285/40R22 Tyre Size: Dimensions, Alternatives & Speedometer Effect

Measured from the ground to the top of the tread, a new 285/40R22 tyre stands 786.8 mm tall (31.0 inches). The sidewall — the rubber between the rim edge and the tread — is 114.0 mm high, the tyre covers 2471.8 mm of road per revolution, and it completes 651.1 revolutions in a mile. Those numbers come straight from the three figures in the size code: 285 mm width, 40% aspect ratio and a 22-inch rim. This guide explains the maths behind them, lists the sizes that match this one most closely, and works out what fitting a different size would do to your speedometer reading.

Before the numbers, one practical point. A tyre size is only correct for your car if it matches what the manufacturer specified, and the place to find that is the placard on the driver's door jamb, not the size currently fitted — a previous owner may have changed it. The dimensions on this page tell you exactly what a 285/40R22 measures, so you can compare it against the placard figure and against any alternative you are considering. If the two do not match, the tables further down show how far apart they are and whether the difference stays inside the commonly used plus-or-minus 3% guideline.

This is a calculation, not a safety approval. Always check your vehicle's door-jamb placard, load index and speed rating, and confirm fitment with a tyre professional before fitting a different tyre size.

What does 285/40R22 mean?

Read the code left to right. 285 means the tyre is 285 mm wide across the tread. 40 is the aspect ratio, so the sidewall is 40% of the width — 285 x 0.40 = 114.0 mm of rubber between rim and tread. R22 means it mounts on a 22-inch rim (558.8 mm). The overall diameter is the rim plus two sidewalls: 558.8 mm + 114.0 mm + 114.0 mm = 786.8 mm. Once you can do that sum, you can decode any size code you meet, and you can see why two sizes with the same rim can still be very different heights.

285/40R22 dimensions

Measurement Value
Overall diameter 786.8 mm (31.0 in)
Sidewall height 114.0 mm
Circumference 2471.8 mm
Revolutions per mile 651.1
Rim diameter 22 in

Start with the circumference: 2471.8 mm per revolution. That is the distance your car covers every time this tyre turns once, and it is what makes the revs-per-mile figure (651.1) what it is — a mile divided by the circumference. Fit a tyre with a larger circumference and each revolution carries you further, so at the same wheel speed the car is moving faster than the instruments report. The sidewall (114.0 mm) is the flexible part: it absorbs the first shock from bumps and potholes, and a low-profile sidewall like this one means a short, stiff sidewall that sharpens steering response but leaves less cushioning over potholes and kerbs. These are nominal new-tyre dimensions, and real tyres vary slightly by brand, model, wear and inflation pressure.

Closest alternative sizes to 285/40R22

If you are looking for a substitute, start here. These are the three nearest sizes by overall diameter, limited to rims within one inch of 22 inches so the wheel itself stays realistic. 275/40R22 is the nearest at -1.0% (-8.0 mm difference). Anything within plus or minus 3% is generally treated as acceptable from a speedometer point of view, but diameter is only one of the checks: the replacement also needs the right load index and speed rating, and enough clearance around the suspension and arches at full steering lock.

Alternative size Diameter Sidewall Diameter difference Within ±3% guideline?
275/40R22 778.8 mm (30.7 in) 110.0 mm -1.0% Within the guideline
305/35R22 772.3 mm (30.4 in) 106.8 mm -1.8% Within the guideline
305/40R22 802.8 mm (31.6 in) 122.0 mm +2.0% Within the guideline

Speedometer effect of changing from 285/40R22

Take the closest alternative, 275/40R22, as a worked example. Its diameter is 778.8 mm against 786.8 mm here, a difference of -1.0%. Because the speedometer counts revolutions, the error follows the diameter ratio: actual speed equals indicated speed multiplied by 778.8 / 786.8. At an indicated 30 mph the car would really be doing 29.7 mph; at 50 mph indicated it would be 49.5 mph; at 70 mph indicated, 69.3 mph. That means the speedometer would read slightly high, so you would be travelling a touch slower than the dial suggests. Even a small percentage matters at motorway speed, which is why the plus-or-minus 3% guideline exists.

Replacement size Diameter change Actual speed at 30 mph indicated Actual speed at 50 mph indicated Actual speed at 70 mph indicated
275/40R22 -1.0% 29.7 mph 49.5 mph 69.3 mph
305/35R22 -1.8% 29.4 mph 49.1 mph 68.7 mph
305/40R22 +2.0% 30.6 mph 51.0 mph 71.4 mph

Wider, narrower or taller than 285/40R22: what actually changes

What actually changes if you move away from 285/40R22? Width first: a wider tyre puts more rubber on the road, which usually helps dry grip and can hurt fuel use a little through extra rolling resistance. Height second: because the sidewall is 40% of the width, widening without lowering the aspect ratio raises the diameter, lengthens the gearing and lifts the car slightly. A shorter sidewall sharpens steering response but transmits more of the road surface into the cabin. The practical rule is to hold the diameter as steady as you can — that is what the alternative table above is for — and to check that a wider tyre still clears the suspension and arches at full lock before committing.

How to check 285/40R22 fits your vehicle

The checks are the same whatever size you are considering. First, the door-jamb placard: size, load index and speed rating. Second, the rim: a 22-inch rim of the right width for a 285 mm tyre. Third, clearance — arches, suspension components and steering lock, with the car loaded as it will actually be used. Fourth, the pressure-monitoring system, which may need a reset or new sensors after a change. Fifth, the spare: if the spare is a different size, know its speed and distance limits before you need it. None of these is a formality, and together they are what turns a calculation into a safe fitment. For the 285/40R22, the 285 mm width and 114.0 mm sidewall are part of that same check.

Mistakes to avoid with 285/40R22

People go wrong in a handful of predictable ways. They trust the fitted tyre instead of the placard. They pick a wider tyre and forget the aspect ratio, so the diameter creeps up. They match the size code but buy a lower load index or speed rating. They mix sizes across an axle. They forget to check clearance at full steering lock, where a tyre that clears going straight can still rub. Each of these is easy to avoid once you know to look for it, and the tables on this page give you the numbers to check against. On a 285/40R22 the figures to check are a 786.8 mm diameter, a 114.0 mm sidewall and 651.1 revs per mile.

Related 285/40R22 sizes and tools

Frequently asked questions

What is the overall diameter of a 285/40R22 tyre?

The overall diameter of a new 285/40R22 tyre is 786.8 mm, which is 31.0 inches. That is the rim diameter (558.8 mm) plus twice the sidewall height (114.0 mm). It is a nominal figure, so an individual tyre can vary slightly by brand, model, wear and inflation pressure.

How tall is the sidewall on a 285/40R22 tyre?

On this page, 285/40r22 tyre size is the case in point: The sidewall is 114.0 mm tall, because the aspect ratio is 40% of the 285 mm width (285 x 40/100 = 114.0 mm). A low-profile sidewall like this one means a short, stiff sidewall that sharpens steering response but leaves less cushioning over potholes and kerbs. The sidewall height is the main thing that decides how much cushioning the tyre gives over bumps.

How many revolutions per mile does a 285/40R22 tyre do?

A 285/40R22 tyre completes 651.1 revolutions per mile, based on its 2471.8 mm circumference. That figure matters because the speedometer and odometer count revolutions: fit a tyre with a different circumference and the readings drift by the same percentage as the diameter change.

What is the closest alternative size to 285/40R22?

The closest size in the chart is 275/40R22, which differs in diameter by -1.0% (-8.0 mm). The commonly used guideline is to stay within plus or minus 3% of the original diameter, and the alternative table on this page shows which sizes meet that. Diameter is only one check, though — load index, speed rating and physical clearance still need confirming.

Will changing from 285/40R22 affect my speedometer?

Yes. The speedometer assumes the original circumference, so a diameter change shifts every reading by the same percentage. Fitting 275/40R22 instead of 285/40R22 changes the diameter by -1.0%, so an indicated 70 mph would really be 69.3 mph. Keep the diameter within plus or minus 3% to keep that error small, and check the placard before fitting anything different.