Measuring Swingarm Angle - Chicagoland Sportbikes
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post #1 of 41 (permalink) Old 05-16-2007, 09:33 AM Thread Starter
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Measuring Swingarm Angle

To get the rear to hook up right swingarm angle needs to be about 12.7 degrees.

Here are a couple pics on how to measure.


Note.... the bike is on it's stands in these pictures - NOT HOW YOU DO THIS.

To measure swingarm angle, bike needs to be on it's tires with the suspension topped out - THIS IS MODIFIED !!

Tom
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File Type: jpg Angle_gauge.JPG (101.8 KB, 41 views)
File Type: jpg Swingarm_Angle.JPG (62.5 KB, 57 views)

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post #2 of 41 (permalink) Old 05-16-2007, 10:03 AM
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Thanks, thats good stuff.

Would one measure this with the rider's weight on or off?
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post #3 of 41 (permalink) Old 05-16-2007, 10:06 AM
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So when you take your measurement the weight of the machine should be on the suspension?

Is there any other way to adjust swing arm angle besides adjusting the rear ride height?

And why is this in the NESBA forum? This is clearly a performance and tech thread. Ohhhh you're a CR.

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post #4 of 41 (permalink) Old 05-16-2007, 10:08 AM
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Quote:
Originally Posted by Grasshopper View Post
So when you take your measurement the weight of the machine should be on the suspension?

Is there any other way to adjust swing arm angle besides adjusting the rear ride height?
you could adjust the swingarm pivot, but not many bikes have that feature.

Chris
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post #5 of 41 (permalink) Old 05-16-2007, 10:09 AM
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Quote:
Originally Posted by Grasshopper View Post
Is there any other way to adjust swing arm angle besides adjusting the rear ride height?
I think sprocket size selection has a lot of effect on swing arm angle, correct? (3 up in the rear vs 1 down in the front type of stuff).

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post #6 of 41 (permalink) Old 05-16-2007, 10:14 AM
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Originally Posted by ronhix View Post
I think sprocket size selection has a lot of effect on swing arm angle, correct? (3 up in the rear vs 1 down in the front type of stuff).
Really?!?! How would the chain and sprockets manipulate the swing arm angle? The chain/sprockets should not affect anything with the rear suspension unless it’s too tight. The location of your rear axle can change the wheel base but not the swing arm pivot. I think.

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post #7 of 41 (permalink) Old 05-16-2007, 10:17 AM
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Nope the axle position will affect the swing arm angle. Granted the 5-10mm you move the axle will have a very minor change in the angle.

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post #8 of 41 (permalink) Old 05-16-2007, 10:19 AM Thread Starter
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Quote:
Originally Posted by ronhix View Post
I think sprocket size selection has a lot of effect on swing arm angle, correct? (3 up in the rear vs 1 down in the front type of stuff).

Ron,


Sprocket size doesn't effect swingarm ( thrust ) angle.


What it DOES do that is similar is affect the angle of the CHAIN ( top run )
compared to the angle of the SWINGARM. That effects the amount of
leverage chain pull has on the jack / squat effect.


1997-1999 GSXR's had a bad issue with this, most race teams ran
stunter size rear sprockets ( instead of dropping a tooth in front like
normal ) to overcome it.



I have always measured it without the riders.


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post #9 of 41 (permalink) Old 05-16-2007, 10:19 AM
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Originally Posted by MM Racing View Post
Nope the axle position will affect the swing arm angle. Granted the 5-10mm you move the axle will have a very minor change in the angle.

Now that I think about it, yes that does make sense. Moving the wheel back in the swing arm will decrease the swing arm angle.

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post #10 of 41 (permalink) Old 05-16-2007, 10:21 AM
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This is confusing. I need to draw this out on a peice of paper now.

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post #11 of 41 (permalink) Old 05-16-2007, 10:23 AM Thread Starter
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Maybe this will help.........

Tom



The angles here are exaggerated to illustrate my point.

I think you can see if they were close to lined up ( like reality ) where small
changes in the angle of the chain run would impact Jack/Squat by a large
amout.


And THAT's not jacksquat !



Tom
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post #12 of 41 (permalink) Old 05-16-2007, 10:25 AM Thread Starter
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Quote:
Originally Posted by Grasshopper View Post
So when you take your measurement the weight of the machine should be on the suspension?

Is there any other way to adjust swing arm angle besides adjusting the rear ride height?

And why is this in the NESBA forum? This is clearly a performance and tech thread. Ohhhh you're a CR.



We were discussing this on the NESBA board and I needed to post some pics, so did it here.





Tom

http://www.nesba.com/TrackTalk/bb/Fo...ML/003480.html

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post #13 of 41 (permalink) Old 05-16-2007, 10:32 AM
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Quote:
Originally Posted by BLARNEY View Post
We were discussing this on the NESBA board and I needed to post some pics, so did it here.





Tom

http://www.nesba.com/TrackTalk/bb/Fo...ML/003480.html
Very interesting topic actually. I have a device like that at home to measure the angle, I'm going to check it out on my bike.

Just to make sure. Is it correct to take that measurement with the entire weight of the machine on the suspension?

The reason why I ask is because I have the motor out of my race bike rite now. Would the measurement be accurate without the motor in?

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post #14 of 41 (permalink) Old 05-16-2007, 10:36 AM
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Quote:
Originally Posted by BLARNEY View Post
Ron,


Sprocket size doesn't effect swingarm ( thrust ) angle.


What it DOES do that is similar is affect the angle of the CHAIN ( top run )
compared to the angle of the SWINGARM. That effects the amount of
leverage chain pull has on the jack / squat effect.
Roger that, Tom. Yep, I remember Max explaining squat / anti-squat now that you mention it.

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post #15 of 41 (permalink) Old 05-16-2007, 10:38 AM
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This is the same for all bikes? I would think each bike would have their own numbers due to design differences?




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Quote:
Originally Posted by HDTony View Post
This is the same for all bikes? I would think each bike would have their own numbers due to design differences?
dude, your bike is the worst!! adjusting the chain really changes the ride height in the rear due to the eccentric adjuster. That's why you have a rear ride height adjuster.

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post #17 of 41 (permalink) Old 05-16-2007, 10:46 AM
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Quote:
Originally Posted by Vcook View Post
dude, your bike is the worst!! adjusting the chain really changes the ride height in the rear due to the eccentric adjuster. That's why you have a rear ride height adjuster.
I'm not an idiot, I know this. thats why I'm asking, my bike has me completely confused when it comes to ride height. I have no idea if it's even close. I can barely touch the ground so I'm guessing its a good thing




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post #18 of 41 (permalink) Old 05-16-2007, 11:02 AM Thread Starter
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Quote:
Originally Posted by Grasshopper View Post
Very interesting topic actually. I have a device like that at home to measure the angle, I'm going to check it out on my bike.

Just to make sure. Is it correct to take that measurement with the entire weight of the machine on the suspension?

The reason why I ask is because I have the motor out of my race bike rite now. Would the measurement be accurate without the motor in?


I have always measured it with the full free-sag weight on the suspension.

No motor would change the measurement....


Tom

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post #19 of 41 (permalink) Old 05-16-2007, 11:07 AM Thread Starter
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Quote:
Originally Posted by HDTony View Post
This is the same for all bikes? I would think each bike would have their own numbers due to design differences?


The THRUST angle number is pretty consistant as this angle defines
the ANGLE OF THRUST from the swingarm against the contact patch.



Think of pushing a broom..... there is an angle at which it feels right.
too steep is hard to push. too shallow and there isn't enough weight
on the broom to do the job..... this is EXACTLY the same dealy-o.


If the swingarm is flat - low swingarm angle - squat is excessive and
thrust is straight back on the hub, this doesn't push the tire DOWN
to the tarmac.....just back.


If the swingarm is steep - high swingarm angle the thrust is pushing
DOWN on the hub rather than BACK on the hub and wheelspin is the
usual result.....bike lifts, wheel spins without that bothersome forward
thrust thing.....


Tom

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post #20 of 41 (permalink) Old 05-16-2007, 11:12 AM Thread Starter
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Quote:
Originally Posted by Vcook View Post
dude, your bike is the worst!! adjusting the chain really changes the ride height in the rear due to the eccentric adjuster. That's why you have a rear ride height adjuster.


THe VFR with the single sided swingarm had a similar issue.

From the factory the eccentric was adjusted to the lower ride height side of tight.


You could spin it all the way loose, then around to tight from the bottom and
increase the rear ride height AND properly adjust chain length.


Bonus, the VFR steered like a bus and the added ride height in the rear helped.



Tony, you should adjust your chain, then set your ride height.

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post #21 of 41 (permalink) Old 05-16-2007, 01:46 PM
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THe 12.7 degrees was the result of a graduate study at Georgia Tech, as chartered by Max McAllister of Traxxion Dynamics. It was the result of an optimization simulation run on a 2000 GSXR 750 with standard gearing.

The optimal angle is a function of swingarm length and sprocket drive ratio. Generally, smaller bikes like more angle (maybe 13*) and bigger bikes like less (12*) due generally to the changing sprocket sizes - as previously mentioned. One way or another, it isn't THAT sensative, so 12-12.5 degrees is a good starting point for anything from a 600 to a 1000.

I love this topic and wish I could contribute more - but am VERY busy at work. Perhaps more later tonight.

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THe hard part is it's ALL related.

The swingarm pivot, axle position, swingarm length, optimal angle,
jack / squat effect of gearing, rake, trail.


Move one, you move them all .... for the most part.


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post #23 of 41 (permalink) Old 05-16-2007, 03:04 PM
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Good topic! I'll be paying close attention here because I run -1 in the front all the time but I run two different sprockets on the rear: stock 42 and +2 at the track. In order to be able to swap back and forth I have a 112 link chain versus the stock 110. When I run the 42 on the rear, I have to slide the axle all the way back to compensate for the extra link and to get the right chain tension. I'm curious about how that affects the optimum swingarm angle. Only thing I've noticed so far is that the bike feels more stable on the gas while exiting a turn onto a straight. I haven't noticed any difference on corner entry or mid-corner. Carry-on, I'm taking notes.

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Only thing I've noticed so far is that the bike feels more stable on the gas while exiting a turn onto a straight. I haven't noticed any difference on corner entry or mid-corner.
I notice the same thing when I run my 42 on the rear instead of my 44. I think it may just be that it allows me to deal with all that motor a little better. With 1 down (16) and 2 up (44), that jiggy thou is a hand full off the corner.

Wink likes to run the 45, but I just scare myself and turn into a big ol' puss with that aggressive gearing.

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Het Ron what tracks are what for your gearing BHF 15/44 RA 16/43 ?

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Het Ron what tracks are what for your gearing BHF 15/44 RA 16/43 ?
Try that again Heath, I don't speak Swahili.

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Good topic! I'll be paying close attention here because I run -1 in the front all the time but I run two different sprockets on the rear: stock 42 and +2 at the track. In order to be able to swap back and forth I have a 112 link chain versus the stock 110. When I run the 42 on the rear, I have to slide the axle all the way back to compensate for the extra link and to get the right chain tension. I'm curious about how that affects the optimum swingarm angle. Only thing I've noticed so far is that the bike feels more stable on the gas while exiting a turn onto a straight. I haven't noticed any difference on corner entry or mid-corner. Carry-on, I'm taking notes.
My bike turns like poop with my fat butt on it. I had the axle all the way forward to help shorten the wheelbase and help this. With -1/+2 I used to get the front end light when exiting corners in first gear or really slamming gears.

I've now gone to -1/+4 on my bike and added a link with a new chain. I have no more issues with the front wheel coming up. The extra links locate my axle to the middle of it's adjustment. The front end is much more stable under power. I have a lot more power on the straights. I had the rear shock rebuilt for more ride height. It turns better now to. Sometimes small changes can make noticeable changes.

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I thought of a way to measure this without the slope gauge.

All you need is a measuring tape and a decent calculator (or the internet)

Get the bike on a level surface and stand it up straight.
Measure from the floor to the rear axle center. Call this number 1
Measure from floor to swingarm pivot. Call this number 2.
Subtract 1 from 2. Call this b.
Measure from swingarm pivot to rear axle center. Call this c.

You can solve the triangle from here or just plug it into a web-based trig calculator like this one.

http://www.engineersedge.com/calcula...solution_1.htm

Angle B would be your swingarm angle.

Mine was around 9 degrees. Its kinda cool to play around with because you can play with the numbers (ride height or axle position) to see what you need to do to get it right.
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post #29 of 41 (permalink) Old 05-17-2007, 01:33 AM
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Mine was around 9 degrees. Its kinda cool to play around with because you can play with the numbers (ride height or axle position) to see what you need to do to get it right.
Interesting. I got 11.4 degrees. That's with -1/+0 gearing, 112 link chain, and a 190/50 Dunlop Qualifier rear.

axle height from center to the ground was 12 inches
swingarm pivot from center to the ground was 16.5 inches
distance from pivot center to axle center was 22.75 inches

I'm gonna see what the numbers do with my other sprocket and track tire set-ups.

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post #30 of 41 (permalink) Old 05-17-2007, 06:33 AM
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Quote:
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This is the same for all bikes? I would think each bike would have their own numbers due to design differences?
Correct.

Some Honda's need as much as 14+ degrees of swingarm angle.

Another way to increase swingarm angle is to lower the tubes in the triple clamps.

As for an exact number, if it were true, then it would be very simple to set up a motorcycle for the track. Riding styles, rider desires, and so on make it necessary for them to be different.

With motorcycles having different length swingarms too, they can't be the same globally.

"Super" Dave Rosno

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