Home Blogs Andrew Trevitt Coasting and Missed Opportunities
Thursday, 03 May 2012 09:10

Coasting and Missed Opportunities

Posted by  IM Admin
Rate this item
(1 Vote)
 A lap of Spring Mountain Motorsports Ranch in Pahrump, Nevada, with speed shown in blue. The red trace at the bottom shows where a more experienced rider is coasting, with neither the throttle nor brake applied; the grey trace shows the same for a less experienced rider. A lap of Spring Mountain Motorsports Ranch in Pahrump, Nevada, with speed shown in blue. The red trace at the bottom shows where a more experienced rider is coasting, with neither the throttle nor brake applied; the grey trace shows the same for a less experienced rider.

One lesson I was taught when I first started racing was that you should always be either on the throttle or on the brakes, as time spent without one or the other applied is lost "coasting." By coasting, you are letting engine braking (or lack of it) control your speed, rather than controlling it yourself with the throttle or brake. Granted, there are some rare occasions where it may work out correctly that the engine provides just the exact amount of braking you want. But more often than not, you — the rider — can do better. Sometimes coasting indicates the rider is overcautious getting on the throttle at the apex of a turn, but an extended amount of coasting can indicate that there is an opportunity for a burst of throttle (and corresponding braking), and that opportunity is being missed.

Using data acquisition, we can look more closely at time spent coasting, and pinpoint areas that could use some attention from the rider. My article in the current issue of Inside Motorcycles talks about utilizing sensors that are already on your bike with a data acquisition system, and here we can use the throttle position sensor and brake switch in particular. Combining the two signals using a math channel, it's possible to find exactly how much time during a particular lap that a rider spends coasting.

The graph shows data for two riders at Spring Mountain Motorsports Ranch in Pahrump, Nevada on the same bike — a stock Suzuki GSX-R750. On a typical lap of just under two minutes, the less experienced rider coasts for 12.5 seconds. The more experienced rider, lapping three seconds faster, coasts for just 4.7 seconds. While some of the difference is accounted for in shifting and the transition from throttle to brake at the end of each straight, a significant chunk of the time is found when each rider releases the brake and applies the throttle at the apex of each turn. The less experienced rider takes up to a second for that transition, while the more experienced rider is typically in the 0.3-second range.

Picking up the throttle quicker reduces time spent coasting, and it also settles the bike's suspension and takes load off the front tire. It's worth noting as well that, in some cases, just picking up the throttle is not enough; at higher speeds or in an uphill turn, it can take as much as 30 percent throttle on a middleweight bike just to hold a constant speed. Any less, and you can consider it coasting.

Another big difference between our two riders is in combinations of corners on the track. Where two corners are close together — for example, at about the 1000-foot mark on the diagram — the more experienced rider fits in a burst of throttle followed by a very short braking period in between, while the less experienced rider uses just a modest amount of throttle and relies on engine braking for slowing into the second turn. These short sections make up another large portion of the difference in coasting time, and have a larger effect on lap time as well.

Keep in mind that while having a data acquisition system is useful for putting numbers and graphs to coasting and seeing improvements, it's not a necessity. Like many aspects of riding, once you are aware of the issue and keep it in mind while on the track, you may find it quite apparent.