Yes , it makes it easy.
If you are a stickler for accuracy, you want to use rolling circumference for your tire measure, as that is true tire measure.
{Some guys do 10 revs and then divide to get a better average]
Use a full tank of gas and normal tire pressure. Measure the ground distance covered by a rev of the tire on the ground and then find Radius for your calculator radius input spec. That will give you exact specs. I use 1K RPM so you then know exact speed per Thousand RPM.. My cars are Euro, so I use the tachs to judge my MPH when traveling. It's just easier then speedo conversion for me.
