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22 inches
Jared Pabis:
--- Quote from: cmc4130;3544425 ---you're right that bb height relative axle line does matter on how quick the front end pulls up. BUT it also matters what wheel diameter. i've experimented with this several times.
see: http://bmxmuseum.com/forums/viewtopic.php?pid=3369360#p3369360
imagine you put some 16"s on your regular 20" bike, see how it feels. or even,the extreme case, let's say you put a couple of large roller-blade sized wheels in your regular 20" BMX frame in the same dropout spots you normally bolt down the axles. the bike is going to pull up quicker becuase the pivoting around the tiny roller blade wheel's axle (3" diameter) is going to be very quick. if you were trying to manual on those tiny 3" diameter wheels, you would have to do really quick adjustments.... does that make sense?
btw, bean22"s faction amero next to a custom 22" top tube STANDARD Trail Boss:
http://bmxmuseum.com/forums/viewtopic.php?pid=3369360#p3369360
:dunno:
--- End quote ---
Those are some good points...especially seeing the Faction next to the custom trail boss. I wouldn't mind trying 22's on my old TRLS 250 that has a 14.25 rear end and 21 inch TT.
I also think that the current 20 inch bike isn't that far from a 22. With tires being so big, we're pretty much riding 21's.
Bunky:
--- Quote from: cmc4130;3544425 ---you're right that bb height relative axle line does matter on how quick the front end pulls up. BUT it also matters what wheel diameter. i've experimented with this several times.
see: http://bmxmuseum.com/forums/viewtopic.php?pid=3369360#p3369360
imagine you put some 16"s on your regular 20" bike, see how it feels. or even,the extreme case, let's say you put a couple of large roller-blade sized wheels in your regular 20" BMX frame in the same dropout spots you normally bolt down the axles. the bike is going to pull up quicker becuase the pivoting around the tiny roller blade wheel's axle (3" diameter) is going to be very quick. if you were trying to manual on those tiny 3" diameter wheels, you would have to do really quick adjustments.... does that make sense?
btw, bean22"s faction amero next to a custom 22" top tube STANDARD Trail Boss:
http://bmxmuseum.com/forums/viewtopic.php?pid=3371046#p3371046
:dunno:
--- End quote ---
I agree that if you put rollerblade wheels on a bmx that manualing would be a lot twitchier, but that would be due to the decreasing of weight off the front end, not because you are pivoting around a smaller tire. You pivot around the axle, not the tire. Your axle doesn't know how big your tire is.
Where's George to bring some physics knowledge into this???
Sasha:
I think the other guys right, Bunky.
Jared Pabis:
The bottom bracket height issue will be trial and error. I have a 24 and the bb sits lower than the rear axle line (maybe 11.5 inches or something). Pulling up and hopping take a lot of work, but once you lock in a manual it feels like you have a wheelie bar keeping you there. I wish the bb was a little higher.
As wheel size increases, the bb should be more in line with the axle line. I think 11.75 would be a good starting point for a 22.
*I looked up the specs on Danny MacAskills frame and the bb is "+10mm" or about 0.40 inches above the axle line. So thats a 12.4" bb height on a 24. Just sayin.
cmc4130:
man, both of you, bunky and jared, are saying good stuff. i still can't quite wrap my head around the 'physics' of it (bunky you're exactly right the "lever" is the same; the contact point with rear tire up to axle is key... so why should circumference of wheel matter?? but somehow it feels like it does??? ) . i've ridden my buddy Vernon's InDust 2Ton 22" bike with a 14"cs http://www.plussizebmx.com/blog/2011/11/7/bike-check-indust-2-ton-22.html and it does not feel as quick as a 20" wheel bike with 14"cs. yes it's quick, but not thaaaat quick. i'll have to go out and experiment again on my different bikes tomorrow. jared, you're definitely right, sometimes "locking in" to manuals is more important--(look at bmx race bikes with long cs's for high-speed and over-roller manuals or mtbmx26"s with minimal bb drop and short cs's....) in the meantime:
i added this little triangle in photoshop to illustrate manual balance points for some how-to thread a while back ... i can't quite put my finger on it, but with my experience with bigger wheeled bikes (22, 24, 26), i feel like there's still a 'wheel effect.'
and for big wheel + short mtb chainstay (like 15-15.5) + small bb drop perspective witness this:
http://www.youtube.com/watch?v=RoWpqzabhpc
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