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Offline 2Bears

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Re: Larger sprocket.
« Reply #30 on: December 10, 2019, 03:35:25 PM »
I appreciate the comment bazzer.
 
It wasn’t my intent to advocate for anything.

As Smithy pointed out, nobody makes an 18 tooth sprocket for the XR.  As jskene observed, the Triumph sprocket I mentioned has a much smaller effective spine engagement length than the stock XR sprocket.  Not knowing why the XR spline engagement is as deep as it is, I would be cautious about trying something like the Triumph sprocket.  You don’t want to damage the gearbox output shaft or have some other kind of failure there.

I found a spline analysis in my Machinery’s Handbook and I can come up with some numbers that potentially show something like the Triumph sprocket working; but there are some unknowns.

The new gear box has an 8% higher 6th gear.  A little bit taller 1st gear doesn’t really affect me in a significant way as far as I can tell.  If someone wants to run high rpms through the twisties they still can with changed gearing.

According to a calculator on the internet a 42 tooth rear sprocket yields a 7.1% change in gearing and a 41 tooth yields a 9.8% change.

Has anyone used a 41 tooth rear sprocket long term?
« Last Edit: December 11, 2019, 07:50:44 AM by 2Bears »

Online smithy

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Re: Larger sprocket.
« Reply #31 on: December 10, 2019, 07:44:14 PM »
*Originally Posted by 2Bears [+]
I appreciate the comment bazzer.
 
It wasn’t my intent to advocate for anything, I was sharing an observation.  Where I live we call that conversation :745:.

As Smithy pointed out, nobody makes an 18 tooth sprocket for the XR.  As jskene observed, the Triumph sprocket I mentioned has a much smaller effective spine engagement length than the stock XR sprocket.  Not knowing why the XR spline engagement is as deep as it is, I would be cautious about trying something like the Triumph sprocket.  You don’t want to damage the gearbox output shaft or have some other kind of failure there.

I found a spline analysis in my Machinery’s Handbook and I can come up with some numbers that potentially show something like the Triumph sprocket working; but there are some unknowns.

The new gear box has an 8% higher 6th gear.  A little bit taller 1st gear doesn’t really affect me in a significant way as far as I can tell.  If someone wants to run high rpms through the twisties they still can with changed gearing.

According to a calculator on the internet a 42 tooth rear sprocket yields a 7.1% change in gearing and a 41 tooth yields a 9.8% change.

Has anyone used a 41 tooth rear sprocket long term?

The reason the front sprocket spline engagement is so wide on the S series engine compared to the Triumph item you mentioned is probably because the base engine for the XR is common with the R (R & XR are essentially identical) and the RR, which has some different internal goodies and an extra ~35hp....I wouldn't want that much hp going through a half sized spline engagement.

41 tooth rear is doable but the top side of the rubber swingarm protection may suffer as the chain may be rubbing on it all the time due to the reduced diameter of the rear sprocket...with the 42 there's no noticeable extra wear other than normal....I've had an aluminium 42t rear sprocket on mine for nearly 20k km...no issues thus far and it appears to be wearing no worse than a normal steel sprocket.

Smithy.
« Last Edit: December 10, 2019, 07:46:50 PM by smithy »
When I die, I want to go peacefully in my sleep like my Grandfather....not screaming like the passengers in his car..!

Offline jokingjimmy

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Re: Larger sprocket.
« Reply #32 on: December 26, 2019, 01:02:32 PM »
Cuban Rider and a couple others with went with 42t and seem to like the results. If I get tired of the higher rev range I'm going 42t and tune it for net zero change.