NOTE ON TIRE SIZES -

NOTE ON TIRE SIZES - The standard formula may not work for bike tires....

After installing a Metzeler 200/60-16 tire on the rear of my VTX I tried to set my Sigma digital speedometer² on my VTX using this formula...

(tire width x .profile) x 2 then divide by 25.4 mm per inch plus wheel diameter = total height in inches
or
200 x .60 = 120 | 120 x 2 = 240 | 240 / 25.4 = 9.44 | 9.44 + 16 = 25.44 inches total height

Total height from formula above would be the diameter then x 3.14 for circumference. However, the sigma readings were way off when I rode her so I measured the tire with a tape. The formula for a Metzeler 200/60 - 16 yields 79.9 inches (2029mm) for circumference, but the measured circumference of the tire is actually 81.39 inches (2067mm). Using the measured 2067mm for the sigma gives dead on readings as checked by radar. Wazznt able to accurately measure the diameter since the tire is mounted but math reveals the formula should give 25.44 inches (646mm) as diameter and the actual measured circ would yield 25.92 inches (658mm) (81.39 / 3.14) as diameter.

I was finally able to measure a new mounted Avon 180/70 x 16 as 80.8 inches (2054mm) while the formula yields 25.92 inches as diameter and 81.39 (2067) as circumference. However, the Metz 200 is a little pinched on the five inch rim which causes the increased height. Measured width of the Metz 200 on this rim is 7.625 inches (193.67mm) while the Avon mounted measures 7.25 inches (184.15mm).

Metzeler 200/60-16	Diameter	Cicumference	Width
by formula	~~25.44in (646mm)~~	~~79.90in (2029mm)~~	7.87in (200mm)
as measured	25.92in (658.2mm)	81.39in (2067mm)	7.625in (193.67mm)
.	.	.	.
Avon 180/70-16	Diameter	Cicumference	Width
by formula	~~25.92in (658.2mm)~~	~~81.39in (2067mm)~~	7.08in (180mm)
as measured	25.75in (654.1mm)	80.8 in (2054mm)	7.25 in (184.15mm)

Metzeler also reports that the tread depth on the 200 tire is 6.5mm while I was able to measure variance from 4.8mm at the outer edge to the deepest which is 5.4mm.