View Single Post
Old 10-27-2013, 08:04 AM   #66
lnewqban's Avatar
Joined: Jan 2012
Location: Florida
Oddometer: 291

Originally Posted by beendog View Post
................So the crux of my misunderstanding lies here: Both tires gain more traction with more weight on them, but because the contact patches are of a certain size, we have the most traction when the weight is distributed in proportion to the contact patch size on the tires!

Now with that in mind, it gives me another question.........
Yes, with more or less weight on the contact patch, the area of contact grows or shrinks some, but it cannot change as much as the vertical load or force applied on the patch.
That means that if you double the load, the area does not double.
Furthermore, the area has much less influence on traction than the vertical force.
Reduce area in half and you may reduce traction in 10%; reduce vertical force in half and you reduce traction at least 50%.

The lateral force also deforms each instantaneous contact patch sideways, forcing the next one to land a little off the trajectory (a micro side-slide among successive instantaneous contact patches) and forcing the rider to over-steer (or under-steer if the rear slides more) to compensate.

In real life, the vertical force can be drastically reduced while the lateral force remains the same (bad because traction is reduced but not lateral force) when rolling over road imperfections that the suspension cannot follow impeccably: right after the crests are the killers because the tire and the weight that it supports float for fractions of seconds, due to the inertia with which the weight of the bike and tire fall or rise.

To make things worse, a nervous rider could interfere with the little self-adjustments that the steering geometry does to adapt to the sideways forces that appear when rolling over road imperfections at substantial angles of lean.

In that way, for bad suspension and bad road, the contact patch constantly goes from deformed to symmetrical to deformed.
As a deformed tire is more rigid than a normal one, the inherent suspension of the tire also constantly goes from bad to good to bad (which worsens the overall suspension).
Some tire's manufacturers claim that their tires grow the area of contact patch as those lean (see schematic below); however, there is nothing they can do about the internal stress of deformation and uneven distribution of vertical forces.
The contact patch of a tire leaned 45 degree is feeling and resisting slide from a lateral force as big as the weight that it is carrying (over 200 lbs for a light sport bike with a 50/50 weight distribution).

As I see it, for a constant lateral force (steady turn, radius and speed) and the actual variable vertical force and area and rigidity of the patch, the less weight and inertia the better to stay within the margins of the traction that is necessary to counter-act that force.
While leaned, the closer to a wheelie attitude, the less critical these things that affect front traction become.

...........Very sorry, Beendog, I couldn't understand your last question.

lnewqban is offline   Reply With Quote