The main difference between MH90-21 and 90/90-21 cruiser tires is their size. An MH90-21 tire is the same size as an 80/90-21 tire, which means it is 10mm narrower than the 90/90-21 tire.
The sidewall of an MH90-21 tire is also slightly shorter than that of a 90/90-21 tire, with a height of 90% of 80mm, compared to 90% of 90mm for the 90/90-21 tire1.
The aspect ratio of a tire is the ratio of the height of the sidewall to the width of the tire. For example, an MH tire with a width of 80mm and an aspect ratio of 90% would have a sidewall height of 72mm.
In contrast, a 90/90-21 tire with a width of 90mm and an aspect ratio of 90% would have a sidewall height of 81mm.
In terms of diameter, a 90/90-21 tire is 0.71 inches (18mm) larger than an 80/90-21 tire. This difference in diameter results in a 2.6% difference in speedometer reading.
It is important to note that mixing brands of tires is generally okay, but it is recommended to avoid mixing different sizes or aspect ratios.
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