# Tire Rack Tech Thread



## [email protected] (Jan 6, 2014)

Tire Dimensions:
The first number is the width of the tire in millimeters, measured from sidewall to sidewall. To convert to inches, divide by 25.4 In the example above, the width is 185mm or 7.28".

The second number is the aspect ratio. This is a ratio of sidewall height to width. In the example above, the tire is 7.28" wide, multiply that by the aspect ratio to find the height of one sidewall. In this case, 185x0.60=111mm or 7.28"x0.60=4.36".

The last number is the diameter of the wheel in inches.

To figure the outside diameter of a tire, take the sidewall height and multiply by 2,(remember that the diameter is made up of 2 sidewalls, the one above the wheel, and the one below the wheel) and add the diameter of the wheel to get your answer.

Example...185/60R14 85H or 185/60HR14

185mm x .60=111mm x 2=222mm + 355.6mm(14")= 577.6mm or 22.74"










Speed Ratings: 
It is important to note that speed ratings only apply to tires that have not been damaged, altered, under-inflated or overloaded. Additionally, most tire manufacturers maintain that a tire that has been cut or punctured no longer retains the tire manufacturer’s original speed rating, even after being repaired. 

In Europe, where selected highways do not have speed limits and high speed driving is permitted, speed ratings were established to match the speed capability of tires with the top speed capabilities of the vehicles to which they are applied. Speed ratings are established in kilometers per hour and subsequently converted to miles per hour (which explains why speed ratings appear established at “odd” mile per hour increments). Despite the tire manufacturer’s ability to manufacturer tires capable of high speeds, none of them recommend the use of their products in excess of legal speed limits.

Speed ratings are based on laboratory tests where the tire is pressed (to reflect its required load) against a large diameter metal drum and run at ever increasing speeds (in 6.2 mph steps in 10 minute increments) until the tire’s required speed has been met. 

Speed Rating - Miles/Hour - Kilometers/Hour - Typical Use 
N=87 MPH, 140km/h, Spare Tires 
P=93 MPH, 150km/h 
Q=99 MPH, 160km/h, Winter, LT Tires 
R=106 MPH, 170km/h, LT Tires 
S=112 MPH, 180km/h 
T=118 MPH, 190km/h 
U=124 MPH, 200km/h 
H=130 MPH, 210km/h, Sport Sedans 
V=149 MPH, 240km/h, Sports Cars 
Z=149 MPH, 240km/h and over, Sports Cars 
W=168 MPH, 270km/h, Exotic Sport Cars 
Y=186 MPH, 300km/h, Exotic Sport Cars 

*Today, the Z-speed rating is the only speed rating that is still branded “within” the tire size, as in P225/50ZR16. All other speed ratings are shown in the tire’s service description.

When Z-speed rated tires were first introduced, they were thought to reflect the highest speed rating that would ever be required. Since that time the automotive industry has found it necessary to add W- and Y-speed ratings (indicated in the tire’s service description) to identify the tires that meet the needs of new vehicles that have extremely high, top speed capabilities. 

While all Z-speed rated tires are capable of speeds of 149 mph and above, prior to the W- and Y-speed ratings were identified in the service, how far above 149 mph was not identified. 

Prior to 1991, the most popular speed ratings were “S,” “H” and “V.” However, while the speed capabilities of S- and H-rated tires still indicate the same speeds as before, the V-speed rating has been modified. Previously a V-speed rated tire with the “V” branded “within” the tire size indicated that the tire was capable of 130+ miles per hour. Today’s new V-speed rated tires are always identified in the tires service description

Tire Rotation:
Tire rotation can be beneficial in several ways. When done at the recommended times, it can preserve balanced handling and traction of the tires and even out tire wear. It can even provide performance advantages. When should tires be rotated ? We recommend that high performance tires be rotated every 3,000 to 5,000 miles, even if they don't show signs of wear. Tire rotation can often be done with oil change intervals while the vehicle is off the ground anyway. Tire rotation helps even out tire wear by allowing each tire to serve in as many of the vehicle's wheel positions as possible. Remember, tire rotation can't correct wear problems due to worn mechanical parts or incorrect inflation pressures. It's also important to check your owner's manual for specific details on what method of tire rotation the vehicle's manufacturer recommends.

While every vehicle is equipped with four tires, usually the tires on the front need to accomplish very different tasks than the rear tires. And the tasks encountered on a front wheel drive car are considerably different than those of a rear wheel drive car. Tire wear experienced on a performance vehicle will usually be more severe than those on a family sedan. Each wheel position can cause different wear rates and different type of tire wear.

While no one likes their tires to wear out, it is actually an advantage when all of the tires on a vehicle wear at the same rate throughout their life. As tire wear reduces tread depth, it allows the tires to respond to the driver's input more quickly and increases dry road performance. Since tire rotation will help all of the vehicle’s tires wear at the same rate, it will keep the tires performing equally on all four corners.

When your tires wear out together you can get a new set of tires, without being forced to buy pairs. If you replace tires in sets you will maintain the original handling balance. And our suppliers are constantly introducing new tires, each of which improves upon their past product's performance. If you replace your tires in sets, it allows you to experience today's technology, instead of being forced to match yesterdays.

On front wheel drive cars, rotate the tires in a forward cross pattern (fig. A) or the alternative X pattern (fig. B) 
On rear wheel or four wheel drive vehicles, rotate the tires in a rearward cross pattern (fig. C) or the alternative X pattern (fig. B) 
If you car has directional wheels or tires, rotate them as shown in fig D. 
If you car has non-directional tires that are a different size from front to rear, rotate them as shown in fig. E. 









































Here is some technical info about after market wheels

Performance benefits:
While many people choose alloy wheels for their looks, there are equally important performance benefits to be derived including...

Reduced Unsprung Weight Compared to Steel Wheels:
This is one of the most critical factors affecting a vehicle's road holding ability. Unsprung weight is that portion of a vehicle that is not supported by the suspension (i.e. wheels, tires and brakes) and therefore most susceptible to road shock and cornering forces. By reducing unsprung weight, alloy wheels provide more precise steering input and improved "turning in" characteristics.

Improved Acceleration and Braking:
By reducing the weight of the vehicle's rotational mass, alloy wheels provide more responsive acceleration and braking.

Added Rigidity:
The added strength of a quality alloy wheel can significantly reduce wheel/tire deflection in cornering. This is particularly critical with an automobile equipped with high performance tires where lateral forces may approach 1.0g.

Increased Brake Cooling:
The metals in alloy wheels are excellent conductors of heat - improving heat dissipation from the brakes - reducing risk of brake fade under demanding conditions. Additionally, alloy wheels can be designed to allow more cooling air to flow over the brakes.

What determines quality?
The Tire Rack’s quality standard for wheels is very high and the manufacturers that we represent in this market understand that we constantly monitor products to ensure that quality products are sold to our customers. But what determines quality? 

Manufacturing Process:
Manufacturing processes and levels of testing are critical to a wheel's structural integrity. (Read more in "Wheel Construction.") International quality standards such as ISO9001, QS9000, TUV of Germany or VIA of Japan, establish important production and quality standards that manufacturers must follow. In addition, dimensional tolerances based on strict, original equipment market standards versus the more “casual” standards allowed for many aftermarket products should be met. Even durability standards for finish are different between the original equipment market and the aftermarket. 

Proper Fit:
An accurate fitment is the difference between good, better and best. Critical wheel dimensions such as width, diameter, offset, center bore, brake clearance, as well as load factor and lug hardware are the basics when it comes to properly fitting aftermarket wheels. Installation also requires a high level of sophistication. Many new vehicles are available with features such as ABS, traction control and other features that create a more difficult environment for installing aftermarket wheels. Stability control systems, run-flat tires, large high performance brake systems and staggered wheel and tire sizes are also factors to be considered when establishing accurate fitments. Wheel manufacturers with product design, research and development teams work to determine proper fitment as part of the manufacturing process. 

Protective Finish:
The type and quality of protective finish on your wheel (as well as proper maintenance) will determine how your wheels look years from now. Check for finish warranties backed by manufacturers with outstanding reputations for quality. 

Reputation and Heritage:
The reputation of a manufacturer is a strong indicator of quality since it is quality upon which a distinguished reputation is built. It takes time to build a positive reputation and a commitment to maintain it is important. And know a wheel company's roots. Many wheel manufacturers first established themselves in the motorsports arena and apply that technological and philosophical foundation to their production of wheels for use on the street. 

The Tire Rack's Commitment to Quality:
The Tire Rack constantly reviews wheel data from new vehicles to be sure that we are aware of the original equipment sizes and packages offered. We physically inspect many of today’s new vehicles and often supply technical data to some of the manufacturers outside the U.S. that may not have access to certain vehicles in our market. For many wheels that we import or represent, we specify certain dimensions that we require to ensure wheel fit and maintain our high quality standards. 

Offset:









The offset of a wheel is the distance from its hub mounting surface to the centerline of the wheel. The offset can be one of three types.

Zero Offset
The hub mounting surface is even with the centerline of the wheel.

Positive
The hub mounting surface is toward the front or wheel side of the wheel. Positive offset wheels are generally found on front wheel drive cars and newer rear drive cars.

Negative
The hub mounting surface is toward the back or brake side of the wheels centerline. "Deep dish" wheels are typically a negative offset.

If the offset of the wheel is not correct for the car, the handling can be adversely affected. When the width of the wheel changes, the offset also changes numerically. If the offset were to stay the same while you added width, the additional width would be split evenly between the inside and outside. For most cars, this won't work correctly. We have test fitted thousands of different vehicles for proper fitment. Our extensive database allows our sales staff to offer you the perfect fit for your vehicle.

Torquing lug hardware:
Proper installation requires that the wheel lug torque be set to the recommended specification for your vehicle. These torque specifications can be found in your vehicle’s shop manual or obtained from your vehicle dealer. Finish tightening the lugs down with an accurate torque wrench. Use a crisscross sequence (shown below) until they have reached their proper torque value. Be careful because if you over torque a wheel, you can strip a lug nut, stretch or break a wheel stud, and cause the wheel, brake rotor and/or brake drum to distort.

NOTE: When installing new wheels you should re-torque them after traveling the first 50 to 100 miles. This is necessary because as the wheels are “breaking in” they may compress slightly allowing their lugs to lose some of their torque. Simply repeat the same torque procedure listed above.









TPMS Facts:

Direct TPMS (Metal Valve Stems for MK6) use a sensor in the wheel/tire to wirelessly relay pressure back to the driver via a display inside the vehicle. Some vehicles have a digital screen that continuously shows all four tire pressures (five if spare has sensor). Others simply flash a "low tire pressure" light on the dash. Additionally, there are two different styles of sensors for a direct system: a valve sensor and a strap/band sensor. Only valve sensors are used on Mitsubishi direct system-equipped vehicles. If you bought an aftermarket SmarTire TPMS, its sensors are held on by a strap around the barrel of the wheel.


Indirect TPMS (Rubber Valve Stems for MK6) systems work in conjunction with the ABS wheel speed sensors that “count” the number of revolutions of each tire. If the right front tire is low (25psi) it will spin faster than the left front tire (35psi). The ABS system will recognize this change and alert the driver with a flashing light and possibly a loud chime. Indirect systems do not affect the fitment of aftermarket wheels.

*More technical info* 

*Wheel search page for ordering*

Tires 

More tire tech 

Tire test results

Tire Rack website for ordering 



Hope this helps

Sonny


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## RBT-Tuned (Dec 24, 2013)

Check your messages Sonny! :thumbup:


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## [email protected] (Jan 6, 2014)

RBT-Tuned said:


> Check your messages Sonny!


Back at you.


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## Jettakent (Nov 2, 2012)

I have been trying to get tire and wheel questions answered forever without sounding too much like a noob! This is a superbly written informative thread. Yes I know it's old, I don't care - it helped me a lot.

Thanks for writing and posting this information.


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## [email protected] (Jan 6, 2014)

Jettakent said:


> I have been trying to get tire and wheel questions answered forever without sounding too much like a noob! This is a superbly written informative thread. Yes I know it's old, I don't care - it helped me a lot.
> 
> Thanks for writing and posting this information.


Glad it was helpful!


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