6 Reasons Why Rear Wheels on a Farm Tractor are Bigger

Man driving a orange tractor

As a new farm tractor owner I was curious as to why rear wheels on a farm tractor are much bigger than the front ones. I know, it’s a very basic questions but not for a new hobby farmer like me!

I, personally, had no clue why the rear tires were so large until I drove our tractor and started leveling some parts of the field. And I was so curious I researched on the internet and asked other farmers.

So here’s what I found out – the big rear wheels are an essential component of a farm tractor and a staple in their design.

Also, a tractor’s large rear tires play a pivotal role in the increased productivity of projects and tasks by providing 6 major benefits. Read on to find out what key benefits large rear wheels provide.

  1. Better Traction or Grip With the Ground
  2. More Pulling Power
  3. Better Visibility in the Front
  4. Ability to Protect and Prepare the Soil
  5. Easier to Navigate Obstacles
  6. Provide Better Weight Distribution

1. Better Traction or Grip With the Ground

Farm tractor tires have a larger diameter and a larger area of contact with the ground. Having more surface area in contact with the ground provides more friction and less slippage.

Therefore, preventing the tires from sinking down and getting stuck in soil, wet mud or loose terrain. Overall, increasing our efficiency and productivity in the field.

This design feature is similar to a racing car, which also have larger rear wheel tires. Because they too want to maximize their traction with the ground.

2. More Pulling Power

Typically, utility farm tractors are two-wheel or rear wheel drive, which are perfect for farming and industrial purposes.  Two-wheel or rear wheel means that the rear wheels are the “drive-wheels” and are connected to the drive shaft.

Farm tractors are designed to go slow, so their rear wheel drive design takes advantage of weight transfer during forward movement, which maximizes traction while using lower RPMs and producing providing higher torque. The engine converts the heavy revolution force into pulling power.

The general law of physics suggests that the larger the diameter of a circle, or the higher the circumference, the larger amount of torque the object will produce.

Whereas, race cars are designed to go fast, so their rear wheel drive design takes advantage of weight transfer during acceleration which increases the tire grip to the pavement while using higher RPMs and producing less torque.

The driving axle on our utility tractor is also situated higher above the ground because of the larger size of the rear wheels. This design feature also allows our tractor to pull more weight without our tractor either tipping over or having the front of it rise up. Which is pretty freaky if you’ve ever had it happened to you!

The driving axle functions similar to a lever – where twice the height provides twice the maximum pulling power.

photo credit: Christy Louth

3. Better Visibility in the Front

The larger rear wheels of our farm tractor (compared to the front tires) put our driver’s seat at a higher elevation. This higher elevation provides better visibility while driving. It’s much easier for me to see over the nose of the tractor and when my husband is doing projects, like leveling our gravel driveway, he can cut corners more efficiently and ensure he isn’t missing any sections.

4. Ability to Protect and Prepare the Soil

As a hobby farmer, we’ve learnt that preparing the condition of the soil before you plant your seeds and protecting the soil throughout the life of the crop(s) are important factors to producing healthy plants.

Plants will not grow or will have a very difficult time growing in compact soil.

Because the rear tires of our tractor have a much larger surface area, the weight of the tractor is distributed across a larger area and the tires don’t compress the soil as much. This helps us prepare and effectively protect our soil.

It’s also worth noting that another factor to prevent soil compaction is tire pressure.  You can reduce tire pressure to as low a pressure as possible. This lower pressure, along with the wider tires will further reduce the compaction of the soil.

However, you don’t want to reduce the tire pressure too much that the tires start turning in on the rims and stability of the tractor gets compromised.

5. Easier to Navigate Obstacles

The larger rear wheels have deeper treads. These treads help us drive over very rough and uneven terrain without getting stuck.  They also help us scale steeper terrain.

We’ve got some humps and bumps on our property – sometime 2 feet in elevation change so we’re thankful to have the large rear wheels.

6. Provide Better Weight Distribution

The average weight of a tractor tire can weigh between 400 and 600 pounds. This additional weight in the back of the tractor provides better weight distribution. The tractor’s engine, which is extremely heavy, is located at the front of a tractor so the large and heavy tires help counterbalance the weight of the engine in the front.

Also, when an implement or piece of equipment is mounted onto the rear of a farm tractor it will increase the weight on the rear axle and remove weight from the front axle. And visa-versa if an implement or piece of equipment is mounted onto the front of a tractor.

The balance of this weight between the two axles is known as the load distribution.

It is very important to monitor your tire pressures and adjust them accordingly to take this load distribution into consideration.

Incorrect loading and incorrect tire pressures can create excess stress in the tires which can cause them to wear out faster.

There are several fancy online tools out there to help you calculate the correct inflation pressure to use. Some even recommend the optimum pressure for the selected application or ground condition.

It’s worth taking the time to investigate this and get the calculation right, as these types of mistakes can be costly.

Related Questions

Why are the Front Wheels on a Farm Tractor Smaller Than the Rear Wheels?

The smaller tires at the front of a farm tractor provide better handling. The small tires make it easier to navigate through narrow and sharper corners in a field. This maneuverability comes in handy for many projects and tasks – like harvesting, ploughing, sowing, as well as leveling fields. The smaller radius of the front wheels provide tighter and more controlled turns.

How to Measure Tractor Tires?

To determine the measurements on your tractor tires, locate the numbers on the sidewall of the tire. There may be 2 or 3 numbers, separated by either the backslash symbol ( / ) or by a dash symbol ( – ).

If there are 2 numbers, these will tell you the width of the tire and then the diameter of the rim (both will be in inches).

If there are 3 numbers, these will tell you the height of the tire, then the width, then the diameter of the rim.

Overall, it is the size of the rims that are the most important factor when replacing your tires.

How Long do Tractor Tires Last?

The 3 main factors that determine how long a tractor tire lasts are:

(1) the surfaces you are driving on,

(2) the weather conditions in your region; and

(3) the soil type.

The best way to determine when your tractor tires need replacing is tire slippage and how much tread is left on the tire. If you are noticing less traction than normal and your fuel costs increasing it may be time for a new set of tires.

However, you may also want to review a few more points and tips we found useful to inspect the life left on tractor tires. We used these helpful points when we were looking to buy a used tractor.

What are the R Codes Found on Farm Tractor Tires?

You’ll normally find the tire tread code on the side of your tractor tire. You will see R1, R3 or R4. Each code classification has it’s own name, size, tread type and characteristics.

photo credit: Priority Tire
  • R1 = Commonly referred to as an Ag or agricultural tire. These tires have the best traction. They are superior in the mud and fields, but can cause the most ground damage. R1 tires are the narrowest compared to the R3 and R4 tires.
  • R3 = Commonly referred to as a turf tire. These tires have less aggressive tread and are meant for tasks like mowing, as they have the least amount of traction. They are commonly used on golf courses or for ride mowers, as they are grass friendly and tend not to tear the ground up, especially in soft wet conditions.  R3 tires are the widest compared to the R1 and R4 tires.
  • R4 = Commonly referred to as an industrial tire. These tires have great traction and are softer on turf than R1 (Ag) tires. They are commonly used by contractors and landscapers as an all-purpose tractor tire.  The R4 tire has a very sturdy sidewall construction capable of handling heavier loading. This means that if you have loader work, these tires will handle it unlike the R1 and R3 with softer sidewalls.

Christy Bouma

Christy is a wife, writer, artist and hobby farmer with an addiction to tractors.

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