Metric System in Canada

Jebby14 wrote:

DrewE wrote:
Aren't you glad that modern tires are sized using one metric measurement (the tread width), one imperial measurement (the wheel diameter), and one unitless quantity (the aspect ratio)? Otherwise, you'd have to change the tires when you change the air; putting metric air in inch tires would cause all sorts of problems.

Aspect ratio is not unitless its just that a ratio. its the sidewall height based on a percentage of the tires width.

From the point of view of dimensional analysis, it's both dimensionless and unitless. You don't measure the ratio in millimeters (or Newtons or foot-candles), and you wouldn't change the ratio if you decided to measure the tread width and sidewall height in inches rather than millimeters.

Not all dimensionless quantities are unitless; angles are probably the most common example of dimensionless but not unitless measurements. But in this case, a ratio relating one length to another, it indeed is both unitless and dimensionless.