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Unit 5302 · 04-14-2001, 12:17 AM

Upon consideration of the argument that the track is off by 3-4mph, I'd have to say that is totally false.

Both the Gtech and the track are off.

Take a 100mph finish speed. We'll say it took 14sec to do the 1380. So 14.00@100.0. At 100mph = about 147ft/sec you'd be travelling the 60ft in about .4sec. Meaning at about 100mph you'd need to accelerate 3-4mph in .4 sec. Now the cars average acceleration from 0-60 could do that. We'll give the hypothetical car a 5.5 0-60. That's 10.9mph/s. Or about 4.4mph in the .4sec timeframe. That would be accurate, but the car doesn't accelerate anywhere near the same at 100 as it would during the 0-60. Since it took a full 14.00 to hit 100mph, that means it took the hypothetical car took 8.5sec to go from 60-100 or an average of about 5mph/s. That would be about 2mph over a given 60ft area at the end of the course. Now here is the fun part. We can acknowledge that the acceleration will be for all reality the same over that 60ft period, which means the average speed difference would then be half of the 2mph (actually, a little under 2) and that gives us a 1mph differential between what the Gtech should read, and the trap speed at the track.

Math used behind this.
0-60 5.5sec
1/4 mile 14.00@100mph
0-60 average acceleration 10.91mph/s (60/5.5)
60-100 average acceleration 4.71mph/s (40/8.5) 40 comes from 100-60, 8.5 comes from 14.00-5.5.
3-4mph inconsistancy in Gtech vs track estimated.
60ft the last section of track where speed is averaged.
ET for last 60ft .41 (60ft/147ft/s <100mph=147ft/s>
ET for last 30ft .205 <since the acceleration can be rounded to even over the last 60ft, the speed given by the traps should be at 30ft before the end, cause that is exactly 1/2 way throught the 60ft>

Now total acceleration over the last 30ft should be slightly under 4.71 x .205 = .96mph. That tell's me that the Gtech should be less than .96mph off what the track reading is.

Since .96< 3 to 4, that means either the track is more inaccurate than we think, or the Gtech is also off slightly higher than real life.

04-14-2001, 12:17 AM	#9
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	Upon consideration of the argument that the track is off by 3-4mph, I'd have to say that is totally false. Both the Gtech and the track are off. Take a 100mph finish speed. We'll say it took 14sec to do the 1380. So 14.00@100.0. At 100mph = about 147ft/sec you'd be travelling the 60ft in about .4sec. Meaning at about 100mph you'd need to accelerate 3-4mph in .4 sec. Now the cars average acceleration from 0-60 could do that. We'll give the hypothetical car a 5.5 0-60. That's 10.9mph/s. Or about 4.4mph in the .4sec timeframe. That would be accurate, but the car doesn't accelerate anywhere near the same at 100 as it would during the 0-60. Since it took a full 14.00 to hit 100mph, that means it took the hypothetical car took 8.5sec to go from 60-100 or an average of about 5mph/s. That would be about 2mph over a given 60ft area at the end of the course. Now here is the fun part. We can acknowledge that the acceleration will be for all reality the same over that 60ft period, which means the average speed difference would then be half of the 2mph (actually, a little under 2) and that gives us a 1mph differential between what the Gtech should read, and the trap speed at the track. Math used behind this. 0-60 5.5sec 1/4 mile 14.00@100mph 0-60 average acceleration 10.91mph/s (60/5.5) 60-100 average acceleration 4.71mph/s (40/8.5) 40 comes from 100-60, 8.5 comes from 14.00-5.5. 3-4mph inconsistancy in Gtech vs track estimated. 60ft the last section of track where speed is averaged. ET for last 60ft .41 (60ft/147ft/s <100mph=147ft/s> ET for last 30ft .205 <since the acceleration can be rounded to even over the last 60ft, the speed given by the traps should be at 30ft before the end, cause that is exactly 1/2 way throught the 60ft> Now total acceleration over the last 30ft should be slightly under 4.71 x .205 = .96mph. That tell's me that the Gtech should be less than .96mph off what the track reading is. Since .96< 3 to 4, that means either the track is more inaccurate than we think, or the Gtech is also off slightly higher than real life.