Hi, I said they were inaccurate and pretty usesless because they are compared to something like a V-box especially with a car that will be accelerating quickly. I don't need maths to prove that, common sense and a bit of knowledge is more than enough.
Plus I have seen several reviews where these apps have been measured against a V-box and they pretty much always exagerate the performance of the car, some more than others.
The evidence is in the results you posted. 0-20mph times are clearly wrong, have a look at this review of an RS6 and R8 using V-BOX figures.
http://www.evo.co.uk/audi/r8/14173/audi-r8-v-audi-rs6-audi-r8-v-audi-rs6
On a perfectly dry track the 0-30 time is around 1.6-1.7 seconds , your results are saying you are getting to 20mph in under 0.3s
. Even the 0.8s time to 20mph is too quick for the car and the conditions. That's 1.14g acceleration .
I forgot to link the calculator I used earlier.
http://www.smartconversion.com/unit_calculation/Acceleration_calculator.aspx
Running 0-30 in 1.6s is 0.85G acceleration a more sensible value, even assuming you could attain this value in the wet to get to 20mph would take around 1.1 s . As I said the big issue with the apps is detecting the actual point when you start moving and starting the timer correctly at that point.
My guess and it is purely a guess was based on the fact that a more reasonable time for the 0-20 was around 1.1 - 1.2 seconds , adding the difference between that and the 0-20 time to the final time gives a ball park figure.
So the one run that appeared to be the slowest at 4.1s was probably in reality the quickest. with a 0.8s time to 20 that was around 0.4s too quick. Add 0.4 onto 4.1 gives 4.5s.
The run with a 0.3s 0-20 is around 0.8s too fast so add that onto 3.9s = 4.7s