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Discussion Starter · #1 ·
So I special ordered some rear sprockets from Vortex so I can find the optimal gearing setup at my track Willow Springs. After installing a 45 rear sprocket I wanted to make sure that my wheel was as far back as possible and add a chain link if needed. As a base point I wanted to see how far back ALL THE WAY BACK was so took out the master link and removed the chain and then rotated the rear hub up/ccw as far as it would go, as far back as the rear wheel could go (as if you were tightening the chain). In doing the rotation I noticed the swingarm lowering. This concerned me because this f*cks with a bike's geometry and on a roadracing bike this is a big deal, we spend a lot of time setting the height of the rear at the shock based on a lot of variables. So I did a test:

I ran masking tape across the chain guard, rotated the hub all the way up ccw as far back as the wheel could go, and drew 2 black lines:




then I rotated the hub down/cw moving the wheel forward as far as it would go. Notice the black line on the sprocket not only moved forward as expected but also dropped, or actually raising the rear a HUGE amount:



For roadracing we want to keep the wheelbase as long as possible for stability and to prevent wheelying, and we usually have a long chain & short chain to use based on the gearing we want to use, that way we keep the wheelbase & chassis setup consistent, but having the rear going up & down as you move the wheel base is not a good thing.

In any case this is where I wound up after tightening the chain, it was pretty close to being all the way back and I could not have added another link in the chain. You can see the black lines are still lined up, however the swingarm is raised quite a bit above the hub/sprocket height, not sure exactly why. Anyone have a good grasp on exactly what's happening here?

 

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Eccentric rotating adjuster ,Terry unfortunately only way you going to get what you want is if you change to a double sided swingarm
 

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So I special ordered some rear sprockets from Vortex so I can find the optimal gearing setup at my track Willow Springs. After installing a 45 rear sprocket I wanted to make sure that my wheel was as far back as possible and add a chain link if needed. As a base point I wanted to see how far back ALL THE WAY BACK was so took out the master link and removed the chain and then rotated the rear hub up/ccw as far as it would go, as far back as the rear wheel could go (as if you were tightening the chain). In doing the rotation I noticed the swingarm lowering. This concerned me because this f*cks with a bike's geometry and on a roadracing bike this is a big deal, we spend a lot of time setting the height of the rear at the shock based on a lot of variables. So I did a test:

I ran masking tape across the chain guard, rotated the hub all the way up ccw as far back as the wheel could go, and drew 2 black lines:




then I rotated the hub down/cw moving the wheel forward as far as it would go. Notice the black line on the sprocket not only moved forward as expected but also dropped, or actually raising the rear a HUGE amount:



For roadracing we want to keep the wheelbase as long as possible for stability and to prevent wheelying, and we usually have a long chain & short chain to use based on the gearing we want to use, that way we keep the wheelbase & chassis setup consistent, but having the rear going up & down as you move the wheel base is not a good thing.

In any case this is where I wound up after tightening the chain, it was pretty close to being all the way back and I could not have added another link in the chain. You can see the black lines are still lined up, however the swingarm is raised quite a bit above the hub/sprocket height, not sure exactly why. Anyone have a good grasp on exactly what's happening here?
Of course it is going to do that. take a 6" circle and put a hole off center about an inch from the edge. Then use that hole as the pivot point and turn the circle. You will see the 12 and 6 oclock points move up and down and the 9 and 3 oclock points move forward and back (your chain adjust) as you rotate the circle.
So the way to compensate is to use lower links, like the adjustable ones that Brock has.
 

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Discussion Starter · #5 ·
thanks for the feedback.
So Ducati has been using the single-side swingarm for a long time now, do their bikes have this same eccentric rotaing adjustment that we have?
 

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thanks for the feedback.
So Ducati has been using the single-side swingarm for a long time now, do their bikes have this same eccentric rotaing adjustment that we have?
Pretty sure all the single sided swingarm setup do the same thing. It would be really hard to keep the whole affair solid using a slider.
 

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It all depend on the centerline of the chain from sprocket center to sprocket center, and its relationship to the swing arm pivot. If it is dead center it will loosen, else it will tighten.
 

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Ted, one way out of this would be to set the chain adjustment and then adjust ride height with a set of Brock's window links.
 

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From memory, this was the same issue that racers had on the 916 - 998 generation Ducati's. But I think they have an adjustable link in the suspension somewhere.

As Bob says, Brocks links are the answer here...
 

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So I special ordered some rear sprockets from Vortex so I can find the optimal gearing setup at my track Willow Springs. After installing a 45 rear sprocket I wanted to make sure that my wheel was as far back as possible and add a chain link if needed. As a base point I wanted to see how far back ALL THE WAY BACK was so took out the master link and removed the chain and then rotated the rear hub up/ccw as far as it would go, as far back as the rear wheel could go (as if you were tightening the chain). In doing the rotation I noticed the swingarm lowering. This concerned me because this f*cks with a bike's geometry and on a roadracing bike this is a big deal, we spend a lot of time setting the height of the rear at the shock based on a lot of variables. So I did a test:

I ran masking tape across the chain guard, rotated the hub all the way up ccw as far back as the wheel could go, and drew 2 black
lines:





then I rotated the hub down/cw moving the wheel forward as far as it would go. Notice the black line on the sprocket not only moved forward as expected but also dropped, or actually raising the rear a HUGE amount:



For roadracing we want to keep the wheelbase as long as possible for stability and to prevent wheelying, and we usually have a long chain & short chain to use based on the gearing we want to use, that way we keep the wheelbase & chassis setup consistent, but having the rear going up & down as you move the wheel base is not a good thing.

In any case this is where I wound up after tightening the chain, it was pretty close to being all the way back and I could not have added another link in the chain. You can see the black lines are still lined up, however the swingarm is raised quite a bit above the hub/sprocket height, not sure exactly why. Anyone have a good grasp on exactly what's happening here?

Racer172

You are at the highest raise/lift point of the eccentric! If you rotated the eccentric 180 degrees CCW, you would be at the lowest/lowered point of the eccentric. If you rotate the eccentric 90 degrees from either the highest or lowest point of the eccentric, this will represent the furthest point the sprocket is from the engine. You only have 90 degrees of rotation for your min/max chain adjustment.
 

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Discussion Starter · #15 ·
Racer172
You are at the highest raise/lift point of the eccentric! If you rotated the eccentric 180 degrees CCW, you would be at the lowest/lowered point of the eccentric. If you rotate the eccentric 90 degrees from either the highest or lowest point of the eccentric, this will represent the furthest point the sprocket is from the engine. You only have 90 degrees of rotation for your min/max chain adjustment.
Yeah I follow & agree with what you are saying, and my pics 1 & 2 show that exactly.
Before the 3rd pic was taken I went fully ccw/all the way back. My broken chain and new master link were just short of connecting, so I rotated cw just enough to connect the chain links and then tightened back up ccw.
So why it finished at such a high point of the eccentric I'm at a loss.
any thoughts?
 

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Yeah I follow & agree with what you are saying, and my pics 1 & 2 show that exactly.
Before the 3rd pic was taken I went fully ccw/all the way back. My broken chain and new master link were just short of connecting, so I rotated cw just enough to connect the chain links and then tightened back up ccw.
So why it finished at such a high point of the eccentric I'm at a loss.
any thoughts?
Probably the angle of the swing arm vs. the centerline of the chain drive.
 

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Yeah I follow & agree with what you are saying, and my pics 1 & 2 show that exactly.
Before the 3rd pic was taken I went fully ccw/all the way back. My broken chain and new master link were just short of connecting, so I rotated cw just enough to connect the chain links and then tightened back up ccw.
So why it finished at such a high point of the eccentric I'm at a loss.
any thoughts?
It's because you installed a larger sprocket, 45 verses 44 tooth. You have possibly two options!

Option 1 - Rotate the eccentric back CCW 180 degrees. Adjust the SAG so the swing arm compresses more, see if you can install the chain. If you can't lower the bike by adjusting the SAG, have someone heavy 200 plug pounds, sit on the bike, then try installing the chain.

Option 2 - Reduce the engine drive sprocket by 1 tooth.
 

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There may be a third option! Can you rotate the hub CCW past 180 degrees, or is there something like a pin preventing going CCW more than 180 degrees. If there is a pin, remove it so you can rotate CCW 190/200 degrees so you can install your chain.
 

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Discussion Starter · #19 ·
Thank you for your ideas.
I spoke with my suspension setup guy and he told me to measure the ride-height difference (in mm) between the 44 to the 45 sprocket, then he'll know how much he needs to adjust the Ohlins shock ride height.
It's been an interesting discussion, thanks for the input.
 
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