Motorcycle Lean Angle

Accident Reconstruction Case Study

In this motorcycle accident reconstruction case study, we examine some of Kineticorp’s unique testing capabilities. This case involved a group of motorcyclists traveling on a mountainous highway. As they approached a curve, one of the motorcyclists lost control and entered oncoming traffic. A fatality resulted. Kineticorp was hired to reconstruct the accident and determine how the rider’s inexperience may have contributed to the accident. The videos below give a behind-the-scenes look at the investigation, testing, and analysis that went into this case.

Video Transcription

Nathan Rose: I’m Nathan Rose, I’m one of the Principals and Directors at Kineticorp. We’re a forensic engineering firm, we do a lot of different types of cases. Today we’re heading out to Los Angeles area, crash that happened out there that we’re working on involved two packs of motorcyclists, on a mountain road. And so our role in this case is one, to reconstruct the accident, figure out what happened. After we determine that, then we’ll be looking at the characteristics of the curve, how difficult is the curve in terms of a motorcycle skill level. And we’ll be doing that based on physical evidence and based on principles of physics.

Neal Carter: What we’re doing here is we’re scanning an exemplar motorcycle. This 3D laser scanner will take millions of measurement points to give us the exact geometry of the motorcycle. Now, we scan it from a couple of different locations. So we have the point clouds from different vantage points of the motorcycle and we’ll be able to see on a component by component level how this fits into the evidence from the accident.  Here I’ve tapped in to the battery of the motorcycle to get a 12 volt power source which is powering our VBox. And the VBox is the frames that’s going to tell us the precise location, speed and lean angle of the motorcycle as we go on our path. I’ve connected first off the power to the VBox, second I’ve connected two antennas. These antennas I have mounted on a rig, this rig is perpendicular to the axis of the bike and these antennas are exactly one meter apart. That’s important that they’re one meter because having two antennas is what allows us to measure the lean angle of the bike and we want to make sure that we have a precise measurement of what exactly that lean angle is.  Now, I also have included a trigger. This trigger will let me start and stop recording events. We’re going to use this to do a run through the Canyon and, in doing so, we’ll know how much lean was required on different turns and at what speed those turns were taken.

William Neale: I’m looking over our map for our a ride today. We’re getting the bike equipped right now with our VBox tracking system and we’re going to take our ride tracking the path of travel.

Neal Carter: Right now we have our primary chase camera on the hood of our vehicle. I’m setting up a secondary camera that’s a little bit lower and that will to give us a better view of the lean angle of the motorcycle as we progress through the route. We’re also going to have a chest camera on William, our rider, and a helmet camera. So we’ll have a total of four cameras capturing the ride.

Nathan Rose: So today we’ll be documenting the geometric characteristics of the curve, will be determining its radius, cross slope, slope. So we’ll be able to bring a very quantitative perspective to analysis of these curves, it won’t just be based on our judgment, but there will actually be numbers behind it. It’ll be based on actual quantitative data, which is really a pretty unusual thing in the industry specifically for motorcycle crashes and looking at a more objective way of assessing how challenging or not challenging a curve is for a motorcyclist.

William Neale: It’s good to be off the bike. It’s a stiff position you’ve got to hold for the whole time. We came through all the curves, this is the subject curve. I went through it and I didn’t notice it as being the subject curve, but now we’re here. We’re going to collect some data.

Nathan Rose: Right now we’re documenting the geometry of the accident site using our 3D laser scanner. And what the device will do is it’ll rotate around, shoot a laser out, will take millions of individual measurement points where certain points on the road are. And then after it does that, it’ll rotate around again, it’ll take photographs and ultimately it can map the colors from those photographs onto the points. So when we view the data, it’ll look like the real scene.

Neal Carter: Unmanned aerial vehicles are useful in accident reconstruction. And we’ve been working with drones for a little over two years now. One of the better uses that I’ve found is actually a shot from about 400 feet. The advantage of that is we get a great view of William as he’s riding through the curve, and also because we are documenting the characteristics of his curve, we can analyze the video to figure out what speed he took the curve at.  This is great, I’m up high enough that I can actually get William on the whole curve. It’s a curve that traverses a little bit more than 180 degrees. So this is a more challenging curve than the subject curve.

Nathan Rose: So this curve we’re on now is a curve we’ve identified as being similar, potentially even more challenging for a motorcycle rider than the curve on which this accident occurred. We’ve been doing some drive throughs with William on the motorcycle and now I’m in the midst of documenting the characteristics of this curve with our laser scanner. On this one, I’m just going to take one scan to get the cross slope of the curve and the up slope and then we’ll use an aerial photograph to get the radius.  We’re heading back to Denver this morning from the Los Angeles area. Collected a lot of great data on this trip, we’ve got video footage of William traveling through various curves that are involved in the route that this accident involves. We’ve got scan data, VBox data, then we’re going to go back to the office and we’re going to start processing that data.  The thing we found surprising yesterday was that the curve that’s involved in this accident, William didn’t even notice it. So one of the issues is how difficult was that curve for the rider to handle. And one of the big next steps that we’ll be looking at is physical evidence for this case. We’ll get all that evidence on the diagram, could be tire marks, fluid marks, rest positions of the motorcycles and riders, that’ll help us determine the speed. So heading back to Denver, to the office to begin looking at all those issues.

Video Transcription

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: 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 up against these limits, that can 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 to 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 the curve such that they utilize all of the available friction that their motorcycle tires have available and they’d slide out, lose control due to that. 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 and there’s actual scraping between the components and 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. 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 in which he takes the turn. We have a theory on this, we 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: 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.

The Process:

This case involved documenting the subject curve and other curves and performing testing to determine how a rider would traverse these curves. Kineticorp’s William Neale traveled the same route as the motorcyclist that was involved in the accident.  A VBOX (an industry accepted data acquisition system) was attached to the motorcycle to measure the lean angle and speed. Nathan Rose and Neal Carter followed William with GoPros attached to the chase vehicle to document the ride and the lean angles. In addition, several curves of the ride were documented via drone footage and scan data. The data was then taken back to the office where Nathan Rose and Neal Carter analyzed the data.

The Results:

Shortly after the testing was performed the case settled. Given the data we collected on this case, it presented a great opportunity to develop a publication based on the analysis of the data which is currently in the works. The research paper will published through the Society of Automotive Engineering.

The Team:

Nathan Rose, William Neale, Neal Carter

Related Case Studies, Content & Research:

SAE 2017-01-1413 – Video Analysis of Motorcycle and Rider Dynamics During High-Side Falls

Collision Magazine, Volume 9, Issue 1, 2014 – Analysis of Motorcycle and Rider Limits on a Curve

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