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How Long Do Mud Flaps Have to Be on a Semi Truck?

Published by: Nathan
Date of Publish:

It is easy to overlook semi truck mud flaps as there are not part of the vital car systems like the brake system. People hardly realize their use and even view them as decorative or cosmetic features. They may be decorative, but they have a solid function that benefits your vehicle. They are protective components that are worth having.

Mud flaps are useful in passenger cars, motorcycles, trucks, semi trucks, etc. Semi truck flaps are available in multiple styles and designs for various car models. Some manufacturers can customize them for you to suit your semi truck's brand and its needs. Some drivers want the mud flaps to match the truck's color, while others want to advertise on them. But how long should the mud flaps be on your semi truck?

Proper mud flaps length: What to know

Most vehicle owners don't know how far up or down mudguards should be after installation. Their length may affect your truck negatively if you don't follow the proper guidelines. Each state has mud flap guidelines you must adhere to when planning to drive there. You may wonder if you must replace mudguards in every state you pass. The answer is no. There are general guidelines about the length that applies to all semi-truck flaps in most states.

Mud flaps regulations exist to protect the truck and any driver driving behind you. Semi-trucks don't carry as heavy loads as industrial trucks. However, if they have a heavy load, it forces the bed and underside to drop lower. So, if the mudguards are too low, when the semi-truck is empty, there's no doubt it will back over them when fully loaded. It can even rip them off, putting the driver behind you in danger of flying rocks or debris.

Laws about mud flaps

We all know that some cars don't have mudguards. Those that have come pre-installed from the manufacturer or the owner have decided to have them attached. But, you cannot drive without mud flaps on your semi-truck in some states. It doesn't matter if you're going on the highway or offroad or if the truck is for regular use or not. With such laws, it is paramount that you pick the correct size and length of mud flaps for your vehicle.

Generally, mud flaps that are at least 6 to 8 inches above the ground meet the set regulations. No one will stop your semi truck to question why your flaps are too long or short. They will be the ideal size where they are neither too long to cause drag or destruction nor too short hence ineffective. The semi-truck must have properly attached flaps behind the wheels for safety measures. Have them at a 22-degree angle for efficiency and to be safe from the authorities.  

Examples of places that follow the mud flaps regulations

While some states have no strict rules concerning mud flaps, few others enforce them strictly. The transportation department ensures they are implemented for locals and everyone else driving through them. They include;


The guidelines here state that semi-trucks must have flaps that cover the rear wheels. They must provide protection from gravel and other debris that may affect the truck.


The rules here are stringent, so it's good to be well prepared before planning a drive there. Any truck without mud flaps isn't allowed on the highway, and they must be the correct size to meet the set standards.


The use of mudguards in this state is vital. Specific rules and regulations direct truck drivers on what is expected of them during the installation of mud flaps and their usage.

Other areas with mud flap regulations exist; we've just mentioned a few. Before planning a drive in your semi-truck, research how the authorities perceive mudguards in the area you are going and adjust things to suit them. Know the recommended length for your safety and that of other drivers and an easy journey.

How to select mud flaps with the proper length

Don't perform guesswork on the mudguard length you need for your vehicle. Most people don't know how to determine the correct length or size. These tips will help you out.

Look for the part code

Most mud flaps have parts codes that you can use to determine the kind you need. The part code usually has an image of the guard indicating the dimensions of the width and span or length. Unless you want to use a different mudguard style or design, the suggested measurements will help you get something similar for your car.

Measure the car tire

You can measure the wheels or guard required as long as you get the correct measurements. Measure the tires' width and span, leaving room for clearance of about 50mm-100mm from the wheel, depending on the fit. Make the clearance distance less if you want a close fit. Alternatively, increase the space between the wheel and the guard if you need more clearance.

Know the size of the tire

It's easier to get a suitable mud flap length for the semi-truck by identifying the tire size. Most sellers have charts to show each tire size with the corresponding mudguard length on the side. It is especially great for first-time mudguard users with no clue where to begin.

Advantages of using mud flaps of the correct length

Stores stock all kinds of mud flaps with varying sizes, styles, and designs. Choosing the best length can be hectic, but a mechanic can ease things for you by measuring your car wheels and the surrounding area. There are reasons why the authorities insist on you buying mud flaps with proper sizing. It's essential not just for you but for your truck which is expensive to repair or replace. The three primary advantages are;

Protection against debris

It is the main reason for using these flaps on your semi-truck or any other vehicle. The wheels of your truck are in constant contact with the ground where they roll over rock or debris, which tend to fly or splash into the air. A semi-truck is heavy and much heavier when loaded with goods. The force the tires move on the ground makes debris bounce off at high speed. These materials are dangerous as they can potentially damage the underside of your car or the body. Once they land on the vehicle's body, the paint chips off, leaving unattractive marks that need repainting.  

Resistant to weather elements

Resistance goes hand in hand with protection; thus, they guard the truck against water, ice, etc., during damp or colder climates. These elements can affect the car's mechanical parts by causing them to rust or corrode. Corrosion wastes away the parts, making them less efficient or stalling the car's performance entirely. Even though regular maintenance is a thing, and you can spot damages before they worsen, the semi-truck may break down unexpectedly while driving.

Mud flaps keep the truck safe from such issues by blocking their access to the car's undercarriage. They create a considerable splash distance that keeps water from the vehicle and other passengers or passersby. Installing mud flaps with good length eases their work and is more efficient.

General safety

As mentioned above, mudguards keep other vehicles and pedestrians safe. The size and weight of the truck on the ground cause large pieces of mud, debris, and other materials to be flung behind. If this happens with trucks with no mud flaps, the people around or drivers driving behind are at risk of injury. Once the debris is lifted, these flaps block them and push them back down, so no one is affected.

What if the mud flaps are too long?

Long mudguards fold under the wheels, causing you to reverse over them or rip them off. Such flaps have low wind resistance and an increased drag which not only slows down the tuck but also causes a decrease in fuel efficiency. The semi-truck consumed too much fuel, which is a significant disadvantage to the driver. During wet weather or when driving out water-filled potholes, long mud flaps, also called traditional mud flaps, compromise the sight of the driver behind. They splash water directly on their windshield, placing their life at risk.

If these mudguards tear or break off due to increased ground contact and the truck weight, too much time is wasted. This is true especially when on the road, and you have to seek for repairment. They cause delays, equipment downtime, and repair costs. The flaps are affordable, but regular impairment can cause an increase in the money required to replace them. Installing mud flaps of the recommended length is advisable to avoid these unfavorable effects.

In Summary

Mud flaps are beneficial, but you can't install them at any length on semi-trucks. There are rules and regulations to guide you on what is appropriate to avoid problems and for efficiency. States or countries have different rules, so it is up to you to know them before driving your truck there. Generally, the mud flaps should be roughly 6-8 inches above the ground. Don't make them too long or short, as it removes their functionality.

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