Came across this write up about tire size, thought it was very well written:
"Recently, I became very curious about the differences and subsequent effects on handling, between the 3 most common sizes of tire available today - 180/55, 190/55 and the 190/50; when mounted on a 6 inch rim.
After much consultation, it became obvious that there were two schools of thought - The pro-180s, and the pro-190s.
I decided to dive into the Internet and other resources to find out as much as I could, so that I could form an educated opinion for myself.
For those that are not aware:
6 inch rear rims are typically found on ALL late model 1000s
5.5 inch rear rims are typically found on ALL late model 600s and some early model 1000s.
If you are not sure, then whip out your tape measure and find out for yourself, you lazy git!
I found this very revealing picture while researching about the pros & cons of a 180/55 tire versus a 190/50 & 190/55, on a 6 inch rim.
What I found validated what some of my most trusted resources divulged to me.
Firstly, if you compare the 180/55 with the 190/50, you will notice that the center of the 190/50 is very flat, this gives the 190/50 heavier steering from vertical. The 180/55 has a much more pointed profile, giving it quicker steering. (True)
It is a popular belief that 190/50s are the original fitment size on most modern 1000s from manufacturers, as they put down a bigger contact patch just off the center of the tread, making it slightly safer for a ham-fisted “newbie” riders. However, this has never been officially acknowledged.
As for contact patch at full lean, the 190/50 may well have less of it than a 180/55, because of the way the 190/50 has to curve around the edges near the end of the tire. The 180/55 gives an almost flat contact patch on each side of the tire, due to the taller profile that makes the shoulders “stick out”, giving it it’s typical “triangulated” shape, which is also steeper in terms of angle.
But when comparing the profiles of the 180/55 and the 190/55, I was surprised to see that they were identical! They both have exactly the same profiles. The only difference is that the 190/55 is uniformly taller than the 180/55 all around. So, it may be correct to say that the 190/55 is a copy of the 180/55 with a little bit more rubber across the whole cross section of the tire, to deal with “drive grip”.
Interestingly, the edges of the tire end at almost the same spot for the 180/55 and the 190/55, which in lay-man speak, may indicate that both tires are probably capable of the same maximum lean angle. This may dispel the myth that 180/55s on a 6 inch rim may not allow you to lean over as far as a 190/55.
The only variable here would be the side wall height, how that height contributes to the stiffness and how that stiffness translates to grip.
These are the heights of each size of tire from tallest to shortest:
(Note: Actual measurements may differ from brand to brand)
Ride height is the width of the tire (eg:190), multiplied by the aspect ratio(eg: 55, which is a percentage of the width.)
Formula: For a 190/55 tire, 190mm x 55% = 104.5mm
190/55 104.5 mm
180/55 99 mm
190/50 95 mm
Surprisingly, the 190/50 is the shortest tire among the three.
As for adjusting the ride height, there seems to be no hard or fast rule.
National racers around the world adjust the ride height EVERY SINGLE TIME THEY CHANGE TIRE BRANDS OR SIZES. Their reason is that different sizes of tire affect the geometry of the bike, which can make it behave very differently. Different brands of tire may also not be of the same size; even if it says so, on the sidewall. (This is a fact.)
Other industry professionals say that it is not necessary, as the tire has been made for it to work straight out of the box. An example of this would be when a 190/55 is fitted to an R1 Yamaha. The increase in rear ride height would make the bike flick much easier than before, and may well be intended to work as such.
This leaves us in the middle, so; if it feels fine, it may be better not to fix it! Or, ask someone you trust.
Contrary to popular coffeeshop ramblings, a 180/55 is a recommended tire for BOTH 5.5 & 6 inch rims. Dunlop actually supplied 180/55s to a certain magazine when they were performing a group 1000s test. Both are also rated similarly (73W).
However, it is WRONG to put a 190 section tire on a 5.5 inch rim. It distorts the profile and leaves it with a multiple radius.
For ultimate grip, the 190/55 is a sure winner on paper. It has the handling qualities of the 180/55 with more rubber all around to deal with drive.
However, it does give away a little in terms of weight and also changes the geometry of the bike. Anyone that has ever used a 190/55 can vouch that they are obviously huge tires.
Their size proportionately affects acceleration, braking and cornering negatively due to the added weight.
It's the same as fitting heavier rims, since both rims and tires are considered unsprung weight. Unsprung weight is whatever the suspension does not have to support.
The 180/55 also does increase the rear ride height by 4mm, but it is a small change when compared to a 190/55 which raises it by almost a full centimeter!
The trend as it seems now is to create bigger and bigger contact patches for drive grip on the side of the tyre. This can be done in 2 ways:
1. Reducing the rim size, ala MOTOGP.
(17inch to 16.5 inch and maybe even 16 inches in the future.)
Making the rim smaller creates more space for more rubber, especially on the side.
2. Increasing the aspect ratio.
(Popular for production based racing where rim sizes cannot be changed.)
If you researched race tires, you will be able to find 190 size tires available in slicks with aspect ratios of up tp 70% (190/70)!!
The second method is proving very popular with racers around the world."
Faster, faster! Until the thrill of speed overcomes the fear of death! (H.S. Thompson)