Low Sided But Not Sure Why (Track Day)

[Lnewqban]

 

I'm a little confused by this.

 

If you accelerate mid turn, the bike will come up if you don't do anything to stop it, right? The shear force on the front tire from the ground, due to the acceleration of the rear tire, pushes on the front contact patch and does the same thing (creates the same resistance at the contact patch) as countersteering the bike up does -- at least, that's my understanding.

 

If that's the case, then if you accelerate, the only way to keep the same radius is to "force" a bigger lean angle by countersteering. Right?

 

Also, by bring the bike out of "balance", do you mean away from the point that it is turning without you needing to maintain pressure on the bar? (As if it is "balanced", once you initiate the turn, you shouldn't have to maintain any pressure to continue at that radius.)

 

 

I understand and agree with your explanations: what I tired to say is that finding a balancing lean angle is the last step of the sequence: you decide radius of turn and speed and the required lean angle will follow, rather than the other way around.

 

The frontal contact patch may be the link of a chain reaction, but not the reason for the bike standing up while accelerating: a wheelie under acceleration tends to run wide as well.

 

Rolling on two or just one wheel, the principle is the same: for the same radius of turn, more speed increases centripetal acceleration and vice verse.

 

That centripetal acceleration (and an apparent force that draws any rotating body away from the center of rotation, caused by the inertia of the body) is applied to the center of mass.

 

Four, two or just one contact patches is all we have to resist that apparent force and to continue following a curve.

 

What brings the lean into this is the fact that there is certain distance or height between the center of mass and the contact patch(s).

 

A couple of opposite forces separated by certain distance always create a torque.

 

That torque would make the bike tip over the external side of the turn.

 

The trick that we use to prevent that from happening is to lean the bike toward the internal side of the turn until we find a new balance.

 

That is the type of balance to which I referred in my previous post: a balance of lateral forces and torques.

 

The tool that we have to induce and find that lean angle is the counter-steering.

 

Just like 90 degrees is the only angle that balances the bike vertically (while moving along a straight line), only one specific lean angle will correspond to balancing the dynamic lateral forces introduced by the inertia of bike plus rider while describing a circular line.

 

A locked steering will allow you to sort any combination of radius/speed; however, once the magic balance is achieved, if you accelerate (or slow down), your bike will fall outward (or inward) as you cannot re-adjust your lean angle (and re-balance) via counter-steering.

 

The steering balance that you mentioned is another thing: some bikes are under-steering (tend to turn wide and you have to keep pressure on the outside handle), some are neutral and some are over-steering (dangerously tend to tighten the line by themselves, reason for which you have to keep pressure on the inside handle).

 

Those tendencies are determined by the geometry of the bike and the steering and by the profile of the tires.

 

 

[mazur]

Learned something fun the other day which may have contributed to my low side.

 

I found the build thread to my bike made by the original owner on the SV forums (http://www.svrider.com/forum/showthread.php?t=121455)%C2'> have learned that my tires are 6 years old from time of manufacture (checked the tire side wall) and 4.5 years old from time of purchase and have roughly 10k miles on them which includes at least 6 track days.

:eek::shifty::confused2:

I never suspected old or bad tires due to how much tread they seem to have left.

[mazur]

Wanted to update this thread with another piece of information which may have lead to the incident. Several months ago when I was riding on the street, I decided to stand up on my pegs and lean over forward to look at the front wheels at speed. It didn't look smooth. Almost as if I was absorbing a lot of tiny bumps. Once I got home, I put the bike on the front stand and spun my wheel to check the run-out. To my surprise there was a significant dent in the wheel causing the tire to shift as much as an inch in the area where the wheel damage was.

 

I have never seen this damage before and believe it's probably been like this since I have bought the bike.

 

I'm hypothesizing this may have ended up the biggest contributing factor to my front giving out in the corner since a quick loading and unloading on the contact patch would wreak havoc on the front's gripping ability.

[Hotfoot]

WOW, that is really interesting and it is GREAT that you spotted it! Thanks for posting this update.