When you hop into a vehicle to take a drive, you want to have confidence that you can arrive at your destination safely.
Several components work together to create that outcome, although the most crucial part is the tires on the vehicle.
Without tires, you’re not driving anywhere!
If you have low-quality tread or a damaged sidewall, the vehicle could suffer a blowout while driving. Who wants to be left stranded on the shoulder, waiting for roadside assistance to arrive?
That’s why equipping your car, truck, van, or SUV with the correct tire size and type is critical to your safety. With several sizes available, it is essential to know how to read the information on each model to ensure it works with your vehicle.
305/55-R20 vs. 35/12.5-R20 Tire Comparison
If you have a 305/55-R20 tire, you’re working with a 33-inch diameter product that comes with a tread width of approximately 12 inches. When you install a 35/12.5-R20 tire on a vehicle, the product is 35 inches wide and has a tread width of 12.5 inches.
When you see the 305/55-R20 compared to the 35/12.5-R20 tires on the market today, it’s essential to remember that the first option is a metric tire size, and the second uses imperial measurements.
The imperial system was first implemented in 1824 when Great Britain passed the British Weights and Measures Act. It has continued to receive amendments over the years to create a comprehensive system that falls outside of the metric system as the primary source of measurement.
That means you’re using inches instead of millimeters to designate the tire’s width.
If you were to convert the 35/12.5-R20 tire size to the metric system, the tire measurement would be 318/60-R20.
That means a direct comparison of the 305/55-R20 vs. 35/12.5-R20 tires shows that the latter one is slightly larger.
The 35/12.5-R20 might be like the 305/55-R20, but it comes with one clear advantage for your vehicle. A larger tire delivers more grip on the road because it covers more surface area. Even though the difference is only 13mm, that could be enough to give you that one small advantage for turning, cornering, or braking when it matters.
Tire Translation: What Do the Letters and Numbers Mean?
At first glance, the letters and numbers that you see on a tire’s sidewalls seem like a foreign language.
They offer a direct insight into the tire size and type while delivering some supplemental information to let you make an informed decision.
If you’re unsure how to translate what a tire is saying, here is a look at what all those letters and numbers mean.
| Brand and Model: | This information gets put on a tire like a cereal company plastering their logo and brand name on a product box. You’ll see the model and company name “printed” on the sidewall. Vehicles typically drive better when all four tires are the same. |
| Tire Type: | Once you get past the brand and model, you’ll see a series of numbers and letters appear. If you saw P305/55-R20, the “P” stands for “passenger vehicle.” If the first sequence was T305, the “T” stands for “temporary,” which means it would be a spare. LT305 would mean “light truck.” Another designation is ST, which means “special trailer.” You would not want to equip that tire to your car. |
| Tire Width: | Using the 305/55-R20 tire as an example, the “305” represents how wide the product is in millimeters. This measurement gets taken from sidewall to sidewall. If you see a small number, such as the “35” in 35/12.5-R20, that means the width measurement is in inches instead of millimeters. |
| Sidewall Height: | This measurement occurs after the “/” in the tire numbers and letters. It represents the aspect ratio of the product, which is the width percentage to sidewall height. In the 305/55-R20 example, you’d know that the sidewall height is 55% of the width. You could get the exact measurement by multiplying 305 by 0.55. |
| Tire Construction: | The “R” in the tire sequence of 305/55-R20 represents how it was made. It means that the manufacturer built it using radial construction. Although most passenger vehicles use that option, you can also find “D” (diagonal bias) or “B” (bias belted) on tires for sale today. |
| Wheel Size: | The final number in a tire labeling sequence represents the wheel size it’s meant to fit. Some people use the term “rim” interchangeably with “wheel” here. For the 305/55-R20 tire, that means you’d need 20-inch wheels to fit the tire. |
Additional Tire Information You Can See on Different Models
Although the primary information you’ll see on a tire represents the six information categories above, most manufacturers include several additional data points for you to consider.
Once you know how to interpret the information found in an example like P305/55-R20, you can spot these additional components.
1. Maximum Permissible Inflation Pressure
This data point lets you know what the maximum PSI rating is for the tire. Some drivers like to slightly over- or under-inflate their tires when driving to achieve specific results. You’ll see what the “max press PSI” is to know that going above that figure could cause a blowout.
Some tires might have this information listed as kilopascals (kPA). It is usually not recommended to inflate them to the maximum rating.
2. Load Index and Speed Rating
You see this information on tires because it is the maximum weight that the vehicle can handle. If you have a model that says it’s rated for 90R, that means it can hold over 1,300 pounds while traveling at speeds up to 106 miles per hour. You’ll need to consult a load and speed index to discover what your tire’s specific rating means.
3. Tire Date
You’ll see a series of letters and numbers on the tire called the DOT code. What you’ll want to look at here is the four-digit combination at the end because that tells you when the product was made.
If you saw the number “4220,” that would tell you the tire got made during the 42nd week of 2020.
4. UTQG Information
UTQG stands for “Uniform Tire Quality Grading.” It’s a system produced in the United States by the National Highway Traffic Safety Administration (NHTSA). This sequence provides information about traction, tread wear, and temperature ratings.
Since testing varies by manufacturer, this information isn’t always practical when comparing tires. It may be more helpful to review the product warranty instead.
Traction ratings range from Grade C to Grade AA, with the latter being the best. Temp ratings follow the same sequence.
5. Uncommon Data Points
Every manufacturer publishes different information about their tires on the sidewalls. Some of them only use the six standard data points, while others include several options that go beyond what has already been reviewed.
- Max Load Rating. This information is sometimes published separately from the load index and speed designation. It’s a specific rating for how much weight the tire supports when equipped to a vehicle.
- Weather Conditions. Some tires have letters that designate their tread differentiation from a standard ribbed design. You’ll see M+S (or some variation), indicating that the product is a mud and snow tire.
- Winter Tires. If you see a triple mountain peak with a snowflake on the tire, this symbol indicates that the product is made for winter driving conditions. Some all-terrain light truck tires earn this designation without being specifically created to operate in the snow, but most are made to be used during the winter months only.
- Tire Ply and Composition. You might see how many plies are part of a tire’s construction for the tread and sidewall. This data point often includes the specific materials used to create the product.
Tips for Having the Safest Driving Experience Possible
When you have larger wheels, that often means you’re working with a thinner tire. It needs to be small enough to fit inside the well without rubbing, which means you’re less likely to handle a rougher road or impact incident.
Thinner tires blow out more often, which could create safety problems. If you want to avoid this issue, a lift kit and wheel well modification might be necessary for some larger tires.
Although you typically want the same tire size on all four points, it’s sometimes acceptable to have different wheels and tires on the front and back. This staggered installation works well for muscle cars, including the Camaro, Challenger, and Mustang. Since the rear wheels don’t turn the same way as the front ones do, this setup creates more road stability.
It is typically more expensive to purchase new tires for larger rims. If you have an unusual size, only a handful of manufacturers might produce a model that your vehicle uses. The average passenger car doesn’t encounter this problem unless the owner modifies the stock setup.
Knowing your vehicle and the tires it needs can help you avoid making mistakes when selecting replacement models. When you understand the comparison of the 305/55-R20 vs. the 35/12.5-R20, that process gets even easier.
Best 20-Inch Rims to Buy for Your Tires
The one point in common that the 305/55-R20 and 35/12.5-R20 tires have is that they both work on 20-inch rims. That makes it a suitable option for running a staggered setup, something with a lift kit, or a different modified look on many racing cars to maximize vehicular performance.
I run 20-inch rims on my truck because it delivers the right level of performance and stability. Although I could install a lift kit and go bigger, most of my driving is on the highway. Our family has a lot of extracurricular activities, so the vehicle feels more like a taxi service.
When one of my wheels failed after rolling over a poorly maintained railroad crossing, it shredded the tire and forced a complete replacement.
I didn’t want to spend a fortune on the replacements, but I also needed something that could handle many miles without me worrying about it.
That’s when I discovered the Giovanna 20-inch rims. These black wheels some as a set of 4 and are built to deliver a strong performance. They’re good enough to use on today’s muscle cars while providing the consistency I want with my truck.
If you are going up in size, you’ll want to think about getting a thinner tire. Since some passenger cars use 16-inch wheels, the four-inch difference could require some extensive modification.
They look amazing, and I love how they changed the appearance of my truck. You can use either the 305/55-R20 or 35/12.5-R20 tires on them successfully.
