Sorry for the delay in responding, work and family pressures are high at the moment.
I don't believe string lining the rear wheel is a chain issue, the possible misalignment is too small to have an impact on the chain. I believe it is only a handling issue.
Nice pickup Hub, and in your opening question too! "Impressive, Obi-wan!" I must confess that I've had the same thoughts about bump-steer, being up on one side and down on the other, but I've not been able to detect that difference.
I've discovered over time that there are three things that upset the handling resulting in bump steer.
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low tyre pressures
wrong tyre profile
misaligned wheels
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The last can be caused by either the rear wheel being misaligned as a result of chain adjustment, or the front wheel is misaligned due to bent or poorly installed forks. Either way the result is the same, when pointing in the same direction, the two wheels are not on the same front-to-rear axis. When misaligned, the direction of the rear is fixed, so the direction of the front is adjusted (by turning the bars) and the bike goes where the rider wants. If the rear is of-axis then it is sending the bike slightly to the right or left and the front is adjusted accordingly. These are minor measures and mostly imperceptible in a straight line, but I notice them when leaning and they are exaggerated by uneven surfaces mid turn.
Others have mentioned that the ZX handles like a barge when pressures get below 40psi. I agree. The same feeling is induced by a rear profile that is too wide or too flat; it is also induced my misalignment.
I can't describe in words what I mind's eye sees; there needs to be a balance between the vertical forces at play. Weight is pushing down through the centre of of the bike at the same angle as the bike. The ground pushes back through the centre of the contact patch of the two tyres. If the rear contact patch is not aligned with the front then both front and rear will be off centre, where centre is the line described by the centre of gravity and the direction of the bike.
I believe that the imbalance in vertical forces resulting from the misalignment is the reason for the barge like feeling.
When the rear contact patch is too wide (low pressure or wrong profile) the vertical forces on the front are correct and the bike wants to turn-in in response to the riders input, the rear forces are not aligned and the rear resists the lean. The front wants to lean and therefore turn while the rear wants the bike to stand up resulting in that familiar barge feeling.
I find that when I get those 3 elements right, the handling transforms; the wheels are aligned with the vector of the bike (CoG+direction), the vertical forces are balanced and the bike feels like it 'falls' into the corner and needs no further rider input to stay at the chosen lean angle and further, requires the rider to stand it back up again. That's when I think the bike feels balanced.
Hub, I hope I addressed your critique. I enjoy your challenges, keeps me on my toes knowing you are going to review my comments with a ruler and whack me over the knuckles when I dribble some BS. But I don't think I understood you comments about 'lift angle'
Your move...
08 sapphire