By The Numbers: Setting Up A Racing Motorcycle Using Chassis Software

Race against time

Riders and teams are in a constant battle against time at the highest levels of motorsport. And I don’t mean just the lap times: every race weekend they have just a few practice sessions to come up with the perfect setup for qualifying and the race. A setup that adapts their bike as well as possible to the nature of the track, helps it to get the best out of the tires on this type of asphalt, and gives their rider the feedback he needs to properly push the bike to its limits. This famous ‘setup’ we so often hear about is actually the combination of all the different parameters that can be adjusted on the bike. And this is where things starts to get complicated, because there are a lot of variables that can be adjusted or changed. And to make matters worse, almost all of them affect each other in some way. In this article I will explain how MotoGP teams deal with the setup.

From graph paper to spreadsheets

In the early days of motorcycle racing, bikes were a lot more basic and had only a few options to ‘tune’ the handling of the bike. Nevertheless, technicians quickly realized that they needed to keep track of some of the bike chassis parameters, such as spring rate, wheelbase, and ride height, just to name a few. With it, you could rebuild a complete bike and not accidentally change the way it handled. The resulting list became known as the setup sheet. It was still a rather short list, but it was enough to help them not to lose their way in tracking how the bike handled. With the lap times added to it later, usually alongside some remarks from the rider about the tires and the gearing, that sheet of paper was all you needed back in the old days.

Then came the first proper race shocks and front fork conversions, along with a lot more springs to choose from. This brought with it a need to calculate the effects of these various spring / preload combinations, plus the effects of fork oil level and top-out springs. That was when the first spring programs where born. When you gave this Excel-based software tool input about your spring rate, preload, top-out spring and fork volumes, it would give you clear diagrams, showing the resulting forces per stroke.

This was extremely useful. It helped us to change the spring rate, for example, and choose a matching preload that kept the bike right in the part of the stroke where we wanted it to be. Without that, we would have ended up with not just the different spring rate we wanted, but probably with a different ride height as well, which we didn't necessarily want.

Or maybe we want to stiffen up the fork springs, but only at the very last part of the stroke. Handy if the rider is very happy with the bike, but the forks are bottoming during hard braking. This is where a spring calculation tool could tell you not to change the spring itself, but to raise the oil volume instead (see example below). In short: a spring tool calculates the forces per stroke on your shock and fork. If you know where in the stroke you need a change in spring force, the tool will help you to find the right combination of springs, preload, air chamber and top-out spring.

An example taken from a front fork spring tool. This comparison shows us what the difference would be if we just raised the fork oil level by 20 mm in the fork. Compared with the standard fork (blue line) the spring rate for the higher oil level (green line) will progressively go up with the stroke of the fork, so more load can be handled before the fork will ‘bottom out’.
An example taken from a front fork spring tool. This comparison shows us what the difference would be if we just raised the fork oil level by 20 mm in the fork. Compared with the standard fork (blue line) the spring rate for the higher oil level (green line) will progressively go up with the stroke of the fork, so more load can be handled before the fork will ‘bottom out’.

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year: 
2020

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Comments

Thanks Peter,

It's great to see how these tools are used. I did a one-day chassis dynamics course in order to understand better what my bike was doing on track and while I feel like I understand the bike a bit better, the real take-away was how beautifully complex the dynamics of a motorcycle are. I'm sure there are many more variables than what you've shown and that at times it isn't easy to understand the cause/effect of some changes or behaviors. Is there any use of machine learning to try to identify patterns in behaviors that might not be well understood?

Bedankt,

Len

they didn't tell me that much ;-) But for sure it was in the pre-spec-ecu area, where also traction control was self learning. At 2D we have a automatic scripting, that works like 'big data'. works for Suspsension movements etc.