Controlling Your Cornering Arc With The Throttle

From the April, 2009 issue of Sport Rider

By Lance Holst

Photography by Brian J. Nelson

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When learning the basics of cornering, most riders begin with separate inputs in a consecutive order. For example: shut throttle, apply brake or brakes (for this column let's use only the front brake), downshift, steer into the corner. As we progress, these previously separate inputs overlap one another and sometimes occur simultaneously which smoothes the overall process and makes better use of the time we have to execute them.

We evolve to what Andrew Trevitt outlined in his Throttle-to-Brake Transition Riding Skills Series column in our January issue. Rather than first shutting the throttle, then reaching for the brake, then downshifting, then steering, we begin by shifting our body position to the inside just prior to smoothly applying the front brake lever while smoothly rolling off the throttle. As soon as we've scrubbed enough speed we begin blipping the throttle to match engine revs on our downshifts as early in the braking zone as possible so that as the corner approaches all of our attention can be focused on precisely setting our corner entrance speed and accurately choosing our turn-in point.

Here again, as we advance our riding technique and smooth our transitions, we slowly release brake lever pressure as we approach the turn-in point and trail off our braking as we increase our lean angle into the corner. This allows the front suspension to remain compressed which steepens the effective rake of the chassis geometry, which in turn allows it to turn in quicker, with less effort than with the fork extended. More importantly, it smoothes the weight transfer from front to rear and minimizes the changes in suspension stroke and chassis geometry. In other words, the fork transitions from its fully compressed state at or near the bottom of its stroke under maximum braking, to where it will settle under cornering load, likely somewhere between 70 to 80 percent of its travel (with fully extended defined as zero travel, fully compressed being 100 percent).

Sorry for the lengthy but necessary lead-in, but now that we've steered into the corner and set our lean angle, we arrive at the subject of this Riding Skills Series column: controlling our cornering arc with the throttle. Later on, we'll get to the most heroic (and most over-stated) example of throttle steering, which is skillfully and purposefully spinning up the rear tire to bring the back end of the bike around in what car drivers call oversteer. Oversteer occurs when the rear steps out, which causes the bike to turn tighter into the corner (hence the term oversteer) and requires a slight outward steering correction (often perplexingly described as steering into the skid) to keep from running off the inside of the corner. First, however, let's cover the more commonly applied use of the throttle in controlling the cornering arc when the wheels are kept in line with one another.

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In my years teaching riders of widely varying abilities on tracks across the country and overseas, one of the key missed steps in advancing rider skill is getting comfortable using throttle application to control cornering arc while leaned over in a turn. As with all advanced skills, absolute smoothness is a requirement. Using the throttle as an on-off switch is sure to put you on your head faster than you can scream "What the H---!" Even with today's incredibly advanced traction control electronics that use GPS systems to allow teams to dial in the percentage of tire slippage on a corner-by-corner basis, the best riders in the world (Valentino Rossi and the handful of riders who are genuine rivals) use the throttle as a rheostat in almost infinitely small increments in both opening and closing the throttle. As we saw this past MotoGP season, the most talented of the new-comers from the 250 class, like the brilliant Jorge Lorenzo, can muster the trust to use modern electronics with brutal effectiveness to produce blinding speed, for a time, but eventually even Lorenzo's shooting star burned too brightly when he was repeatedly launched heavenward the several times that even the best Magneti Marelli magic couldn't save him. So the bottom line is that the fundamentals of smoothness still apply; electronics are no substitute for experience and ability.

In the real world for riders who ride with their wheels always aligned, the smooth use of the throttle while banked into a corner is an indispensible tool in precisely adjusting your line through a corner. Your bike's trajectory or curved path through a corner is primarily determined by two factors: your speed and your lean angle. Increasing lean angle quite obviously tightens your cornering line while increasing your speed has the opposite effect. In other words, once you've set your lean angle you can tighten your line by simply reducing your speed or widen your cornering arc by increasing it; without ever changing your lean angle. Keeping your engine rpm between 60 and 80 percent of redline also enhances its throttle response, though the higher rpm also demands greater smoothness.

As riders build their cornering confidence they focus most of their attention on lean angle; specifically, achieving ever increasing levels of it. In their quest for pushing the limits of lean, however, riders often find themselves needing to alter their line mid corner and panic often ensues. We tend to do a predictable number of things when we panic (we tense up, target fixate, slam the throttle shut and grab the brakes) and all of them hinder our ability to control a motorcycle. It's better to practice controlling our speed as well as our lean angle before panic sets in. As riders build their confidence in leaning their motorcycles it's important to gain experience in varying the throttle position as well

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After steering into the corner while setting your corner speed by trailing off the brakes, there comes a point where you need to slightly open the throttle to neutral throttle, the point at which you maintain the desired speed, neither accelerating nor decelerating. If you don't crack open the throttle, the bike will continue to slow and corner at an ever-decreasing arc. This is caused by two factors: the first is that, lacking the centrifugal force of hard cornering, most bikes tend to continue to lean into the corner if the throttle isn't cracked open to arrest the lean; the second is that all other things being equal, simply slowing your speed tightens the cornering arc as well. Ironically, it's this situation--the feeling that the bike is falling into the corner--that triggers the panic reactions that many riders find the most difficult to overcome. The simple solution is to open the throttle to the point where it both arrests the lean angle and it increases the speed to the point of widening the cornering arc. As simple as this sounds, our instinctual panic responses are programmed to do the opposite: tense up, target fixate, close the throttle and grab the brakes. By either avoiding panic by increasing our speed and lean angle in small increments or reprogramming our ability to overcome panic when we feel it begin to take hold, we can keep ourselves out of trouble and in control.

The opposite situation is needing to tighten your cornering line while you're already at the lean angle limit that your confidence allows (note that for most but not all riders, this limit is below that of the maximum lean angle that either the cornering clearance of the chassis or the traction of the tires allow). Here is where the need for sublime smoothness on the controls is most needed. The degree of input while rolling out of the throttle to tighten your line is only a few percentage points of the quarter-turn available. Let's say, for the sake of argument, that neutral throttle is 17 percent of the total throttle opening. If you're nearing the physical limitations of the chassis, simply shutting the throttle completely could overwhelm the available traction by transferring more load to the front contact patch than the tire can handle. In this admittedly rare but critical instance you need to have the feel to relax the twist grip perhaps as little as two or three (or at most five to seven) percentage points of available throttle angle to tighten your cornering line. That slight reduction of throttle will transfer the bike's weight distribution forward, subtly compressing the fork and increasing the front tire's contact patch, both of which enhance the bike's ability to steer into the corner. These factors, in addition to the slight reduction of corner speed all combine to tighten your cornering line. Too much reduction in throttle, however, and the fork could compress to the point of compromising cornering clearance or overwhelming the available traction of the front tire.

Delicate applications of either the front or rear brake can also be used but that's a subject for another column.

However it's done, it's a delicate balance best executed with a calm, practiced touch which brings us back to advancing in gradual increments with equal awareness in how lean angle as well as throttle position effect our ability to adjust cornering lines in those perilous mid-corner moments that life can throw at us.