swing arm angle - Kawasaki ZX-10R.net
 
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post #1 of 6 Old 09-09-2013, 03:18 PM Thread Starter
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swing arm angle

How do you go about measuring the swing arm angle. I have heard it is supposed to be about 12 deg. From where?
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post #2 of 6 Old 09-09-2013, 06:19 PM
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Put the bike on a paddock stand and do whatever is needed to shim up the front tire so that it is the same height off the ground as the rear tire (bike level on paddock stand).

Have an assistant lift up on the bike to unload the suspension (or carefully jack it from below - just enough to top out the suspension, not enough to lift it clear of the stands).

Measure from the center of the rear axle to the ground, measure from the center of the swingarm pivot to the ground. Subtract the former from the latter to get the difference.

Measure from the center of the rear axle to the center of the swingarm pivot to get the effective length of the swingarm.

Now the trigonometry.

Swingarm angle = inverse sin (difference in height / swingarm length)


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post #3 of 6 Old 09-09-2013, 06:34 PM
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Quote:
Originally Posted by GoFaster View Post
Have an assistant lift up on the bike to unload the suspension (or carefully jack it from below - just enough to top out the suspension, not enough to lift it clear of the stands).
Isn't the swingarm angle measured with load?
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post #4 of 6 Old 09-09-2013, 11:04 PM
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Quote:
Originally Posted by El Zilcho View Post
Isn't the swingarm angle measured with load?
You can, but, swingarm angle is very dynamic. The angle under full throttle will be different than part throttle or mid corner vs. corner entry and so on and so on. The idea of measuring the angle with the suspension topped out, removes a few of the variables and simply helps set a base line to start tuning. Just don't forget about trail

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post #5 of 6 Old 09-11-2013, 10:43 PM Thread Starter
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swing arm angle

What is the angle supposed to be without load and with load?
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post #6 of 6 Old 09-12-2013, 07:02 AM
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The down-angle is supposed to be somewhere near 12 degrees with the suspension unloaded. Don't go by what it is with the suspension loaded - go by 12 degrees with the suspension unloaded and whatever the correct rider-aboard sag is front and rear, and under those conditions, the angle is whatever it is.

Too-flat swingarm angle is one of the reasons that bikes with lowered suspension and/or extended swingarms have poor rear-end grip when accelerating out of corners. If you have swingarm down-angle, then when the chain starts pulling and the axle starts applying force to accelerate, the down-angle applies a force downward at the axle that largely offsets the extra weight transfer, so that the rear suspension doesn't have to compress before the tire gets planted against the ground.


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