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I really doubt Yamaha has been misprinting the manual for 6 - 7 years, plus, myself and several other riders have set the slack with Yamaha specs and no problems at all. A friend has ridden his for almost 20k miles since 2016 and NO PROBLEMS. Plus, measuring on centerstand WILL throw different readings, try it, I did.
Stop typing and do this.
Go adjust your chain to 15mm then sit on the bike. Now have someone check how far they can move the chain. Now have your girlfriend push down on the rear of the bike while the other someone tries to move the chain. There's your answer. Keep in mind your girlfriend came no where near how much farther the rear suspension will compress.
 
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When the engine is putting tension on the chain the stresses are limited to only being on one side of the chain. If you make your chain tension too tight that it's putting stress on things when travelling through the suspension stroke the tension is on both sides of the chain allowing significantly more stress to the assembly (easily more than double) so if the chain tension is setup wrong it can definitely be "intense" for the bearings.

A few others have already said it, Yamaha has left the same tension range in the manual for the past 6 years. If it was an issue they would have discovered that and changed it by now. If you look up the tension range for the Tracer (same bike, different purpose) the manual tells you a range of 35-45mm for the same bike. The difference is that chain tension is measured on a center stand rather than the side stand on the MT-09 that dictates 5-15mm of play. It's all relative to the centerline through the sprockets and swingarm pivot like in the picture below. The chain is most taut when the centerline passes directly through the swingarm pivot from sprocket to sprocket. As the swingarm travels further away from this position the chain will become less taut therefore creating more play in the chain. If the MT-09 is on it's side stand one can assume the centerline is very close to the center of the swingarm pivot therefore not requiring a lot of free play in the chain. When the bike is on a center stand the wheel drops down making the line from sprocket to sprocket further away from the swingarm pivot which is why the tracer manual calls for 35-45mm of play.

Does this make sense? Yamaha's response is because they are unsure if anything has been changed on the motorcycle. If the bike is stock they will tell you to refer to the manual. If your shock length has been changed or you've made any changes to the rear geometry or sprockets they will have to work with those changes to find the proper chain tension for your setup.

The tracker has a longer swingarm....
 

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The [Tracer] has a longer swingarm....
Yes. It's 60mm longer. So according to astcyr’s own diagram he posted, that means another 1.2 mm of slack compared to the MT. Hmm, not exactly a 20-40 mm jump, as the manual would imply, is it?

Here’s the link that diagram came from. If you read it carefully, you’ll see that the figure of 2% slack applies when the chain is at its tightest point, as shown in that diagram. So the MT, with around 24-25” of distance between centers, would indeed require around 12 mm of slack at that point - with the rear suspension compressed and roughly 1/2 of the rear travel taken up. Sitting on the sidestand will not accomplish that. You’ll either need a couple of friends to sit on the bike while you measure slack, or you’ll have to remove the rear shock and support the bike while you move the swingarm into that position.

Or, you could adjust it to 25-30 mm slack with no weight on the back end and call it a day.
 

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You will get different measurements because or cordial rise associated with the momentary position of the sprocket teeth.
 

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You will get different measurements because or cordial rise associated with the momentary position of the sprocket teeth.
Can you restate that, but in English? ?
 

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I got it! A Momentary Lapse Of Reason--------Epic stuff
158199
 
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Yes. It's 60mm longer. So according to astcyr’s own diagram he posted, that means another 1.2 mm of slack compared to the MT. Hmm, not exactly a 20-40 mm jump, as the manual would imply, is it?

Here’s the link that diagram came from. If you read it carefully, you’ll see that the figure of 2% slack applies when the chain is at its tightest point, as shown in that diagram. So the MT, with around 24-25” of distance between centers, would indeed require around 12 mm of slack at that point - with the rear suspension compressed and roughly 1/2 of the rear travel taken up. Sitting on the sidestand will not accomplish that. You’ll either need a couple of friends to sit on the bike while you measure slack, or you’ll have to remove the rear shock and support the bike while you move the swingarm into that position.

Or, you could adjust it to 25-30 mm slack with no weight on the back end and call it a day.
Again, the MT-09 chain tension is done on the side stand and the Tracer is done on a center stand. When the tracer is on the center stand it allows the wheel to drop fully with no pre-load due to the weight of the motorcycle being on the center stand and the wheel being off the ground. I'm glad it was pointed out the difference in length of the rear end on the tracer and I'm sure that contributes to the different value Yamaha states between the two manuals. I don't understand how people disagree with the manual provided by the manufacturer. It hasn't changed for the 6 years they've made the bike so if someone is to say the value is no good they should be able to provide concrete evidence of failure due to the value. Has ANYONE had something fail on their MT-09 from tensioning the stock chain to the manufacturers recommendations??? Having a friend sit on the bike and feeling the chain is not of any value as far as I'm concerned in comparison to the Yamaha engineers who designed and thoroughly tested the motorcycle. I mean sure the first gen had it's issues but guess what, Yamaha corrected them and amidst all those corrections they still didn't changed the chain tension value in the owners manual. Hmmmmmmmmmmm
 

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I just set mine to ~20mm on a rear stand. Seems okay.
 

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Getting back to this old thread. When measuring chain slack do you press chain up AND down to get the reading? I have been only pushing chain up and let it drop down to take the measurement. I mean you get a lot larger slack reading if you push the chain down also.
 

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I mean I used to do it that way (with other bikes) where I gently push the chain up and down to get the reading, but in those cases the recommendation was to set the slag around 35-40 mm.

If I would set it this way (push up and down) to the manual recommendation (5-15mm), the chain will feel super tight to me (and there are many discussions about it). Even 20-25 mm feels too tight. Thats why I conviced myself that yamaha means in the manual to set it up to 5-15 mm of 'droop' slack (you only push up and let it drop). But I guess I was wrong then.

(On my last bike the instruction was to measure slack by pushing the chain down and measure from this down position the distance to a certain point at the swing arm)

Edit: in short, I have been doing (with yamaha) it like in this video (push only up)
 

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Can you restate that, but in English? ?
Sorry I missed this reply. As the chain roller moves around the sprocket it’s position can affect the perfect center dimension between front and rear sprockets. This happens because there is a polygon effect. Imagine the roller is located at the corners of a polygon which represents the cutout between teeth. When the polygon point is down versus the flat side down there will be a difference in distance from the sprocket centerline to the chain exiting. I apologize for misspelling chordal the first time. See diagram for better explanation of chordal rise.

161001
 

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Sorry, I lost interest in this thread several months ago. Carry on, though...
 

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I havent been around and this is the first thing I see logging back in. If you feel safe with your chain slack, just send it boys and girls. Whats everyone using for oil and tires?
 

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Sorry I missed this reply. As the chain roller moves around the sprocket it’s position can affect the perfect center dimension between front and rear sprockets. This happens because there is a polygon effect. Imagine the roller is located at the corners of a polygon which represents the cutout between teeth. When the polygon point is down versus the flat side down there will be a difference in distance from the sprocket centerline to the chain exiting. I apologize for misspelling chordal the first time. See diagram for better explanation of chordal rise.

View attachment 161001
I don't think this has much affect with a 16 tooth sprocket
 

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Getting back to this old thread. When measuring chain slack do you press chain up AND down to get the reading? I have been only pushing chain up and let it drop down to take the measurement. I mean you get a lot larger slack reading if you push the chain down also.
I measure at the mid point between the front and rear sprocket, on the bottom run of the chain. Push down as far as possible, line up a scale with the other hand on one of the chain pins, then push the chain all the way up as far as possible while holding the scale in the same position. The total chain slack is the total down to up distance the chain moves. I run ~25mm at mid-point with the bike on the side stand - works well, and the chain never changes slack. I keep it well lubed also with Maxima Chain Wax.
 
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