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How to determine the right tire size for your car

My 1995 Mazda 626 DX takes tire size P195/65R14. I want new all-season tires. My usual garage, who I trust, cannot find tires in that size, and suggests I substitute P185/70R14. A tire retailer confirms this. A Mazda dealer says there are a few tire models in the original size P195/65R14. Help! Who is correct?

Are there no tires in P195/65R14, or are there? If I changed to the substitute P185/70R14, that is a narrower tire. Would that not reduce control and possibly increase braking distance? 70 is higher aspect ratio than 65, so does that higher profile therefore have less control, less lateral stability and less steering response? Is it possible instead to substitute with a wider tire with same or less aspect ratio? – Alan in Toronto

There is indeed limited availability of tires in the 195/65/R14 size. General Altimax and Kumho are the only ones I can find.

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It is common to Plus Size tires when looking for replacement tires and Minus Size when switching to winter rubber that you have to change to a wider/narrower tire with a lower/taller aspect ratio – ensuring you stay within a small variance of the overall diameter of the original tire supplied by the vehicle manufacturer.

Going wider is the general practice for summer or all-season tires because the wider tread allows more contact with the road and helps with steering and braking response. But don't put too much significance into the changes to steering and braking as they would be hardly noticeable at this size. Similarly, going to a narrower tire is common for winter as the slimmer tread allows the tire to cut through snow more readily.

In addition to width, the changes in Plus and Minus Sizing include the depth of the sidewall, the distance from the rim to the road or aspect ratio, as it is called. The wider tire will have a lower sidewall and less room for impact absorption – it will ride rougher. Conversely, a narrower tire brings a taller sidewall with more shock absorbing capability.

Generally speaking, you give up on one front and gain on another – ride versus grip. Plus Zero sizing means keeping the original wheel diameter – 14-inches in your case. Plus One would mean a 15-inch wheel with a wider tire with a lower aspect ratio. Minus One a 13-inch wheel with a narrower tire and a taller aspect ratio – unwise in this application, but applicable when preparing vehicles with 18- to 20-inch tires for winter.

In your case, if switching wheels, you could conceivably also go to a Plus Two, which would mean a 16-inch wheel.

You appear to have three choices: the General Altimax in the original size, available at Canadian Tire; a narrower and taller tire on your original wheels or change wheels to Plus One size – the ideal choice in my opinion.

There is a wide selection of 205/60/15 tires and this may mean more competitive pricing and room to buy the larger wheels, leaving the originals available for winter rubber.

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Whatever your choice, it is important to maintain the same overall tire diameter as the original. This is critical for several reasons, including speedometer accuracy, driveline gearing and the proper operation of ABS, stability and traction controls systems.

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