I have thought about the issue, and am at a loss. My car could not be shifting into 3rd at more than about 62 or 63 mph assuming (1) that R&T's speed per gear values are based on (1) a 275 / 35-18 tire size (as is implied) and (2) that R&T's 6.5k rpm max speeds in 2nd/3rd of 62 and 95 are correct--given this tire size.

And, I completely missed what you said above: "You are right about the diff in ratio due to tire size.The standard goodyear RSA 225/50 are 25.9" dia. Guessing you have PS2 that are 245's(19")dia. is 26.7." But, no, my tires are 275 X 30-19 and, thus, have a diameter of about 25.7" diameter. Thus, I acutally have a very small effective rear-end factor better than yours rather than what we have been saying.
[/quote]

I have been thinking and doing some number crunching about the speed anomaly we discussed earlier.There is another possible explanation(maybe the correct one).After analizing some of my 0-80 & 1/8 times & speeds,I noticed a pattern.Although I don't have a 1/8 speed that is lower than my 0-80 speed,I do have one that is the same(0-80-8.65,1/8 time 8.93 & 80mph).This also doesn't sound possible since I am still accelerating at about 5.5 mp sec @ 80mph.My 1/8 time of 8.93 is .28 seconds after I have reached 80mph.Multiplying .28 X 5.5=1.54,my speed at the 1/8 should be 81.5 mph.If I use this logic on all other runs I find that all 1/8 speeds are lower than expected.

Now for the explanation.The speed at the 1/4 at a drag strip is not measured right at the finish line,but is measured in a 66' long trap ending at the finish line.Thus giving you an average speed over the last 66'.Your speed at the start of the trap could be 102 and at the end of the trap 104,giving you a speed of 103 for the 1/4.Applying this to our 0-80 & 1/8 speeds(a 66' trap)you could be going 78.5 at the begining of the trap,80.5 at the 1/8 mark for an average of 79.5mph.Somewhere in that trap you reached 80mph before the 1/8 distance.Since the 0-80 reading is an instantaneous,not an average it is higher than the average reading given for the 1/8 speed.

At this point this is only a theory,but I intend to call Passport to find out how the GT2 measures speed at a given distance.It could be the answer to our 1/8 speeds.Hopefully I did't make this more complicated than it should be.

Wow you have got a lot of tire.I don't know why I assumed your tire size,I should have just asked.It does mean our effective axel ratio's are almost the same.

 

Way to go again grogan. I'll bet that's the answer since Passport would, in principle, want to make GT2 times comparable to dragstrip times. I talked to Passport, and they had no explanation, but I did not have your thoughts in hand. What you have said brings up the issue of how the auto mags deterimine all their times to speed and to distance. It would be nice if they told us exactly how they calculate things. I am going to do some more calcs with my data. Thanks much for the thoughts.

Oh, and for some reason, until yesterday, I thought that you had 225 X 45-17's. Oh, well, at least we finally eliminated one noncomparability.

 

Way to go again grogan. I'll bet that's the answer since Passport would, in principle, want to make GT2 times comparable to dragstrip times. I talked to Passport, and they had no explanation, but I did not have your thoughts in hand. What you have said brings up the issue of how the auto mags deterimine all their times to speed and to distance. It would be nice if they told us exactly how they calculate things. I am going to do some more cals, along the lines you did, with my data. Thanks much for the thoughts.

Oh, and for some reason, until yesterday, I thought that you had 225 X 45-17's. Oh, well, at least we finally eliminated one noncomparability.
[/quote]


When I call Passport I will try to speak to the developement engineer for the GT2.The customer service people may not be well versed in the inner calculations.If I am in correct in my assuption we are back to square one with the 1/8 mile speeds.

 

If it means anything, in the example data that the manual shows, there's one display that has the 1000ft and 1/8 mile times and for speed, the caption says "trap speed", so I think Grogan is right that the GT2 is also measuring trap speed at 1/8 mile as well as 1/4 mile and not the actual speed at that exact distance.

 

When I call Passport I will try to speak to the developement engineer for the GT2.The customer service people may not be well versed in the inner calculations.If I am in correct in my assuption we are back to square one with the 1/8 mile speeds.
[/quote]
Where did you get the 5.5 value? And, why do you say we are back to square one on the 1/8 speeds? We still have the average for the trap.

Good eye. Thanks.

 

When I call Passport I will try to speak to the developement engineer for the GT2.The customer service people may not be well versed in the inner calculations.If I am in correct in my assuption we are back to square one with the 1/8 mile speeds.
[/quote]

 

Edit: The data given below have been corrected for an initial omission. See discussion below.

Hi Guys:

I didn't have time to say what's new today, but early this morning I did another run trying to gain more data on the "anomoly" and just for general purposes. I got all the way to 100 mph. Previously, I reported briefly on another recent run on which I got to 90 mph--which also is stretching a point given the location of my "strip." Given the data from these two runs and my priior three bests runs, I was able to do a fairly complete comparison with the test results of the big three US auto mags. Below, I present the auto mag data first, my data second, and a graph third--which shows the "patterrns" of interest very well. I used an assumed value for the mags for zero to ten. The averages and other key values are in bold. The averages also are shown in the graph as its data. Note that the 13.5 shown in the graph data is 13.457 rounded.

Big Three US Auto Mag Test Results:

Headings--Datum/MT 8/04/R&T 6/05/MT 10/05/Ave/Change (Except 1/4 Mile Speed)

1/4 Mile Speed 102.10 104.00 102.80 102.97
1/4 Mile Time 13.70 13.70 13.80 13.73 0.43 See use of .43 below.
0-10013.60 12.70 13.60 13.30 2.35
0-90 10.90 11.00 10.95 2.18
0-80 8.90 8.40 9.00 8.77 1.62
0-70 7.10 7.20 7.15 1.78
0-60 5.40 5.20 5.50 5.37 1.32
0-50 4.00 4.10 4.05 1.15
0-40 2.80 2.90 3.00 2.90 1.15
0-30 1.60 1.90 1.75 0.65
0-20 1.10 1.10 0.78
0-10 0.32 Assumed
0-0 0.00

Znod Test Results--Best Five Runs

Headings--Datum/Znod Test 1/Znod Test 2/Znod test 3/Znod Test 4/Znod Test 5/Ave/Change (Except for 1/8 Mile Results)

1/8 Mile Speed 80.40 80.50 80.50 80.00 80.40 80.36
1/8 Mile Time 8.78 8.71 8.71 8.71 8.73 8.73
1/4 Mile Time (Est) 13.457 0.5565 *Calculated below
0-100 12.90 12.90 2.42 (shift at about 94 MPH)
0-90 10.48 10.55 10.52 1.86
0-80 8.72 8.65 8.65 8.60 8.67 8.66 1.85
0-70 6.82 6.75 6.82 6.90 6.77 6.81 1.67
0-60 5.14 5.07 5.22 5.22 5.07 5.14 1.25 (shift at about 61 MPH)
0-50 3.89 3.82 3.92 3.95 3.88 3.89 1.08
0-40 2.82 2.76 2.83 2.87 2.78 2.81 1.11 (shift at about 34 MPH)
0-30 1.72 1.65 1.70 1.72 1.70 1.70 0.75
0-20 0.97 0.89 1.00 0.95 0.95 0.95 0.66
0-10 0.32 0.25 0.30 ,27 0.28 0.29 0.29
0-0 0.00

*The 13.457 agrees almost exactly with grogan's formula's result. I would have to add .567, rather than
.5565, to 12.90 to get his result of 13.467 exactly.

The calculation of the .5565 values is:

Ave of Differences 70 to 80 = 1.85 and 80 to 90 = 1.86
Ave. of Above Aves. 1.86
10 MPH / 1.86 = 5.39083558 = Rate of Acceleration Per Second
1 sec. [(103 - 100) / 5.390836] = 0.5565 Assumes terminal velocity is 103 = the approx. mag ave = 102.97

Note that the diff. for my single 90 to 100 run can't be used above because a shift occurs at about 94 MPH.

 

When I call Passport I will try to speak to the developement engineer for the GT2.The customer service people may not be well versed in the inner calculations.If I am in correct in my assuption we are back to square one with the 1/8 mile speeds.
[/quote]
Where did you get the 5.5 value? And, why do you say we are back to square one on the 1/8 speeds? We still have the average for the trap.

Good eye. Thanks.
[/quote]

I got the 5.5 figure by taking the time diff between several 70-80 runs & several 80-90 runs and averaged them.The average time to advance 10mph(70-80,80-90)was 1.82 seconds.Divide 10mph/1.82 sec=5.49.Thus the rate of acceleration is 5.49mph per second.

I had a "hiccup in my spelling(in correct).It should have read."If I am not correct about the way the GT2 timer calculates 1/8 speeds we are back to square one".

 

Hi Guys:

I didn't have time to say what's new today, but early this morning I did another run trying to gain more data on the "anomoly" and just for general purposes. I got all the way to 100 mph. Previously, I reported briefly on another recent run on which I got to 90 mph--which also is stretching a point given the location of my "strip." Given the data from these two runs and my priior three bests runs, I was able to do a fairly complete comparison with the test results of the big three US auto mags. Below, I present the auto mag data first, my data second, and a graph third--which shows the "patterrns" of interest very well. I used an assumed value for the mags for zero to ten. The averages and other key values are in bold. The averages also are shown in the graph as its data. Note that the 13 shown in the graph data is 13.03 rounded. (I fouled the label for the horizontal axis of the graph up; I will fix it later. The values should be 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110.)

Big Three US Auto Mag Test Results:

Headings--Datum/MT 8/04/R&T 6/05/MT 10/05/Ave/Change (Except 1/4 Mile Speed)

1/4 Mile Speed 102.10 104.00 102.80 102.97
1/4 Mile Time 13.70 13.70 13.80 13.73 0.13 See use of .13 below.
0-100 13.60 13.60 13.60 2.65
0-90 10.90 11.00 10.95 2.18
0-80 8.90 8.40 9.00 8.77 1.62
0-70 7.10 7.20 7.15 1.78
0-60 5.40 5.20 5.50 5.37 1.32
0-50 4.00 4.10 4.05 1.15
0-40 2.80 2.90 3.00 2.90 1.15
0-30 1.60 1.90 1.75 0.65
0-20 1.10 1.10 0.78
0-10 0.32 Assumed
0-0 0.00

Znod Test Results--Best Five Runs

Headings--Datum/Znod Test 1/Znod Test 2/Znod test 3/Znod Test 4/Znod Test 5/Ave/Change (Except for 1/8 Mile Results)

1/8 Mile Speed 80.40 80.50 80.50 80.00 80.40 80.36
1/8 Mile Time 8.78 8.71 8.71 8.87 8.73 8.77
1/4 Mile Time (Est) 13.03 0.13 Assumed using mag results from above
0-100 12.90 12.90 2.42
0-90 10.48 10.55 10.52 1.86
0-80 8.72 8.65 8.65 8.60 8.67 8.66 1.85
0-70 6.82 6.75 6.82 6.90 6.77 6.81 1.67
0-60 5.14 5.07 5.22 5.22 5.07 5.14 1.25
0-50 3.89 3.82 3.92 3.95 3.88 3.89 1.08
0-40 2.82 2.76 2.83 2.87 2.78 2.81 1.11
0-30 1.72 1.65 1.70 1.72 1.70 1.70 0.75
0-20 0.97 0.89 1.00 0.95 0.95 0.95 0.66
0-10 0.32 0.25 0.30 ,27 0.28 0.29 0.29
0-0 0.00

*This result seems too quick. But, it is my best estimate given the data. I would have to add .567 to 12.90 to be consistent with grogan's formula's result of 13.467. So, I believe that the truth is somewhere between 13.03 and 13.467.
[/quote]

The data looked good until you got to the 0-100 mph times.Where did you get the 13.60 seconds for 0-100 mph?The only reference I have is the road test in the June 2005 R & T magazine.their 0-100 time is 12.7 seconds.This looks logical because their trap speed for the 1/4 is 104mph(it took 1 more sec to advance 4 mph).

OOps! I am sorry I see that you used 2 MT tests for your 0-100 mph.After analizing the MT 0-100mph times I am very suspicious.Note that the first MT test 0-100 was reached in 13.6 seconds and the 1/4 time was 13.7 sec at 102.10 mph.This is not possible to advance 2.1 mph in .1 sec.This is an acceleration rate of 21mph per sec.The second MT test also was 0-100 in 13.60 sec,but the 1/4 time is 13.80 @ 102.8 mph.Also not possible to advance 2.8 mph in .2 sec(acceleration rate of 14 mph per sec.)I don't know if we can trust MT times based on this info.

I have the R & T magazine(6-05) and their 0-100 time of 12.70 sec and 1/4 time of 13.70 @104 makes perfect sense(acceleration rate of 4 mph per sec).My earlier figure of 5.5 mph per sec was between 70 and 90 therefore the rate is higher than it would be at over 100mph.

To sum it up I don't believe the MT 0-100 times,now I wonder about all of their times.The other times do seem to be plausable.

 

Way to go EuroCarFan you already taught us "experts" to read the instructions thoroughly.I spent a lot of time coming to my conclusions when all I had to do is read the instruction manual.