Firestone ANS will tear us apart

I'm swinging for the fences - will these beauties fit on my '81 CB750K?

The rear will, but the front is a 3.50 19, and the closest tire is a 4.00 19. Still not entirely sure what these numbers mean - what can I do to get this beast on my bike?

Note - this post sounds better with Kyuss - Asteroid

Edited to add - most things sound better with Kyuss

Numbers like "3.50" are width of the rim. Numbers like "19" are diameter of the rim.

Front Tire Size Conversions Rear Tire Size Conversions
Metric Alpha Inch Metric Alpha Inch
80/90 MH90 2.50/2.75 110/90 MP85 4.00/4.75
90/90 MJ90 2.75/3.00 120/90 MR90 4.50/4.75
100/90 MM90 3.25/3.50 130/80 5.00/5.10
120/80 4.25/4.50 140/80 5.50/6.00
120/90 MR90 4.25/4.50 140/90 MU90 5.50/6.00
130/90 MT90 5.00/5.10 150/80 MV85 6.00/6.25
150/90 MV85 6.00/6.25

Tire Speed Rating Chart
Motorcycle Tire Speed Ratings Max. Design Speed Test Speed
J Type 62 100
N Type 87 140
P Type 94 150
S Type 112 180
H Type 130 210
V Type 149 240
Z Type 149+ 240+

Here is a handy chart real quick
The rims need to be narrower than your tires for safe mounting.

Look for the rim size stamped into your rims, or measure it.

Thanks man, not sure I understand the chart though - what do the different colour boxes (grey, blue) represent and what does STD mean? I might be being a bit dim...

Std size for that rim

Grey box means the tire size on the left fits on the rim size above

Example, gs750 wheel is 16-2.15 so the smallest i can fit is a 3.00-16 and the widest is a 4.00-16
In metric 80-16 to 100-16