By Bob Burns:
As you begin to get into the off-road world, there seems to be a lot of talk about tires. Types of tires, tire size, what fits, what doesn’t. Who makes the best tires? What tires should I choose for my 2021 Ford Bronco? The off-road forum sites that discuss tires will make your head spin. So much information, so many choices, so many opinions. How do you narrow down the right tire for you? Tough question, but maybe it is an easy answer.
The key question to start with is what tire works best for how you intend to use your Bronco?
Initially, we’ve seen that the new Ford Bronco offers at least 6 different tire choices depending on the model chosen. We could spend hours reviewing all of the letters and numbers that are found on a typical tire sidewall. For now, let’s focus on type and size and getting an understanding of how to decode all of that.
This list of tires can tell us a lot about what the tires are intended to do best. When you combine the tire type with the Bronco model it is available on, it actually starts to make some sense.
What do these letters and numbers mean?
Let’s start with P and LT. The tire sizes are in a metric format, both P metric and LT metric sizing.
The P in a tire size tells us it is a tire designed for passenger car use. So, what’s that doing on a Bronco? We will get there.
The LT means Light Truck, which seems more Bronco-like, right? The P and LT designations tells us how the tire will perform based on its design. There are pluses and minuses to both depending on your primary use of your Bronco.
P designated tires are designed to carry a bit less weight or load than an LT tire. So, unless you are towing or carrying heavy loads, a P tire may be perfect for your needs. It will generally ride a bit better than an LT tire. It will usually be quieter and possibly have a longer tread life as the tread pattern may be a bit less aggressive and may contribute to better fuel economy from its design and materials.
So, what’s the LT tire all about? As the initials imply, LT, Light Truck tells us something. Designed to work in a light truck environment, it is designed to carry heavier loads and would be recommended to run with higher air pressure to carry those loads. It will have a stiffer composition meaning a stiffer sidewall and maybe even a deeper tread compared to its P rated counterpart. It will hold up to tough off-road use a bit better and carry heavier loads better, but it will give up some ride comfort, probably some fuel economy, and will be a bit noisier.
As with everything on a car or SUV, there are compromises that you’ll need to consider based on the everyday use of your Bronco. The good news is that there are no bad choices. All the tires are selected by Ford engineers to perform and be safe well above expectations.
What about all those numbers following the LT or the P designation?
The numbers tell us how big a tire is in width, overall height and in sidewall height. You may see a lot of references to 33” tires, 35” tires, or even 37” tires in the forums or on the Ford sites. Those measurements refer to overall tire height. The metric measurements also will give us tire height, width, and more.
For the sake of example, let’s take a look at the Sasquatch package. The Sasquatch package gives us an LT315/70 R17. Let’s break that down and convert it to off-road speak in inches.
- LT tells us this is a Light Truck specification and will be happy off-road.
- 315 tells us that this tire’s tread is 315 millimeters wide or 31.5 centimeters wide (about 12.4 inches). That’s a fairly wide tire.
- 70 refers to the “aspect ratio.” This helps us determine the overall height of our tire and wheel combination. It allows us to calculate the height of the tire sidewall. The 70 is a percentage of the tire’s width. With our Sasquatch tire, the width is 315 mm, so the side wall height is 70% of 315, or 220.5 mm.
- R refers to the radial construction of the tire vs. a bias ply type tire.
- 17 refers to the size of the wheel or rim that this tire is made for but measured in inches. We actually have both metric and imperial dimensions on the tire side wall.
So how tall is this tire in inches? Time for some math.
We’ve calculated that the tire sidewall is 70% of the tread width. 0.7 x 315=220.5. We know we have two sidewall heights to add in – the top and the bottom. So, we have 220.5 x 2 = 441.5 mm.
We now know that the actual wheel or rim is 17 inches in diameter or height, which is 431.8 mm.
When we add 431.8 and 441.4, we have 873.2 mm. That comes out to 34.4 inches, very close to 35”, indicating the Sasquatch has 35” high tires and also letting you know details like tread width and sidewall height.
Ford has been very generous with allowing a large range of tire sizes to be fitted to the Bronco. We said size matters and, as with everything, there are trade-offs both good and some not so good depending on your needs. Engineers spend a lot of time defining the proper tire size to put on the final product. Bottom line is tires are heavy. Bigger tires are even heavier.
Bigger is not always better. The engineers work hard to tune suspensions to provide a comfortable ride and safe, predictable handling. Tires can affect both in many ways. Bigger tires offer a larger “footprint” to generally provide better grip, but bigger also brings with it a weight penalty that the suspension has to control. So, there tends to be a balance. Believe it or not, a tire can be so big in relation to the vehicle weight that it actually provides less grip! Large tires also make the braking system work harder. Being heavier makes it harder to stop.
Now add off-road use to the conversation. Bigger tires are an advantage in providing more ground clearance to get over obstacles and have a larger rolling diameter. Think about driving your bicycle over a curb and then try that same curb with a skateboard – size matters. Bigger tires can provide a larger footprint to help us “float” over sand or mud. The larger diameter can help us clear obstacles in the trail and at the same time look cool. But remember, in everyday on-road driving, the ride comfort and handling may suffer a bit as would fuel economy and braking efficiency.
In summary, tall tires are great for off-road ground clearance, but they are heavier. LT tires may provide a bit of a rougher ride, may be a bit noisier, may wear faster, and take away some fuel economy on the paved roads. P tires are generally quieter, provide better fuel economy, wear longer by design, and will perform pretty well in many off-road environments.
A lot of choices for you to make. The good news is that an army of Ford engineers have provided several choices for you on the new Bronco and engineered a vehicle that will perform safely and handle well regardless of choice. The amount of engineering that goes into modern tires is jaw dropping. When we consider what we ask a tire to do, they are truly amazing feats of engineering.
Whatever your use for your Bronco, there is an appropriate tire choice available, so do your homework to best understand the differences and determine which is best for how you will use your Bronco!
What tire size are you choosing and how will you be using your Bronco? Share in the forums!
Bob Burns is an experienced off-road driving expert, architect of multiple off-roading courses around the world, and a valued member of the Bronco Nation team.