Aftermarket modifications and crash protection: what to check before you modify or buy
How lifts, bumpers, seats and tires can change how air bags and belts protect you
Safety Behind the Wheel Foundation built this guide from National Highway Traffic Safety Administration (NHTSA) guidance, Insurance Institute for Highway Safety (IIHS) research, the Federal Motor Vehicle Safety Standards and federal law, and the inspection rules of Pennsylvania, Virginia and Maryland. Every source is listed at the end.
Why a modification is a safety change
Crashworthiness means how well a vehicle protects the people inside during a collision. The frame and crush zones soak up energy. Seat belts hold you in place. Air bags cushion you. Seats keep your body where the belts and bags expect it to be.
The federal government sets minimum safety rules called Federal Motor Vehicle Safety Standards, or FMVSS. Separate standards cover lighting, stability control, tire pressure monitors, seats, steering, air bags and belts, belt anchors, side impacts and roof strength [1].
These systems save lives. Federal estimates cited by the Insurance Institute for Highway Safety (IIHS), a research group funded by auto insurers, credit frontal air bags with saving 70,059 lives through 2019 [2]. In frontal collisions, front air bags cut driver deaths by 29 percent [2].
With any modification, the key question is not whether the part looks right. It is what job the original part did in a collision, and whether the new part still does it.
Four questions to ask about any modification
Use these questions whether you plan a change or are looking at a vehicle someone else changed.
- What did the factory part do in a crash? A bumper is not just trim. A steering wheel holds an air bag. A seat may hold a side air bag.
- What changed? Look for differences in height, stiffness, weight and position.
- Which other systems rely on that part? Air bag sensors, stability control, cameras, radar and belts can all depend on the factory setup.
- Is there proof the new part was designed and tested for this exact vehicle? Look for written guidance from the automaker or part maker, plus the installer’s records.
If you cannot answer one of these questions, treat that modification as unchecked until a qualified shop looks at it.
Lift kits and lowering kits: height changes everything
A suspension lift changes springs, shocks or other suspension parts. A body lift adds spacers between the body and the frame. Lift blocks are solid spacers placed between an axle and its springs.
Center of gravity and rollover
The center of gravity is the balance point of a vehicle’s weight. A lift, or much taller tires, raises that point. A higher balance point makes it easier to tip over in a sharp turn or a sideways slide.
Federal rules already treat height as a rollover issue. Certain SUV type vehicles built for occasional off road use must carry a label warning of a much higher rollover rate than other vehicles [3]. Their owner’s manuals must explain design features behind that risk, such as a higher center of gravity [3].
In 2024, rollovers were involved in 38 percent of pickup occupant deaths, 33 percent of SUV occupant deaths and 20 percent of car occupant deaths [4]. Those same manuals must warn that an unbelted person is much more likely to die in a rollover [3].
Bumpers that ride over other vehicles
Height also affects people in the other vehicle. IIHS explains that older SUVs and pickups were extra dangerous to people in cars partly because their bumpers and energy absorbing parts sat higher [5]. In a collision, they could ride up over a car’s hood [5]. In IIHS’s 2017 to 2022 data, people in cars were no more likely to die in a crash with an SUV than in one with another car [5].
A tall lift can move a truck’s bumper and frame rails back above a car’s crash structure. That can undo some of that progress.
People on foot
IIHS reports that when vehicles with hoods taller than 40 inches hit pedestrians, deaths were about 45 percent more likely [6]. That was compared with vehicles that had hoods under 30 inches and sloped fronts [6]. Taller vehicles with upright fronts also caused more head, torso and pelvis injuries [6].
A lift plus a tall, squared off steel bumper moves a vehicle toward that risky shape.
Lowered vehicles
Lowering cuts suspension travel, which is how far each wheel can move up and down. With less travel, a vehicle can bottom out on bumps, dips and driveways. Pennsylvania fails a vehicle whose front suspension is lowered with spring shackle kits or blocks [7].
Aftermarket bumpers, grille guards and winch mounts
A factory bumper is part of a crash system. Behind the cover sits a reinforcement beam with mounts that tie into the structure. Air bag sensors start measuring crash severity the instant a collision begins. If it is severe enough, they fire the bags in a fraction of a second [2].
So the key question is how a heavy steel bumper, grille guard or winch mount changes the forces those sensors feel. Ask the part maker whether the part was designed for your exact model and its air bag system.
The federal bumper standard aims only to limit damage in low speed bumps, using tests at 1.5 and 2.5 mph [8]. It sets a test zone 16 to 20 inches above the ground. It does not apply to multipurpose passenger vehicles, a federal class that includes many SUVs [8, 3].
States may add limits. Maryland caps bumper height at 20 inches for passenger cars and 28 inches for light trucks and multipurpose vehicles [9]. It also rejects bumper extensions added to make up for suspension changes [9].
Before you install or buy a custom front end, ask:
- Does it cover a camera, radar unit, parking sensor or headlight?
- Does it stick out past the body or add sharp edges?
- Is it bolted to the frame where the part maker specifies?
- Did the installer check for warning lights afterward?
If a new part covers or moves a sensor, see our guide on why cameras and sensors need checks after crash repairs.
Steering wheels and the driver’s air bag
The steering wheel contains the driver’s frontal air bag [10]. A replacement wheel without an air bag takes that protection away. A separate federal standard covers impact protection for the driver from the steering system [1].
Air bag parts are not a place to save money. The National Highway Traffic Safety Administration (NHTSA) warns that counterfeit air bags have failed in ways ranging from not inflating to throwing metal pieces [11]. NHTSA advises having a deployed air bag replaced promptly by an authorized repair center [11]. Safety Behind the Wheel Foundation gives drivers the same advice.
Some states check steering wheel size. Pennsylvania rejects a wheel that is not round or is under 13 inches across [7]. Virginia rejects a wheel under 13 inches across unless it came from the factory that way [12].
If the air bag warning light stays on, or never glows briefly at startup, have the system checked.
Seats, belts and seat covers
Factory seats are crash parts. A federal standard covers seats, their mounts and how they are installed, so they do not fail under crash forces [13]. Each seat must hold up under a forward pull of 20 times its own weight [13]. A seat on a homemade bracket may not meet that bar.
Many seats also hold safety gear. IIHS describes side air bags that deploy from the seatback [2]. A replacement seat without one removes that protection. NHTSA also explains that many advanced systems turn off the passenger air bag when they detect a child or small adult [11]. If someone swapped the front passenger seat, ask whether that sensing still works.
IIHS advises against aftermarket dash or seat covers, because they can get in an air bag’s way or change the direction it inflates [2]. Check your owner’s manual to see whether your seats contain air bags before adding any cover.
Seat position matters too. NHTSA recommends at least 10 inches between your breastbone and the air bag cover [11]. A seat mounted higher or farther forward can shrink that gap and change where the belt crosses your body. Pennsylvania also rejects a vehicle missing a seat belt at any seat that had one from the factory [7].
Wheels, tires and spacers
Tires affect braking, steering and stability. NHTSA advises buying tires that match the original size or another size the automaker recommends [14]. The right size is on the tire and loading label on the driver’s door edge or post, or in the owner’s manual [14].
Bigger wheels and tires add weight and height. Before a size change, ask whether the automaker approves that size for your model. Also ask whether the speedometer or stability control settings need an update.
Cars, light trucks and vans from model year 2008 on must have a tire pressure monitoring system [14]. When you change wheels, make sure the pressure sensors move with them.
The track is the distance between the left and right wheels. Pennsylvania rejects spacers thicker than one quarter inch used to widen the track [7]. It also rejects tires whose tread sticks out past the wheel well, including fender flares [7].
In 2024, 511 people died on the nation’s roads in tire related collisions [14].
What federal and state rules say
As of October 2026, federal law covers manufacturers, distributors, dealers, rental companies and repair businesses. It bars them from knowingly making inoperative any device or design feature installed to meet a federal safety standard [15]. A repair business is anyone who offers to repair vehicles or equipment for pay [15]. A narrow exception applies when the business reasonably believes the vehicle will not be used while the device is off, other than for testing during repair [15].
In plain terms, a shop may not knowingly disconnect your air bag or strip out required safety gear. The law names businesses, not individual owners. That does not make a do it yourself change safe, or legal in your state.
Switches that turn an air bag off need NHTSA’s authorization. They are allowed only in limited cases, such as a rear facing infant seat that must ride in front or a medical need [11].
States add their own rules, often through safety inspections, and they differ widely.
Comparison compiled by Safety Behind the Wheel Foundation
Example state rules on modified vehicles
| State | Example rules on modified vehicles |
|---|---|
| Pennsylvania | Main bumper bar must sit 16 to 20 inches high on cars and 16 to 30 inches on light trucks and multipurpose vehicles. Front lift blocks and rear blocks over 5 inches are rejected [7] |
| Virginia | A body raised more than 3 inches above the factory mounting points or frame rail is rejected, as are front lift blocks [12] |
| Maryland | Bumpers may be no higher than 20 inches on cars or 28 inches on light trucks and multipurpose vehicles. Bumper extensions to offset suspension changes are not accepted [9] |
Your state’s rules may be stricter, looser or checked differently.
When a modification is medically needed
Some modifications help people with disabilities drive or ride safely, such as hand controls, lowered floors and wheelchair lifts. NHTSA says registered mobility equipment dealers may modify federally required safety equipment to adapt a vehicle [10].
Those dealers must give you a written statement about the work. They must also list on a label any federal safety standards their work affected [10]. Keep that paperwork with the vehicle for future shops, insurers or buyers.
Small changes still matter. NHTSA notes that lowering a van floor by even half an inch can make equipment harder to use or block part of the driver’s view [10]. Before work begins, ask whether any existing safety features will need to change [10].
Buying a modified used vehicle
A modified vehicle can be safe, but you are buying someone else’s choices, often without records. Use this routine before you sign.
If the seller cannot explain a change, assume no one checked it.
Ask your agent whether custom parts are covered and how they would be valued after an accident. A gap there can leave your family paying out of pocket to get a safe vehicle back on the road.
Frequently asked questions
Is a lifted truck legal?
It depends on your state and how the vehicle was lifted. Virginia, for example, rejects a body raised more than three inches above the factory mounting points [12]. Pennsylvania and Maryland set bumper height limits [7, 9]. Check with your state DMV or inspection program.
Does a lift make a rollover more likely?
Raising a vehicle raises its center of gravity, and federal rules link a higher center of gravity to the higher rollover rate of utility vehicles [3]. In 2024, 38 percent of pickup occupant deaths happened in rollover crashes [4]. Slow down for curves, avoid sharp swerves and buckle up on every trip.
Can I put an aftermarket steering wheel on my car?
If your vehicle has a driver’s air bag, it is in the steering wheel [10]. A wheel without one removes that protection, and front air bags cut driver deaths in frontal collisions by 29 percent [2]. Some states reject small steering wheels at inspection [7, 12].
Are seat covers safe if my seats have side air bags?
IIHS advises against aftermarket seat covers because they can get in an air bag’s way or change the direction it inflates [2]. Check your owner’s manual to see whether your seats contain air bags. If they do, ask the dealer’s service department whether any cover is approved for that seat.
Can a shop turn off my air bag if I ask?
In most cases, no. Federal law bars repair businesses from knowingly making required safety equipment inoperative [15]. NHTSA allows switches that turn an air bag off only with its authorization, in limited cases [11]. Registered mobility equipment dealers may change safety equipment to adapt a vehicle for a disability, with a label and written statement [10].
The bottom line
Recommendation from Safety Behind the Wheel Foundation
Safety Behind the Wheel Foundation urges anyone who plans or buys a modified vehicle to have every change checked before trusting it on the road. Lifts, bumpers, steering wheels, seats and tires can all change how your vehicle protects you and others in a collision. Factory parts were chosen to work with the air bags, belts, sensors and structure. A new part may look better and still weaken that team.
Treat every modification as a safety change. Ask what the original part did, what changed and whether anyone tested the result. Get records, get an independent inspection and check your state’s rules.
Related articles
Sources and further reading
- 1Office of the Federal Register, Electronic Code of Federal Regulations. 49 CFR Part 571, Federal Motor Vehicle Safety Standards. Up to date as of October 1, 2026. ecfr.gov/…/part-571
- 2Insurance Institute for Highway Safety and Highway Loss Data Institute. Airbags. Updated July 2026. Data year: 2012 and 2019 (federal lives-saved estimates). iihs.org/research-areas/airbags
- 3Office of the Federal Register, Electronic Code of Federal Regulations. 49 CFR 575.105, Vehicle rollover. Up to date as of July 30, 2026. ecfr.gov/…/section-575.105
- 4Insurance Institute for Highway Safety and Highway Loss Data Institute. Fatality Facts 2024: Passenger vehicle occupants. Posted June 2026. Data year: 2024. iihs.org/…/passenger-vehicle-occupants
- 5Insurance Institute for Highway Safety and Highway Loss Data Institute. Vehicle size and weight. Updated August 2026. Data year: 2009 to 2022. iihs.org/research-areas/vehicle-size-and-weight
- 6Insurance Institute for Highway Safety and Highway Loss Data Institute. Pedestrians and bicyclists. Updated August 2026. iihs.org/…/pedestrians-and-bicyclists
- 7Pennsylvania Code, via Cornell Law School Legal Information Institute. 67 Pa. Code § 175.80, Inspection procedure. Accessed October 2026. law.cornell.edu/…/67-Pa-Code-SS-175-80
- 8Office of the Federal Register, Electronic Code of Federal Regulations. 49 CFR Part 581, Bumper standard. Up to date as of October 1, 2026. ecfr.gov/…/part-581
- 9Code of Maryland Regulations, via Cornell Law School Legal Information Institute. COMAR 11.14.02.07, Bumpers. Accessed October 2026. law.cornell.edu/…/COMAR-11-14-02-07
- 10National Highway Traffic Safety Administration. Adapted Vehicles. Accessed October 2026. nhtsa.gov/vehicle-safety/adapted-vehicles
- 11National Highway Traffic Safety Administration. Vehicle Air Bags and Injury Prevention. Accessed October 2026. nhtsa.gov/vehicle-safety/air-bags
- 12Virginia Administrative Code, via Cornell Law School Legal Information Institute. 19VAC30-70-110, Steering and suspension. Accessed October 2026. law.cornell.edu/…/19VAC30-70-110
- 13Office of the Federal Register, Electronic Code of Federal Regulations. 49 CFR 571.207, Standard No. 207; Seating systems. Up to date as of October 1, 2026. ecfr.gov/…/section-571.207
- 14National Highway Traffic Safety Administration. Tire Safety Ratings and Awareness (TireWise). Accessed October 2026. Data year: 2024. nhtsa.gov/vehicle-safety/tires
- 15U.S. Government Publishing Office, GovInfo. 49 U.S.C. 30122, Making safety devices and elements inoperative (United States Code, 2023 edition). Published 2023 edition. govinfo.gov/…/USCODE-2023-title49-subtitleVI-partA-c…
This article reflects the safety priorities of occupant protection and safe vehicle modification. It is general education, not legal, insurance or mechanical advice for your vehicle. Laws and inspection rules change, so verify details with official sources. For your own situation, contact a qualified repair or inspection shop, your vehicle maker, a registered mobility equipment dealer, your state DMV or inspection program, or your insurance agent. Reviewed October 2026.
Cite this article: Safety Behind the Wheel Foundation. “Aftermarket modifications and crash protection: what to check before you modify or buy.” drivewithcare.org, https://drivewithcare.org/aftermarket-modifications-crash-protection/. Reviewed October 2026.
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