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-   -   06 999S with 180/55 and 38t sprocket? (https://www.ducati.org/forums/999-749/114865-06-999s-180-55-38t-sprocket.html)

ruley74 November 25th, 2019 11:39 PM

06 999S with 180/55 and 38t sprocket?
Hi there,

Curious if anyone has been able to run a 38t rear sprocket on the stock chain (96 link) with a 180/55 rear tyre fitted.

I tried on Friday but struggled to get the chain to do so I put the 36t back on... was I just have a 10 thumbs day of is it a no go?



Shazaam! November 28th, 2019 06:55 AM

Here's the deal:

Every additional tooth on the rear sprocket shortens your distance between sprocket centers (and wheelbase) about 4 mm. So going from a 36 to a 38 tooth rear sprocket shortens it 8 mm. A shorter wheelbase will reduce your high speed handling stability.

If you're running out of room in the chain adjuster, you can add two links to the chain.

A chain has links that alternate inner-outer-inner-outer, so in order to lengthen any chain you have to add two links at a time. The links in a 5XX chain have a pin-to-pin distance of 16 mm. So when you add two links at a time, the distance between sprocket centers increases 16 mm.

16 mm minus 8 mm gives you a longer wheelbase of 8 mm.

If you are willing to live with a shorter wheelbase but your tire can't move forward enough and preventing you from getting the chain over the sprockets you could deflate the tire to get more space and try again.

ruley74 December 3rd, 2019 03:28 AM

Thanks, I'm good with the geometry and math, just curious in the 180 tyre given it's a taller (be it small) profile. Anyhow, bought a new chain and going with a 40t rear, With 2 links that ends up reducing my sprocket centre's just over 1mm. Perfect.

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