Translation guide
A car that has been altered from its factory specifications, often for performance or aesthetic reasons.
The broad concept of a car that has been modified in any way.
General term for a modified car. Neutral and widely understood.
He owns several modified cars.
Loanword from English 'custom car'. Often implies aesthetic or personalization modifications.
I went to a custom car show.
Specifically a car modified for performance, especially engine tuning. Common in car enthusiast circles.
His tuned car puts out 300 horsepower.
A car modified primarily for appearance, such as body kits, paint, or stance.
Car modified for visual appeal, like body kits, wheels, and interior styling.
He won the dress-up car contest.
Can also refer to visually modified cars, but is broader.
That modified car has flashy aero parts.
A car modified for increased speed, handling, or power.
A car modified in ways that violate vehicle regulations.
改造車 is the broadest term for any modified car. カスタムカー emphasizes visual customization, while チューニングカー focuses on performance tuning. Use 改造車 when unsure.
The direct translation 'modified car' is not commonly used in Japanese. Instead, use the specific terms above depending on context.
Illegally modified cars won't pass inspection.