Harry's GPS Suite Forum

I used LapTimer in the following configuration:

v15.0.5
iPhone 4s
internal GPS
iPhone was attached to my belt using a clip
Rental kart league, 0.44 mile track, top speeds around 45 mph

I had the following problems using it during my karting league race:

-Laptimer could not distinguish between the back straight and a nearby section of the track, splitting laps into two separate times.

-On one lap, the top speed was less than the average speed.

-Laptimes from Laptimer did not match transponder times well (> 0.5 second errors)

Are there any LapTimer setting changes that I can make to improve performance? I really can't justify spending another $100 for an external GPS, and would like to optimize my current setup. We only have a couple of races left for the season, but I think it would be very valuable to monitor my lap time during qualifying to know if I am improving.

Setting up triggers for Karting is tricky. Laps are typically very tight and one needs to find a way to find triggers on the one hand, and not get them on counter straights on the other. The basic rules for kart tracks are as follows:

1. You need really good GPS accuracy. No idea if your 'clip to belt' solution yielded that, but please check the GPS signal displayed (see viewtopic.php?f=8&t=2).
2. Switch the detection corridor to 'Narrow' in LapTimer Settings - especially if LT catches the Stop / Go trigger when racing the counter straight.
3. In case you can't fix it like this, set trigger 'tactically': instead of setting them to the middle of the start / finish line, move them to the outside of the track so they have a bigger distance to the counter straight. Switch back to 'Normal' detection corridor to not miss it when passing start / finish.

On average / max speed: average speed is calculated from lap time and overall distance. Speeds on track are delivered by the sensor. So there are at least two sources for your situation: either the the overall distance calculation delivered some too big values (e.g. if you have a bad fix in the plot - far away from the track), or the sensor missed max speed (peak detection is not a GPS strength).

The last one is another indication your GPS accuracy has been low. Please check #1 above. You may export one of the 'badly' measured laps to KML, open it in Google Earth, deselect everything except 'Accuracy', 'Track', 'POIs', and post a snapshot here.

- Harry