MPH and RPM spike 30% higher than reality at the same time

[swbca3691]

This picture shows 109 mph when I was going about 85 based on all the other laps. The RPM shows 6868 when the Audi A4 Tiptronic transmission automatically upshifts at 6200 RPM.

are bad RPM values being used for the MPH reading, or are bad GPS values reading into the RPM reading, or is there some other explanation ? In the video the RPM and MPH ramped up in perfect sync over a 2 second interval to values that are higher than "real".

[Harry]

I assume the OBD connection has been lost shortly and LapTimer interpolated them wrongly. It is difficult to see after the fact, but maybe you can see something in the RPM and Speed Charts.

- Harry

[Harry]

You can recognize drops when the line stops to develop chaotic and gets a linear function (i.e. a line).

- Harry

[swbca3691]

OK, but why is the MPH too high at exactly the same time ?

I am using the OBDLink MX. In one other instance during the day the video shows a downshift to 3rd and 8093 RPM at 93 MPH. In this case 93 is the actual speed. The transmission won't let you downshift to 3rd at 93 mph.

[Harry]

#1 all OBD values including speed get interpolated to GPS fixes, so in case no data is coming in from OBD, LapTimer may extrapolate data for a few seconds beyond or below what is realistic.
#2 gears are calculated from speed, rpm, wheel sizes and ratios. This works only in case the clutch is closed. While it is open, there is no defined relation between rpm and speed (consider raving while standing still). This means gear display can jump shortly. Workaround shift faster or use a dual-clutch-transmission

- Harry

[swbca3691]

Sorry, my real question was concerning the cause of 8093 RPM readout which is far above cutout. Is this probably another example of a dropped connection to the OBDLink module ?

Unfortunately, in a stock Audi A4 the driver and video cannot hear the engine or exhaust with the windows down and noisy racing tires, so there is no audio information to verify if the RPM spikes.

[Harry]

Sorry, my real question was concerning the cause of 8093 RPM readout which is far above cutout. Is this probably another example of a dropped connection to the OBDLink module ?

Unfortunately, in a stock Audi A4 the driver and video cannot hear the engine or exhaust with the windows down and noisy racing tires, so there is no audio information to verify if the RPM spikes.

I assume the OBD connection has been lost shortly and LapTimer interpolated them wrongly. It is difficult to see after the fact, but maybe you can see something in the RPM and Speed Charts.

- Harry

[gplracerx]

You can elect to use GPS speed instead of OBD wheel speed in the overlay options.

[ereynold60]

see my post at http://www.gps-laptimer-forum.de/viewto ... 7&start=10... not sure if it might help or not.