Subaru Ascent tires

The trap on an Ascent is the trim badge. A Premium was sold on both wheel sizes, and the two sizes take different pressures. If you quote an Ascent from the badge on the tailgate you have a one in two chance of being two psi out on all four corners.

The sizes Subaru fitted

The first generation runs from 2019. Sizes and pressures here are confirmed on the 2023 car.

• 245/60R18 on Base and Premium.
• 245/50R20 on Premium, Limited, Touring and Onyx Edition. This size covers the most trims.

Note the overlap. Premium appears on both rows, which is why the wheel has to be identified rather than assumed. On most cars wheel diameter moves with trim; on this one the trim does not settle it. The Ascent is also the heaviest vehicle in the Subaru range, so the load index on a replacement is part of the specification rather than a detail. See finding your tire size.

Where the Ascent puts its placard

The driver-side door pillar. Subaru's own owner's quick guide says the tire pressure specifications are on the tire information placard on the driver's side door pillar.

That is the pillar, not the door edge. It is the upright post between the front and rear doors, the one beside your shoulder when the driver's door is open. Anyone who learned to look at the door edge on another make will find nothing here and conclude the sticker is missing. It is not. Our tire pressure placard guide covers which makes print it where.

How to read it once you find it

1. Cold pressure, front.
2. Cold pressure, rear. Equal to the front on this vehicle.
3. The original tire size, which is what settles the 18 against 20 question on a Premium.
4. The spare, printed separately and usually at a much higher figure.

Cold means the vehicle has been parked at least three hours, or driven under about a mile. A tire warms as it rolls and its pressure rises with it, so a reading taken after a school run or a highway stretch is high.

The verified pressures

Two independent pressure sources agree exactly, on both fitments:

• 245/50R20: 33 psi front and rear.
• 245/60R18: 35 psi front and rear.

Front and rear are equal on both, so the axle split that catches people on a Crosstrek does not apply here. The two psi step between the fitments does, and it is the whole problem with the Premium trim. A 20-inch Premium set to 35 is two psi over on every corner. An 18-inch Premium set to 33 is two under, which on a loaded three-row SUV in summer is the direction that generates heat.

Replacing fewer than four

Symmetrical all-wheel drive is standard on every Ascent. It is the strictest mainstream system on tire matching, and a single odd tire can damage the centre differential. One damaged tire on an Ascent is a four-tire conversation, or a shave-to-match job where the new tire is machined down to match the worn ones.

There is a figure, and the attribution matters. Tire Rack's per-manufacturer matching table gives Subaru's requirement as a circumference difference of no more than 6 mm, a quarter of an inch, between tires. That number is Tire Rack's, from their article on whether all four tires need to match on an all-wheel-drive vehicle. We could not find a numeric tolerance published by Subaru itself, so we attribute it to Tire Rack rather than to the manufacturer.

Six millimetres of circumference is a small amount of wear. On a heavy vehicle that covers miles with people and luggage in it, a set reaches that in less time than owners expect. See how many tires and mixing tire brands. Where the damage is a puncture in the tread, repair against replace is worth reading first, because a sound repair keeps the matched set together.

What changes on a mobile Ascent fitting

• Direct TPMS, with a sensor in each road wheel, so the job ends with a reset or a relearn.
• Two fitments, two psi apart, with the Premium trim available on either. The wheel gets identified before anything is inflated.
• 245/50R20 wheels are large and heavy. Nothing special is needed to fit them, but the vehicle needs a flat, firm place to sit.
• The label is on the pillar, not the door edge.
• On a one-tire job, the matching question is settled before we fit, not after.

What we do

We supply the tires and fit them where the vehicle is parked. Pressure is set to the figure on your own door pillar placard rather than to a database, the TPMS is reset or relearned where the vehicle supports it, and the old tires leave with us. Pricing is on our mobile tire replacement page.

Questions people ask

• What psi does an Ascent take? 33 front and rear on the 20-inch fitment, 35 front and rear on the 18-inch. Two sources agree on both.
• I have a Premium. Which is mine? Either. Premium was sold on both wheels, so read the size off the placard or the sidewall.
• Where is the placard? The driver-side door pillar, the upright post beside your shoulder. Not the door edge.
• Do I have to replace all four? Usually. Tire Rack's matching table puts the Subaru limit at 6 mm of circumference difference, and worn tires exceed that quickly.
• Is that 6 mm figure from Subaru? It comes from Tire Rack. Subaru publishes no numeric tolerance we could find, so we cite the source we actually have.
• Are front and rear different? Not on this vehicle. Both axles take the same figure on both fitments.