znod

I agree with your SmkmUp thoughts. Still, the adjustments are the only way to attempt comparisons across cars. On the 500' idea, what do you think the average drag strip altitude is? I searched on "drag strip altitude" last night, and I kept turning up altitudes in the neighborhood of 1,000'. I wonder what the average US altitude is. I'll be happy to adjust your data. Be sure and give me your actual altitude too. I need it to get the original density altitude. I think I have a method for determining whether the correction factors apply to all times to distance. I'll get back to you. Good luck with your passes. May they all be sub 5.

Bokke

Gents, an interesting post from the M5Board.....

http://www.m5board.com/vbulletin/showthread.php?t=68993

znod

It is interesting. I would like to know his altitude and weather conditions.

znod

Hi g-man:

Note what I said above, and here goes:

Attempt to Calculate Time to Speed Adjusted to 500'--1/8 Speed:
.................................................. .................................................. ..........Avg
Regression....................83.500...83.276...83 .275...83.106...82.987...83.229
Two Calculators.............83.463...83.522...83.390.. .83.598...83.244...83.443
One Calculator-NHRA.....83.431...83.489...83.357...83.547...83.22 8...83.410

Note that my regression approach explains about 58% of the variability in my raw 1/8 speeds. Thus, I am confident that the regression approach works within highly tolerable error limits. But, note that both the two-calculators and calculator-NHRA approaches yield values that are not too far from those produced by the regression approach. In this regard, I had trouble getting essentially the same values under the former two approaches. I think that error somehow occur when moving to the NHRA table. On average, the two-calculators approach is different from the regression approach by .256462%, while the one-calculator/NHRA approach is different by .217%. I think that reducing 1/8 speeds obtained using the one-calculator-NHRA approach by about .22% is likely to yield good estimates.

Note that my regression approach explains, incredibly, about 92% of the variability in my raw 0 to 60 times. So, 0 to 60 estimates made using this approach are virtually guaranteed to be highly accurate. If you want, I will do an analysis similar to what I did on 1/8 speeds to see what % might be applicable in adjusting 0 to 60 values obtained using the one-calculator-NHRA approach.

Attempt to Calculate Time to Distance Adjusted to 500'--1/8 Time:
.................................................. .................................................. Avg
Regression....................8.756...8.700...8.75 0...8.732...8.763...8.740
Two Calculators.............8.768...8.760...8.804...8. 740...8.801...8.775
One Calculator-NHRA.....8.772...8.762...8.801...8.745...8.803...8 .777
grogan545's formula......8.846...8.750...8.821...8.781...8.816 ...8.803

Similar to the case of my 0 to 60 times, my regresson approach incredibly explains about 96% of the variability in my raw 1/8 times. So, as above, 1/8 time estimates made using this approach are virtually guaranteed to be highly accurate. In this case, I was able to calculate essentially the same values under both of the other approaches. In this case, each method yields results on average that are about .4% higher than those of the regression approach. Here, I think that reducing 1/8 times obtained using either approach by about .4% is likely to yield good estimates. I had hoped that grogan545's formula would have done better, but the above data probably reflect conditions that were not present in the data used in developing the formula.

Happy reading and thinking. Please let me know what you think, of course.

wolverine

I may have already weighed in on this, but you are absolutely right. You MUST do runs in both directions, unless you are on a dragstrip. You just cannont 'eyeball' a level road. I've been doing timed runs on the same 'absolutely flat' section of road for 12 years, and one direction is consistently a few tenths quicker every time.

znod

Generally true, but if you do passes in both directions and find no significant differences or if you only use the slower direction, then you only have to test in one direction unless there is wind. And, all drag strips are not level--or even flat.

znod

I had never noticed the following with respest to the formula. If the 1/4 mile speed is very high in relation to 1/8 mile speed (estimated) then, the 1/8 mile time (predicted) will suffer. I notice this "feature" of the formula when trying to estimate 1/8 times for the mags. So, for example, not using the actual mag times:

1/4 Mile Time (given)..............13.70.....13.70........13.70
1/4 Mile Speed (given)..........102.00....104.00.....103.00

1/8 Mile Speed (estimated).....81.00......81.00.......81.00
1/8 Mile Time (predicted)...........8.89.......8.95.........8.92

So, no wonder the forumula does not work too well above.

grogan545

Still digesting your last several posts Zman.I will get back to you latter this evening or tomrrow.Weather here is not cooperating(rain)for testing.Hopefully tomorrow will be better.

znod

Cool. Good luck tomorrow. We had much rain yesterday, but it is clear as a bell today. I'll be out in morning. I went to REI and bought a wrist weather meter/predictor. It has a barometer and a thermometer, but no dew- point ometer, of course. I just wanted to have something to check my altitude where ever to use on trips, etc. I calibrated it at the airport. It revealed that a better estimate of my altitude is 1,600' rather than 1,550' given by my car. I corrected all of my results for this difference, but, of course, the correction for only 50' made little difference. The thermometer turned out to be useless because it adjusts to the outside temperature too slowly. The barometer appears to be very accurate. Of course, I have the airport temperature, pressure, and dew point readings for serious use. I don't really trust my car's external temperature reading. What do you make of the accuracy of your's.

grogan545

Hi Zman.Very interesting information.I am not totaly disatisfied with "grogans formula".I had hoped that it was within .05 sec,which it is vs the calculators,but not with your regression calculations.The major problem in estimating the 1/4 et in the formula is having to use an estimated speed for the 1/4.I think I have been under estimating my 1/4 speeds.I still only have 1 actual 1/4 speed of 105.5,but as I get more full 1/4 runs I hope to fine tune the formula for future use.It is still much safer to do 1/8 runs for me due to available roads.I am not sure the formula works as well in estimating 1/8 times and speeds from actual 1/4 info.I am thinking of making another trip to the drag strip in the spring,but I will make sure the weather is suitable before I go this time.I would like to get about 4 runs and also getting info from the GT2.This should give us a good basis on the accuracy of the GT2.