Doug Beimler's QH Automotive

You know you need new tires, but you’re not sure what type. You look at a tire to get the size: 225, 50, R, 16, 92, H. All the way to the service center you keep repeating it over and over. You even say it over in your mind while waiting in line. Then you get to the counter and the manager asks what size you need. Then your mind goes blank.

Tire size can be confusing. There’s so much on the side of the tire, and it’s hard to keep straight.

Even though there’s a lot on a tire – if you know what it all means, it’s actually more helpful than confusing. Let’s start with the size number.

For example, let’s say a tire reads: 225 50 R 16 92 H. The 225 part is the width of the tire in millimeters – the width between the sidewalls of an inflated tire with no load. The 50 is the aspect ratio – the ratio of the sidewall height to the tread width. Off-road tires will have a higher number and high performance tires will have a lower number.

The R signifies it’s a radial tire. And 16 is the rim or wheel size in inches.

The 92 is the load rating index – it’s the load carrying capacity of a tire. The higher the number, the more it can safely carry. Your empty vehicle can be safe with a lower number, but you’ll need a higher rating if you routinely haul heavy loads. The next letter is the speed rating. Not all tires are speed rated. The ratings generally follow the alphabet: the further up the alphabet, the higher the speed rating – with the exception of H – it comes between U and V (don’t ask why).

There’s a lot of fine print that you probably need a magnifying glass to read. But there are a couple of other large print items of interest. One is the tread type: highway, mud and snow, all season, severe snow, etc.

And then there’re the Uniform Tire Quality Grading System markings. The first is a tread wear index. 100 is the base line – a lower number is poorer and a higher number is better. All things being equal, a tire rated 200 would wear twice as long, on a government test track, than one rated at 100. These wear grades are only valid within a manufacturer’s product line – you can’t compare with other manufacturers. And it’s important to note that a lower rating might be just what you want – a high performance, sticky tire has a softer rubber compound and won’t wear as long, but boy, will it take those corners.

The next is a traction grade. This measures the tire’s ability to stop on wet pavement in government tests. A – the best, B – intermediate, C – acceptable.

Temperature grade measures a tire’s resistance to heat build up in government tests. A, B and C – from best to acceptable.

It’s safe to go with the original equipment recommendations that came on your car. But if you want to make adjustments, you’ll now be better equipped to communicate with your tire professional.

Hey Los Angeles County, are your tires worn out? What is the standard for our California streets? How can you tell on your truck?

While there may be legal requirements for the Los Angeles County area, there are safety concerns that go beyond meeting minimum replacement mandates.

2/32 is the depth of the tire tread wear indicator bars that US law has required to be molded across all tires since August 1, 1968. When tires are worn so that this bar is visible, there’s just 2/32 of an inch – 1.6 millimeters – of tread left. It’s that level of wear that’s been called into question recently.

We’re referring to the Consumer Reports call to consider replacing tires when tread reaches 4/32 of an inch, or 3.2 millimeters. And the recommendation is backed by some very compelling studies.

The issue is braking on wet surfaces in and around Los Angeles County. Most of us think of our brakes doing most of the work, but if you don’t have enough tread on your tires, the brakes can’t do their job. When it’s wet or snowy, the tread of the tire is even more critical to stopping power.

Picture this: you’re driving over a water covered stretch of road near Los Angeles County, California. Your tires must be in contact with the road in order to stop. That means that the tire has to move the water away from the tire so that the tire is actually contacting the road and not floating on a thin film of water.

Floating on the surface of water is called hydroplaning. So if there’s not enough tread depth on a tire, it can’t move the water out of the way and you start to hydroplane.

In the study a section of a test track was flooded with a thin layer of water. If you laid a dime on the track, the water would be deep enough to surround the coin, but not enough to cover it.

A car and a full-sized pick-up were brought up to 70 miles per hour, or 112 kilometers an hour and then made a hard stop in the wet test area. Stopping distance and time were measured for three different tire depths:

• New tire tread depth
• 4/32 of an inch
• 2/32 of an inch

So what happened with the 2/32 tires on the car? Get this – when the car had traveled the distance required to stop with new tires, it was still going 55 miles an hour. Stopping distance was nearly doubled to 379 feet and it took 5.9 seconds.

Wow! That means if you barely have room to stop with new tires, you would hit the car in front of you at 55 miles an hour with the worn tires.

Now, with the partially worn tires – at 4/32 of an inch – the car was still going at 45 miles an hour at the point where new tires brought the car to a halt. It took nearly 100 feet more room to stop and 1.2 seconds longer. That’s a big improvement. We can see why Consumer Reports and others are calling for a new standard.

Of course, stopping distances were greater for the heavier pick-up truck.

How do you know when your tires are at 4/32 of an inch? Easy; just insert a quarter into the tread. Put it in upside down. If the tread doesn’t cover George Washington’s hairline, it’s time to replace your tires. With a Canadian quarter, the tread should cover the numbers in the year stamp.

You may remember doing that with pennies. A penny gives you 2/32 to Abraham Lincoln’s head. The quarter is the new recommendation – 4/32.

How do people feel about replacing their tires earlier? Well, tires are a big ticket item and most people want to get the most wear out of them that they can. But do you want that much more risk just to run your tires until they are legally worn out?

For us, and we would guess for many, the answer is “no”.

Doug Beimler’s QH Automotive
226 West Avenue I
Lancaster, California 93534
661-949-8484