GPS data available through the AiM EVO4 data acquisition system helps illustrate the compromises a rider must make when racing in the rain as opposed to dry conditions. GPS data available through the AiM EVO4 data acquisition system helps illustrate the compromises a rider must make when racing in the rain as opposed to dry conditions. Photo by Richard Coburn

Trevitt’s Blog: Racing in the Rain

Written by  on Thursday, 11 September 2014 11:06

At the final round of the Mopar Canadian Superbike Championship this year, held at Canadian Tire Motorsport Park, Saturday's Superbike race was held in very wet conditions while Sunday's race was in near-perfect sunny and cool weather. Comparing data from the two races provides some insight into how the rider adapts to those conditions, and we can even put some numbers on those aspects.

The rider in this case is Jodi Christie, on his Accelerated Technologies Honda CBR1000RR superbike. In Saturday's wet race, Jodi finished second with a best lap time of 1:40.825 on the last lap, for an average speed of 142 km/h. On Sunday, Jodi turned his best lap early in the race, a 1:22.469 for an average speed of 173 km/h. It's worth noting that as conditions changed even during Saturday's race, Jodi's lap times changed accordingly with a spread of seven seconds between his quickest and slowest laps; that is much more than the more typical two-second range in Sunday's dry race.

It's obvious that speed is lower everywhere in the rain, but using the team's AiM EVO4 data acquisition system we have access to GPS data that can be used to determine just what other compromises must be made.

Given the speed differential, it would make sense that braking and acceleration are also significantly less, but that is not the case. In the dry, Jodi's maximum braking is typically seen entering Moss Corner (the turn 5 hairpin), a value of 1.15 g. In the rain, Moss is notoriously slippery and braking force drops dramatically, but in turn 8 (at the end of the backstraight) Jodi brakes at .97 g, a drop of just 15 percent from his normal braking force there. Acceleration values drop even less in the rain, from a maximum of .75 g to .68 g, for a decrease of less than 10 percent.

Cornering forces show more of a decrease in the rain, dropping from a peak of 1.5 g to 1.1 g (both in the first part of Moss Corner, 5a), or more than 25 percent. Lean angle is likewise less; Jodi's typical lean angle at CTMP ranges from 45 to 55 degrees, whereas in the rain it is between just 30 and 35 degrees in most corners.

One way to determine how smooth a particular rider is at the controls is to look at the rate of change of various channels - in math terms, this is the derivative function. For example, how quickly the rider opens (or closes) the throttle is shown by the rate of change of the TPS channel, in units of percent per second. Here we see a major decrease: In the dry, Jodi uses 100 percent throttle for 28 seconds per lap and his quickest opening rate is almost 200 percent per second. But in the wet, Jodi uses 100 percent throttle for less than 10 seconds with a peak opening rate of 130 percent per second. Likewise, we can look at the rate of change of the braking and acceleration channels, or even lean angle. Between the dry and wet laps, these values all show a drop of approximately 30 percent, about the same decrease as in the cornering forces.

As I have discussed before, we can use GPS data to determine loading on the front or rear tire, and this number is a good measure of how "safe" a rider is at any given moment. Here, the values drop between 30 and 35 percent from dry to wet, slightly more than some of the other channels. More telling though, and perhaps the biggest indicator of how much smoother Jodi rides in the rain, is looking at the rate of change of these channels - how quickly or smoothly Jodi is transferring weight from front to rear and loading the tires. Here the values drop by 50 percent, much more than some of the other channels.

It's the rate-of-change channels that show the biggest decrease in the rain, and especially the rate of change in the tire loading channels. All this points to smoothness being the key to riding well and staying upright in dodgy conditions, with any abrupt control inputs or even movement on the bike kept in check.

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Last modified on Tuesday, 16 September 2014 09:57
Published in Andrew Trevitt

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