Tech Center

Learn the basics

Wheels and tires, explained in plain language.

Bolt patterns, centerbore, offset, speed and load ratings, TPMS — the terms you'll see on every product page, and what they actually mean for your car. Bookmark this page, or jump straight to the section you need.

Wheel specs Tire ratings & glossary TPMS guide Storage & care

Wheel specs

Bolt pattern

A vehicle's bolt pattern (or bolt circle) is the diameter of an imaginary circle drawn through the centres of the wheel's lug holes. Most of today's vehicles use 3-, 4-, 5-, 6-, 7- or 8-lug patterns.

Reading it A bolt pattern of 5x120 means a 5-lug pattern on a circle 120 mm in diameter.

Dual bolt pattern

More and more manufacturers build wheels with two bolt patterns, which expands the number of vehicles a wheel fits. A wheel listed as 4x100/114.3, for example, has 8 lug holes and fits both 4x100 mm and 4x114.3 mm vehicles.

Centerbore

The centerbore is the large machined hole in the middle of the wheel, usually hidden by a centre cap. On your factory wheels it's machined to exactly the diameter of your vehicle's hub, so the wheel sits perfectly centred and vibration is minimized.

Hub-centric

Factory wheels: the centerbore matches the hub exactly. Vehicle-specific.

Lug-centric

Most aftermarket wheels: a larger centerbore so one wheel fits many vehicles, leaving a small gap at the hub.

Hub centering rings close the gap Usually plastic or metal, they fill the space between the hub and a larger centerbore, properly centring an aftermarket wheel for a vibration-free drive. We include them in our hardware kits.

Hardware kit

Why do I need a hardware kit with new wheels? Two reasons.

Smaller pilot holes

Most aftermarket wheels have smaller pilot holes than factory wheels, so your original nuts or bolts — and the key that fits them — won't fit inside. Our hardware kit includes the right quantity of nuts or bolts, 4 hub centering rings, 4 valves and a thin-wall socket adapter, so you can always remove a wheel for a flat or a rotation.

Wheel seating

The seat is the contact area between the hardware and the wheel. The three common types are cone (conical), ball (radius) and flat-with-washer. Aftermarket wheels often use a different seat than your factory wheels; a mismatch causes vibration and hardware that loosens over time. We send hardware matched to your new wheels and your vehicle.

Offset

Offset is the distance, in millimetres, between the wheel's hub mounting surface and its centreline. Every wheel falls into one of three brackets.

Positive

The mounting surface sits closer to the face of the wheel. Typical of front-wheel-drive cars and newer rear-wheel-drive cars.

Zero

The mounting surface lines up exactly with the wheel's centreline.

Negative

The mounting surface sits closer to the inner lip, further from the spokes. Common on classic muscle cars and lifted pickups.

Tire ratings

Tire speed rating chart

The letter at the end of a tire size (for example the H in 225/45R17 91H) is the maximum speed the tire is rated to sustain when correctly inflated and loaded.

Tire speed ratings
Rating	Max speed
L	120 km/h	75 mph
M	130 km/h	81 mph
N	140 km/h	87 mph
P	150 km/h	93 mph
Q	160 km/h	99 mph
R	170 km/h	106 mph
S	180 km/h	112 mph
T	190 km/h	118 mph
U	200 km/h	124 mph
H	210 km/h	130 mph
V	240 km/h	149 mph
W	270 km/h	168 mph
Y	300 km/h	186 mph
(Y)	over 300 km/h	over 186 mph
ZR	over 240 km/h	over 149 mph — appears in the size, e.g. 245/40ZR18

Always follow your vehicle manufacturer's recommended speed rating or higher. A tire's speed rating is not a recommendation to drive at that speed.

Tire load rating chart

The load index (the 91 in 225/45R17 91H) is the maximum weight a single tire can carry at its rated pressure. Multiply by four for the set, and never go below the index your vehicle calls for.

Tire load index 75–92
Index	kg	lbs
75	387	853
76	400	882
77	412	908
78	425	937
79	437	963
80	450	992
81	462	1,019
82	475	1,047
83	487	1,074
84	500	1,102
85	515	1,135
86	530	1,168
87	545	1,202
88	560	1,235
89	580	1,279
90	600	1,323
91	615	1,356
92	630	1,389

Tire load index 93–110
Index	kg	lbs
93	650	1,433
94	670	1,477
95	690	1,521
96	710	1,565
97	730	1,609
98	750	1,653
99	775	1,709
100	800	1,764
101	825	1,819
102	850	1,874
103	875	1,929
104	900	1,984
105	925	2,039
106	950	2,094
107	975	2,150
108	1,000	2,205
109	1,030	2,271
110	1,060	2,337

Tire load index 111–126
Index	kg	lbs
111	1,090	2,403
112	1,120	2,469
113	1,150	2,535
114	1,180	2,601
115	1,215	2,679
116	1,250	2,756
117	1,285	2,833
118	1,320	2,910
119	1,360	2,998
120	1,400	3,086
121	1,450	3,197
122	1,500	3,307
123	1,550	3,417
124	1,600	3,527
125	1,650	3,638
126	1,700	3,748

Reading the sidewall

Passenger

225

Section width (mm)

/45

Aspect ratio (%)

Radial

Rim diameter (in)

Load index

Speed rating

Reading a tire size: P225/45R17 91H, broken down.

What's inside a tire: tread, steel belts, body ply, sidewall and bead.

Glossary

The tire terms you'll run into, A to Z.

Aspect ratio: The height of a tire's sidewall expressed as a percentage of its width.
Asymmetric: A tread pattern whose two sides are not identical.
Balance / imbalance: A tire and wheel are balanced when their weight is distributed evenly as they spin. To correct an imbalance, a technician adds small weights to the inside or outside of the wheel.
Blocks: The individual raised rubber segments that make up the tread.
Carcass: The part of the tire that forms the foundation for the tread, belts, bead and sidewall.
Casing: The structure of tire cords locked around the wire beads.
Chafer: A finishing strip of calendered fabric that protects the bead area from the rim.
Compound: The chemical formula of the tread material — mainly rubber, carbon black, plasticizers, curing agents and ozone retardants. Different compounds give different characteristics: heat resistance, traction, treadwear, cut resistance, cold resistance and so on.
DOT: Department of Transportation. The 10-digit code after "DOT" identifies the week and year of manufacture, plus the manufacturer, plant, tire line and size.
Filler: Material that fills the area above the bead between the inner and outer sidewall; in larger form it stiffens the lower sidewall.
Grooves: The circumferential channels between the tread ribs.
Light truck tires: Tires designed for off-road and on/off-road use on sport-utility, small commercial and recreational vehicles.
Load rating: A rating of a tire's load-carrying capacity (letters such as B, C, D) relative to its ply rating.
Low-profile: A tire with a low aspect ratio or series.
M+S: A sidewall marking indicating the tire is approved for mud and snow use by the RMA (Rubber Manufacturers Association).
Metric tire size system: Sizing by section width (mm), aspect ratio, speed category, construction and rim diameter (inches). Example: 185/70SR13.
P-metric system: Sizing by section width (mm), aspect ratio, construction type and rim diameter (inches). Example: P225/45R17.
Ply: A layer of rubber-coated fabric or wire that makes up the casing.
Radial tire: A tire whose casing plies cross the crown at 90 degrees.
Ribs: The parts of the tread pattern formed by grooves running around the tire.
Rolling resistance: The force needed to keep a tire moving at a steady speed. Lower rolling resistance means less energy — and fuel — to keep rolling.
Series: A numerical expression of aspect ratio; for example, 50 series.
Shoulder blocks: Raised tread segments nearest the sidewall.
Sipes: Small slits cut into the tread surface to improve traction.
Staggered: A fitment with larger (usually wider) wheels on the rear than on the front.
Steel belt: A belt material used in radial tires; its stiffness gives good handling and low treadwear.
Stud holes: Small cavities in the tread designed to hold studs for extra traction on snow-covered roads.
Tire profile: The portion of a tire measured as its aspect ratio or series.
Tread blocks: Raised rubber segments on the visible outer part of the tire.
UTQG: Uniform Tire Quality Grade. A government-mandated rating of treadwear, traction and temperature resistance, branded on the sidewall.

TPMS guide

Tire Pressure Monitoring System (TPMS)

A TPMS warns you that one or more tires are significantly under-inflated, which can create unsafe driving conditions. Here's how the systems work, what we sell, and how new sensors get synced to your car.

What we carry

Max TPMS sensors

We're proud to carry Max sensors — among the most popular TPMS brands, with 98.5% vehicle coverage. Their amplified antenna makes them easier and faster to read and program through tires of any size or thickness: up to 40" in diameter and 12-ply F-rated.

Small and lightweight
Shipped pre-programmed to the frequency your vehicle requires
Quick relearn with any BARTEC, ATEQ, MATCO, NAPA or Max sensor tool (see Syncing)

Types of TPMS

Indirect TPMS

Uses the ABS wheel-speed sensors: an under-inflated tire has a smaller diameter, so it turns more times per kilometre than a properly inflated one. It doesn't measure pressure directly — hence "indirect."

Shortcomings: it can't tell you which tire is low; if all four lose pressure at the same rate you won't be warned; false alarms are common on wet or icy roads where a spinning tire looks like a low one; and there's no real-time pressure reading.

Direct TPMS

A sensor mounted inside each wheel measures real-time pressure and sends it to the car's computer. When a tire drops 25% below the manufacturer's recommended pressure, a dashboard light comes on.

Direct sensors also monitor the temperature inside the tire and warn you if it exceeds the manufacturer's limit, helping prevent overheating.

Original vs. universal sensors

Original (OE-style)

Pre-programmed to one vehicle's frequency, so there's a different part number for every vehicle and a retailer must stock many sensors.

Universal

Programmable to any frequency, with the same shape, size and weight regardless of vehicle. Their adaptability and reliability have made them the popular choice.

Programming

Our Max sensors ship pre-programmed to your vehicle's frequency — which is why we ask for your year, make and model when you order. We enter that into our programming machine and your sensors arrive ready to install.

Syncing (the relearn procedure)

Once programmed, your vehicle's computer still has to "learn" the codes of the new sensors. The relearn procedure depends on your year, make and model, and takes one of three forms:

Auto-learning

The vehicle recognizes the new sensors on its own after about 10 minutes of driving between 35 and 100 km/h. A dash light appears after installation and goes out once the sensors are learned. Common on Mercedes, Volkswagen, Ford, Mazda and Hyundai.

Manual relearn

A specific sequence of actions — it may involve the clutch, the ignition, even the horn — outlined in your owner's manual. Often seen on Audi, Mercedes, BMW and Porsche.

Programmed relearn

A dedicated tool (BARTEC, ATEQ, smart-sensor tool) is needed to link the sensors to the vehicle. Most garages have one.

To find out which procedure your vehicle uses, check your owner's manual.

Troubleshooting the TPMS light

Blinking

One or more tires are approaching the low-pressure limit — 20% below the recommended pressure.

Blinks at start-up and keeps blinking

One or more sensors are defective. Each sensor needs to be removed and tested to find the faulty one. If this happens while driving, contact us and we'll help you find a solution.

Stays on while driving

One or more tires have low pressure. Once corrected, the light turns off on its own.

TPMS won't warn you about over-inflation Too much pressure wears the centre of the tread faster and reduces grip. Check pressures with a gauge, not just the dash light.

Storage & care

Wheel storage

Proper storage keeps your wheels looking new and avoids premature wear. A few tips:

Clean and dry wheels thoroughly before storing them.
Remove the centre caps before storage.
Keep chrome and machined finishes away from harsh winter conditions — salt and calcium pit them and wear them prematurely. Fully painted finishes suit rough winters best.
Store away from humidity, direct sunlight and heat sources.
To avoid flat spots, store mounted packages lying flat, stacked one on top of the other.
Avoid tire bags — trapped humidity and calcium residue can tarnish the finish.

Cleaning your alloy wheels

Regular cleaning keeps alloy wheels looking new. A few tips on doing it without damaging the finish:

Only wash wheels when they're cold. Washing hot wheels straight after a drive can damage the finish.
On chrome or machined finishes, use only mild detergents — abrasive cleaners eat into the clear coat. Our rule of thumb: if you wouldn't use it on your hands, don't use it on your wheels.
Use a soft wash mitt or sponge. Brushes and abrasive pads can scratch the finish.
Apply a coat of car wax three or four times a year. It keeps the new look longer and makes wheels easier to clean. Reapply as needed.

Still have a question?

Our wheel and tire specialists are happy to help, Monday to Friday, 9:00 a.m. to 5:00 p.m. (ET).

1-866-935-9493 info@wheelwiz.ca Contact form