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Offline Jared Pabis

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22 inches
« Reply #135 on: March 31, 2012, 10:18:37 AM »
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:


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.

Offline Bunky

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« Reply #136 on: March 31, 2012, 10:58:23 AM »
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:



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???
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Offline Sasha

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« Reply #137 on: March 31, 2012, 11:35:39 AM »
I think the other guys right, Bunky.

Offline Jared Pabis

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« Reply #138 on: March 31, 2012, 12:10:19 PM »
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.

Offline cmc4130

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« Reply #139 on: March 31, 2012, 09:24:59 PM »
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
« Last Edit: April 01, 2012, 04:01:30 AM by cmc4130 »

Offline ssteinbr

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« Reply #140 on: March 31, 2012, 10:23:30 PM »
Quote from: cmc4130;3544633
i feel like there's still a 'wheel effect.'


There is.  There isn't much but it is there.  Think of rocking on rocking chairs with various radius rockers.

Offline Dr. Lucien Sanchez

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« Reply #141 on: April 02, 2012, 04:25:24 AM »
The 'wheel effect' matters for the side to side balance point in manuals and going round corners and stuff - the pivot point for side to side is where the wheel meets the ground

With the up and down motion you and the bike revolve around the axle NOT where the wheel makes contact with the ground

However it's pretty much impossible to manual properly without adjusting weight in all directions (same as riding along in a straight line isn't actually straight) so there is a difference in wheel size with same length chainstays

Offline G

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« Reply #142 on: April 02, 2012, 09:54:33 AM »
IF you had a perfectly smooth rolling hub, then the bike would only really pivot around the hub axle as long as you stay off the brake, but as soon as you start touching the brake it will start to roll around the tyre as well. So any friction in the hub (hubs are very smooth but not perfect, and when you are balancing you may notice this, especially if there is significant drag in your driver say if it is a bushing one rather than one with proper rolling element bearings and you run a tight chain) will be a similar effect.

:)
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Offline cmc4130

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« Reply #143 on: April 02, 2012, 10:02:46 AM »
Quote from: G;3545027
IF you had a perfectly smooth rolling hub, then the bike would only really pivot around the hub axle as long as you stay off the brake, but as soon as you start touching the brake it will start to roll around the tyre as well.  . .  .  .


That sounds true . . . but I would add any time you are off the balance point, that will happen.  Rather than talk about manuals, let's look at peg wheelies and hang 5's (or any other flatland peg trick). You are standing on the axle.  I have ridden flatland on 24"s. www.youtube.com/watch?v=CQA2E71iWUE It's harder to get up into the hang 5; once you're fully locked in it's not any different, but any time you make an adjustment, it's slower.

And . . . to get this thread back to 22"s, here's my buddy Vernon on his InDust 2Ton 22".   He's getting a short run of 4 more frames made right now; they're almost done.  Can't wait to ride one.

« Last Edit: April 02, 2012, 10:13:37 AM by cmc4130 »

Offline Dr. Lucien Sanchez

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« Reply #144 on: April 02, 2012, 10:59:25 AM »
But even using the brake your pivot point is still around the axle?

The bushing in a driver shouldn't have an effect whilst manualling, only the spring/pawl set up?

Tha hang 5 thing, maybe cause there is marginally more weight further away from the rider than a smaller wheel?

Actually thinking about it maybe a bigger size wheel of similar weight has more angular momentum (gyroscope)?

I kinda like the look of 22" bikes

Offline Sasha

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« Reply #145 on: April 02, 2012, 11:16:47 AM »
Quote from: AGGIEBMX;3545041
Actually thinking about it maybe a bigger size wheel of similar weight has more angular momentum (gyroscope)?


Right, time to leave the internet.

Offline G

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22 inches
« Reply #146 on: April 02, 2012, 03:12:45 PM »
Quote from: AGGIEBMX;3545041
But even using the brake your pivot point is still around the axle?

The bushing in a driver shouldn't have an effect whilst manualling, only the spring/pawl set up?

Tha hang 5 thing, maybe cause there is marginally more weight further away from the rider than a smaller wheel?

Actually thinking about it maybe a bigger size wheel of similar weight has more angular momentum (gyroscope)?

I kinda like the look of 22" bikes


Imagine locking up the back wheel, the bike will then be like a solid lump and roll around the tyre.

You are absolutely right, the boshing wont matter, just the pawl drag as you say... dont know what I was thinking...

When you make a correction in either a hang 5 or a manual you do so because your centre of gravity is no longer over the contact point. When you correct you shove your weight back towards the contact patch, but you also pull the bike back under you. So weight and momentum will be "felt", however until you brake or add drag I dont think that the specific radius is important except as so far as it effects rolling and momentum.

I do love my 24"

:)
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Offline ssteinbr

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« Reply #147 on: April 02, 2012, 09:23:57 PM »
Quote from: cmc4130;3545030



Trail pirate!!!  Hippie is the man!  That's it I am getting a the S&M or Indust 22 this summer.

Offline ssteinbr

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« Reply #148 on: April 03, 2012, 09:38:45 PM »
Amero looks nice and will be available soon.  But it only has clearance for a 26t chainwheel.

Offline cmc4130

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« Reply #149 on: April 05, 2012, 08:28:14 PM »
Quote from: ssteinbr;3545637
Amero looks nice and will be available soon.  But it only has clearance for a 26t chainwheel.


that's not uncommon with bigger wheeled bikes that also have short chainstays. (they have to bow out to accept the wheel that close to the bottom bracket).  the Liquid Feedback 24" is the same.  the Sunday Wave C 24" as well if I'm not mistaken.

check this out. just a little experiment as I'm waiting for my custom frame. an S&M 22" fork and 22" wheels on a We The People Avenger 24" frame (same geo as 1st gen Model C--21.25"tt, 13.75"bb). the shorter fork drops the bb a bit, but it still looks like a good height. and the head angle is not as affected as i thought it might be. it looks highly rideable. of course the brakes won't line up and you're not getting the benefit of a shorter cs designed around a 22" wheel.


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22 inches
« Reply #149 on: April 05, 2012, 08:28:14 PM »

 

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