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Rob MacGregor (LAURA LEYSHON/LAURA LEYSHON/THE GLOBE AND MAIL)
Rob MacGregor (LAURA LEYSHON/LAURA LEYSHON/THE GLOBE AND MAIL)

Rob's Garage

How can I be sure it's time to re-tire? Add to ...

Hi Rob, great blog by the way.

Hey, all this talk lately about winter tires and summer tires and worn out tires, how do I know when to install new tires? Is there some sort of tool or something that I can use? There is nothing in the owner's manual of my car; it even has a tire manual in the glove-box.

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Look forward to hearing back

Doug Stuart

Hi Doug - I love it when people write as though they've been a buddy for years, and lots of questions.

To start, in most instances re-tiring time is pointed out by service techs. Good ones or those techs that you become familiar with, will usually look after regular customers by keeping a watchful eye on your car. It's quite unusual for people to be pro-active like you Doug, in figuring out when it's best to wrap new skins around your bling. Good on ya.

Tires are basically constructed the same, whether they are summer, winter or all-season. They have some sort of tread block, and grooves or sipes running around the circumference as well as across the tread blocks.

Without going into all the gory details on tire construction, we are getting close to answering your question Doug. In addition to the myriad funky tread patterns out there, the tire manufacturers have been mandated to include small rubber bumps at the bottom of the grooves between the blocks of rubber, called tread wear indicators or wear bars. These bars do not protrude past the surface of the large tread blocks so they do not affect the intended performance of the tire.

Now, to your question: As a tire wears out, the tread block wears down, decreasing its height in relation to the bottom of the grooves and sipes. As this process continues, the tread blocks will eventually match the height of the wear bars. A tire at this stage not only requires replacement, but it is actually illegal to use on a public roadway. In this condition, a vehicle pulled over by a police officer will have to be parked until the tires are replaced...either at the side of the road or towed to a shop - no fun.

Doug, this is the Readers Digest version. There are tread dept tools to measure the height of the tread blocks - which is what your technician uses. You can pick one up at an auto parts store, but you can monitor your own tires by observing the wear bars as they seemingly approach the surface of the tire tread telling you it's time to re-tire.

...and thanks for your comment.

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