The top left XY Plot compares the front roll (red) with the rear roll (blue). As you can see, there isn't a big difference between the two. The top right XY Plot compares the car's pitch to lateral Gs. Since the relatively flat line shows that the pitch of the car is not that sensitive to lateral Gs. I suspect that this chart can be very different for a closed wheel car such as a sedan. The bottom left and bottom right XY Plots compare the front and rear ride heights to lateral Gs. The graphs look very similar but they actually end up looking that way in exact opposite ways and I have shown this by adding some arrows and descriptions of what is happening. As you can see, as the driver gets on the brakes the front goes down and the rear goes up and then as the driver transitions from braking to accelerating while entering the corner the data points are generated on the bottom side of the front (red) XY plot and on the top side of the rear (blue) XY plot. Then as the driver begins to accelerate the Lateral Gs are at their max and as the driver unwinds the steering wheel the data points are generated on the top side of the front XY plot and on the bottom of the rear XY plot. What these plots really show though is that the front ride height is a little more sensitive to lateral Gs (the ride height changes more) than the rear. It also shows that max Gs happen at the lowest ride height so the lower that you can run the car the better. Btw, I don't think the ride height measurements shown above are accurate. I made a lot of changes to the car on this day and I didn't stay on top of my constants as I made changes. In this case that doesn't matter because you are really just looking at the shape of the graphs.
If the driver is doing everything that he can do to keep the car as fast as possible but isn't happy with how the car is handling then he needs to figure out what to change on the car based on what the car is doing at what point in the corner (i.e., entry, middle, exit). The data can confirm or contradict what the driver thinks is happening. If it is determined that a change to the car needs to be made than the driver or engineer need to figure out what to change. I personally use a pocket setup guide if I'm not sure what to change. The fact is that different combinations might need to be tried and it isn't necessarily an easy process and I certainly can't go into all the different options here. However, another thing that can be looked at if shock sensors on the car is shock histograms.
These graphs show the percent of time that each shock is in high speed bump (compression), high speed rebound (extension), low speed bump, or low speed rebound. The low speed percentages are shown in the shaded areas and those are more important than the high speed percentages. The high speed percentages come into play when the car is going over bumps and the shocks are moving very quickly. But the low speed percentages come into play when the car is cornering. The theory is that the more equal the bump percentages are equal to the rebound percentages and the more equal the histograms are equal to each other than the more balanced the car is going to be. That may or may not translate to faster lap times because the driver may like a car that is not 100% balanced and as a result may be faster. Either way, a change in the bump or rebound on the shocks can be made and the change can be verified by looking at these histograms.
Another important aspect of having shock sensors is that you can see whether or not there is a problem with one of your shocks or any other component of your suspension that is causing that corner to not work smoothly. Below are shock scatter XY plots which compare the shock length to the shock velocity. These should look like a shotgun blast pattern as they do below but if there was a problem with one of the corners then you would see vertical lines going through them. This could save you a lot of time when trying to figure out why the car isn't handling right.
Staying on the topic of diagnosing problems or potential problems, you can also look at what the engine is doing and what aspect that is always important is oil pressure.
The XY plots above show how the oil pressure changes based on Lateral Gs, Longitudinal G's, and RPMs. As you can see the oil pressure in the Honda Fit engine stays above 60 psi and below 80 psi no matter what is happening -- which is fantastic! I can tell you that certainly was not the case in my FV motor. You can also look at fuel pressure, water temp, air temp, etc.
Again with the help of math channels, it is possible to keep track of the amount of time or miles on the engine or really any other component (such as brake pads) which can help determine when to perform maintenance. For example, during 2012 I know that I have put 811 miles on my engine and 445 of those miles were at wide open throttle.
Again, everything I have touched on in this blog regarding data analysis is really just scratching the surface of what can be done with data acquisition and the more you use it the more you will figure out different aspects that can help. Does it take a lot of time? Yes. But I hope that I have shown that it is worth spending the time with it. Most of the time that I spend with it is done at home in front of the TV. However, I have also taught myself quite a bit by using data acquisition when I'm on iRacing.
The point is, use the resources that are available to you and the more resources that you can use the better off you will be. At the very least, take John Block's courses (www.auto-ware.com) and read Bob Knox's book! Both John and Bob also have software that have been extremely helpful to me. I have been using John's Tire Analysis software and Bob's Stars program. The Tire Analysis software helps me determine what setup changes to make based on tire pressures and temps and the Stars software helps me keep track of the setup changes and determine what gear ratios to use.
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