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Changing sprocket sizes

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BillyJ
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Joined: 07 Jan 2013
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PostPosted: 16:22 - 28 Feb 2016    Post subject: Changing sprocket sizes Reply with quote
Hello all,

I want to go +2 on the rear sprocket of my Ducati 900ss

My question is, what do I need to do to maintain full use of the chain adjuster on the bike?

Do I need to get the standard chain and then add 2 links to compensate for the larger diameter?
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Had: '06 CBR125R + '01 GSF600 + '07 SPRINT ST 1050 + '80 CB250 RSA + '93 Ducati 900SS
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Kickstart
The Oracle



Joined: 04 Feb 2002
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PostPosted: 16:33 - 28 Feb 2016    Post subject: Reply with quote
Hi

Yes, a chain 2 links longer will compensate (within a gnats). I would assume there is enough clearance for the larger sprocket.

As an aside, why change? Easier to just use a lower gear and still have the option to change up when you want.

All the best

Katy
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-Monty-
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Joined: 20 Apr 2012
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PostPosted: 16:33 - 28 Feb 2016    Post subject: Reply with quote
I bought a longer chain for my Speed Four after putting a +2 rear sprocket on, and had to get the extra link taken out as it was too long.
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Pete.
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Joined: 22 Aug 2006
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PostPosted: 16:39 - 28 Feb 2016    Post subject: Reply with quote
A standard one will probably fit since the +2 sprocket requires the wheel be moved only 8 or 9mm forwards over the stock one, and if it does you'll get more range of adjustment.
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Rogerborg
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Joined: 26 Oct 2010
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PostPosted: 17:36 - 28 Feb 2016    Post subject: Reply with quote
Kickstart wrote:
As an aside, why change? Easier to just use a lower gear and still have the option to change up when you want.

On the standard F650GS, 1st gear is just a little too short for roundabouts, 2nd is just a bit too long. Going down a tooth on the front sprocket has made 2nd much more usable at low speed.
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Pete.
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Joined: 22 Aug 2006
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PostPosted: 17:58 - 28 Feb 2016    Post subject: Reply with quote
-Monty- wrote:
I bought a longer chain for my Speed Four after putting a +2 rear sprocket on, and had to get the extra link taken out as it was too long.


Yes many people make the same mistake.

If you increase the tooth count by two the chain only engages one extra tooth, since it only wraps half the rear sprocket. Now you need to allow for one tooth of slack in the the chain but because there is a top and a bottom chain run you can divide that slack between the two runs and therefore only need to move the wheel half a chain pitch forwards. A5xx chain has 5/8" pitch or about 16mm so you only use about 8mm adjustment to allow for two teeth on the sprocket.
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BillyJ
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Joined: 07 Jan 2013
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PostPosted: 18:27 - 29 Feb 2016    Post subject: Reply with quote
Thanks very much for the replies Thumbs Up

I got a +2 sprocket today, and ordered one extra link for my new chain just in case it needs it.
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Had: '06 CBR125R + '01 GSF600 + '07 SPRINT ST 1050 + '80 CB250 RSA + '93 Ducati 900SS
Have: '13 GSXR-1000 + '01 CB500S
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Val
World Chat Champion



Joined: 03 Nov 2012
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PostPosted: 22:46 - 02 Mar 2016    Post subject: Reply with quote
Pete. wrote:
A standard one will probably fit since the +2 sprocket requires the wheel be moved only 8 or 9mm forwards over the stock one, and if it does you'll get more range of adjustment.


^^^ This.

You can find out the exact change here:

https://www.gearingcommander.com/

+2 rear sprocket is small change, gearing commander calculates that as -8.56mm

BTW -1 front equals to +3 rear change in terms of ratio change.

I have to ask why so small change? +2 rear is only 5% change of ratio. Why not go bigger. You can actually go with front -1 and rear +2. Making the front smaller negates the rear increase. In that case the change will be -4mm. The ratio change will be 12%.

I have -1 on my bike no big chain links difference at all. You just regulate your chain using the standard way moving the rear wheel.
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Matt B
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Joined: 01 May 2012
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PostPosted: 11:26 - 03 Mar 2016    Post subject: Reply with quote
Val wrote:
I have to ask why so small change? ...Why not go bigger.


Then

Val wrote:
I have -1 on my bike


I have to ask why so small a change, why not go smaller?
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Val
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Joined: 03 Nov 2012
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PostPosted: 13:49 - 03 Mar 2016    Post subject: Reply with quote
Matt B wrote:
Val wrote:
I have to ask why so small change? ...Why not go bigger.


Then

Val wrote:
I have -1 on my bike


I have to ask why so small a change, why not go smaller?


Glad you have asked. Because different bikes have different ratio.

On my bike 1 tooth front change has bigger impact than on the Ducati.

Hence my change is bigger compared to the OP question and equals to 7% change.
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