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08-09-2017, 10:07 PM | #29 |
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8k RPM redline = higher top speed!
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08-10-2017, 12:32 AM | #30 |
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I'd have to test, but I'm willing to bet the speedo doesn't stay stuck at a speed when the dash loses power. This isn't like an old mechanical watch.
I'm betting he wasn't going nearly that fast, though the car is capable of doing it, you need a lot of road to get there. |
08-10-2017, 10:15 AM | #31 | |
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08-10-2017, 12:53 PM | #32 | |
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Speedos are unreliable.
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08-12-2017, 03:43 AM | #33 |
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08-12-2017, 06:05 AM | #34 | |
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Also GPS isn't ideal either, certainly not normal domestic grade GPS devices. They typically have a low refresh rate (1Hz or less) and aggressive data smoothing functions to accommodate for poor precision timers and accuracy. Most do not account for the vertical component, not just in vertical speed but in altitude which effects the accuracy of the position. A domestic GPS might calculate a grouping of positions with a 10-100m error and take the average (usually fairly accurate) but with each subsequent readings of a stationary vehicle the position can jump instantly 3-5m which would cause a speed reading of potentially many hundreds of mph. To prevent this the speed is sampled over a much longer averaging window. Thus the speed provided by the GPS is an "indicative" approximate speed. Best conditions: * Perfectly straight road. * Perfectly level road * At sea level * When a full set of required satellites are being received * At a constant speed maintained for at least 10-20 seconds. Aero-grade or military grade GPSs have much higher refresh rates, such as 10Hz or 100Hz and include the correct calculations and offsets for vertical position and speed. They also have better receivers and better high precision timers, better smoothing, better error correction and better averaging functions. Cheap radar guns can be inaccurate due to the high precision timers being affected by temperature. They need to be re-calibrated routinely for accurate readings. Readings can also be out as the most accurate reading is taken from directly in front, directly aligned with the vehicles path... ie. it will hit you unless you are on a gantry. Other things that can affect the reading are the beam bouncing off a wheel spoke etc. The easiest way to detect an actual speed which doesn't requrie high precision timing and calculating with the speed of limit, like GPS and Radar is a simple speed trap with two beams set an exact distance apart (like 1 meter). Then you simply measure the time between the two beam breaks. The reciprocal of this will give you the exact speed in m/s (assuming a 1 meter spacing).
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08-12-2017, 06:22 AM | #35 |
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Some references:
https://stackoverflow.com/questions/...mooth-gps-data http://www.gpsvisualizer.com/tutoria...k_filters.html https://gis.stackexchange.com/questi...ccuracy-of-gps http://gpsinformation.net/main/gpsspeed.htm Note these mention the doppler shift method of speed calculation which is inaccurate if done to 2D like most domestic and auto-motive GPSs. Remember you have to include the Azimuth of the satellites in the 3D calculation, not just you terrain elevation/slope. Position based calculations are most likely also used in cheaper devices which are even less accurate. The highest top speed of the GT86 according to an app on my phone was 758mph. I have also taken track logs that showed me, while half way to work, teleport to the Azure islands and back again registering a speed close to that of C.
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08-12-2017, 06:36 AM | #36 |
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Putting things in perspective likely accuracy:
Speedo: +/- 10% more likely + (or greater if you have custom or worn tyres or have diff modifications) Cheap Domestic GPS: +/- 3-5mph Decent Domestic GPS: +/- 3mph Aero-grade GPS: +/- 0.5mph For radar it highly depends on the accuracy of the timer or the doppler accuracy. For the dual beam speed trap is depends on the accuracy of the timer. But a timer with an accuracy or +/-0.005 and a precision of 0.01 (1/100th of second) would give you an accuracy of 99%. Better timers are easily available and most motorsport venues are accurate to the 1/1000th second (milisecond) and that gives an accuracy of 99.9%.
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08-12-2017, 02:17 PM | #37 |
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01-17-2018, 01:55 PM | #38 |
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ive been 135 Stock. slowed down it got sketchy on the road where i live
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01-17-2018, 04:47 PM | #39 |
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No, that's just the math involved to go that fast. What isn't shown is the sheer amount of space it takes to get going that fast. How many miles do you think did it takes for a stock FRS to reach 150 (let alone 158)?
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