Here are a few charts you may find handy.
Why not print this page off and keep for future reference?
http://barebones.net/charts.htm

 
SPEED RATINGS
Type

Max Design/Test Speed

  MPH KM/H
J Rating 62 100
L Rating 75 120
M Rating 81 130
P Rating 93 150
S Rating 112 180
H Rating 130 210
V Rating 150 240
Z Rating 150+ 240+
NB: HR = H rated radial; VR = V rated radial; ZR = Z rated radial
TIRE PRESSURES
BAR PSI BAR PSI
1.5 22 2.3 33
1.6 23 2.4 34
1.7 24 2.5 36
1.8 26 2.6 37
1.9 28 2.7 39
2.0 29 2.8 40
2.1 30 2.9 42
2.2 32 4.0 44

 

 
TIRE SIZE CONVERSION
Street
Front Tires Rear Tires
Metric Imperial Metric Imperial
80/90 2.50/2.75 110/90 3.75/4.25
90/90 2.75/3.00 120/80 4.50/4.75
100/90 3.25/3.50 120/90 4.50/4.75
120/80 4.25/4.50 130/80 5.00/5.10
120/90 4.25/4.50 140/80 5.50/6.00
130/90 5.00/5.10 150/80 6.00/6.25
    150/90 6.00/6.25

 

TIRE SIZE CONVERSION
Off Road
Front Tires Rear Tires
Metric Imperial Metric Imperial
60/100 2.50/2.75 80/100 2.50/3.60
70/100 2.75/3.00 90/100 3.60/4.10
80/100 3.00/3.25 100/100 4.00/4.10
    110/100 4.00/4.50
    120/100 5.00/5.10