Things to remember when downsizing tires
If you’ve recently retired an older ride and moved up to something newer, you can be excused if you experience some sticker shock when shopping for winter tires. Vehicles of almost every type, price point, and function now seem to come equipped with larger diameter, low-profile tires. And tire prices seem to rise almost exponentially when you hit rim sizes above 16 inches and profiles below 60 per cent.
Tires are sized by their width in millimetres, their profile or height as a percentage of their width, and their rim size in inches. So a tire with its side wall marked 225/65R17 means the tread is 225 mm wide, the side-wall height is 65 per cent of the tread width (or 146.25 mm) and it will fit a 17-inch rim.
When you hit the 19- to 20-inch size and up, things can get really expensive and, to avoid a creditcard meltdown, many consumers shop around for smaller-diameter tires to be installed on winter-use rims. But how low can you go? And will your ride be able to live with your choice?
There are things to consider when downsizing your tires and rims for winter. Will smaller rims clear the braking units on your vehicle’s wheels?
Dealership parts departments and tire retailers can usually answer this question. Will different-sized tires have clearance for turning and not rub on inner fender liners?
The three per cent solution answers this concern. Three per cent refers to the tire circumference size change limit (either up or down) that most tire-industry experts recommend. But circumferences aren’t printed on the side wall of tires, nor does this spec appear in any publicly accessible tire catalogues.
To find out what the circumference is on any particular tire, you could grab a length of string and measure it, or simply Google “tire size calculator” and choose from a long list of sites that will allow you to do a side-by-side comparison by entering your tire size and what you may be considering as a winter tire. If the two circumferences are more than three per cent apart, check out another size.
Another thing to consider is that computers on vehicles today require an accurate and constant idea of how far and fast a vehicle is travelling.
Most get this information from wheel-speed sensors, which means if you put the wrong sized tires on a vehicle, the speed/distance data for those computers will be inaccurate.
This can lead to check-engine lights, shifting troubles, anti-lock brake malfunctions and can even cause a stall of the engine, which will not restart.