The hum grows a little every month, and you have started to wonder whether it is the road or the tires. You can settle a good part of that in about 60 seconds. Run your palm across the face of a front tire, out to the edge and back the other way. If the tread feels smooth in one direction and sharp and stepped in the other, you have found feathering. You were right to look at the tires. Bring what you found from Danville to Driven Auto Care of San Ramon. We read the depths on all four tires before anything gets rotated.

What Do You Feel Across the Tread?

A penny reads depth in one spot. Depth in one spot is not the shape. You find the shape with your hand, months before it would show in a photograph. When a wheel is not pointed quite straight ahead, the tread scrubs sideways a little on every turn. Each rib then wears low on one side and stays tall on the other. Several shapes all get called uneven tread, and they come from different places.

Count the Edges Before the Rotation

Front tires steer, and on a RAV4 they carry most of the pulling and braking, so they wear faster than the rears. Even depth all the way across, with the fronts lower than the rears, is ordinary front-tire wear. One worn outside edge is a different finding. Alignment is the most common cause of a single worn edge. One worn edge and two worn edges come from different places. Have the alignment checked before that tire moves anywhere. A rotation moves that worn edge to a fresh corner without stopping the cause.

Which Patterns Come From Air and Suspension?

Wear on both shoulders with a good middle usually comes from a tire that has run low for a long time. An underinflated tire rides on its edges, and a RAV4 loaded up for a trip pushes the wear the same way. Too much air wears the middle down first. Set the pressures cold against the placard in the door jamb, then read that same corner again a week later. If it comes back low, air is escaping somewhere. Scalloped patches around the tire, with a ride that has gotten busier, are often a suspension issue, a balance issue, or a tire-construction issue. Two of these causes can act at once.

How Much Does a Rotation Fix?

Rotation moves each tire to a different corner. That spreads the work across all four. Toyota puts tire rotation on the RAV4's regular 5,000-mile or six-month service. The schedule for your own model year is the one in your maintenance guide. A set comes out when its worst tire is done, so keeping the four wearing evenly buys you the full life of the set. Rotation does nothing for wear that comes from alignment or from pressure, so those two get their own fix first. We rotate on the pattern specified for your RAV4, and we rebalance the wheels when there is a vibration.

Does All-Wheel Drive Change Anything?

All-wheel drive is built around four wheels that cover the same ground. As tread depths drift apart, the wheels stop turning at matched speeds, and the parts that split power between the axles work harder every mile. That is why the four tires need to stay close to each other in depth, and any number for that gap comes from your owner's manual. Raise that at the counter before replacing one tire. A RAV4 Hybrid drives its rear wheels with a separate electric motor, so those axles are not linked the same way. Matched tread still matters there for handling and for the stability systems.

We Measure Three Points Across Each Tire

Most people take one reading in the center, and edge wear does not show up there. We measure depth at the inner, center and outer points of each tire, and at more than one place around it. Then we compare all four against each other, because a reading from one tire has nothing to sit against. California's legal minimum is 1/32 inch in any two adjacent grooves. The number from the penny test is a replacement guideline that sits above that legal floor. Wet grip falls off before you reach either number.

Note which tire it was and which direction felt sharp under your palm. Give Driven Auto Care of San Ramon a call at (925) 830-4701 with those two details. We'll gauge every tire cold and read each one at three points across the face. You'll see photographs of the shapes we found on your own RAV4. Then we match the work to the shape, and your four tires wear down together.