How To Measure Rim Width With Tire On

The width of your rim determines the width of the tire on the road.

This simple fact should tell you why it’s important that you know your rims’ width before purchasing tires. Incorrectly matched rims and tires will lead to your tires’ premature failure, so let us show you how to measure your rims.

Make a note of the size in your vehicle handbook.

Quick Questions Before Starting

Measuring your wheel rims is a relatively simple task. If you have wheel rim calipers, it’s straightforward.

How Difficult Is This to Complete?

This is a simple task that can be done on your own.

How Long Does it Take to Complete?

This shouldn’t take you more than 30 mins.

How Much Do Materials Cost?

Buying a set of calipers used by a tire fitment center will cost in the region of $30 to $35. If you use a tape measure and a straight edge, then the cost is zero as these are items found in every home.

Items Needed to Measure Rim Width (By Method)

There are three ways that you can easily measure the rims on your car. Let’s look at what you need to measure your rims using each method. In the next section, we’ll cover how to do the job.

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1. Using the Identification Letters on the Rim (Cost: $0)

The jack for your car
The wheel spanner to undo the wheel nuts
A bucket with soapy water and a rag

2. Measuring With a Straight Ruler and a Tape Measure (Cost: $0)

The jack for your car
The wheel spanner to undo the wheel nuts
A straight edge – something like a piece of straight wood or a long ruler
A tape measure

3. Measuring With Tire Caliper (Cost: Between $30 – $35)

A set of tire calipers

Measuring the rim’s width with the tire on can be a simple task if you have the correct tools, or it can be more complex if you’re using straight edges and a tape measure.

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Method 1: Using the Identification Letters on the Rim

To read and interpret the letters stamped into the rim of the wheel, you’ll need to remove it as this is usually stamped on the backside of the rim. Please observe all safety rules when working around a vehicle that’s jacked up. Keep children and pets away, so nothing is bumped while working near the car.

Ensure the handbrake is on and chocks are in front of the wheels that will remain on the ground.
Jack the car up using the correct jacking point for the particular wheel that you’re removing. Your manufacturer’s handbook will indicate where this is.
Undo the wheel nuts and remove the wheel from the car.
Turn the wheel over and clean the inside of the rim.
Look for the manufacturer’s stamped mark. It’ll look something like “7.5Jx16H2 ET35.”
Reading this mark:
1. 7.5 – This is the wheel size in inches, so this wheel is 7.5″ wide from one edge of the rim to the other (THIS ISN’T THE TIRE SIZE)
2. J – This is the profile of the bead. Each different type of tire has its identification letter. For example, J is for passenger cars, JJ for SUV 4X4, D for motorcycles, P and K for older passenger cars such as the Beetle.
3. 16 – This is the wheel diameter in inches.
4. H2 – This is the wheel rim section profile. To make rims stiffer, manufacturers put humps into the rim. These are in specific places and follow a specific pattern denoted by a code such as H2.
5. ET35 – This is the wheel offset expressed in millimeters.
6. Return the wheel to the hub and tighten the wheel nuts.

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Method 2: Measuring With a Straightedge and a Tape Measure

This method requires you to use a little math to calculate the width of the tire.

Remove the wheel, following points 1 to 3 from above.
Lay the inside of the rim flat on the ground.
Take a straight edge or a straight piece of wood and lay it on top of the rim, so it protrudes past the tire.
Using a tape measure, measure the distance from the ground to the straight edge.
Write down this measurement and call it A.
We know that the rule of thumb for the lip of the rim is 1″ in total (1/2″ each side), so to calculate the rim size: Rim size = A – 1”

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Method 3: Measuring With Tire Caliper

If you have a set of calipers similar to those used when balancing wheels, you can use these to quickly measure the width of the rim.

Take the calipers, extend them to their widest, and then place one arm on the rim in front of the tire and one arm on the rim at the rear of the tire.
Ensure that the calipers aren’t placed on the lip of the rim.
Gently close the arms of the calipers until they touch the rim on either side of the tire.
Read off the scale to find the size of the wheel in total. Subtract 1″.

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Why Checking Rim Width Matters

The rim width range for the tire that you have will identify the widest to the narrowest rim that the tire is designed to fit. This means that the width of the rim will determine the width of the tire.

Fatter tires give better road holding but have greater rolling resistance to the road, so they can affect your fuel consumption. Narrow tires are excellent for cutting through water and have comfortable ride qualities but aren’t good for quick acceleration as they don’t have a large patch of rubber on the road.

Checking the width of the rim ensures that the tires will fit correctly and not be under stress while fitted on the rim. It’s not desirable to try and fit oversized or undersized tires to the rim.

If the rim is too narrow for the tire’s recommended width, the tire will distort sideways under cornering. This stresses the tire at that point, and failure is certain in time. On the other hand, if the rim is too wide for the tire, the vehicle will have a harsh ride as the sidewalls won’t have the curvature to flex and soak up the bumps. Again, this places unnecessary stress on the tire, and failure is certain.

This is the reason that there are ranges of rims that fit tires and tires that fit rims. See your local dealer to get the correct information and marry the sizes correctly for safe, comfortable motoring.

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Conclusion

Knowing the size of the rim is important when fitting tires. There are standard tables available that will assist you in ensuring that the balance between tire and rim is correct. It’s not advisable to ignore the manufacturers’ recommendations. There are enough options available to ensure there’s a rim and tire match that will suit you.

How To Measure Rim Width With Tire On – Easy Steps