Only tire dealers (not manufacturers) will recommend tires larger than stock, because they are more expensive, or they have in-stock they want to move. They don’t give better performance. And as an added benefit fo dealers, they won’t last as long, either, requiring more frequent replacement.
550 has a narrow rim, 1.85 inches. Wide tread and narrow mount point pinches the tire where it mounts, resulting in a steep sidewall angle, that allows the tread patch to shift sideways, and makes the bike squirm about in corners. Not good. To overcome this condition, the tire pressure must be increased to add sidewall support. But, over pressure forces the tread crown to balloon, causing the center wear faster and flat spot the crown. The resulting geometry forces the rider to add more and more counter steer when leaned over as the tire progressively wear.s. You lose completely the neutral steering characteristics of the CB550. As you can’t normally find the actual stock 3.75x18, you can order a 4.00x18 for your bike, for a pretty good match for the rim. And, dealers will do this if you insist.
When you buy tires, make certain the maker specifies proper fitment to your rim width, in order for the tire to perform as the tire maker has designed it.
Also, be aware that stock size inch size tires were 95%-100% aspect ratio. Metrics in equivalent width measurements will only be 90% aspect ratio, resulting in less overall tire height, that the original bike geometry was not designed to have.
If you want your bike to look good while parked, get “bigger tires”. If you want your bike to handle well for the duration of tire life, put on the closest to stock size you can find.
So, I put Metzeler 4.00x18 on my 550s, with a 3.25x 19 front. You can ride them and steer with body lean, hands off bars. Not that I recommend you do that. But, riding is far less fatiguing with a bike that handles that way.
Cheers,
