As I mentioned in a previous blog, recent advances in tires, chassis and electronics have put more emphasis on corner entry and trail braking rather than corner exits, as this is currently the part of the track where riding skill and technique can make the most difference.
With more racing classes using spec tires and more motorcycles equipped with very good traction control systems, it’s hard to get any kind of an advantage over a competitor on corner exit – everyone has pretty much the same traction, and the bikes in any give class are usually very equal in terms of power. This, however, does not mean that you can be lazy on corner exits and just let your electronics do all the work for you. Getting on the gas smoothly and quickly when exiting a corner is still important.
In my last couple of blogs I talked about trail braking, and how the motorcycle’s front tire can only provide so much traction; you can split that traction into some portion for braking and some portion for cornering, but the vector sum of the two must be less than the maximum available from the tire. For accelerating out of the corner with the bike still leaned over, all the same concepts apply to the rear tire and we can use the same vector addition and GPS data to look at performance in this area.
Just as you must release the front brake as soon as you begin your arc into a corner so as not to overload the front tire when trail braking, at the initial part of the corner exit you must lift the bike from maximum lean at least some amount before you can begin accelerating. From that point, the bike must be brought progressively more vertical as more throttle is applied for more acceleration. During the entire transition from full lean to full vertical, the vector sum of the cornering and acceleration forces must be less than the total traction force available from the tire; this data can be graphed and evaluated in a similar manner to trail braking data as I outlined in my previous blog.
That said, there are some significant differences to consider due to the fact that throttle position is not directly proportional to acceleration; furthermore, that relationship can change drastically with speed. In slow corners it may not take much throttle for the motorcycle to accelerate, but at high speeds, or in an uphill turn, it can take a significant amount of throttle just to hold a constant speed; I have data for a 600cc machine in an uphill, 150-km/h corner that shows more than 30 percent throttle required before the motorcycle actually accelerates.
At the very exit of the corner, full throttle at low speeds can net 1g of acceleration on some bikes but acceleration is much less at higher speed even with the throttle fully opened – until at top speed the motorcycle stops accelerating altogether. This means that at higher speeds a significant amount of lean angle can be combined with full throttle.
When trail braking on the entry to a corner, you must begin to release the brake just as you tip into the corner, and the brake must be completely released just as you reach full lean. On corner exit, our natural tendency is to do the same thing: lift the bike from full lean the moment the throttle is opened, and not open it fully until the bike is completely vertical. But the reality is that some amount of throttle can be used at full lean and the throttle can be fully open before the bike is vertical, and the combinations are very dependent on speed. This means that every corner is different, and your corner exit technique must change accordingly.