Odd Steering

V

Vince

Hero member
During a discussion on a ride the other day,we were taking suspension and I mentioned that when I turned the bars on my Pantah from full lock to full lock at a standstill with me on it I could feel the bike rise and fall. Full lock had it down and straight ahead had it at its highest.At a guess, it feels like maybe 20mm. It's a very odd feeling, evenly low either side and high in the straight-ahead position. My Laverda doesn't do this, neither does my Huskies. I haven't felt this on any other bike that I can remember. Anyone else found this on another bike? It almost feels like wheel flop that racked out choppers can exhibit, bike steers ok. Fork still is as stiff as hell re suspension.
 
Wouldn't that be because the tyre contact point moves from the centre, the highest point, to an off-centre point, which is lower?    Depending on the tyre profile, the change would be more or less noticeable.
 
I have found this phenomena (the front drops really something 20mm) on my small trial bike, but only condition in where I found it harmful is if I try to ride under 5km/h without hands. On that condition it can force the steering to either side. On any higher speeds the steering centers very well.
 
I would expect the front contact patch to not move with the bike staying vertical and stationary. Moving the bars at speed causes the tip in thing and the bike to bank over, countersteering effect, but not stationary and the bike held vertical. As I said I have never felt it on another bike, even slow steering Bevels with huge rack and trail, I think from memory. Just did it in the shes, closer to 10mm but still this up and down feeling through the bars.
 
All bikes do that. It's simply because the steering axis isn't vertical. You just haven't noticed it on your other bikes.

Sometimes the key to picturing this sort of thing in your mind is to imagine the extreme case of the forks and steering axis being horizontal. As you turn the steering, the centre of the wheel will lift up and over the contact point.

OK, I know the steering axis isn't horizontal, but being at an angle, it has a horizontal component.
 
I get the horizontal bit, that's why I described it like a chopper. Maybe I have some notchiness in the steering head bearings, it sits on the front wheel on the centre stand. I will jack the front and give it a feel.
 
Dellortoman said:
All bikes do that. It's simply because the steering axis isn't vertical. You just haven't noticed it on your other bikes.

Sometimes the key to picturing this sort of thing in your mind is to imagine the extreme case of the forks and steering axis being horizontal. As you turn the steering, the centre of the wheel will lift up and over the contact point.

OK, I know the steering axis isn't horizontal, but being at an angle, it has a horizontal component.
Click to expand...

+1

The contact point of the front tyre shifts as the forks are turned , moving forward and laterally towards the direction of turn which brings the centre point of the front wheel (the axle) lower.

The greater the fork angle deviates from vertical the greater the effect.
 
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