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Old 09-17-2021, 05:31 PM   #1
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What's Your Speed

I'm running across I-64 this afternoon and I looked at the speedo and the needle was covering the 65 MPH line. GPS on Google Maps says I doing 66. I got the 5 Star tune SCT programmer mounted on the dash and plugged in for kicks. (Yeah, I'm kinda geeky that way) Anyway, the data on the SCT programmers bouncing between 63.5 and 64. So GPS is 66, Speedo is 65, and SCT under 64ish.

Which one is the most accurate?
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Old 09-17-2021, 05:40 PM   #2
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A man with one watch knows what time it is. A man with two is never sure.
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Old 09-17-2021, 05:41 PM   #3
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A man with one watch knows what time it is. A man with two is never sure.
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Old 09-17-2021, 05:45 PM   #4
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One could argue you are a distracted driver. Maybe.
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Old 09-17-2021, 05:47 PM   #5
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Average them and call it good.
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Old 09-17-2021, 05:55 PM   #6
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You have WAY too much time on your hands…
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Old 09-17-2021, 06:03 PM   #7
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You forgot to add or subtract for 26,000 plus miles per hour the planet is going... did you every study significant difference ? So I believe there is no significant difference..
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Old 09-17-2021, 06:07 PM   #8
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......

Which one is the most accurate?
What is the accuracy of your judgement for estimating your stopping distance?

I was a slide rule engineer who started out as an operator reading an analog gauge.

All three of your speed reading are accurate enough to get the job done. If the needle is over 65 and the ground is flying by, ignore the computer generated number that says you are stopped.

I also ignore the computer voice telling me to make a u-turn on a bridge.
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Old 09-17-2021, 06:28 PM   #9
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The way I check a speedo is to drive at 60mph indicated on the speedo. Preferably on level ground to make it easy to maintain a steady speed. Wait for a mile marker, when you pass it, start a stop watch. Keep the speed at 60 indicated, til the next mile marker(one mile later) stop the watch. It should read 60 seconds if the speedo is accurate. If it’s more than 60 seconds the speedo reads faster than you are going. Most read fast by 2 or 3 mph. Well it’s really a percentage.

Maybe have your co-driver do the stop watch, and watch GPS, and 5Star.
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Old 09-17-2021, 06:28 PM   #10
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You forgot to add or subtract for 26,000 plus miles per hour the planet is going... did you every study significant difference ? So I believe there is no significant difference..
Did you ever study Statistical Difference?
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Old 09-17-2021, 06:33 PM   #11
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The way I check a speedo is to drive at 60mph indicated on the speedo. Preferably on level ground to make it easy to maintain a steady speed. Wait for a mile marker, when you pass it, start a stop watch. Keep the speed at 60 indicated, til the next mile marker(one mile later) stop the watch. It should read 60 seconds if the speedo is accurate. If it’s more than 60 seconds the speedo reads faster than you are going. Most read fast by 2 or 3 mph. Well it’s really a percentage.

Maybe have your co-driver do the stop watch, and watch GPS, and 5Star.
Might be good for checking odometer error.
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Old 09-17-2021, 07:06 PM   #12
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I'm running across I-64 this afternoon and I looked at the speedo and the needle was covering the 65 MPH line. GPS on Google Maps says I doing 66. I got the 5 Star tune SCT programmer mounted on the dash and plugged in for kicks. (Yeah, I'm kinda geeky that way) Anyway, the data on the SCT programmers bouncing between 63.5 and 64. So GPS is 66, Speedo is 65, and SCT under 64ish.

Which one is the most accurate?
GPS is the least accurate of them because it's not a constant sample, but an average of the sample points.
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Old 09-17-2021, 07:56 PM   #13
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Folks.. be nice. I have seen this difference myself. Yes, it might not be “significant”, but it is still noticeable. I did the stopwatch thing with mile markers, and turned out the gps appeared more accurate. Whether I go with the gps or the dash reading, in practice, depends on how much of a hurry I am in (or am not)...
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Old 09-17-2021, 07:59 PM   #14
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A man with one watch knows what time it is. A man with two is never sure.
So true
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