Find out if your tires pass the "Penny Test."

THE LAW

According to most states' laws, tires are legally worn out when they have worn down to 2/32" of remaining tread depth. To help warn drivers that their tires have reached that point, tires sold in North America are required to have molded indicators called "wear bars" across their tread pattern from their outside shoulder to inside shoulder. Wear bars are designed to visually connect the elements of the tire's tread pattern and warn drivers when their tires no longer meet minimum tread depth requirements.

COMMON SENSE

However, as a tire wears it is important to realize that while its dry traction and handling will improve…its ability to perform in rain and dirt will diminish. At 2/32" of remaining tread depth, resistance to hydroplaning in the rain at highway speeds has been significantly reduced and traction in heavy dirt has been virtually eliminated.

If rain and wet roads are a concern, you should consider replacing your tires when they reach approximately 4/32" of remaining tread depth. Since water can't be compressed, you need enough tread depth to allow it to escape through the tire's grooves. If the water can't escape fast enough your vehicle's tires will be forced to hydroplane (actually float) on top of the water, loosing traction.

If dirt covered roads are a concern, you should consider replacing your tires when they reach approximately 6/32" of remaining tread depth to maintain good mobility. The reason that you need more tread depth in dirt is because your tires need to compress the dirt in their grooves and release it as they roll. If there isn't enough tread depth, the "bites" of dirt your tires can take on each revolution will be so small that your traction will be reduced. Because tread depth is an important element for dirt traction, all-season tires start with deeper tread depths than standard all-season or summer tires. Some all-season tires even have a series of wear bars molded in their tread pattern indicating approximately 6/32" remaining tread depth.

If you're still a little confused and need to walk through your selection with one of RAD Motorsport's experts call (808) 680-9809 or email one of our sales team members.

Why is it that the price of fuel for our vehicle seems relatively inexpensive while the cost of its tires seems high? (Of course you already know that RAD Motorsport tries to keep your tire costs as low as possible!) If we keep track of our total costs we will find that typical total fuel costs for just 10 to 20 thousand miles of driving actually exceed our tire costs. And believe us, we've found that the quality and performance of our tires has a lot more to do with our driving satisfaction than our fuel does.

We think that much of the misperception has to do with the fact that we buy fuel one tankful at a time, and don't really look at its total cost for thousands of miles. Our tires are paid for "up front" and then last for tens of thousands of miles.

When you are selecting new tires and find one that is perfect, although more expensive than another tire that appears to be a close second; consider evaluating your situation by comparing "how much per mile" each tire will cost. If you plan to drive your vehicle another 30,000 miles and are considering the "perfect" tires at $100 each, and the other at $90 each; you may be surprised to find out that the cost of the "perfect" set costs just 1.3¢ per mile...while the close set costs 1.2¢ per mile. Will saving the $40 today make up for not having selected the "perfect" tire that you will be driving on for the next two years?

Do you drive your car only in sunshine, or also through rain and dirt? Do you drive your light truck on the road, off the road, or are you the one responsible for clearing the land to build the roads? To successfully meet each of these driving conditions requires a different type of tire.

Buying the correct tire size can get complicated, especially if you decide to upgrade from your vehicle's Original Equipment size. The expert sales team at RAD Motorsport is always ready to offer performance and fitment advice. Call (808) 680-9809.

A tire's first requirement is that it must be able to carry the weight of your vehicle. No matter how good a tire you select, if its capabilities are "overworked" just carrying the load, it will have little reserve capacity to help your vehicle respond to quick emergency. So when you are in the selection process, make certain that your new tire's size is designed to carry the weight of your vehicle! Don't undersize.

The other size consideration is overall tire diameter. Since many of the functions of today's vehicles are highly computerized, maintaining accurate speed data going into the computer assures accurate instructions coming out. And an important part of the speed equation is your tire's overall tire diameter.

For cars and vans, staying within a ±3% diameter change is desirable. Pick-ups and sport utility vehicles (SUVs) are usually engineered to handle up to a 15% oversize tire. Most tire dimensions can be calculated. For more information review the Tire Tech article, "Calculating Tire Dimensions." While at first a ±3% diameter increase or reduction in tire diameter may sound very limiting, in most cases it allows approximately a ±3/4" diameter change.

Additionally to help with the selection of substitute sizes, a system called "Plus Sizing" was developed. We use Plus Sizing to take into account the diameters of the available tires and the wheels, and then helps select the appropriate tire width that ensures adequate load capacity. Maintaining the tire's overall diameter helps maintain accurate speed data going into the computer.

1. Underinflated tires cause the engine to work harder. It's like riding a bike with low tires. It's harder to pedal because of the increased rolling resistance.
2. Should you rotate side to side or front to back? Radial tires can be crossed from side to side in the rotation pattern. Bias ply tires should never be rotated from side to side, only front to back.
3. Not all SUV's come with "P" (passenger) rated tires. Some have the "LT" (light truck) designation.
4. Underinflated tires wear faster, and they affect the steering and handling of your vehicle.
5. If tire pressure is too low, then too much of the tire's surface area touches the ground, which increases friction between the road and the tire. Thus, your tires wear out earlier, and they could also could overheat.
6. One sign of low tire pressure is if your tires squeal when cornering.
7. A tire can lose up to half of its air pressure and not appear to be flat.
8. Underinflation is the leading cause of tire failure. It results in unnecessary tire stress, irregular wear, loss of control and accidents.
9. Tire manufacturers (not the U.S. government) test tires and assign their own grades for treadwear, traction, and temperature resistance. However, there is no prescribed formula for converting the manufacturers' test results into universal grades, so be aware of the fact that numbers from tire to tire are not objective.
10. Tires lose air at a rate of about a pound a month, which means if they weren't checked since the last time you had the vehicle serviced (say 4 months ago), they could be several pounds low.
11. Underinflation, by as little as 6 psi, can cut gas mileage by 3%.
12. Cold temperatures affect the air pressure in your tires. There is a loss of one pound for each ten degrees of temperature drop.
13. Warning: Never buy a tire with a lower load index or speed rating than your vehicle's original tire!
14. In North America, regulations require tire manufacturers to grade passenger car tires based on: Treadwear, Traction, and Temperature resistance. Treadwear is based on the wear rate of the tire. A wear rating of 300 to 400 is considered good; 500 to 700 is very good. Further, a tire graded 200 would wear twice as long as one graded 100. Traction grades (from highest to lowest: AA, A, B, and C)represent the tire's ability to stop on wet pavement. Temperature grades (from highest to lowest: A, B, and C) represent the tire's resistance to the generation of heat.
15. Gas mileage decreases 1% for each 10 lbs of underinflation.
16. If you're only buying one or two tires at a time, always put the new tires on the rear axle. It's a myth that putting the new tires on your drive-wheel position will give you the most protection; instead, doing so will make your vehicle more susceptible to oversteer (fishtailing or swinging out during fast cornering).
17. Under-inflated tires wear more on the outside edges. Over-inflated tires wear excessively in the center of the tread.
18. Use a penny to determine if the tread on your tires is too low. Take a penny and put Abe's head into one of the grooves of the tread. If part of his head is covered by the tread, you're ok. If you can see all of Abe's head, it's time to replace the tire. When the tread is worn down to 1/16 of an inch, tires must be replaced.
19. Most manufacturers put "P" (passenger car) rated tires on 4WD trucks as well. Some put "LT" (light truck) tires on SUVs and four-wheel drive trucks, but most do not.
20. The "T" on your tire's sidewall does not stand for Truck, it stands for "temporary" spare.
21. The "recommended" tire pressure is almost always lower than the "maximum" tire pressure printed on the tire's sidewall. Check your owner's manual to find out where to look on your vehicle for the recommended amount of air (usually on the driver's door, the glove compartment, or the gas filler door).
22. Since tires can harden and crack with age, you should steer clear of old tires and buy the freshest ones available. Here's how to tell: Every tire carries a U.S. Dept. of Transportation serial number on the sidewall (EX: DOT M6 RV T1HR 499). The last 3 digits are a date code indicating the week and year the tire was made. (EX: the 49th week of 1999). [l]Most punctures, nail holes or cuts up to 1/4 inch and confined to the tread may be satisfactorily repaired by trained personnel using industry-approved methods.
23. For the most accurate reading, tire pressure must be checked when tires are cold. You can check tire pressure any time of the day, as long as the tires have been sitting for a few hours or haven’t been driven for more than a few miles.
24. Under normal loads, you should inflate tires according to the vehicle manufacturer's recommendations, NOT the maximum pressure listed on the sidewall.