# Lean Angle Part 2 Case Study

Nathan Rose and Neal Carter return from their scene inspection in California where they gathered data to determine the lean angle of a motorcycle on a curve. In part two of this case study they discuss their analysis of the data and what it means for future motorcycle accident reconstruction.

[Neal Carter]: We got back from Southern California and we have a lot of data to sift through. So, we’re going to look through this data, we’re going to organize it, and we’re going to start analyzing that to objectively quantify how our rider took the turns.

[Nathan Rose]: So, when we were in LA gathering data and we had William do the ride through, we had the motorcycle instrumented, ultimately what that was about was gathering data related to the lean angle that riders would utilize on various curves at various speeds. When a motorcyclist crashes on a curve there are a number of limits that we will look at, because when a rider comes against these limits, that could lead to a crash and it could be something that explains why a particular crash happened.

These are the three limits that we look at when a motorcyclist crashes on a curve. We look at if the crash was caused by the rider exceeding one of these limits. The friction limit would be where the rider is going fast enough around a curve such that they utilize all of the available friction that their motorcycle tires have available and they slide out, lose control due to that. The geometric limit would be, the motorcyclist is going around a curve fast enough that they have to lean to the point that components from the motorcycle come into contact with the ground. There’s actual scraping between the components on the ground that lead to a loss of control. Next limit is the rider’s willingness limit, or psychological limit. This is really an experience issue, rider comfort issue where there are limits on how much a particular rider will lean. So, if a rider goes into a curve and the speed at which they enter that curve requires them to lean to a certain degree, if they’re not willing to go to that lean angle that’s required of them, then they’ll depart the curve. They won’t successfully navigate it.

[Neal Carter]: There’s equations that we can use to determine the lean angle that a motorcycle rider should have when he traverses a turn and that’s based on the CG height of the motorcycle, the tire width of the motorcycle, the speed at which he takes the turn, and the path at which he takes the turn. And, we have a theory on this. We’ve published a paper on this, but what we want to do in this case is we want to look at that through time and see how close the theory comes to our measured data.

[Nathan Rose]: And we compared it to the results that this equation would give us for those curves and we found that this equation does a really good job of telling us what the rider’s lean angle needs to be. It’s an inference based on calculating the lean angle, understanding the studies that are out there about what riders are willing to do, and then looking at that particular rider and their experience level.

We’re publishing the results of that study, it’s currently under peer-review with the Society of Automotive Engineers, but we basically took the data from this case and used it to verify that this equation gives us reasonable results. The case actually ended up settling shortly after we got back and so we never ended up using the data for the case, but actually that works out great for me because now I can use the data for my research purposes. The way we’re going to use it in the future is exactly in relationship to evaluating these three limits and evaluating motorcycle crashes that occurred on a curve and why did they occur. Why did the rider ultimately lose control of their motorcycle and crash as they went around a curve. So, we’ll use it to look at these limits.

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