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I did a quick search and found very little on this topic.
I am toying with replacing the (stage 1) Celtic tuning remap on my B8 S4 with a Revo Stage 1+ and pulley upgrade, but thought to try out a couple of speedometer apps on my phone to checkout the car's current performance. Ulysse Speedometer, as with others, comes with 0-60, 0-100, 1/4 mile stats. Just enable, drive and look at the result afterwards.

On a private road I got the following results (just the one I'm afraid).
Is the app being highly optimistic? I would have expected around the 5.0 second mark for 0-60, and slower for 0-100 and 1/4mile too. The speed on the app virtually matches the dashboard speed so I think the GPS is accurate, and I would have thought if there was a lag in GPS during acceleration then the figures would show slower than reality rather then quicker.
Does anyone have any experience with the accuracy of these apps, maybe compared to dedicated hardware?

0-60 4.3 seconds
0-100 9.83 seconds
1/4mile 12.53 seconds
Stephan

Most phones GPS doesn't "refresh" fast enough for accurate timing as they're updated at 1hz (once per second) so inbetween each 1 second it has to "guess" what happens with speed/distance etc.

The VBox Performance box updates at 10hz (10 times a second) and that is around the minimum you'd need for "accurate enough" figures. 20hz is much better but usually more expensive so isn't that common - *edit* the new Vbox Sport does 20hz but only links to an iphone app (no android) or to a PC/Laptop via SD card and shown via VBoxes own software.



and you can get the same accuracy on your phone by buying a 10hz Bluetooth GPS "dongle" for about £80 on eBay (vs the £300 Vbox). I have this one which is extremely easy to use - http://www.qstarz.com/Products/GPS%20Pr ... 18XT-F.htm



which pairs to your phone, then you tell the app to use this accurate GPS data (dependent on whether the App can do it, most can) and then off you go.