Motorcycling 101: Counter-steering essentials

August 17, 7:46 AMDC Motorcycle Travel ExaminerMark Poesch

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Motorcyclists, it would seem, can disagree about just about anything: sport bikes vs. cruisers, attire, helmets, helmet laws, clutchless up-shifts….  So, it should come as no surprise that there is also strenuous disagreement about counter-steering.

Spain's Dani Pedrosa rides his Honda during the MotoGP race of the Czech Republic Motorcycle Grand Prix at the Brno circuit in Brno, Czech Republic, Sunday, Aug. 16, 2009. Pedrosa finally placed second in the race. (AP Photo/Eckehard Schulz)

In fact, the core of the disagreement is actually “violent agreement,” with the major points of contention hinging on the particular balance and handling behaviors of different classes of bikes, riding styles, and most importantly, semantics.

Starting with first-principles:

1) For counter-steering to be a dominate force, the speed must be above a critical threshold; typically 10 - 15 MPH.  Below this threshold, conventional steering turns the motorcycle.

2) Speed is determined before the turn.

3) Counter-steering (the act performed by the rider) involves pushing with forward force on the inside grip causing the front tire to angle away from the turn.

4) The front tire steers to the outside of the turn (out-tracking) and the bike and rider pivot around their combined center of gravity (CG) -- the bike leans to the inside of the turn.

More succinctly, 3 and 4 can be summarized: The lean angle of the combined CG is determined by the out-tracking caused by the forward force applied by the rider to the inside grip (counter-steering).

5) Once leaned into a turn of a given radius, the force that must be applied to the inside grip to maintain a constant speed, constant radius turn depends on a number of factors, including the bike’s speed, the turn radius, the bike’s handling characteristics, the rider’s position on the bike, and force on the outside grip.

Note: Many modern sport-bikes are so neutrally balanced that once the lean has been initiated, little or no counter-steering input is required to maintain a constant speed, constant radius turn [this is a major source of contention].  Many bikes, however, are designed for stability such that continuous forward pressure on the inside grip is required to counter the bike’s tendency to up-right itself.  Riders experienced with these bikes tend to find it inconceivable that other motorcycles could behave in any other way.

6) The radius of the turn is determined by speed and lean angle of the combined CG of the bike and rider.

While there are additional forces neglected here, the equation describing the dominate forces simply states that lean angle determines the reactive force which counters the tendency of the bike to steer straight (also know as centrifugal “force”).  Or, mathematically speaking:

Centrifugal “force” = Mass * ( Speed^2 / Radius ) [force of inertia pushing the bike / rider out of the turn]

Is equal to:

Reactive Force = Mass * Gravity * Tangent( CG Lean Angle ) [reactive force at the tires pushing the bike into the turn due to the CG lean angle]

Dividing the mass of the rider and the bike out of the equations and simplifying yields:

Radius = Speed^2 / ( Gravity * Tangent( CG Lean Angle ) )

7) A change to either the speed or the lean angle will affect a change to the turn radius.  So, increasing speed while maintaining a constant force on the inside grip will cause a wider radius turn.

Warning: Reducing speed by braking with the front brakes does not decrease the turn radius until after the braking is complete (unless additional steering input is applied)!

8) Braking with the front brake in a turn introduces a new force at the front tire contact patch with the road -- at typical street speeds, the braking force reacting against the inertia of the bike can easily be larger than the force associated with counter-steering to the outside of the turn -- the result is that this reactive force causes the bike to sit up, and run out of the turn.

Put simply: Trail-braking notwithstanding, braking in a turn causes the bike to sit up (reduce lean angle) which leads to a wider radius turn.  Additional counter-steering force can counteract some of the braking force, but the combined forces can exceed the traction of the tire(s).  If the combination of braking and steering “feels” as if the bike is fighting the turn, it’s because  it is!  To turn, stop braking, and push forward on the inside grip!

For more information:
- Counter-steering revisited
- Counter-steering revisited: Redux -- how it works
- Motorcycling 101: Steering - how to turn a motorcycle on the street
- Motorcycling 101: Braking - how to stop a motorcycle on the street
- Motorcycling 101: Clutchless up-shifts
- Motorcycling 101: Getting started - motorcycle training and licensing for the DC area