NEED TO KNOW: TIRES
We use them everyday but do you really know why? The following page will teach you everything you need to know about tires including a brief history, their purpose, different types & also how to read the secret code on the side.
Why Tires?
It’s suggested that the wheel was invented over 3000 years BC and did not look like the wheels we have today. They were made of wood and it’s believed that they were first used on chariots.
A problem with these wooden wheels was that they “wood” wear out. They also provided a pretty rough ride with little traction but we will get to that in a moment.
The first attempt to solve this problem was to wrap leather bands around the wooden wheels and then iron. In the mid 1800’s the English began to shrink fit railway car wheels with malleable iron which is where the word tire came into existence, rooting from attire, the idea of a “dressed” wheel.
Then in 1888 a Scots-born veterinarian by the name of John Boyd Dunlop noticed that his 10-year-old son was getting headaches while riding his tricycle on rough pavement. His solution was to create a pneumatic tire (filled with air). This would cushion the bumps allowing for a smoother ride. Little did he know at the time but this would “pave” the way for the tires that we use today.
Tires Today…
Skipping ahead, although we have stuck with the same principles, automotive tire design has come a long way providing two basic functions. Comfort & Traction, acting as a soft cushion and providing friction between the wheel and the road.
Tires typically consist of synthetic & natural rubber, fabric ,wire, carbon black and other chemical compounds.
Elastomer
Elastomer is what forms the tread and encases the cords. This protects the cords from abrasion and holds them in place. It can be composed of different composites of rubber and chemical compounds such as carbon black and silica.
Cords
Cords are used within the tire to provide tensile strength which is a must when trying to contain the inflation pressure. These cords are often composed of steel, natural fibers like silk or cotton, or synthetic fibers like nylon or Kevlar.
These cords are what determine the construct of the tire being either a bias ply, a belted bias tire or a radial tire.
Tire Constructions
Bias Ply
These plies run on an angle from bead to bead with each angle being reversed from ply to ply. They do not use belts and as a result of this construction, the body of the tire can easily flex providing a smoother ride. A negative to the bias ply tire is that they reduce traction at higher speeds and they have a higher rolling resistance.
Belted Bias Ply
Similar to the previous with the addition to belts which lie under the tread area to increase tread stiffness. Having two stabilizer belts and two or more plies improve tire performance providing a smooth ride with good traction and reduce rolling resistance.
Radial Ply
Unlike the bias ply which runs on an angle from bead to bead, the radial runs straight across. They also have stabilizer belts which lie beneath the tread which can be made of steel, flexten, fiberglass, or other materials. Radials take advantage of having a flexible sidewall along with stiff tread to provide a stiff footprint, improving safety, cornering, wear and braking. A disadvantage would be that a harder ride may be produced at lower speeds.
Identifying Your Tires
Typically the specifications and size can be found listed on the side of the tire. The trick is understanding what these numbers mean. An example of a number you may find is P205/65 R15 94H.
(BMW of Stratham. (2018). Retrieved January 3, 2021, from BMW of Stratham website: https://www.bmwofstratham.com/how-to-read-tire-size-stratham-nh/)
When looking at the following chart, you can see how vital it is to take note of this information when trying to find a replacement tire for a vehicle. Also worth noting is that just because the tire fits the rim size, the width or height may not be appropriate for the application which could cause the tire to rub against the vehicle.
|
P |
Passenger vehicle |
|
205 |
Tire width measured in millimeters |
|
65 |
The percentage of the sidewall height compared to the
tire width |
|
R |
Radial tire construction |
|
15 |
Rim diameter in inches |
|
94 |
Load index |
|
H |
Speed rating |
Service Descriptions
Since 1991, it has been required that all speed rated tires must include a service description on the sidewall. This is identified as a number and a letter. For example, 94H.
Load Index
The load index is represented by a 2-3 digit number. The higher the number, the more weight capacity the tire has. To determine what the actual weight capacity of the tire is, you will need to reference the number with a chart like the one below.
94 = 1,480lbs. (pounds)
Speed Rating
Just like having a weight restriction, tires are also bound to certain speed limitations. Tested in labs, each model of tire is designed to handle a maximum speed which is represented by a letter. If the rating does not match up with the application, performance and safety can be compromised as a result.
H = 210 km/h
Tread Types
Being that one of the main purposes of a tire is to create traction between the wheel and riding surface, it’s important that the tread design suits the environment. The more surface area you have in contact with the ground, the more friction you will encounter resulting in better traction.
“The most amount of friction occurs right before it starts to slip”
So why do tires have grooves in them?
If you have perfect road conditions where there is no dirt or water on the pavement, a tire with no tread would show the best performance allowing for better acceleration and would stick to the roads while cornering. The only problem is these perfect road conditions are far and few between. You'll encounter rain, dirt, or snow which would come between your tire and the road reducing friction. Tread allows the tire to cut through these obstructions and with the proper design even push everything outwards. The challenge is determining the proper ratios of surface area and tread.
Another thing to keep in mind is that the tread can affect how much noise is produced so although the tire may have great off-road traction, it could be noisy driving down the road.
With this information, it makes sense that there should be different categories of tires for various road conditions. Listed below are a few common types.
Summer
Best suited for warmer clients, these tires perform in wet and dry conditions. Summer tires have circumferential grooves to prevent hydroplaning and offer solid contact patches that prevent slippage.
All-Season
Like summer tires, all seasons contain symmetrical circumferential grooves for wet weather grip but have a more aggressive tread for light snow conditions. These tires are popular because they are designed to provide a comfortable ride with reliable handling.
Touring Tires
Aside from having a higher speed rating, touring tires are a lot like all seasons. The main difference is that later is designed with comfort in mind. They typically feature an asymmetrical tread pattern with reliable all season traction.
Winter Tires
These tirs are designed primarily to give superior traction in winter conditions. The compounds used are meant to perform their best at very cold temperature and feature heavy siping with deep circumferential grooves to expel snow and slush buildup from the contact patch.
* Siping improves traction in wet or icy conditions by cutting thin slits across the rubber surface.
* Synchronous tires have matching tread pattern on both sides.
*Asynchronous tires have a unique tread pattern design on each side.
Honorable Mentions:
There are so many different types of tires available on the market today so instead of going through everything, here are some some others worth noting. Highway, All-Terrain, Performance, Track / Competition, Mud-Terrain, All-Purpose, Ribbed, Sport Truck
Do You Really Need Snow Tires?
Although all season tires are designed to be able to perform in snow conditions. It’s only recommended for light snow. Since they are meant to work in all seasons, there is an emphasis on creating a comfortable ride and reliability in multiple temperatures.
Winter tires have a more aggressive tread and are softer to accommodate for the colder temperatures. Driving with these tires in the summer would equal a less comfortable ride with more noise and they would also wear down quicker.
With that being said, if you live in an area where heavy snow is a regular occurrence, being specifically designed for the climate it is recommended that you use snow tires. If you live in an area where days of heavy snow are far and few between, all-season would definitely do the trick.
Measuring Tread Depth
It’s common for tires to wear down and depending on their properties, some wear quicker than others. Since tires depend on tread for performance, it’s important that you monitor the tread depth to insure that you have a safe ride. This can be checked by measuring within the grooves. If the depth is 2/32” or less, the tires need to be replaced and are considered unsafe.
As an additional guide, tires are typically equipped with wear indicators that sit between the treads. If the tread height is equal to the wear indicators height it’s time for replacing.
Reading Tire Wear
There is a lot riding on your tires and if everything isn’t working in sync, it’s possible that your tires will show uneven wear. The good thing is that if you know what to look for, there are certain indicators that can point you in the right direction to fixing the problem.
The previous images display what you should be looking for when checking your tires.
Tire pressure is typically in the owners manual or on a sticker just inside the drivers side door. It’s very important that you regularly check your tires because both underinflation and over inflation can cause excessive wear. Under would cause even wear on the outside of your tires and over would wear the center due to bulging.
It’s also possible that improper wheel alignment, balance and worn out suspension can cause unique wear patterns.
Nitrogen Filled Tires
As an indicator, if you come across a green cap on your wheels valve stem, this means that your tire is filled with nitrogen.
Typically tires are filled with air to a recommended PSI ( pounds / square inch ). They recommend a specific PSI to insure that the tire will provide optimal performance. It’s natural that tires will lose a small amount of air even without any punctures. Roughly 1 - 2 psi per month.
The theory behind using nitrogen is that the molecules are larger than oxygen which would make it harder for it to escape through the porous rubber. In return this means that it’s more likely that you will be driving at the recommended PSI improving gas mileage and handling.
The downside is that it costs more money to use nitrogen and it’s less accessible. In theory it sounds like a great idea but in reality the improvement is minimal showing a difference in loss of only 1.3 PSI over an entire year.
Competition Tires
Here are a few videos showing you what tires are actually capable of when used competitively.