Shinko 712 Rear 110/90H 18
Shinko 712 Front 100/90 19
Stock Rims
76 CB550K
Well, there it is. Oversize tire on the front, imo.
From:
http://www.shinkotireusa.com/faq.php
"Is it okay to put wider tires on my motorcycle?
Wider tires should only be installed with the approval of the motorcycle or tire manufacturer. If wider tires are approved for a particular motorcycle, one size designation it is the typical permissible size increase. Be sure to consider clearance for width and diameter, the effect on stability and handling, and whether your rim is wide enough. Always allow for some tire growth, as all tires will increase in size after they have been inflated and ridden on for a few hundred miles."I couldn't find info about rim sizing for their tires on Shinko's web site. But, I think it matters. You will certainly need higher pressures in the front to keep the tire's sidewall stable on the narrow rim and keep the tire crown arched. The Metzler tire in that metric size does allow for fitment onto 1.85 rims, but, it is at the lower limit, and yields a steeper sidewall angle than optimum. You'll need higher pressure than "normal" to compensate. Probably have to experiment with different pressures until you can live with the characteristics.
FYI:
a 100 tire is about (4"x 90%) 3.6 inches tall. The stock 3.25 in. tire is certainly no taller than 3.25 inches.
a 110 tire is about (4.5"x 90%) 4 inches tall. The stock 3.75 in. tire is certainly no taller than 3.75 inches.
The aspect ratio for inch size tires usually about 98% to 100%
The oversize tires have raised the front end and increased the rake somewhat, which would slow the turn rate. (Chopper people like this. Sport bike people, not so much.)
The bigger tire is almost certainly heavier than the stock size tire, so making it turn requires more force.
From experience, I've noted that the 550 is neutral balanced with the stock tire sizes. This allows steering with weight shifting in the seat (or upper body). The steering simply complies with the lean angle, and requires almost no bar pressure for a turn. I find this a wonderful characteristic of the Cb550.
However, when the oversize (120) tire fitted on the rear squared off due to abnormal wear patterns (I'd had to raise the tire pressure to stabilize the steep angle sidewall, thus wearing the center tread faster) one got used to fighting the bars in the turn as it wanted to steer into the turn while leaning over. And, without counter bar pressure you couldn't hold your desired line in the corners.
Perhaps, this is what you are noticing, going from a worn rear tire to one that has the proper crown shape. You previously had to counter steer in the turns, and it became "normal" for you as you adapted for it. If the new tires have restored neutral or closer to neutral handling, you may have to adapt to the new tires with more weight shift (even if only head movement) to establish your desired turn line and not fight the expected bar counter steer you needed with the worn tires.
Just some thoughts...
