​Last week’s email discussed literature analyzing the lean (roll) angle tolerance of motorcyclists. There’s a lot to it, but several papers indicate novice riders aren’t likely to exceed 20°. Most of the papers relied on theoretical calculations and basic photogrammetry to estimate lean angle.

If lean angle is important to my analysis, I’ll often perform both theoretical calculations and testing. The path a rider chooses can have a notable effect on the resultant lean angle, and sometimes a ride-through is the best way to get a feel for the differing paths. Let’s save the theoretical calculations for another day and talk about measurement.

After experimenting with many data acquisition systems, I found a setup optimized for measuring motorcycle lean angle should have a robust, Kalman-filtered IMU. That allows for reliable lean angle measurement with respect to vertical. It’s also useful to know the instantaneous lean angle of the motorcycle with respect to the roadway. To do this, I acquired a set of laser ride height sensors. With one mounted on each side of the bike, some quick math gets the answer. I decided to use the ScenePro CI 200 MTS-E for the heart of the system, and PMC RHLs for the ride height sensors.

1: My trusty XSR900 equipped with the data acquisition system. 2: The ScenePro head unit, IMU, and GPS antenna. 3: The bar-mounted dash unit allows for control and monitoring during testing. Knowing I’m actively recording brings me sweet peace of mind. Usually, that’s my main goal. 4: Laser ride height sensor mounted to the swingarm.

The system works really well. My only complaint is the ride height sensors don’t register in direct sunlight, so you need to make some shade or pick the right time of day.

Last week I threw the system on my bike and ripped through a stretch of my favorite canyon to see what lean angles I’m hitting as I navigate the mean public streets. Data from a few curves are shown below (pure beauty).

In the four turns shown here, my lean angle topped out between 36 and 38 degrees (lateral acceleration ~ 0.8 g). This experiment made me consider something important: is this an indication of my lean angle tolerance? Without talking to the rider, that’s tough to answer. Maybe it was a speed tolerance.

In my case, I wasn’t close to dragging my knee, but I typically drag my knee during track days and always did when racing. So, this doesn’t represent my lean angle tolerance… it probably represents my risk tolerance.

Here, I was riding on fairly cold track day tires (that require a lot of heat to get grippy), on a chilly evening, on a tight two-lane roadway, with oncoming traffic and no shoulder; lined with trees, fences, and rock. The curves were tight and visibility downstream was limited. Weighing all these factors, I picked a maximum speed that felt reasonably safe, and the lean angle followed.

With all that in mind, a useful study might equip motorcycles with a sophisticated data acquisition system and ask riders to navigate a closed track that offers plenty of visibility, good runoff, and no potential hazards. I suspect that would tease out a rider’s true lean angle tolerance and be a good addition to the current body of literature.

Any feedback is welcome, this is a topic I'm still thinking about and experimenting with.

Thanks for reading, keep exploring!

Lou Peck
​Lightpoint | Axiom