Tire Basics and Information

[GotTorque?]

Here is some basic information I put together about Wheels and Tires.  I will add to it whenever I see something.

If you have anything you'd like me to add, please PM me and I'll put something together! 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


About Tires (i.e. they’re not just round and black):
I would propose that your tires are the most important part of your car.  You have all those parts contributing to power and handling, but the only thing that can connect the car and the ground and transmit all the acceleration, braking, and cornering forces are your tires.

The amount of contact area between your tires and the ground, for many cars, can fit on an 8.5X11 sheet of paper.  That’s not a lot to hold you to the road if you think about it.

Your total contact area is a function of tire pressure and vehicle weight.

Tire Sizes:
Passenger and light truck tires have the following  size designation:

For example, we have a complete tire size: P245/45R17  95W

The ‘P’ indicates that the tire is primarily intended for use on a ‘Passenger’ vehicle.  LT denotes a tire primarily intended for use on a ‘Light Truck’ vehicle.  T stands for ‘Temporary Use Only’.  This prefix letter (s) indicate the service conditions as part of the T&RA (Tire and Rim Assoc- based in Ohio) size designations.  It's purpose is to differentiate between service types to give you the different load and inflation conditions.

The ‘245’ is the tire SECTION WIDTH, in millimeters.  To convert this width to inches, just divide the number by 25.4

The ‘45’ is the ASPECT RATIO, in percent.  This is the height of the tire section divided by the width.  The higher this percentage, the taller the sidewall.

The ‘R’ denotes this is a radial tire.

The ‘17’ is the nominal RIM DIAMETER, in inches

The '95' is the LOAD RATING

and 'W' is the SPEED RATING

Rim Size:  Rim sizing is marked using the rim diameter, radius, and contour.  Ex. 17X9J is a rim that has a 17 inch radius, an 9 inch rim width and a J- contour.

To fit a tire to the correct rim width, consult the tire manufacturer or a tire dealer.


Speed Ratings:

Letter
Designation    Speed
                      (mph)    
M                    81   
N                    87   
P                    93   
Q                    99   
R                   106   
S                   112   
T                   118   
U                   124   
H                   130   
V*(VR)          149   
W**(ZR)        168   
Y**(ZR)         186


Tire Inflation Pressure:
One of the most important factors in running tires safely and effectively is proper tire inflation pressure.  You should check your inflation pressure once a month, or every two to three fuel fillups. 

Improper tire inflation can lead to severe internal tire damage or even failure or rapid wear.

The amount of inflation pressure your tires should have is usually located on a sticker in the door frame, owners manual or glove box.  This number is the ‘cold inflation pressure’.  As your tire operates, the air heats up and the pressure will increase.  It is important to check the pressure before the air heats up.

Also, when buying new tires, spend the extra couple bucks and get new valve stems.  This can save you lots of money and hassle down the road- old valve stems can develop slow leaks and slowly deflate your tires.



For more tire information, check out http://www.tiresafety.com/ or http://www.nhtsa.dot.gov/cars/rules/TireSafety/ridesonit/brochure.html  These are very good resources on tire care.

[GotTorque?]

Radial vs. Bias Ply Tire Construction

Radial Tires: Radial tires have an innerliner that takes the place of an innertube, blocking moisture and retaining air, a layer of rubber coated cords (usually polyester) stretching from one steel bead ring to the other, two layers of rubber coated steel cord (at opposite angles), and tread compound.  Most of the times the tires will have some type of nylon cap under the tread.  There are many different rubber and polymer compounds in tires, from the sidewall to the innerliner to the tread.



Bias-Ply: Instead of having radial body ply layers, these tires have diagonal layers of rubber coated fabric (usually nylon) and often do not have steel belts under the tread. 

Here's a picture that shows the basic differences between the two: