Change your rims
On the ”classic bikes” you’ll find varying codes which don’t always match to today’s ones e.g.
“2 3/4 x 18” or “2.75 x 18”
2.50 = nominal tire width in inches
18 = nominal fixing diameter of rim in inches
The tire ”size” is nowadays defined by a code found on the side e.g.
120/70 R 17 M/C 58 H
120 = nominal tire width in millimeters
70 = nominal ratio (ratio between height / width in percentage: i.e 70% of 120=84mm)
R = it reflects the kind of tire, here it means radius
17 = nominal rim fixing diameter in inches
M/C = motorcycle
58 = load index
H = max. speed index (in this case upto 210 km/h).
Other eventual elements found on tire could be ”DOT” (Department of transport USA e.g. American homologation), four figures referring to production date (week/year), an arrow denotes wheel rotation etc..
A rim is universaly identifiable if you know:
- raw material (steel,alloy, etc.)
- surface treatments (painting, chrome plating, anodize etc..)
- section type (UNI, AS, FS, WO, MT, WM..)
- section (in inches)
- diameter (in inches)
- number, position, diameter of holes and bulges
- punching characteristics (English/ Italian)
- punching degrees (based on wheel hub)
- valve hole
- hub sort and size
To measure offset, place the wheel (hub side) on a level surface and measure from surfave to rim’s outer edge; add half of the rim width.