Vident Partners provides vetted tire, wheel and brake expert witnesses for cases involving tread separations, tire age, wheel separations, brake failures, FMVSS 139, 135 and 121 compliance, and commercial vehicle maintenance. Request a referral today.
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A tires, wheels and brakes expert decides why a vehicle lost grip, lost a wheel or failed to stop, and whether the cause was a defect, wear, poor maintenance or the crash itself. A blown tire at highway speed or a brake fade on a grade can begin a catastrophic crash, and the first fight is often whether the component failed before impact or because of it. This page covers these components on cars, light trucks and commercial vehicles. General crash reconstruction belongs to an accident reconstructionist, the carrier's safety program to a trucking expert, and the vehicle's wider design to an automotive engineer.
The expert reads the component itself, photographs, service and tire purchase records, recall notices, inspection reports, event data recorder downloads and manufacturing specifications. Preservation comes first. A failed tire, its wheel and any fragments should be kept together, unwashed and out of the sun, and destructive examination should wait for a joint protocol.
Federal standards apply at manufacture. FMVSS 139 specifies tire dimensions, test requirements and labeling for new pneumatic radial tires for light vehicles 1. FMVSS 135 sets requirements for service brake and parking brake systems on light vehicles, with the purpose of ensuring safe braking performance under normal and emergency driving conditions 2. FMVSS 121 establishes performance and equipment requirements for braking systems on vehicles equipped with air brakes 3. Compliance with a standard is evidence, but it is not always the end of a defect case, and the effect varies by state.
Low pressure is its own topic. Under FMVSS 138, a tire pressure monitoring system must warn at or below 25 percent under the manufacturer's recommended cold inflation pressure, or a table value if higher 4. A warning that lit and was ignored, or a system that was disabled, can shift the focus from product to user or shop.
Tread separation disputes are the classic case. Plaintiffs' experts look for manufacturing or design causes such as poor adhesion. Defense experts look for signs of underinflation, overload, road hazard injury or a bad repair. Each side reads the same physical marks, so experience and method matter. The opinion has to explain why one cause fits and the others do not.
Age is often in play. The tire identification number's date code identifies the week and year of manufacture 5. NHTSA says that as tires age, they are more prone to failure, and that some vehicle and tire manufacturers recommend replacing tires that are six to 10 years old, regardless of treadwear 8. That is a recommendation from manufacturers, not a federal age limit, so an expert should not state one as a rule. A seller's or installer's duty regarding an old tire depends on state law and on what the shop knew.
Trucks and buses have in-service rules that set a clear test. Under the federal motor carrier rules, a front tire on a bus, truck or truck tractor must have a tread groove pattern depth of at least 4/32 of an inch, and other tires at least 2/32 of an inch 6. Tires with exposed ply or belt material, a tread or sidewall separation, a flat or audible leak are barred 6. Every motor carrier must systematically inspect, repair and maintain vehicles subject to its control 7. The expert compares those rules with inspection reports and the components on the truck.
Brake cases on heavy vehicles often turn on adjustment, lining condition and heat. An out-of-adjustment brake leaves less stroke in reserve, so the expert measures what can still be measured and looks for signs of fade. Air brake systems add valves, lines and antilock components, each with its own failure signature. Post-crash movement of adjusters can confuse the picture, so the inspection should be documented step by step.
Look for a tire engineer or brake engineer with design, testing or failure analysis experience in the same type of component, not a general mechanic for a design question. An experienced heavy truck technician may suit maintenance and inspection issues. Materials and rubber science may also be needed. Ask how the expert has handled competing causes.
Federal motor carrier rules require at least 4/32 of an inch of tread on a truck or bus front tire, and at least 2/32 of an inch on other tires.
Case Types
Tread separations and tire blowouts
Aged tire sale and installation disputes
Wheel separations and failed fasteners
Brake failure and brake fade
Air brake adjustment and maintenance disputes
Tire pressure monitoring failures
Commercial vehicle out-of-service conditions
Faulty tire repair and shop negligence
Qualifications
Related Specialties
FAQ
Look for design, testing or failure analysis experience with the same component and class of vehicle. A tire engineer suits a separation case, and an experienced heavy truck technician may suit a maintenance case. The expert should be able to explain how competing causes were ruled in or out.
The rules cited here do not state one. NHTSA says tires become more prone to failure as they age, and that some vehicle and tire manufacturers recommend replacement at six to 10 years. Any duty regarding an older tire depends on state law and the facts.
The tire identification number on the sidewall carries a date code that identifies the week and year of manufacture. NHTSA says the last four digits of the number show this. An expert should photograph the number before any testing.
Federal motor carrier rules require at least 4/32 of an inch of tread on front tires of a bus, truck or truck tractor, and at least 2/32 of an inch on other tires, with listed exceptions and measuring rules. The rules also bar tires with exposed ply or belts, separations, flats or audible leaks.
No. Keep the tire, wheel and fragments together, unwashed, and protected from sun and heat. Any destructive examination should follow a joint protocol with all parties. Handling can change surfaces that the experts need to read.
In general, tire and brake expert fees are determined by the expert themselves, based on a variety of criteria. Among those criteria are engineering credentials, testing experience, inspection needs and the volume of records to review. Vident does have some influence over expert fees by comparing experts within a specialty, but ultimately it is a personal decision by the expert.
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