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[Smitty2u]

Can the Screaming Eagle Pro Race Tuner modify the ECM to reflect a change in gearing from a 32T to a 31T transmission sprocket?

[Unbalanced]

no it cant

[InfernoCVO]

 Had my SERT upgraded to a TTS Master tune to correct spedo after a 30th swap if this is what you were concerned about.

[Smitty2u]

Had my SERT upgraded to a TTS Master tune to correct spedo after a 30th swap if this is what you were concerned about.

That is what I'm concerned with.  How much was the upgrade and what was involved?

[InfernoCVO]

upgrade was $100, had to contact TTS and hook up to computer to see if its eledigable ( witch my local H-D dealer did for me) then they send you a form to send in with the tuner takes 7-10 days to get back.  I believe it has to be an older one that they made when they still made them for harley. You can go to their web site and get the info, Hope this helps

[glens]

Can the Screaming Eagle Pro Race Tuner ... ?

If that's what you have, it's not something that can become a TTS.

[Smitty2u]

If that's what you have, it's not something that can become a TTS.

I'm in the midst of a build and the SEPRT is the tuner we chose.  Since the motor was torn down and the only cost to add a different geared sprocket was the cost of the sprocket, we decided a couple days ago to go ahead and do it.  I have not talked to the builder yet to ask how he planned to address the speedometer. 
Is there another way the dealer can adjust that variable?

[glens]

I don't know.

Hopefully you won't have to resort to something like the Dakota Digital unit.

[Smitty2u]

How much of a change will there be going from 32T to 31T?

[glens]

31÷32=0.9688

Multiply whatever your speedo is reading by that factor to determine your true speed.  Assuming your speedo is correct at present.

60 indicated will be 58, etc.

[kraut]

it's not really a problem as it should be a constant deviation and if you compare your speedo readings with the speed indicated on your Zumo you will find a difference there again. In Germany speedos have to read slightly high by law, this does not apply to GPS units so I trust Garmin more anyway. .96 would not even be enough to compensate my speedo's high reading.

[Smitty2u]

31÷32=0.9688

Multiply whatever your speedo is reading by that factor to determine your true speed.  Assuming your speedo is correct at present.

60 indicated will be 58, etc.

Are you sure that's the formula?  I can see that .9688 is the percentage of change of the new gear, but does that percentage of change directly relate to the percentage of change in the spedo?

[grc]

Are you sure that's the formula?  I can see that .9688 is the percentage of change of the new gear, but does that percentage of change directly relate to the percentage of change in the spedo?

Yup.  So you can figure on roughly a three percent speedometer error, which when compared to the kind of error the stock speedo's seem to have on average might mean that your speedo will now be more accurate than it was to begin with.  I wouldn't worry too much about correcting anything until you actually test the bike with the new ratio.  Assuming your dyno guy has an accurately calibrated setup, he should be able to tell you exactly how much it's off.

If you had gone to the 30 tooth, then you would be more likely to want to correct the speedo.


Jerry

[Unbalanced]

As someone said Dakota Digital as well as S&S has a speedo calibration device if its needed.

[glens]

31÷32=0.9688

Multiply whatever your speedo is reading by that factor to determine your true speed.  Assuming your speedo is correct at present.

60 indicated will be 58, etc.

Are you sure that's the formula?  I can see that .9688 is the percentage of change of the new gear, but does that percentage of change directly relate to the percentage of change in the spedo?

Yeah, all the other values (primary and trans ratios, rear wheel sprocket, distance traveled per tire rev) remain the same and factor out so the relationship you're looking for is simply the old and new number of cogs on the one item you're changing.

Your speedo is likely somewhere in the neighborhood of a few percent high already, so this change in most cases is going to increase the discrepancy.  Say you were previously 97% of indicated.  That times another 97% is going to become 94%, or roughly 56 at 60 indicated, and it's all down hill from a new rear tire.  Your odometer will also be high by the inverse of whatever percent error you end up with, as well your fuel mileage if you don't factor it when you make that calculation.  (42 "indicated" mpg will be 39.5 @ 94% and it would really take you another few tanks of fuel to get to the 10k miles shown as accumulating on the odometer, etc.)

I'd probably opt for the Dakota Digital unit were I in your shoes.  It's certainly cheaper at this point than getting a TTS kit :-)