Am I correctly understanding tire size?
 

I'm upgrading from 15" to 16" (maybe 17" if I can figure out if it wouldn't look too big, but we'll pretend with a 16" wheel) wheel and I'm going for pretty much the same overall diameter of wheel/tire to maintain speedometer accuracy.

My current tires are 195/65-15. (15 inches = 381 mm) Overall diameter:

381mm + (0.65 * 195mm) = 507.75mm


If my new tires are 205/50-16. (16 inches = 406.4mm) Overall diameter:

406.4mm + (0.50 * 205mm) = 508.9


So in conclusion, with a 205/50-16 on a 16" wheel I won't be increasing the overall diameter by much more than 1mm. Is this right? I want to make sure I get the right size.

Also, as a side note-question, has anyone seen a 6th gen accord with 17's with roughly the same overall diameter? Is there too much wheel? Thanks.

This service is available free online. One is:

Tire Size Calculator - Compare Tire Sizes

Looks like about 1" or 25 mm difference in diameter. Speedometer will read fast by about 3.8%.

good luck

Perfect! Thank you. My diameter calculations were somehow off. Calculator clears it up, and I love the side-by-side view.

EDIT: I screwed up by not taking into consideration BOTH sections of tire. Measuring from one end straight across you'll cross one section of tire, the wheel, and one other section of tire. I should have multiplied by two, but it doesn't matter because the calculator works best.