Custom replacement seats can provide you with improved comfort, enhanced driving support for your body, and add tremendous eye appeal to the interior of your car. Searching the web provides you with any number of choices of color and style, and you can be pretty sure that your car will stand out from the crowd when you open the door.
There are several important things to consider when deciding if this is the way you want to go in your customization plan, however. First and foremost, as an automotive engineering director for a number of years, you need to understand that the seat in your car is just one piece of the overall safety system that is engineered into your ride to make it legal from a federal safety perspective. That seat has been included in tests ranging from front and rear impact, front, side and possibly seat-mounted airbag deployments, seat belt pull tests, seat frame deformation and pull-out; and several other possible tests. The passing results of those system and vehicle tests allows your car to be sold to the public.
When you change the seats in your car, unless full-vehicle tests have been performed and your car certified with the same seat you installed, the results of all of those previously made safety compliance tests are nullified. Installing a seat that is stronger in some regards can in fact cause the results of some tests to give failing instead of passing test results. Any single element of the vehicle system that changes how the test dummy (or human occupant's) body moves in a crash can alter the geometry of an airbag depolyment and cause HIC (Head Injury Criteria) numbers to exceed allowable limits, for example.
In today's highly engineered cars, changing things like seats, belts and other components is the equivalent of turning the driver into a test pilot. In the event of a crash, the others in the car can now name you, as owner, and the person and/or company who modified the car in a lawsuit, the same as they can sue the original manufacturer such as Honda, Toyota or GM. I am not certain, but I believe that the act of altering the compliance of a motor vehicle by a company could violate some federal laws in the same way that altering airbags or emissions equipment does.
The second factor to consider is comfort. I highly recommend actually sitting in the same model of seat in the same model of car that you are customizing before you buy. Car seats feel differently based upon the location of the steering wheel, shifter, windshield, etc; and nothing is worse than spending money on a custom seat and finding out after it is too late that the results are not comfortable.
