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Discussion Starter · #1 ·
I changed my gearing from 16/47 to 15/47.
Now the speedometer is VERY wrong and shows more than 15% more speed than real I think.
On top of that, i am afraid that the odometer does the same mistake, writing way more miles than it should.
Apart from a speedohealer which is an expencive solution, what else could I do?
I tried correcting it with the TuneECU but it seems like this function is not active on my bike.
Are there any specific VIN numbers that have an ECU which can not have its speedo and odo corrected via a TuneECU? Why can't I correct it?
My bike is a 2008 Daytona 675.

thanks
 

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i went with a speed-o-healer from heal-tech to correct mine. yes if you changed it it will affect mph, and milage. i dont think your anywhere close to 15% off. i went 15,49 and according to website calculations, and my own with that setup im 14.8% off, so you should be less than that. your looking to be 11.1% off with your change.
 

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TuneECU will do it for sure, mine did no problem. You can correct up to 25% difference plus or minus, so try entering -15%, but don't forget you need to download the whole tune to your bike again after changing the speedo.
 

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Discussion Starter · #4 ·
Thanks guys. I ll try the TuneECU again tomorrow. Maybe i did something wrong. Although i think i did everything as suposed to..
Are you sure all VINs have the same ECU that has the same functions?
 

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Thanks guys. I ll try the TuneECU again tomorrow. Maybe i did something wrong. Although i think i did everything as suposed to..
Are you sure all VINs have the same ECU that has the same functions?
No, the ECU's and tunes are slightly different between years but that doesn't matter as long as you save the tune from your bike, modify the speedometer on it, then download it back to the bike without having changed anything else. I've used the same program on my 09 and 06-07's.
 

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Discussion Starter · #6 ·
No, the ECU's and tunes are slightly different between years but that doesn't matter as long as you save the tune from your bike, modify the speedometer on it, then download it back to the bike without having changed anything else. I've used the same program on my 09 and 06-07's.
OK, i get it! I ll do it tomorrow! Thanks!
 

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Discussion Starter · #8 ·
thank you very much for your advice! Problem solved! Did what you told me and everything worked fine with TuneECU!

-11% Was the error.
 

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How do you guys calculate the % difference to make the correction or is that all in the program?
 

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You need to use an accurate speed measuring device and compare it the actual speedometer reading. So either time yourself through a measured mile at a constant speed or use a GPS.
You can also calculate it based on your gear ratio, I found that to be accurate. If you have stock gearing, there's a pretty consistent -6% error (reads too high). If you change gearing, you just need to calculate the % ratio you've changed it. Here's an example with going from 16/47 (stock) to 16/49:
Stock ratio = 47/16 = 2.9375
New ratio = 49/16 = 3.0625
% change = 100 x (2.9375-3.0625)/3.0625 = -4.1% change
Total error = -6% stock error - 4.1% change = -10.1% error
So if you change your speedo by 10.1% it should be spot-on with that gearing.
 

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That doesn't take into account different tires have a different overall circumference. I've found that the differences in tires alone can change speedo error as much as 2% not to mention what happens as they wear. I wouldn't guess with this it's too easy to get a GPS most phones have one and if you don't have a smart phone that can access this it's likely you know someone that has a regular GPS you can borrow for a few minutes. Also speedo error is different a little bit from bike to bike. So taking the differences in speedo and tires into account it would be really hard to get this accurate without doing testing on a bike per bike basis.
 

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That doesn't take into account different tires have a different overall circumference. I've found that the differences in tires alone can change speedo error as much as 2% not to mention what happens as they wear. I wouldn't guess with this it's too easy to get a GPS most phones have one and if you don't have a smart phone that can access this it's likely you know someone that has a regular GPS you can borrow for a few minutes. Also speedo error is different a little bit from bike to bike. So taking the differences in speedo and tires into account it would be really hard to get this accurate without doing testing on a bike per bike basis.
Wow I hadn't even thought about that. We tested it with an iPhone on OEM Pirellis and Michelin Power Ones and it was spot-on both times, guess I just lucked out.
 

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I know my speedo is off. When I drive by a 30 MPH radar street sign they all ways say that I am going 27MPH. I have driven by a lot of different signs with the same result. My question is the error constant or would it be more of a linear or exponential error? I am just not sure I want to tweak it in the ECU since it will throw off the odometer.
 

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What if I had someone in their car drive in front of me at a constant speed? Let's say they were going 35 and I followed behind but was showing 40mph. Is that an accurate way of determining the difference? If so then I show myself off by 8.75%. Is that correct or no? Thanks.

What's the formula to calculate if you go with a constant speed for a measured mile and it takes how much time?
 

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My question is the error constant or would it be more of a linear or exponential error? I am just not sure I want to tweak it in the ECU since it will throw off the odometer.
The error is arithmetic, ie a constant 8% or whatever it is. Your odometer is already off, and reading too high by a small percentage. If you tweak it, it'll be more accurate.
 
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