Been thinking about this for a while and I'm interested to see what others points of view on the subject is. We know that if the swingarm is the conventional two sided one and if the rear axle for chain adjustment isn't at right angles across the swingarm; the front wheel will turn to run parallel to the skewed rear wheel and the frame itself is skewed to the direction of travel, because the wheels aren't in line, only parallel (What we call crabbing).........Yes? So, assume the swingarm is off-centre to the frame (ie, incorrect shimming) but the rear axle is correct at right angles to the swingarm; what is the effect on the front wheel direction? I reckon the frame still runs straight because the rear wheel is straight and the front wheel should be parallel but not in line with the rear. Or does it? If the swingarm is say, too far to the left of the bike, would the front wheel point left or right? And would the rear wheel be dragging to one side with the frame skewed to travel direction? AL
Never considered it before but I would think it would naturally try to align the wheels and so leaving the frame not parallel to the direction of travel and the rear wheel dragging...
It's a 600SS part complete cafe cafe racer built from parts acquired over the years..... The damn bike without a proper fuel tank (gravity fed from a steel can!) and airbox in the way clearly shows that the front wheel is 'steering' left when the bike is going along.......it can be seen from the angle of the fork legs and the yokes in comparison to the frame. We have slackened of the forks several times and bounced etc etc, plus the forks have been checked for straightness (besides, another pair of forks have been tried). The frame was checked for straightness by Motoliner and is AOK. The swingarm was also checked by Motoliner as was a spare and both have been tried. The shimming of the swingarm, my mate says is OK.....but I think it is approx 0.3mm too far to the left....however, I can't see it would make that much difference to the front wheel direction. The rear axle / chain adjustment is correct by measuring from the swingarm spindle to the rear axle. We have even measured the distances betwen the engine frame mounting bolt holes and they seem to be OK. Tyre 'wear' for what little distance has been covered doesn't indicate any rubbing / dragging to one one side.....(but that is only about 5 miles around back roads where Plod doesn't seem to go). However, I feel that the bike drops into a left hand corner easier than it does into a right hand bend (which is kind of obvious considering the front wheel attitude). I'm stumped to be honest.
0.3mm would make bugger-all difference, certainly not noticeable by itself but if several tolerances (frame, forks, swingarm etc.) are out then maybe they add up to something noticeable? How do the wheels align with respect to each other when the steering is 'straight'?...
Perfect alignment......well, as good as it can be, using straightedge and string methods...... .....the moment the bike is rolling above say, 20mph; is when it becomes obvious. One of our colleagues on here has sensibly suggested tweaking the rear axle alignment to see if it will cure it (assuming the chain alignment is still OK), even though that would make the swingarm pivot to rear axle different by possibly up to 2mm.....the left side distance would be the shorter one. That would apply to either swingarm used as well, so it isn't a swingarm fault as I see it.
