Changing Road Camber: Why the feedback from your handlebar grips seems to change?

[Motofool]

Copied from
http://www.soundrider.com/archive/sa...g_unglued.aspx

......... But you may have noticed that sometimes the bike seems to hold a lean with very little pressure on the low grip, and sometimes you've got to push hard on the low grip, or even pull on the low grip to maintain the same lean angle. What's going on? Why isn't steering effort the same all the time?

Part of the answer is road camber, the slant of the road in curves. Some roads slant toward the curve (positive camber), some slant away from the curve ("off-camber") Consider a bike leaned over to the same angle in three different curves, one with positive camber, one with the pavement level, and one off-camber. Notice that the lean angle of the bikes is the same in all three turns.



In a positive-camber turn, steering should feel very neutral. In a level turn, you may have to push on the low grip to maintain the same curving line. In the off-camber curve, a much stronger push on the low grip will be needed to hold the same line.)

In the positive-camber turn, the contact ring will be close to the bike centerline, so side drag from the tire will be minimal, and steering should feel very neutral. In a level turn, there will be a moderate amount of offset drag, requiring more push on the low grip to maintain the same curving line. In the off-camber curve, the tire will drag much more towards the inside, requiring a much stronger push on the low grip to hold the same line.

If you think about how roads snake up and down hills and around corners, it should be obvious that road camber is constantly changing. Even on a straight road, the surface may stagger from a left slant to a right slant, and back again. Most of those twisty two-lane roads we like to ride have a crowned center to allow rainwater to run off, so where you position the bike in the lane makes a difference in the camber under your tires at the moment. If you follow our suggested "delayed apex" line, your tires will cross different cambers at different parts of the curve. That helps explain why the feedback from your handlebar grips seems to change from one moment to the next.

Back in the "good old days", road camber didn't have as much effect, because those old round-profile motorcycle tires didn't cause as much of a sideways shift in the position of the contact ring as the bike leaned over. There can't be much side drag on a 2.75-18": or 3.25-19" tire. Dunlop even designed a "Trigonic" front tire that had a triangular cross section more like a V than an O. The idea was to have maximum tire contact with the bike leaned over. But one result was that the contact ring remained close to the bike centerline right up to about 40 or 45-degree lean angles. And with the harder rubber compounds available in those days, riders had to be pretty nervy to lean the bike over that far. Those few riders who were adequately nervy discovered that when the tire suddenly made full contact on the flattish side of it's tread, a bike could make some surprising changes of direction, or produce some scary wobbles.

[Alex]

Good info.

[Triple Jim]

Did you say off-camber turn?

(My DT100 on the supermoto track)

[SLOWn60]

^^^ That's not off camber, Jim. That's off line!

[Triple Jim]

Oh, I'm off line for sure, but the fence posts are vertical... it's extremely off camber. That photo was taken on my 1st or 2nd lap on that track, which is the kart/supermoto track at VIR.