My rims are stock. What would you consider stock tires? 3.25-19? 90/90 is the closest equivalent isn't it? Are you telling me that I will feel a difference between a 90/90 and 100/90? When will I feel this exactly, when I'm carving out corners at 75mph? My 77 is more of a mileage eater than any type of racer or show bike. I use it to commute and it does it well.
I did a lot of commuting with the CB550. The widest rear tire I put on those rims in the rear was 120/90 18. Tire salesmen convinced me that wider was better, which suited their profit purposes.
They didn't handle that bad when brand new, but was so squirmy that I had to run higher tire pressures to stiffen the unsupported sidewalls. As the tire wore, it wore mostly in the center, which made the tire lose its radiused tread profile. A new 120 fixed that, but the symptom recurred with mileage, of course. The loss of tread radius meant that one had to push the low bar in turns in order to keep your turn line. This is quite noticeable on freeway on/off ramp sweepers and winding roads. And the more the rear squared off, the more push was required. It is manageable, but, as I learned, unnecessary.
You're right the 90/90 is the closest metric size to 3.25 19. But if you convert that to inch size to metric equivalent 3.25 = 82.55mm/100 percent aspect ratio or 82.5mm and 82.5mm tall, whereas a 90/90 is 90mm wide and 81mm tall.
The 90/90 metric is not terribly bad for the front. But, I've driven 550s with a 100/90 and it was like a truck in comparison. Must push bars for even the slightest turn. Hardly any response to body leaning and none for a head nod.
When I learned that the stock inch size tires were still available, even if they do have to be ordered special, I decided to try those. 3.25 19 front and 4.00 18 rear. I know it should have 3.75 rear. But, not easy to find in a quality tire, like Metzelers. Of course, new tires always feel better when replacing ones worn out, but the neutral handling and utter predictabilty of the bike was completely restored. No need to push or pull bars for turn line stability. You can drive about just with head leaning for many turns and return to straight ahead the same way. Body leaning works, too. No, I don't normally drive hands off bars. But, any hand pressure for turning is mostly unneeded. It doesn't seem like much, but it is far less fatiguing when not fighting the bars. This is the neutral handling the CB550 is famous for. And the 750 works pretty much the same way, except it has a higher CG and more weight, as well. So, not quite a nimble.
During commutes, the bike is just more responsive requiring less focus on getting the bike's tires exactly where you want them on the road. Since using the stock size tires, I haven't squared off the tread of any of the stock size tires, as I can run with the low pressures intended for the bike and still have the sidewalls supported properly.
While I don't think they still have the same tread radius as when brand new, the radius has not changed so much as to make a dramatic change in turning bar pressure needed.
Finally, I worry that tire manufacturers will abandon the inch sizes, to streamline their production costs. Certainly there are less offerings now for inch sizes than in the past, even now. But, if demand evaporates, so will ANY offerings.
Then there won't be any neutral handling 550s anywhere.
Will the bike still roll and drive with metric tires? Yes, of course. Will the bike lose it's unique and pleasant driving character? I believe so. The 550 with proper tires is more like wearing the bike and it becomes a natural extension of what you do with your body. With the metrics, the bike was more in command and your body was just dragged along for the ride, apart from shoulder, arm, and hand pressure. I came to enjoy the former.
Cheers,
