Thanks to the popularity of NASCAR, most people are familiar with drafting and how it works. Obviously it plays a big part in stock car racing, but it's also important in motorcycle racing - especially at tracks with long, fast straights.
At the recent Canadian Tire Motorsport Park round of the CSBK series, I was able to put some numbers on the benefits and see how important drafting really is, thanks to data from Jodi Christie's Accelerated Technologies Hondas during practice and the races.
Drafting takes place when two or more motorcycles are together on the straight, with one following the other closely. The lead rider breaks the air for the following rider, who then has less air resistance to deal with and can go faster. A traditional "slingshot" pass occurs when the following rider is some distance behind the leader but close enough to experience some drafting effects. That initial benefit quickly grows, pulling the trailing rider closer with an increasing boost of speed. Directly behind the leader now, the follower has enough extra speed to pull out of the draft and pass the helpless rider that did most of the work up the straight.
Just as the trailing rider reaps the benefits of drafting, however, the leader does also. The rear aerodynamics of the motorcycle - how the pocket of air closes up after passing around - are just as important as the front, and the leading rider in a drafting pair also sees some additional speed as well. The result is that two or more riders, drafting and all taking advantage, can go significantly quicker than one rider alone.
The Mario Andretti Straight at CTMP is just over a kilometre long. During Sunday morning's Hindle Pro Sport Bike practice at this year's Mopar Canadian Superbike races, Jodi was on his own most laps up the straight. His top speed over several laps as recorded by his AiM Solo GPS lap timer averages out to 242.2 km/h. Plenty of drafting occurred in the Sport Bike race later that day, with four riders all taking turns at the front of a pack for the lead. During those laps, Jodi's top speed averages 250.3 km/h, a difference of more than 8 km/h. AiM's Race Studio 2 software analysis package includes a "time-difference" channel that is useful for seeing how much time is gained or lost over a certain section of the track, and this channel shows that drafting in the Sport Bike race was worth about a half second every lap compared to Jodi's practice laps, a significant drop.
Making the same comparisons for Jodi's Honda CBR1000RR SP in the Mopar Superbike class, in Sunday morning's practice session his average top speed was 277.6 km/h. In the race, when again four riders contested the lead for the first several laps, that number increased to 282.4 km/h. Using the time-difference channel, drafting in the Superbike race saved Jodi about .3 seconds every lap. Even though speeds are higher on the superbike, the benefits of drafting are less, according to the data collected at CTMP.
It's easy to see then, how packs of multiple riders often form at CTMP and other tracks with long, fast straights, especially in the smaller classes. Once a group has formed and starts saving that half second or so every lap, it's very difficult for an individual rider to break away from the group and pull out a lead. On the other hand, drafting allows an otherwise slower rider to keep up with a group during a race. This is why we almost always see such entertaining races at CTMP with close finishes: A tight pack with several riders that usually end up fighting for the win over the last few corners, as it's very difficult to make a break from the drafting group.
Jodi was in the thick of those drafting battles during Saturday's and Sunday's races at CTMP this year, finishing second in Hindle Pro Sport Bike and third in the Mopar Superbike feature on Saturday. Unfortunately an electrical gremlin slowed his charge in Sunday's Sport Bike race, relegating him to a seventh-place finish, and he crashed out of the Superbike race when he caught a false neutral downshifting for turn 8 off the Mario Andretti straight. As always at CTMP, all four races came down to last-lap, last-corner battles with multiple riders, thanks to all the drafting that occurs at that particular track.
- By Andrew Trevitt