Here’s the latest reader question, along with my reply!
Martin asks: I have been thinking about putting a set of smaller tires on my car – which came from the factory with 17 inch wheels – to improve gas mileage by reducing rolling resistance. What do you think about this?
My reply: I think it’s already being done by the factory! If you take a look at cars like the Toyota Prius which emphasize economy, you’ll discover a significant MPG difference between the car with say 17 inch wheels/tires and the same car with a 15 inch wheel/tire package. Rolling resistance and weight are reduced.
But, there’s a catch.
Swapping out wheels/tires that came from the factory may upset the car’s computerized equilibrium. The speedometer and other such (ABS/TCS and Tire Pressure Monitor) may not work correctly without the computer being recalibrated. This is something to look into before you commit to buying the new set of wheels/tires.
Also, be sure that the new set will fit without causing mechanical problems such as unwanted changes to the car’s ride height and be aware that handling/braking characteristics will be affected.
That said, you will save money on gas – and on tires. As a general rule, the 17 inch and larger tires now commonly fitted to new cars are more performance-oriented and so have softer tread compounds that don’t last as long. Also, they have shorter sidewalls, which stiffens up the ride (you feel bumps and potholes more).
Going to a 15-inch package – with tires that have taller sidewalls – should make the car’s ride noticeably softer, too!
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Just use one of the tire size calculators online to find a different size/aspect/wheel that is the same overall diameter as your factory tires/wheels.
For instance, I swapped from 215/50R17 to 205/65R15 which gives a better ride, better traction in snow/mud, and better MPG. There is only a few hundreths of an inch difference in overall diameter so the speedometer is the same. And the 15″ tires are almost $50 each cheaper than the 17″ tires which means the savings in the purchase of just one set of tires paid for the used rims almost twice over.
Note: you just have to make sure the smaller wheels will fit over your brakes front and rear.
If it were me, I’d leave well enough ALONE. The engineers designed and built the car for 17″ wheels & tires, so it will function optimally so equipped. If the smaller tires are really an issue, then it might be better to get a car that comes with them from the factory, e.g. the Toyota Prius, Mitsubishi Mirage, etc.