What Tire Size Fits My Car? A Practical Guide for Ontario Drivers

Before you can price a tire, you need to know which one your car actually takes. It sounds trivial, and for most drivers it is — but the number of vehicles running the wrong size, or a size a previous owner chose badly, is higher than you would expect.

Here are the three reliable ways to find your size, in order of trustworthiness, plus what to do when they disagree.

Method 1: The Door Placard (Most Reliable)

Open the driver door and look at the frame, around where the latch sits. Almost every vehicle sold in Canada has a tire and loading information placard there. It lists:

• The original equipment tire size, front and rear
• The correct cold inflation pressure in PSI or kPa
• Sometimes the spare tire size and pressure

This is the manufacturer telling you what the vehicle was engineered for. It is the number to trust. If the placard is missing or unreadable, check the glovebox lid, the fuel filler flap or the owner manual.

Important: the placard pressure is the one to use, not the maximum pressure moulded on the tire sidewall. Our tire pressure guide explains why that distinction matters.

Method 2: The Sidewall of Your Current Tires

Your existing tires carry their size on the sidewall, in a format like 225/60R17 99H:

• 225 — section width in millimetres
• 60 — aspect ratio: sidewall height as a percentage of the width
• R — radial construction
• 17 — rim diameter in inches
• 99 — load index
• H — speed rating

Our full walkthrough is in how to read a tire size, and the last two characters are covered in detail in speed ratings and load index.

The catch: this tells you what is currently fitted, which is not necessarily what should be fitted. On a used car especially, treat it as a clue rather than gospel.

Method 3: The Owner Manual

The manual usually lists the original size plus any factory-approved alternatives — useful because manufacturers often offered several wheel packages on the same model. If your car came with 17-inch wheels and the manual also lists an 18-inch option, both are engineered-approved.

When the Placard and the Sidewall Disagree

This is common on used vehicles and it always deserves a second look. Possible explanations:

• A previous owner fitted aftermarket wheels. If they did it properly, the new size has a similar overall diameter and an equal or higher load index. If they did it cheaply, it may not.
• A winter set on different rims. Perfectly normal — winter setups are often a narrower size on smaller wheels, which is a deliberate and sensible choice.
• Someone simply fitted whatever was cheap. This is the one to worry about.

The two things that must not be compromised are load index and overall diameter. A tire with a load index below the placard figure is not safe on that vehicle, full stop. And a diameter more than roughly 3% off the original will throw out your speedometer, odometer, ABS and stability control calibration.

If you are unsure, bring the vehicle or the numbers to us and we will check it properly. Call +1 (204) 962-8513.

Which Alternative Sizes Are Safe?

You are not always locked into one size. A substitution is generally acceptable when:

• The overall diameter stays within about 3% of original
• The load index is equal to or higher than the placard value
• The speed rating is equal to or higher (winter tires are the recognised exception)
• The tire physically clears suspension, brakes and bodywork at full lock and full compression
• The width suits the rim width you are fitting it to

A common and genuinely good substitution is going narrower and taller for winter — a 205/60R16 in place of a 225/50R17, for example. Narrower tires cut through snow better and there is more sidewall to absorb potholes. See plus sizing and low-profile tires on Ontario roads.

Front and Rear Different Sizes

Some performance and rear-wheel-drive vehicles use a staggered setup — wider tires at the back. If your placard lists two different sizes, that is deliberate and you must keep it. Staggered setups usually cannot be rotated front-to-back; see tire rotation for what that means for wear.

Do Not Mix Sizes or Types on an Axle

Both tires on the same axle should be the same size, type and ideally the same wear level. On all-wheel-drive vehicles the requirement is stricter still — mismatched rolling diameters can damage the differential. Our guide on AWD tires and whether you must replace all four explains the tolerances.

Frequently Asked Questions

Where do I find my tire size?

Check the placard inside the driver door frame first, as it shows the manufacturer specified size. You can also read it from the sidewall of your current tires or the owner manual. The door placard is the most reliable of the three.

Can I fit a different tire size than the one on my car?

Often yes, provided the overall diameter stays within about three percent of original, the load index is equal or higher, the speed rating is equal or higher, and the tire physically clears the suspension and bodywork. If in doubt, have it checked before buying.

What if my tire sidewall size is different from the door placard?

That usually means a previous owner changed wheels or fitted a winter set on different rims. Verify the fitted size has an adequate load index and a similar overall diameter. If it does not, go back to the placard size.

Can I use a narrower tire in winter?

Yes, and it is often a good idea. A narrower, taller winter tire cuts through snow more effectively and gives extra sidewall to absorb pothole impacts, as long as the overall diameter and load index remain correct.

Do all four tires have to be the same size?

On most vehicles yes. Some performance and rear-wheel-drive cars use a staggered setup with wider rear tires, which is shown on the door placard. Never mix different sizes on the same axle.

What happens if I fit the wrong tire size?

Your speedometer and odometer will read incorrectly, ABS and stability control calibration is affected, and an under-rated load index is a genuine safety risk. Rubbing against suspension or bodywork can also damage the tire.

Not Sure Which Size You Need? Ask Us

Send us your vehicle year, make and model, or a photo of your door placard, and we will confirm the correct size and quote you from stock.

Atika Auto Parts stocks brand-new all-season, all-weather, winter and light-truck tires at 80 Hale Rd, Unit 3, Brampton — with expert fitting and delivery across the GTA. Browse our current tire stock, call +1 (204) 962-8513, or send us your vehicle details and we will quote you the same day.