Almost any modification that changes a car's value, performance, or risk profile — from a performance exhaust to a lift kit to aftermarket wheels — needs to be disclosed to your insurer, since undisclosed mods are one of the top reasons US insurance claims get denied or reduced after an accident or theft. Cosmetic and performance mods typically add 10-30%+ to premiums depending on the mod and insurer, while some, like factory-style safety upgrades, can occasionally have little or no effect; either way, get modification cover added in writing before you install anything significant, not after.
At a glance
| Modification type | Typical insurance impact |
|---|---|
| Performance mods (turbo, exhaust, ECU tune) | Often the largest premium increase; some insurers decline to cover at all |
| Lift kits/lowering kits | Moderate increase; may also affect standard-policy liability if it alters handling |
| Aftermarket wheels/tires | Usually needs declared value coverage above stock value |
| Audio/electronics upgrades | Can be added as scheduled/stated-value equipment coverage |
| Undeclared mods discovered after a claim | Can result in reduced payout or denied claim entirely |
Why insurers care about modifications at all
Standard US auto policies are priced around the risk profile of the factory-spec vehicle. A modification that increases power, changes handling, raises value, or increases theft appeal changes the actual risk the insurer is taking on — so from their perspective, an undisclosed mod means you've been paying for a policy that doesn't match the car you're actually driving.
What typically needs to be disclosed
- Performance changes: turbo/supercharger additions, ECU tunes/remaps, exhaust systems that increase horsepower.
- Suspension changes: lift kits, lowering springs/coilovers, especially where they affect ride height significantly.
- Body and appearance changes that add value: wide-body kits, custom paint, wraps.
- Wheel and tire upgrades beyond stock size/spec, particularly expensive aftermarket wheels.
- Audio, infotainment, or lighting systems added beyond factory equipment.
What happens if you don't disclose
If you file a claim and the insurer discovers an undisclosed modification during the investigation — which is routine after any significant accident or theft claim — they can reduce the payout to reflect only the factory-spec value, deny the claim for the modified parts entirely, or in some cases void the policy for misrepresentation, depending on state law and the specific policy terms.
Post-accident and post-theft investigations frequently include a vehicle inspection or review of maintenance/repair records, both of which can reveal a modification you didn't declare. The cost of disclosure upfront is almost always lower than the cost of a denied claim.
How to get mods properly covered
- Contact your insurer before or immediately after installing a significant modification, not at renewal.
- Get a written endorsement or rider added to your policy specifically listing the modification and its value.
- Keep receipts, photos, and installation invoices for every modification — this speeds up any future claim and proves the value.
- Ask specifically whether the insurer covers performance mods at all — some standard carriers exclude them entirely and you may need a specialty insurer for a heavily modified car.
- Re-check coverage after any additional mod, since coverage is typically itemized rather than a blanket allowance.
Specialty insurers for heavily modified vehicles
If your car is significantly modified — a build with substantial performance, off-road or show-car changes — a standard personal auto insurer may decline to cover it fully or at all. Specialty and agreed-value insurers that focus on modified, classic, or enthusiast vehicles typically offer more realistic coverage, though usually at a higher premium and sometimes with usage restrictions (e.g. limited annual mileage).
State factors that affect the picture
Coverage rules and what counts as a material misrepresentation vary by state insurance regulation, and some states have specific rules about how insurers must handle modified-vehicle disclosures and claim disputes. Check your state's department of insurance guidance or ask your agent directly how your state treats undisclosed modifications in a claim dispute.
Frequently asked questions
Do I have to tell my insurer about every car modification?
Will modifying my car always raise my insurance premium?
What happens if my car is stolen and it had undisclosed modifications?
Can I get insurance for a heavily modified or custom-built car?
Does an ECU tune void my car insurance?
Sources & further reading
- National Association of Insurance Commissioners (NAIC) — auto insurance basics
- III (Insurance Information Institute) — car modifications and insurance
Figures, prices and policy details were current at the last-updated date above. Automotive pricing, incentives and regulations change frequently — verify time-sensitive details with the linked primary sources. Read our editorial policy and fact-checking standards.
