Body Positioning and Traction

A fan, Mike (from Ireland), sent me an email regarding traction and where to put your body while cornering. Mike’s question is a common question I get asked by both street and adventure riders alike. This is a typical but very complicated topic that deserves a blog post. I have done my best to balance the line between too much detail or abstract conceptualization and simple black and white, yes/no answers.Here’s his email:

email

Before I can answer Mike’s questions, I have to clean up a few issues in the opening assumptions. There are several common beliefs that are not correct in in his statements of ‘advice’. I refer to these statements as assumptions, as they establish a baseline of understanding to work from.

The first assumption in Mike’s email is his statement about cornering in high traction conditions (ie. a dry racetrack). The statement was “Riders should keep the bike as upright as possible to maximize the contact patch…”.

Assumption #1 Part 1:
A tire leaned over has less contact area than a tire that is vertical.

Assumption #1 Part 2:
More surface area between the tire and road = more traction.
Both of these assumptions are wrong. Traction is far more dynamic and complex than simply surface area, and surface area alone does not increase traction.

New tires seldom offer more contact area when vertical than when the tire is leaned over. New tires commonly offer similar contact area in both the vertical and leaned positions. Performance street and track tires commonly provide more contact area (traction patch) with the ground at full lean than when the tire is vertical. As tires wear out they develop a flat spot from riding on level ground which will increase the contact area when vertical and decrease the contact area at a lean angle just after vertical.  Even with a tire that has squared off (flatten out from wear) the tire will likely still have the same contact area at full lean as when the tire was new.

The second assumption came from the statement “…(a.k.a hanging your ass off the side or ‘getting your elbow down) to allow the rider to get around the corner.”  This has little to do with the three main questions in the email but I just can’t keep myself from making a comment. “Hanging your ass off” has little effect; moving the upper body or total body into an area of neutral energy is the primary objective when talking about weighting the inside of a turn or body positioning. For simplicity I will call the method of positively weighting the inside of the curve ‘positive body positioning’.

To understand the advantages of counter weighting vs. riding proud vs. positive body positioning, it is easiest to just look at the extremes: positive body positioning vs. counterweighting (weighting the outside the curve):

Riding proud is a choice that does nothing to counteract centrifugal or gravitational forces. This isn’t necessarily a bad choice. When riding at modest speeds and lean angles (most street speeds fall into this category) riding proud or modest adjustments in body placement is all that is needed to balance the changes in centrifugal forces, lateral forces and gravity.

Now that I’ve addressed the assumptions, let’s move onto the three questions Mike posed.

Is the difference between weighting the inside vs counterweighting related to speed more than to grip?

Speed and traction have to be considered as a package when choosing whether to weight the inside, ride proud or counterweight.   Here are two examples of a rider cornering on a paved surface (high traction) at high speed:

1. Riding Proud: A rider is at a track day and riding at speeds well above speeds we can obtain on a public road. As the rider enters the first corner at 100mph/160kph, he keeps his body in the ‘ride proud’ riding position, not moving inside or outside the centerline of the motorcycle.  He presses hard to the inside handlebar, holding pressure to get through the corner. As the rider approaches the apex of the corner, the foot pegs begin to grind away. Slowly easing up on the handlebar the rider accelerates out of the corner.

As the motorcycle leans into a corner, the centrifugal force exerted on the motorcycle tries to throw the motorcycle out of the curve. Because tires have traction at the point at which they contact the ground and the top of the motorcycle is not restricted, the upper half of the motorcycle (including the rider) are thrown outside the curve by centrifugal forces. To counteract the centrifugal force, the rider has to push harder on the inside handlebar to lean farther into the corner. This requires more input (energy) from the rider and a greater lean angle for the motorcycle, subsequently giving up what is often critical ground clearance.

2. Positive Body Positioning: On the next lap, the rider approaches the same corner at the same speed but this time moves his body (mass) low and inside the curve. The rider leans forward and to the inside of the fuel tank to maximize the shift in the combined center of mass of the rider/motorcycle. Applying pressure to the inside grip to initiate lean, the rider slowly reduces pressure on the inside grip as the motorcycle reaches its desired lean angle until there is neutral pressure on both the inside and outside grip.
As the rider passes the apex, the foot pegs hover happily above the pavement and never touch ground. Without changing any pressure at either grip, the rider adds speed using the throttle and the bike slowly increases its arc to the outside of the curve where the rider moves his weight back to the centerline of the motorcycle, resulting in the motorcycle moving back to vertical.

To reduce both the input required from the rider and the required lean angle of the motorcycle for any given speed/lean, the rider can apply centripetal force by moving lower to the ground and farther inside the curve. When the rider moves far enough to the inside to counteract the centrifugal force, he/she no longer feels the bike trying throw them to the outside of the curve and they have found what I refer to as the “neutral state”. Finding the neutral state is the objective of every rider in every corner.

A rider who uses positive body positioning by weighting the inside of a corner illustrates two critical benefits:

1. Reduced lean angle (conserving ground clearance): Lean angle = the combined mass of the rider and motorcycle + speed + radius.

The rider can decrease the lean angle by altering any one of these three elements: decreasing speed, increasing the corner radius or moving their body mass lower to the inside of the curve.

2016-Ducati-Multistrada-1200-Enduro-launch-Bret-Tkacs-6-1024x682 There are arguably no high-traction environments other than slow-speed maneuvering where counterweighting is likely the best technique. Counterweighting should be reserved primarily for low-speed cornering with low or unpredictable traction.

Positive body positioning shifts the rider’s mass lower to the inside of the curve. If the rider shifts weight farther to the inside of a corner then the motorcycle requires less lean to balance the total mass of rider & motorcycle, thereby conserving ground clearance. Being proficient using positive body positioning with low clearance bikes like Harley Davidsons reduces the chances of crashing due to a loss of ground clearance.

2. Less rider input:
When the rider uses positive body positioning to neutralize the centrifugal force that tries to throw him/her outside the corner, it also reduces the input at the grip to initiate lean and also eliminates the need for pressure to maintain that lean.

If the rider is skilled enough to find the area of neutral energy, the bike will continue to track through the intended arch at the desired lean angle with zero pressure at the grip. There is an entire blog of subsequent benefits that I won’t address here.

Two examples of body positioning in a dirt scenario:

1. A rider in the dirt is making a hard left turn and has a berm that can be leaned into; this rider may move far forward on the motorcycle to load the front tire and then lean deep into the turn, accelerating hard to drive out of the turn.

Because the bike is leaning into the turn but the tires are actually vertical to the ground (or cradled by the surface), the rider can treat this corner similar to the high-traction scenario and use positive body positioning as I have already discussed.

2. Approaching a turn, the rider stands on the pegs and leans the bike deep into the turn, while staying above the point of traction using counterweighting. As the bike slides sideways, they accelerate to cause the back of the bike to pivot around the front tire, which reduces the side slip of the front tire. As the bike returns to vertical, the rider remains directly above the point of contact.  Due to the high expectation that the motorcycle would slip, the rider needed to be directly above the point of traction. This allows the rider to stay on top of the bike as the bike slides to the outside of the curve and underneath the rider. Had the rider stayed in a ride proud or positive body position, the points of traction (where the tires touch the ground) would have slid away from the rider, making it difficult or impossible for the rider to maintain a neutral energy/balance position and almost guaranteeing the chance of a low-side fall. Centrifugal forces and ground clearance are generally less of a concern in this example because the cornering speeds are so much less. In this scenario, it is far more important for the rider to maintain a neutral position above the point where the tires contact the ground than to counteract centrifugal forces or conserve ground clearance.

How do I know which approach is the most appropriate for any given scenario?

When riding in high traction environments, weighting to the inside of the curve can offer a real benefit of using less effort to counteract the centrifugal forces as well as increasing ground clearance reserves. This which could be critically important on a bike like a low-slung cruiser.

If ground clearance is not limited and speeds are low enough to not create significant centrifugal forces, then staying in the ride proud position is perfectly acceptable and possible the best position to find neutral. In most real-world riding, there are seldom major advantages to using positive body positioning for casual street riding.

Can you offer any guidelines on which approach to use in various conditions?

There are exceptions to every rule and when choosing any technique for riding, you must consider all of the factors. Some of the factors worth considering before committing to any technique should include but not be limited to:

  • Traction predictability
    Tire type
    Rider skills and experience
    Type of motorcycle
    Suspension
    Sight line
    Approach speeds
    Level ground vs berms or angles
    Type of ground surface
    Motorcycle load
    Rider fatigue
    Rider attitude/mood
    Other traffic
    Run-off
    Laws/rules
    Ambient temperatures
    Tire temperatures
    Tire condition
    Rider confidence
    Margins for errors

Once these factors are considered, then you can apply the following general guidelines to when you might use counterweighting vs. proud riding vs. positive body positioning.

When to counterweight:
– Low speed (under 15mph/25kph)
– Low traction (such as gravel or dirt roads as speed above 15mph/25kph)
– Anytime steering with the rear wheel is intended (brake or power)
– When on the street where traction could rapidly change (patches of sand/gravel)

When to use positive body positioning:
– Very high speed corners (counteract centrifugal force)
– When ground clearance is very limited
– When near traction threshold on a high traction surface (Shifting weight to the inside of a corner DOES NOT provide more traction but does provide more ground clearance and moves the rider to the inside where the bike can move and recover more freely from side slip)
– When the rider has a bank or berm that can be used to reduce the slip angle of the tires
– When a camera-man is nearby and you want to look cool

When to ride proud:
– Normal, everyday street riding
– In situations where ground clearance is not a concern
– When not on dirt or gravel

Each of these topics addressed above are simplified for easy digestion and are much deeper if we dive into each element. Please use my answers as a guideline, and to help generate more questions.

2 thoughts on “Body Positioning and Traction

  1. Love the way you are able to articulate cornering Dynamics. I am new to dual sport riding after years of riding sport bikes on road race tracks and streets. I am continuing to learn the new to me cornering techniques on loose surfaces. Thanks for the article!

    Like

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.