The basic tire codes:
Example: P205/55/R15 80H M+S
P: P is a designation for what kind of vehicle it is made for.
P is passenger car
LT is light truck
ST is special trailer
T is temporary spare (doughnut)
If its not there, assume its a P.
205: This is the tire width.
It is the "nominal width" so basically the widest part, not necessarily the tread width.
55: This is the aspect ratio.
This describes the height of the sidewall as a function of the width.
In the case of this tire, the sidewall height is 205*0.55 = 112.75mm or 55% of 205mm.
R: This describes the construction of the tire.
R is radial, and really the only ones you're interested in.
B is biased belt
D is diagonal bias
15: This is the rim diameter in inches. Pretty straight forward.
80: This number describes how much load the tire can hold at max press.
-A number from 0-279.
-There will be a table online to tell you what load each number corresponds to.
H: This is the speed rating, the fastest safe speed the tire can go.
-Remember your speedometer reads diff speed, not wheel speed. You can exceed this number even if your speedometer doesn't say so, if you're running bigger than stock tires.
-There will be a table online to see what the codes correspond to.
M+S: This is the conditions the tire is good for. Mud and Snow (all season)
-There is the snowflake for winter, and other options too.
You can also determine make and model, production date, max press, etc etc etc. I'll do that later.
Rims:
Rims all have a code on them in seemingly non standard formats...
Example: 5.5 - JJx14 +45
5.5: This number is the rim width in inches.
-Pretty straight forward.
JJ: This is the rim contour.
-This describes the shape of the "spokes", or whatever piece connects the hub to the tire seat.
-If this doesn't match, or work with your car, your caliper may hit the wheel.
14: This is the rim diameter in inches.
+45: This is the rim offset in mm.
-This describes where the surface that touches the hub is relative to the centreline of the wheel.
-A positive offset moves the wheel closer inside the car.
-A negative offset pushes the wheel out.
-Google image this to see what the effects are.
There's lots more... but my study break is over
