Tech Info About Wheels And Tires

Get answers to your technical questions about wheels and tires

Tech Info About Wheels

This refers to the opening in the back of the wheel that centers the wheel on the hub of the car. Since most wheels are mass produced, they have a large centerbore to accommodate different vehicles. If there is a vibration problem, it is recommended that you use hubcentric rings. Hub rings are hard plastic rings that link the wheel to the vehicle. This centers the wheel and makes your wheel hubcentric. Without hub rings it is possible to get vibrations even if the wheel and tire package is completely balanced.

The wheel offset is the distance from the hub mounting surface to the centerline of the wheel. There are three types of offsets.

Positive Offset

A positive offset means the mounting surface of the wheel is positioned in front of the true centerline of the wheel. Most factory rims will have this type of offset.

Zero Offset

When the hub mounting surface is centered within the rim, it is known as a zero offset.

Negative Offset

If the hub mounting surface is on the brake side of the center line of the rim, it is considered a negative offset or "deep dish".

A wheel's bolt-circle-diameter is the diameter of an imaginary circle drawn through the center of the wheel's mounting-bolt holes. Bolt patterns vary by vehicle make and model.

If the pattern has an even number of mounting holes (four, six or eight lugs) simply measure from the center of one stud hole directly across the center of the wheel to the center of an opposite stud hole.

With a five-lug pattern, measure from the center of one stud hole to the center of the farthest stud hole, skipping the adjacent hole. The resulting measurement is slightly smaller than the actual bolt-circle diameter.

For example, a vehicle with a bolt pattern of (5 x 120) means this vehicle's hub has five bolts or lugs, which measure 120 millimeters apart from one another diagonally. Below is a chart on how to measure bolt patterns. Wheelfire's fitment program calculates this for you.

Four Lug
Five Lug
Six Lug

Wheelfire has pioneered a fitment program that ensures a 100% proper fit for your vehicle. Our staff is constantly at work making sure wheel specifications are compatible with your vehicle. If you have any upgraded brakes or suspensions please contact our staff before you order.

Plus sizing your wheel and tire package can enhance vehicle performance and looks by allowing fitment of larger diameter rims and lower profile tires. If you make plus sizing changes, keep the overall tire diameter within 3% of the original equipment. Exceeding 3% can lead to a number of problems.

Protect your investment by keeping your wheels clean at all times. Dust or dirt sitting on your wheels might destroy the finish. Always wait until your wheels are cool before cleaning them. Never use steam cleaners or automatic car washes; they can damage your wheels. The best wheel cleaning product is mild soap. Clean one wheel at a time and rinse immediately to avoid soap scum buildup. After the wheels are clean and dry apply a very light coat of wheel wax to protect your wheels from the elements.

It's important to torque the lugs on your wheels properly. The best way to torque your wheels is by hand, using a torque wrench. Wheels are frequently over-torqued onto a vehicle's hub bore. Over-torquing can lead to brake problems or cause the lugs to break off the wheel. Your owner's manual contains the optimal torque specifications for your vehicle. Always re-torque after your first 50 miles.

Most alloy wheels are made in one-, two- or three-piece construction types. One-piece wheels are made in a mold as a single piece of metal. Two-piece wheels are made of separate center and barrel pieces that are welded or bolted together. Three-piece wheels are made of three separate pieces bolted together.

The most common methods of wheel manufacturing are: Forging, Low pressure Casting and Counter Pressure Casting.


This is the process of forcing a solid billet of aluminum between the forging dies under an extreme amount of pressure. This creates a finished product that is very dense, very strong and therefore very light.

Low Pressure Casting

This is the most common form of rim manufacturing. Liquid metal is poured into a mold and allowed to harden until the finished wheel is cool enough to be taken out of the casting.

Counter Pressure Casting

This method actually sucks the metal into a mold using a vacuum. This reduces impurities making the wheel much stronger than a low pressure cast rim.

Tech Info About Tires

Speed rating is a letter that indicates the maximum speed capability of a tire. In Europe, speed ratings were originally developed to help owners of high performance sports cars choose replacement tires designed to match the speed capabilities of their vehicles. The speed rating of any tire is a measurement of the top safe speed the tire can carry a load under specified conditions. It is also a suggestion of how the tire will handle at lesser speeds. A higher rated tire will give you better traction and improved steering response.

Below is a listing of common speed ratings:
  • Q = 99 MPH, 160km/h
  • S = 112 MPH, 180km/h
  • T = 118 MPH, 190km/h
  • U = 124 MPH, 200km/h
  • H = 130 MPH, 210km/h
  • V = 149 MPH, 240km/h
  • Z = 149 MPH, 240km/h and over
  • W = 168 MPH, 270km/h
  • Y = 186 MPH, 300km/h

It is important to know how to read the side of a tire. For example P225/50R17 89W

  • P = Passenger Car Tire
  • 225 = Section Width in Millimeters
  • 50 = Aspect Ratio
  • R = Radial Construction
  • 17 = Rim Diameter in Inches
  • 89= Load index
  • W = speed rating

The load index for any tire indicates the maximum weight that each tire is able to sustain.

Load Index Pounds Kilograms
60 551 250
61 567 257
62 584 265
63 600 272
64 617 280
65 639 290
66 662 300
67 677 307
68 695 315
69 717 325
70 739 335
71 761 345
72 783 355
73 805 365
74 827 375
75 853 387
76 882 400
77 908 412
78 937 425
79 964 437
80 990 450
81 1018 462
82 1047 475
83 1074 487
84 1102 500
85 1135 515
86 1168 530
87 1201 545
88 1234 560
89 1278 580
90 1323 600
91 1356 615
92 1389 630
93 1433 650
94 1477 670
95 1521 690
96 1565 710
97 1609 730
98 1653 750
99 1708 775
100 1764 800
101 1819 825
102 1874 850
103 1929 875
104 1984 900
105 2039 925
106 2095 950
107 2149 975
108 2205 1000
109 2271 1030
110 2337 1060
111 2403 1090
112 2469 1120
113 2535 1150
114 2601 1180
115 2679 1215
116 2750 1250
117 2833 1285
118 2911 1320
119 2999 1360
120 3080 1400

The best possible tire performance requires proper tire inflation. Tire pressure can vary over time due to many factors such as climate, regular air loss, and your driving style. To maintain proper inflation, you should check your tires at least once a month. Under and over inflation of tires can lead to early or uneven wear, traction problems, and possible tire failure.

The best place to find proper tire pressure is in your owner's manual. Never inflate your tires to the maximum PSI, it can cause serious damage. Remember to check your tire pressure monthly.

The Uniform Tire Quality Grading System (UTQGS) is a tire information system that provides buyers with information on three categories:

  • Treadwear
  • Traction
  • Temperature

Each tire manufacturer performs its own tests in these areas, following government prescribed test procedures. Each manufacturer then assigns grades that are branded on the tire. This is known as the Uniform Tire Quality Grade Labeling (UTQGL).


Treadwear grades typically range from 60 to over 500, in twenty point increments. It's important to remember that the actual life of any tire is determined by the road surface quality, driving habits, inflation, wheel alignment and the rotation it experiences. To receive a treadwear grade, a tire is tested under controlled conditions on a government prescribed test course, which does not necessarily simulate the actual application for which a given tire is designed to perform. As a result of these test parameters, there is no reliable way to assign miles of wear to treadwear grade points.

Treadwear ratings are determined on a 400 mile government test course covering specified sections of public roads near San Angelo, Texas. A group of not more than four test vehicles travels the course in a convoy so that all tires experience the same conditions. Tread groove depths of the tires being tested are measured after each 800 miles. The same procedure is followed for a set of control or "course monitoring tires". Upon completion of the 7200 mile test, the rating results of both tests are compared, and the tires being tested are assigned a treadwear rating by the tire manufacturer.

The best way to use treadwear ratings when selling tires is to compare one rating to another. For instance, a tire with a treadwear grade of 400 might be expected to last twice as long as a tire that has a grade of 200.


Traction grades indicate the measurement of a tire's ability to stop a car in straight-ahead motion on a wet test surface pavement. It does not measure straight-ahead acceleration. It's important to remember that traction rating tests are performed only for straight-ahead sliding on concrete and asphalt surfaces that have a specified degree of wetting that simulates most road surfaces in a rainstorm. The ratings that result from these tests may not apply to cornering traction or peak values of straight-ahead braking those experienced in non-skid braking tests. Traction grades range from "A" to "C", with "A" being the highest attainable grade.

Traction ratings are established on government maintained skid pads. Twenty measurements are taken with an industry standard control tire on an asphalt surface and averaged. The same numbers of measurements are made on a concrete surface. Corresponding measurements are then made on the tires being tested. Once the results of the tests are compared, traction ratings based on government prescribed coefficient levels are assigned to the tires that were tested.


Temperature grades also range from "A" to "C", with A being the highest. Temperature grades represent a properly maintained tire's ability to dissipate heat under controlled indoor test wheel conditions.

Temperature ratings are determined by running tires on an indoor roadwheel test under specified conditions. Successive 30 minute runs are made in 5 mph increments starting at 75 mph and continuing until the tire fails. A tire is graded from "A" to "C", with "A" being the highest.

Some of the most common causes of noise and vibration problems (There could be others):

  • Tire and wheel out of balance
  • No hub centric rings on aftermarket wheels
  • Incorrect hardware for aftermarket wheels
  • Irregular tire wear
  • Rim is damaged
  • Tire is damaged

Do not ignore pulling or vibration. If you have this problem have a professional inspect the issue. provides users the latest technology available for mounting and balancing your wheel and tire packages. We use the top-of-the-line Hunter TC3500 tire changer to insure proper mounting. We also Road Force test and balance your wheels with Hunter's state-of-the-art GSP9700 to measure radial and lateral tire forces.