Troubleshooter: One little tag can say a lot

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Shopping for a pre-owned vehicle is something few of us look forward to, and it’s a task made even more intimidating thanks to recent supply chain problems that have driven prices for more popular models up to ridiculous levels. But all this is no reason to let your shopping savvy senses get dull. When kicking tires, whether on a licensed retailer’s lot or on a private seller’s driveway, there’s one little decal you should look at. The information it contains may save you a world of headaches and buyer’s remorse.

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On every vehicle there will be a small decal affixed to either the driver’s door edge or the door frame. It’s commonly known as the tire pressure label. It will contain the vehicle’s serial number, paint code, recommended tire pressure, and most importantly the original tire size. Why is this last piece of information so critical? Auto makers seem to be pushing the limit lately in terms of larger diameter wheels and extremely low-profile tires. As anyone who has done any tire shopping lately knows, that combination makes for some expensive rubber. So many owners will opt for a different size for a lower price.

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Troubleshooter: One little tag can say a lot Back to video

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These size changes can work well, if the shopper and their tire consultant take the time to compare the original size and any potential new sizes to see if the circumferences are compatible. The standard guideline from most in the tire industry is to never choose a size that has a circumference difference of greater than 3% (either larger or smaller). Greater differences can cause problems with anti-lock braking and all-wheel drive systems as well as transmission operations. And of course they can play havoc with the accuracy of the speedometer and odometer.

For example, if someone equipped their ride with tires that were 8% larger in circumference than the original equipment, the odometer would read 8% less than the actual distance travelled. So if you were making an offer based on what the odometer displays, you might be paying too much. And if the vehicle in question was still within terms of a manufacturer’s warranty, and you took it to a dealer for a covered repair, you might be out of luck. All carmakers’ warranty terms contain a clause that will deny coverage to any vehicle where “the distance travelled cannot be readily determined”. And a vehicle with the wrong sized tires fits that bill.

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If you want to know how a different tire size affects all this, simply pop ‘tire size calculator’ into your favourite web search window and find one that has a side-by-side comparison feature. Put both sizes (original and existing) into the calculator to see the results.

You can also use that label to compare the vehicle serial number to the one found at the left side of the dash-top (visible from the lower corner of the windshield). If they don’t match, don’t walk away from the deal — run. The same applies if the label is missing altogether. This can be a sign of VIN washing, and that a car has been rebuilt from another wreck — or even stolen.