Better Performance for less than four bucks?

By: Chris Neprasch

In the quest for more power, better handling and improved braking it’s real easy to overlook the basic stuff. The lure of flashy parts like huge 14-inch rotors with six-piston calipers or 30-way adjustable coilover setups tend to take precedence over the fact that no matter what you do to your car, there are only four small contact patches where the car actually touches the track, street or whatever surface you’re driving on. Those four patches are responsible for stopping and cushioning a load and if you were to take the amount of rubber that touches the ground it would equal the size of about an 8 1/2 by 11 inch sheet of paper.

During a recent trip to test the Bridgestone Blizzak LM-25 winter tire we had a chance to spend some time talking with Bill VandeWater, the consumer products manager of sales and engineering for Bridgestone Tires. We expected him to go into a deep philosophical lecture about proprietary compounds, cutting edge tire construction and futuristic tread designs that will revolutionize the automobile world. Instead what we got was a tire pressure gauge handed to us and an in-depth discussion on proper inflation. Sounds odd at first, but once you put some thought into it then it all makes sense and VandeWater was right on the mark.


Underinflated tyres reduce braking efficiency, handling accuracy and stability.
Ducati M400 Manual

Think about this: Tires lose about 1 psi per month. They also lose 1 psi for every 10-degree Fahrenheit drop in temperature. If you air your tires up in June during a 90 degree heat wave and don’t check them until a chilly 40 degree November night, it’s a combined loss of 11 psi. Not only does it affect gas mileage, this little excerpt was taken from the Ducati M400 Owner’s Manual on other effects and those things only have half the wheels. “Underinflated tyres (Yes tyres because that’s how them Italians spell it – OVB) reduce braking efficiency, handling accuracy and stability,” the manual says.

If you think you’re exempt from having to check tire pressure because your car is equipped with a tire monitoring system then think again – most of them won’t warn the driver until the pressure drops 25 to 30 percent lower than manufacturer recommended pressure. Think that you can save some time by looking at your tires to see if they seem low? Wrong again. Above we have pictures of the same tire inflated to 35 psi, 30 psi and 25 psi. Before reading the next paragraph try to figure out which is which.

Now we return to our little present from VandeWater and Bridgestone. A tire gauge is your friend and can be purchased for less than $4 from your local auto parts store. We know this because we left the gift at home and had to buy another one for photography purposes and even we could spare the extra money. And as for the answer the title of this article poses, yes if your tires are severely underinflated you will get better performance and mileage out of your car for less than four bucks. If they aren’t, well at least you’ll be able to maximize what you already have. A good tire gauge is more accurate than the naked eye and here’s the proof: If you had a hard time figuring out which tire had what pressure in the previous paragraph, the same pictures are above this one too and in the same places. In the center shot the tire is at 35 psi, the one on the right is 25 psi and the one on the left is 30 psi.

Using a tire pressure gauge isn’t difficult; make sure the tire is cold – as in it hasn’t been driven on for at least the past four hours – then unscrew the cap, place the gauge over the stem and read what number the stick comes out to. If it’s too high then let some pressure out or if it’s too low then add some air. Put the cap back on and be on your happy, merry way. Now figuring out the proper tire pressure is a whole new ballgame.

If you still have the OEM wheels and factory-sized tires then life is a lot easier for you. The recommended tire pressure is usually printed on a sticker located on the driver’s side doorjamb. In the instance that local hoodlums stole the sticker or if it plain didn’t come with one then the owner’s manual should have the information in it.

There has to be an easier way!
Tires have a load index and it changes depending on inflation. The load index is a number that is part of a code assigned to tires to indicate the maximum load they can carry at the tire’s maximum speed level and it varies. For instance, a 205/60R16 with a load index of 92 (SL) will have a load capacity of 1069 pounds at 26 psi, 1157 pounds at 29 psi, 1257 pounds at 32 psi, 1345 pounds at 35 psi and 1389 pounds at 38 psi. P-Metric and Euro-Metric also have different load indexes which should be taken into account. Load index alone should not be used to determine inflation pressure and a tire should never be inflated past the max pressure printed on the tire sidewall to achieve the proper capacity. Bridgestone has devoted an entire handbook for their tire dealers to ensure that the pressure is right when changing wheel diameter and tire sizes.

Believe it or not, there is a proper pressure for your tires if you have aftermarket wheels with oversized tires or a different wheel diameter. Running the manufacturer recommended pressure for the 205/60/16s isn’t always the same pressure required when you switch to a 215/45/17.

The easiest way to determine what pressure you should be running is to contact the tire manufacturer and ask. Tire companies want you to be safe and happy with your new tires and they are usually more than willing to help. Before you pick up the phone, make sure to jot down a few details so they can better assist you. Record the OE tire size for both front and rear. Write down the load index, speed rating and make sure to not miss any prefixes or suffixes like P, LT, or XL. Check the owner’s manual or the sticker in the door jamb for this information just in case a previous owner or you have changes the tires before. Also include the OE recommended inflation pressure and if you’re putting bigger tires on the factory wheel then don’t forget to find out the width of the OE wheel. If you’re running aftermarket wheels then include that in the list you’re preparing as well as the new tire size and model.

Once you get the information from the manufacturer it’s a good idea to write it down and place it in the owner’s manual or glove compartment so you won’t be going through the drill once a month which is how often you should be checking your tire pressure. While you have the glove compartment door open you might want to toss your $4 tire gauge in too because you’ll want to keep it handy. After all, coilovers and brakes don’t work as well as they could when you’re 15 psi short on your tire pressure.


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