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Discussion Starter #1
As I was sick and tired of having the same conversation with mechanics, especially dealership mechanics, regarding the chain slack for the whole MT/XSR/Tracer 900 range I decided to email Yamaha directly to see if I could get a definitive answer to the issue once and for all. This crock of shit was their response:

Good Morning Will,

Thank you for your enquiry and apologies for the delay in our response.

The owner’s manual is a guide and 5-15mm is the advised tension, however our dealers can adjust with further free play subject to the bike set up.

Kind Regards

Katie Nash


There, I'm glad that's cleared it up for everyone.

Now, could anyone please tell me what 'bike set up' would require a looser chain because I'm confused as to WTF she's talking about.
 

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I'm sure that any adjustments to ride height, preload, shock length, or lowering links could easily affect the required chain tension as compared to the stock setup. I know this from experience on my own bike.

Neil
 

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Just give it 1.25-1.5" and go ride the darn thing!

Sent from my Moto Z (2) using Tapatalk
 

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Discussion Starter #5
1.0" (25 mm) is pretty much the ideal slack based on dozens of threads on this subject.
Agreed. That certainly seems the sweet spot on mine. Each to their own though.
 
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20 to 25mm no matter what anyone else says....they set the chain drive of the space shuttle to this and if its good enough for them then its good enough for me....(I read this on the internet so it must be true)
 

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The amount of chain slack required for any bike is based on the geometry of the swingarm. It's calculated by fully extending the back suspension of bike and measuring the distance between the center of the drive shaft to center of the rear wheel axle. Then compress the rear suspension to mid way and measure again. Then compress it fully and measure again. The FZ09 has about 5" of rear suspension travel and you will find the movement of the swing arm is very linear and the distance between the driveshaft (center of front sprocket) to center of rear axle only grows by 1/4" or about 5mm from full extended to fully compressed. That is the minimum amount of chain slack needed to not affect the proper movement of the rear suspension. So they recommend 5-15mm of chain slack and no more is needed. You can add more to this but it can add vibrations to the bike. On a dirtbike that has 11" of travel you will find this distance a lot greater, about 1.5" or more so 2" chain slack is recommended.

For bike setup you can add or remove chain links to shorten or lengthen the wheel base. This changes how the bike handles in tight corners or on high speed bumps but can affect the minimum chain slack required. Someone who just commutes might not benefit from this but a track or canyon rider would. This just one example of bike tuning that can be done for an individual or specific riding area.
 

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1.0" (25 mm) is pretty much the ideal slack based on dozens of threads on this subject.
This is what makes most sense given that every other bike I know of has about this listed for tension.

The amount of chain slack required for any bike is based on the geometry of the swingarm. It's calculated by fully extending the back suspension of bike and measuring the distance between the center of the drive shaft to center of the rear wheel axle. Then compress the rear suspension to mid way and measure again. Then compress it fully and measure again. The FZ09 has about 5" of rear suspension travel and you will find the movement of the swing arm is very linear and the distance between the driveshaft (center of front sprocket) to center of rear axle only grows by 1/4" or about 5mm from full extended to fully compressed. That is the minimum amount of chain slack needed to not affect the proper movement of the rear suspension. So they recommend 5-15mm of chain slack and no more is needed. You can add more to this but it can add vibrations to the bike. On a dirtbike that has 11" of travel you will find this distance a lot greater, about 1.5" or more so 2" chain slack is recommended.

For bike setup you can add or remove chain links to shorten or lengthen the wheel base. This changes how the bike handles in tight corners or on high speed bumps but can affect the minimum chain slack required. Someone who just commutes might not benefit from this but a track or canyon rider would. This just one example of bike tuning that can be done for an individual or specific riding area.
But then I read things like this that if the numbers are correct, I can't mathematically disagree with. But even if swingarm extension with suspension travel is that small, let's say at the tightest, most extended point the slack is 15mm – isn't that still a little intense for the bearings, etc.?
 

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Discussion Starter #9
This is what makes most sense given that every other bike I know of has about this listed for tension.



But then I read things like this that if the numbers are correct, I can't mathematically disagree with. But even if swingarm extension with suspension travel is that small, let's say at the tightest, most extended point the slack is 15mm – isn't that still a little intense for the bearings, etc.?
jrheat This is my point. I don't really care what people believe and what tension they subscribe to, what annoys me is the reluctance of Yamaha to write back to me and definitively give an answer and not that fluff I received. I just don't buy that 'bike set up' nonsense. If that's the case then why when my bike is more or less stock do the local Yamaha dealership adjust it to 25mm after a service then? And why do they look at me like I'm a retard when I say that the manual states X? I'll tell you why because they ain't been told shit.

If the manual is right then the dealers should stick by it and know about it. If the dealers are correct and it should be looser then Yamaha should come out and say it. That's why I went to the organ grinder in the hope of some clarity. It shouldn't be that difficult for them to get their act together and this is whats really gripping my shit becuase everytime I get work done it's the same old tiresome argument about it.
 

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But even if swingarm extension with suspension travel is that small, let's say at the tightest, most extended point the slack is 15mm – isn't that still a little intense for the bearings, etc.?
No, it wouldn't really be "intense" for the bearings. Think about how much force there is in the chain when 100 HP is going through it, and how much load that puts on the bearings. Even if there is a small amount of chain slack when the swingarm position is at the point that gives the least chain slack, then the chain isn't getting tight enough at that point to make any real difference to the bearing load.
 

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The biggest effect is chain and sprocket wear. The tighter the adjustment, the more it feels like it’s binding if you spin the wheel while it’s up in the air. Easy to do with the bike on a stand. Most bikes I’ve owned specified approximately 1” which has always been very smooth. Previous posts on this site, including some in depth testing using measurements throughout the entire swingarm range of motion, indicates 3/4” to be the sweet spot on the FZ. No matter how the suspension is set or how it may be loaded, assuming you will use the full suspension travel should dictate your chain adjustment.
 

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The amount of chain slack required for any bike is based on the geometry of the swingarm. It's calculated by fully extending the back suspension of bike and measuring the distance between the center of the drive shaft to center of the rear wheel axle. Then compress the rear suspension to mid way and measure again. Then compress it fully and measure again. The FZ09 has about 5" of rear suspension travel and you will find the movement of the swing arm is very linear and the distance between the driveshaft (center of front sprocket) to center of rear axle only grows by 1/4" or about 5mm from full extended to fully compressed. That is the minimum amount of chain slack needed to not affect the proper movement of the rear suspension. So they recommend 5-15mm of chain slack and no more is needed. You can add more to this but it can add vibrations to the bike. On a dirtbike that has 11" of travel you will find this distance a lot greater, about 1.5" or more so 2" chain slack is recommended.

For bike setup you can add or remove chain links to shorten or lengthen the wheel base. This changes how the bike handles in tight corners or on high speed bumps but can affect the minimum chain slack required. Someone who just commutes might not benefit from this but a track or canyon rider would. This just one example of bike tuning that can be done for an individual or specific riding area.
Thanks for the answer based on mechanical specifications. I always doubted that Yamaha has been printing user manuals with the incorrect chain slack for 6 years in a row. I'll stick to the 5-15 mm as stated in the manual.
 

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No, it wouldn't really be "intense" for the bearings. Think about how much force there is in the chain when 100 HP is going through it, and how much load that puts on the bearings. Even if there is a small amount of chain slack when the swingarm position is at the point that gives the least chain slack, then the chain isn't getting tight enough at that point to make any real difference to the bearing load.
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.

 

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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.

On point!
 

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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.
This is correct.

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.
This is NOT correct.

When the bike is on its side stand, the shock will be very nearly - if not completely - topped out. The swingarm will be virtually at its lowest point relative to travel, and it isn't much different than it is when it's on a centerstand. You can check this for yourself. With the bike on the side stand, grab the far side of the seat and pull the bike over so that you take all the weight off the rear wheel. See if the swingarm extends downward any more than it was when it was resting on the side stand. If anything, it may go another 3 or 4 mm.

Think about it another way: When you're setting suspension sag, you want your sag number to be around 30mm or so - with you sitting on the bike. So if the rear travel is, say, 5 inches, you would have to compress the rear end 2.5 inches - or over 60mm - to get the swingarm inline with the drive sprocket, which would put the chain in its tightest point.

In other words, side stand or centerstand, it makes no difference when it comes to measuring your chain slack. And in no way does it explain the discrepancy between the FJ09 specs and the MT09 specs. My belief is that it's simply a misprint in the manual that they haven't bothered to correct.
 

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This is correct.



This is NOT correct.

When the bike is on its side stand, the shock will be very nearly - if not completely - topped out. The swingarm will be virtually at its lowest point relative to travel, and it isn't much different than it is when it's on a centerstand. You can check this for yourself. With the bike on the side stand, grab the far side of the seat and pull the bike over so that you take all the weight off the rear wheel. See if the swingarm extends downward any more than it was when it was resting on the side stand. If anything, it may go another 3 or 4 mm.

Think about it another way: When you're setting suspension sag, you want your sag number to be around 30mm or so - with you sitting on the bike. So if the rear travel is, say, 5 inches, you would have to compress the rear end 2.5 inches - or over 60mm - to get the swingarm inline with the drive sprocket, which would put the chain in its tightest point.

In other words, side stand or centerstand, it makes no difference when it comes to measuring your chain slack. And in no way does it explain the discrepancy between the FJ09 specs and the MT09 specs. My belief is that it's simply a misprint in the manual that they haven't bothered to correct.
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.
 
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