underinflate

under- +‎ inflate

underinflate (third-person singular simple present underinflates, present participle underinflating, simple past and past participle underinflated)

1. (transitive) To inflate too little.
   • 2007 February 18, “Letters”, in New York Times‎:

     Maybe the tire could emit the scent whenever it is underinflated — after all, a car with properly inflated tires gets the best gasoline mileage.

• overinflate