Sustainability Tip of the Week
A Simple Wish for a Better Tomorrow
Car Tire Inflation In Winter
How Much Does Tire Pressure Affect Fuel Economy?
A National Highway Traffic Safety Administration (NHTSA) study revealed every 1% decrease in tire pressure correlated to a 0.3% reduction in fuel economy.
For example, let’s take a small sedan rated for 25 MPG and with tires that should be set at 32 PSI. If the driver ignores the tire pressure for a month — tires naturally lose 1 PSI to 2 PSI per month — the resulting pressure drop could reduce fuel economy to 23.1 MPG, on average.
Even in the same day, the temperature can swing over 20 °F, affecting our sample commuter’s fuel economy by a couple of MPGs.
Changing from summer to winter, a typical drop of 50 °F translates to about 5 PSI under inflation. In addition to the cold-weather fuel economy impact, the extra rolling resistance will reduce fuel economy to just 20.3 MPG — a loss of 5 MPG!
How to Get Winter Tire Pressure Right
Once a month, have your pressure checked when the tires are cold (meaning the car is parked outside and hasn’t been driven in four hours) and inflate them to what’s indicated on the placard located on the inside of driver’s door.
If your TPMS (tire pressure monitoring system) warning light goes on during a cold snap, it may not mean your tire has a leak.
Tire pressure can decrease about 1 PSI (pound per square inch) for every 10 degrees the temperature drops. It’s not that more air is escaping your tires, but rather the air inside the tire condenses, taking up less space when it’s cold. It’s similar to how a cake, just out of the oven, flattens out a bit as it cools.
Tires also lose about 1 PSI per month just from seepage of air around the edge of the rim and through the tread itself.
These two factors combined can cause the air pressure in a tire to drop 25 % below the recommended fill pressure. This is what triggers the sensing transmitters inside your tires to illuminate your TPMS dash light. Whenever your TPMS light comes on, have your air checked and bring your tires up to the proper pressure.
Winter Tire Pressure
Temperature changes outside affect your tire pressure. If it gets up to 45 degrees by day and drops to 15 degrees at night, your tire pressure will vary 3 PSI, not counting normal air loss. This is why it’s not unusual to have the low-pressure indicator light go on first thing in the morning, since it’s usually coldest overnight.
The light may shut off on its own after you drive 20 minutes or so, as the air in your tires warms and expands and proper inflation level stabilizes.
Regardless, you should get your air checked right away. The TPMS light means your tires are at least 25 % below the proper air pressure. This is a safety risk, especially if you’re carrying a load close to your vehicle’s max capacity. There’s a greater chance of tire failure, compromised handling and increased wear and tear on your tires. Your gas mileage could also suffer.
When you top off your tires, the TPMS light will go off as the tire regains the proper pressure.
Note: If the warning light is flashing, this is a problem with the vehicle’s TPMS system, not your tires, and you should take your car to the shop.
For more information regarding TPMS with your vehicle, please review your owner’s manual.
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Published: Mon, 17 Feb 2020 13:09:45 +0000 by j.coons