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Old 12-04-2010, 09:30 AM   #1
Darth Lefty
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Settle a bar bet - lean angle

My friend - we'll call him Mr. RT - often goes on rides with another person I know, Mr. GS. He mentioned when talking bikes the other day that Mr. GS seems to him to be less leaned over than he is, in the same turn.

I argued to Mr. RT that this is an optical illusion. Bikes make coordinated turns (I claimed) unless you are leaning off, and so for a given turn (speed, radius) there is a lean angle that goes with it, regardless of bike. Mid turn, in your reference frame, the bike ahead of you is also above and leaned towards you, making his lean angle difficult to judge.

He however argues that Mr. GS is indeed at a different lean angle, and that this is due to the difference in steering geometry between the two bikes. I tend to agree that the GS is insanely easy to ride at any speed, but this seemed to me like hooey.

What do you think? (Exhaustive proofs encouraged).
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Old 12-04-2010, 09:46 AM   #2
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Re: Settle a bar bet - lean angle

Sounds like to me you need to ride more and think less!....LOL
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Old 12-04-2010, 10:09 AM   #3
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Re: Settle a bar bet - lean angle

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Originally Posted by Jafo28 View Post
Sounds like to me you need to ride more and think less!....LOL
The roads, they is wet
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Old 12-04-2010, 10:15 AM   #4
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Re: Settle a bar bet - lean angle

Lean angle is dependent on both speed and wheelbase length: for a given rate of turn, more distance between the axles requires more lean angle than the same sort of misbehavior on something shorter.

Coordinated turn?....

Wrap your head around this one: while a bike is turning, the rear wheel will always track inside the front's path, unless you're steering with the throttle enough that it tracks on the other side.
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Old 12-04-2010, 10:44 AM   #5
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Re: Settle a bar bet - lean angle

Hence the term "crossed up" as in the picture above.
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Old 12-04-2010, 11:03 AM   #6
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Re: Settle a bar bet - lean angle

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Coordinated turn?....
By which I mean, the acceleration vector is going (approximately) straight down in your own seat. (It's an allusion to airplane dynamics.) The other stuff you mention ought to all be negligibly small angles and distances by comparison, unless you are at cop moto rodeo speeds. Mathematically the calculation is the same as the one from high school physics for a banked track.

This is all assuming "normal" riding, no knee down or sliding or sidecar rigs up on the wrong 2 wheels or other goofy exceptions you are welcome to post pics of!
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Old 12-04-2010, 11:34 AM   #7
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Re: Settle a bar bet - lean angle

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...The other stuff you mention ought to all be negligibly small angles and distances by comparison, unless you are at cop moto rodeo speeds.
Well, Kevin Cameron and I both disagree with you. If, as you contend, the "stuff I mentioned" truly were not relevant:

1) Why are racebikes always as short as possible in the wheelbase department?. It's not for weight saving; it's for quicker steering and requiring less lean angle (ie: more ground clearance) when turning.

2) If you've ever hopped on a tandem bicycle, your initial reaction at the first real turn will be that you're about to crash. It's caused by the fact that the much-longer tandem bike has to lean a lot more than your own experience is accustomed to for a given rate of turn, and the alarm bells go off...you see the approaching turn-in point, and as soon as you start to push the bars everything is either way too much (lean angle) or not enough: using the expected "normal" amount of lean angle results in going wide. Once you become accustomed to it, no worries.

Btw... "ought to be" and a comparison to "cop moto rodeo speeds" isn't much of an argument. Leave the obfuscation to the politicians.


Quote:
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Mathematically the calculation is the same as the one you did in high school physics for a banked track.
Try again, as it's not the case at all. On a banked track, once your speed and lean angle gets up to the no-steering pace, from your point of view, the path of travel is swooping upwards. As long as you're in the bowl, you're climbing straight up a never-ending hill.


Relatively flat pavement and a heavily banked track are two very different situations.



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Sounds like to me you need to ride more and think less!....LOL
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Old 12-04-2010, 04:16 PM   #8
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Re: Settle a bar bet - lean angle

Oh, this is going to be exciting!!!
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Old 12-04-2010, 04:34 PM   #9
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Re: Settle a bar bet - lean angle

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Oh, this is going to be exciting!!!

I still want to know what the bet is...

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Old 12-04-2010, 05:26 PM   #10
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Re: Settle a bar bet - lean angle

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Originally Posted by Jafo28 View Post
Sounds like to me you need to ride more and think less!....LOL
Translated: Yer killin' me Smalls!
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