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Retired Pipe Polisher C2H6O+
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Discussion Starter · #1 ·
The only way I can see to do it without special jigs is to use a string to make a straight line between the sprocket center and swing arm pivot. Continue that back to over the rear axel and measure the distance down to the center of the rear axel. With those two measurements and the swing arm length I can calc the angle but this leaves a lot of room for error. How do the pros do it?


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I saw a jig that a specialty shop used to make custom race bikes, lasers and everything,...
 

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Retired Pipe Polisher C2H6O+
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19,081 Posts
Discussion Starter · #3 ·
LOL. Gee thanks. :)


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Retired Pipe Polisher C2H6O+
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Discussion Starter · #4 ·
Maybe if I give a little more background it'll generate more interest. :)

I've been trying to learn as much about suspension geometry as I can with my limited ability to comprehend. :)

I watched on youtube a great learning session put on by Traxxion Dynamics. When he got down to the nitty gritty about suspension setup I was really interested in what he had to say about anti and pro squat and swingarm angle. With my very crude measurements on my Monster I think I have about 7-8 degrees of anti-squat with my ride height adjustor cranked out as long as it can go.

According to them optimum starting point is between 12-13 degrees. Based on how they describe the characteristics of a bike with too little anti-squat I agree that I need more. After the apex when I open the throttle the bike understeers and heads for the outside of the track. I'm not talking about whacking the throttle, just opening the throttle to accelerate.

So I'm pretty sure I need to still raise the back more to get more anti-squat and I've ordered a longer suspension rod from Motowheels but I'd still like to be able to measure what I have and where I'm go going for a better reference.
 

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Maybe if you measured the swing arm angle with a digital spirit Level and compared it to a known angle on the chassis such as the steering head or forks.
 

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Mike, wouldn't you affect the front geometry by raising the rear ride height too?
 

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Old school still works the same it is just harder to read and you need to know what you are looking at. Measure from center of axle and center of swingarm then draw the line and measure that angle. Simple except in practice you need to get those base line from a real bike with many things in the way. A automated system like described is getting its benefit from the ease of use which should make it more repeatable. As well as the most important thing quicker for the average person to do which equals more money for the shop doing the work.

Duckman your statement that you have the stock adjuster maxed out and are still having squat does not sound right to me. Have you checked/set sag yet? Your bike should be having zero squat with the right spring, damping and adjusted swingarm angle and I do not find the angle need to be modified unless you are starting with the fixed rod or a lowering rod. Make sure your preload is 10-20mm max on that spring and then set compression damping first. If you get too extreme on the swingarm angle know that you will have some side effects (less stable) in high speed straights.

Yes effecting the rear will effect the front geometry as well so measure everything and then be prepared to change things you did not expect. Chassis setup is one part science and one part experience. Use the science to gain the experience and do not be afraid to make mistakes, learn from them and keep on trying until you find what you are looking for. going to a suspension specialist is more about the experience then the science as long as you are willing to put in the legwork you too can get there.
 

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Retired Pipe Polisher C2H6O+
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Discussion Starter · #9 ·
After doing a little more research and watching some Dave Moss videos I learned I was taking my measurements totally wrong. I was thinking the angle of the swing arm was taken relative to a straight line drawn through the counter shaft sprocket and the swing arm pivot. Now I learn the angle is actually relative to the ground, true horizontal.


This morning I rigged up, with some tiedowns, a way to hold the bike up sitting level on both wheels. I removed the rear sets and pulled a piece of cord tight between the center of the rear axel and the swing arm pivot. Using a digital level on the iPhone I measured as close as I could, without bending the cord, between 12 and 13 degrees. According to the experts that's just about the perfect starting point.


ducvet, about what I was feeling at the track, the bike wanting to run wide exiting on the gas was really specific to one turn at Little Tally that I was having problems with, Turn 3. I was just thinking about how to help with that specific turn. I really don't have enough experience yet to truly understand if it was just me, maybe the turn is a little off camber on the exit, or what. I'm just brainstorming and trying to learning as much as I can. Thanks for the help.
 

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Retired Pipe Polisher C2H6O+
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19,081 Posts
Discussion Starter · #10 · (Edited)
Mike, wouldn't you affect the front geometry by raising the rear ride height too?
Hey Mike. Yes it does but my forks are 40mm longer than stock so I have plenty of room for adjustment. I'm currently running the front up so that it's really close to stock factory specs. The manual say 24 degrees and I just now measured mine at about 23.7.
 

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Hey Mike. Yes it does but my forks are 40mm longer than stock so I have plenty of room for adjustment. I'm currently running the front up so that it's really close to stock factory specs. The manual say 24 degrees and I just now measured mine at about 23.7.
I figured you had a handle on it. :nerd: I only have a basic knowledge of suspension. 0:)
 

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Retired Pipe Polisher C2H6O+
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Discussion Starter · #12 ·
Me too. But I’ve learned enough to be dangerous. :)


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It’s great to dig into these topics, but I’ve found the more I know, the less I actually understand lol. Saying that 13* is the ideal starting point for swingarm angle is a shot in the dark at best without more information.

Ultimately the job for the rear suspension is to promote drive grip for the motorcycle. The more powerful the bike, the more important that becomes. Searching for ideal swingarm angle without taking into account chain pull angle, swingarm pivot height and ride height is pretty moot. But searching for answers is nonetheless a good path.

I found this article very helpful
https://www.sportrider.com/more-fun-geometry
 

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Excel Addict
2001 900SSie
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5,345 Posts
My iPhone has an app called Level.
It is in the Utilities folder.
Measures inclination/slope in one degree increments.
 

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Excel Addict
2001 900SSie
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iphone app is great.
Sorry a bit of a bum steer.

The app is Measure, then select Level.

Watch out for the buttons on either edge of the phone depending which side you are using.
A quick test shows they add one degree, so make sure the button(s) are not touching your flat surface by skewing the phone a bit.
 
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