Austicus, If you are able to a GPS I just wanted to share an e-mail exchange I had with 12oclock Labs.
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Hello,
I am in the process of installing the speedoDRD and I have a question about the correction percentage. The bike is a 09 with -1/+2 gearing and I used a GPS to find the actual speed. However as my speed increased so did the difference. My question is what correction percentage should I use from the results listed below? Or should I calculate an average and start with that?
GPS Speed/ Speedo Reading/ Differance/ Correction Percentage 30mph/ 36mph/ 6mph/ -16.7 50mph/ 62mph/ 12mph/ -19.4 70mph/ 86mph/ 16mph/ -18.6 90mph 107mph 18mph -15.9
Thanks, Dave
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Hi Dave,
Since your Speedometer and most GPS devices will only show whole numbers, you may be traveling at 50.9mph, but your speedometer says 50mph,
When using whole number calulations it is always possible you could be up to 0.99 off, so if taking multiple measurements it's best to just average them together. With the numbers you provided, here what I came up with....
GPS / Speedo / Correction Percentage
your results -----------------------possible actual speeds
30mph/ 36mph/ -16.7 ---> (30mph / 36.52mph = -17.9)
50mph/ 62mph/ -19.4 ---> (50.9mph / 62mph = -17.9)
70mph/ 86mph/ -18.6 ---> (70.6mph / 86mph = -17.9)
90mph/ 107mph/ -15.9 --> (90mph / 107.9mph = -16.6)
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your average: -17.65 ...................... possible actual average: -17.57
Our averages are within 0.08% of each other.
The high speed (90mph) being off around 1% more is most likely due to centrifugal force tire expansion, which could cause a nominal -1% difference.
Based on your test results I would recommend a correction percentage of -17.6%
Thanks,
-Brooks
(937) 719-1518
www.12oclocklabs.com
