more agile in the air, low bb feels more agile on the ground; high is harder to control while manualling, low is easier.
short cs are easier to pull up but more precise to control (I deliberately don't say 'harder' as I find my 14.5" Howie easier to control than most other frames but the manual point is a bit shorter so to speak), longer cs are harder to pull up but less precise to control.
It gets more difficult when both factors are combined e.g. a low bb short cs frame like most decent 26" hardtails or a high bb with longer chainstays (like most bmx frames from 7-8 years back compared to the frames that are common now). The way I feel it is low bb short cs (minus 15" + 12.something) on a 26 feels right whereas low bb and short cs (like the WTP frames from a couple of years back) feels like ass on a 20 and vice versa..
24 can go both ways I think although I do find a Sunday cruiser one of the most horrible feeling bikes I've ever ridden..
short cs are easier to pull up but more precise to control (I deliberately don't say 'harder' as I find my 14.5" Howie easier to control than most other frames but the manual point is a bit shorter so to speak), longer cs are harder to pull up but less precise to control.
It gets more difficult when both factors are combined e.g. a low bb short cs frame like most decent 26" hardtails or a high bb with longer chainstays (like most bmx frames from 7-8 years back compared to the frames that are common now). The way I feel it is low bb short cs (minus 15" + 12.something) on a 26 feels right whereas low bb and short cs (like the WTP frames from a couple of years back) feels like ass on a 20 and vice versa..
24 can go both ways I think although I do find a Sunday cruiser one of the most horrible feeling bikes I've ever ridden..
i paint-shopped these for a pinkbike thread (i know yall already know this!!).
a 20" bmx set up with 8" rise bars gives you roughly 35 inches from grips to the ground and 35"-11.75"bb = 23.25" of stance height.
on a 26" dj bike, you can set it up with that same stance height by using completely flat no-rise bars, or you can go 3+ inches taller. so, a roughly 18" axle to crown, stem slammed, with 3 inch bars gives you roughly 39" to the ground. 39 - 12.75 = 26.25"
1970's Scwhinn Stingrays had the bb pretty much on axle level. with 20" wheels, that puts your pedals a little to close to the ground, so they had to use short cranks. (i can't remember where i read it, but i remember reading somewhere that there was actually a manufacturing law about minimum specifications for bicycles which said there had to be such-and-such ground clearance for pedals....) so when big guys started riding little bikes, they wanted longer cranks, but the only way to do that with 20" wheels was to make the bb higher.
compare 1976 Schwinn Scrambler
http://bmxmuseum.com/bikes/schwinn/16468
to the version meant for BMX:
1976 Schwinn "competition" Scrambler
http://bmxmuseum.com/bikes/schwinn/7241
EDIT: to quote Bob Osborn:
http://bmxactiononline.com/index2.php?option=com_content&do_pdf=1&id=17
There had been earlier, unsuccessful attempts to improve 20-inch bikes for racing, but the real progenitor of today's BMX bike was built late in 1973, probably in late September. It was a modified Schwinn Sting-Ray.
Originally the Sting-Ray had a short wheelbase, low bottom bracket, and 4½-inch cranks…geometry and leverage not conducive to BMX racing. The modifications consisted of removing the curved top and down tubes and replacing
them with longer straight tubes, thereby extending the bike's wheelbase. Reassembly involved rotating the rear A-frame structure in order to raise the bottom bracket. This allowed the use of Schwinn Diamond 6½-inch cranks, which produced more speed and power than the original 4½-inch cranks. The longer frame kept the front wheel on the ground when the increased power was applied and made the handling of the bike more predictable under racing conditions.
a 20" bmx set up with 8" rise bars gives you roughly 35 inches from grips to the ground and 35"-11.75"bb = 23.25" of stance height.
on a 26" dj bike, you can set it up with that same stance height by using completely flat no-rise bars, or you can go 3+ inches taller. so, a roughly 18" axle to crown, stem slammed, with 3 inch bars gives you roughly 39" to the ground. 39 - 12.75 = 26.25"
1970's Scwhinn Stingrays had the bb pretty much on axle level. with 20" wheels, that puts your pedals a little to close to the ground, so they had to use short cranks. (i can't remember where i read it, but i remember reading somewhere that there was actually a manufacturing law about minimum specifications for bicycles which said there had to be such-and-such ground clearance for pedals....) so when big guys started riding little bikes, they wanted longer cranks, but the only way to do that with 20" wheels was to make the bb higher.
compare 1976 Schwinn Scrambler
http://bmxmuseum.com/bikes/schwinn/16468
to the version meant for BMX:
1976 Schwinn "competition" Scrambler
http://bmxmuseum.com/bikes/schwinn/7241
EDIT: to quote Bob Osborn:
http://bmxactiononline.com/index2.php?option=com_content&do_pdf=1&id=17
There had been earlier, unsuccessful attempts to improve 20-inch bikes for racing, but the real progenitor of today's BMX bike was built late in 1973, probably in late September. It was a modified Schwinn Sting-Ray.
Originally the Sting-Ray had a short wheelbase, low bottom bracket, and 4½-inch cranks…geometry and leverage not conducive to BMX racing. The modifications consisted of removing the curved top and down tubes and replacing
them with longer straight tubes, thereby extending the bike's wheelbase. Reassembly involved rotating the rear A-frame structure in order to raise the bottom bracket. This allowed the use of Schwinn Diamond 6½-inch cranks, which produced more speed and power than the original 4½-inch cranks. The longer frame kept the front wheel on the ground when the increased power was applied and made the handling of the bike more predictable under racing conditions.
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generally speaking,high bb feels more agile in the air, low bb feels more agile on the ground; high is harder to control while manualling, low is easier.
It gets more difficult when both factors are combined e.g. a low bb short cs frame like most decent 26" hardtails or a high bb with longer chainstays
These are both counter to what I have found. a higher BB is easier to pull back and hold a manual but less stable cornering than low BBs. Also, the trend in 20s right now is a lower BB height (11.5-11.8) and shorter stays 13.25-13.75.
i have found that shorter stays do effectively the same thing as a higher BB. To enhance manualing, hopping, spinning.
It gets more difficult when both factors are combined e.g. a low bb short cs frame like most decent 26" hardtails or a high bb with longer chainstays
These are both counter to what I have found. a higher BB is easier to pull back and hold a manual but less stable cornering than low BBs. Also, the trend in 20s right now is a lower BB height (11.5-11.8) and shorter stays 13.25-13.75.
i have found that shorter stays do effectively the same thing as a higher BB. To enhance manualing, hopping, spinning.