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Old 04-29-2014, 07:24 PM   #1231
UnsureFooting
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Originally Posted by crofrog View Post
When you get on the throttle of a chain driven bike, the ground clearance increases not decreases because the chain torque extends the rear swing arm.
Ummmm.....
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Old 04-29-2014, 09:03 PM   #1232
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Originally Posted by UnsureFooting View Post
Ummmm.....
True statement.


Issue is that throttle is built into the torque equation for the rear so fucking up with the the thottle is still bad new bears.
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Show folks something with a clutch and carburetor, and it's like teaching a baboon to use a Macbook.
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Old 04-29-2014, 09:33 PM   #1233
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But... The chain pulls on the sprocket ABOVE the axle. Which makes me think the swingarm would rise, reducing clearance.
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Old 04-29-2014, 09:56 PM   #1234
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isn't it a wheelbase thing ? ...
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Old 04-29-2014, 11:29 PM   #1235
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Well, according to this FF, I'm wrong.
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Old 04-30-2014, 03:41 AM   #1236
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Originally Posted by crofrog View Post
When you get on the throttle of a chain driven bike, the ground clearance increases not decreases because the chain torque extends the rear swing arm.
It may extend or compress depending on a number of variables. And please don't quote me Keith Code as the source of wisdom. There are any number of technical publications that will explain why a bike can either squat or rise under acceleration. Here's just one.

http://www.peterverdone.com/archive/rideheight.htm

Basically weight transfer will try and compress the rear suspension, and the swing arm will try and drive under the swing arm pivot point lifting the rear suspension. The rear suspension height (angle) is just one influence. Even changing the sprocket sizes will upset these competing forces. The bottom line is there is no absolute rule. As the article above explains a little squat is desirable. GP bikes have a number of adjustments that are used to control and achieve the desired squat under heavy acceleration.

JohnCW screwed with this post 04-30-2014 at 04:44 AM
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Old 04-30-2014, 05:57 PM   #1237
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Originally Posted by UnsureFooting View Post
But... The chain pulls on the sprocket ABOVE the axle. Which makes me think the swingarm would rise, reducing clearance.
Other way, doesn't matter in relation to the axel, it masters from the pivot, and the longer the swing arm the more anti squat generated
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Show folks something with a clutch and carburetor, and it's like teaching a baboon to use a Macbook.
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Old 04-30-2014, 09:23 PM   #1238
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Other way, doesn't matter in relation to the axel, it masters from the pivot, and the longer the swing arm the more anti squat generated
That, I will disagree with. I read through the chain pull section in the book I posted.

The relationship that matters is the positions of the top of the rear sprocket, swing arm pivot, and top of the drive sprocket. Even then, it also matters what the center of gravity angle of movement is doing.

The geometry involved says that if the swingarm was infinitely long, there would be no change in attitude.


I honestly didn't understand all the math or physics involved, but it was detailed enough to convince me, lol!

Edit - I agree, not disagree.
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Old 04-30-2014, 11:15 PM   #1239
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I think that the riders apparent Parkinson's disease had more to do with the crash, than whether the swing arm wanted to extend or compress ;-)
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Old 05-01-2014, 04:34 PM   #1240
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Originally Posted by UnsureFooting View Post
That, I will disagree with. I read through the chain pull section in the book I posted.

The relationship that matters is the positions of the top of the rear sprocket, swing arm pivot, and top of the drive sprocket. Even then, it also matters what the center of gravity angle of movement is doing.

The geometry involved says that if the swingarm was infinitely long, there would be no change in attitude.


I honestly didn't understand all the math or physics involved, but it was detailed enough to convince me, lol!

Edit - I agree, not disagree.

Easy enough to test, hold the front brake and gas it, see if the tail doesn't rise.
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Old 05-01-2014, 06:52 PM   #1241
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Originally Posted by UnsureFooting View Post
But... The chain pulls on the sprocket ABOVE the axle. Which makes me think the swingarm would rise, reducing clearance.

Nope. Chain is the hypotenuse of the triangle. It pulls the swingarm down.

Go watch some dyno videos and you'll see it.
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Old 05-01-2014, 07:18 PM   #1242
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Originally Posted by Tripped1 View Post
Easy enough to test, hold the front brake and gas it, see if the tail doesn't rise.
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Originally Posted by LuciferMutt View Post
Nope. Chain is the hypotenuse of the triangle. It pulls the swingarm down.

Go watch some dyno videos and you'll see it.
I'm not sure either one of these is a good example of a motorcycle in motion. And that's a pretty flat triangle.

It sure feels like the rear squats out when I goose my 640A.
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Old 05-01-2014, 09:00 PM   #1243
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Originally Posted by LuciferMutt View Post
Nope. Chain is the hypotenuse of the triangle. It pulls the swingarm down.

Go watch some dyno videos and you'll see it.
I already posted that I was wrong, and why.
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Old 05-02-2014, 09:25 AM   #1244
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Originally Posted by Boon Booni View Post
I'm not sure either one of these is a good example of a motorcycle in motion. And that's a pretty flat triangle.

It sure feels like the rear squats out when I goose my 640A.

No one said it doesn't squat, it will, moreso when you apply enough thrust to start lifting the wheel.
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Old 05-02-2014, 12:03 PM   #1245
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Originally Posted by JohnCW View Post
Yes he's lousy on the throttle, but seemed to me it was the peg dragging that brought him undone. So perhaps an incorrect set sag (front but mostly back), possibly incorrect spring rate causing the bike to squat even lower as he gets on the throttle, and a failure to hang off to at least some degree are the possible reasons.
I would think its both, when you let off the throttle in the middle of a turn the bike will want to fall into the turn, and I would think if you already really low, letting off the throttle would drop the bike down to low and the tires (maybe he had cold tires) would slide out, or he would scrap the peg and panic twitch causing him to go down.
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