I2 pro overlay questions

[Bullitt]

To the Motec community

Recently I started using I2 pro for data acquisition to overlay and compare two similar touring cars. Both cars are using a common beacon, running the same track at the same time etc. One of my functions is to summarize the data and sit down with the drivers after every session. It should be noted that I have only been using Motec for two events, so I am still a novice. Typically when overlaying the data I review the graphs for rpm, corner speed and braking. A few questions have come up:
1)For the over-lay is it better to compare the two cars using “Time” or “Distance” for the x axis? Basically I am looking for braking point, entry, mid and exit speeds between the two cars. In other words, who is on the brakes the latest and who carries the higher speed through.
2)For the section time tab, is the reliable data? The reason I ask is that in some case I have seen the data conflicting (I.e. One drivers corner speed is faster on the graph and yet the section time is slower then the other driver). Do any of the other times on the form use the section time tab?

Your help would be appreciated.

Respectfully
Michael L. Thompson

[PaulGM]

Mr. Thompson,

Viewing the compared laps on a distance scale would seem to be the most appropriate, as you would see the dynamic markers (braking point, entry, etc.) overlaid exactly as they occur over the distance of the lap. Under time mode, it may appear that two events are occurring simultaneously which actually occur at different locations on the track, simply because they occur at the same amount of time after a beacon hit (which has some error associated with it). Keep in mind, however, that the distance measurement itself can have error; if it is a result of wheel speed, then slip can alter distance recorded, and if it is GPS then positional accuracy goes down with the number of acquired signals.

As for sections, you may see differences between your estimation of section timing by speed and i2's section timing because of how section timing is recorded. If GPS is not used and section beacons are not used, then section timing is the measurement of time between two points of distance accumulated in a lap, and is therefore subject to the error of the distance measurement. If GPS or section beacons are used, they are subject to their own levels of error but can be more accurate.

If you want to match a dynamic event (such as a minimum corner speed) between laps and you don't believe your distance is accurate on one or both of the laps, you can match up an event using the "Show Data Offset Axis" function ('O' key) and simply sliding the laps left and right.