Buying Tips

Creating the Perfect Fit: New Car Seat Design

A few years ago, Toyota engineers decided to play corporate nanny and deliberately designed a vehicle seat they figured consumers wouldn't like. Americans needed to demonstrate better posture, they believed, and if only drivers would sit erect in it, this seat would eliminate back fatigue. But if drivers slouched, their muscles would tire and ache.

Not a good idea. "It got just terrible reviews from the market, because the customer didn't appreciate being 'told' exactly how they needed to sit," admitted Michael Sweers, who at the time was one of those patronizing engineers — and now is general manager of engineering design for Toyota Motor Engineering & Manufacturing North America. Toyota won't reveal which vehicle that seat was in but, Sweers said, "We learned."

"In days gone by, it was just a seat," said Roger Campbell, a seat-engineering supervisor for Chrysler. "But now, with competitive pressures in the marketplace and technology advancing, we're really migrating toward being able to take customer data and their wants and create systems that delight the customer."

Nowadays, car seat designers are harnessing digital technology to get more precise and objective ideas of what kind of fit will please the most commonly shaped consumer and yet also extend to the needs of the smallest and largest Americans. Vehicle seat supplier Lear, for example, has a patented process it calls Comfortech that involves "pressure mapping" of hundreds of individuals while they're sitting in car seats, to determine ergonomic "hot spots" where designers must make comfort adjustments.

Fitting Body Parts in Seat Parts
Each aspect of the human body poses distinct design and engineering challenges for the car-seat part to which it corresponds.

Backs: Seat designers pay more attention to backs than anything else because how our backs fare is the biggest overall determinant of whether a seat feels comfortable. But it is getting more difficult to satisfy everyone, in part because Americans' posture varies. GM, for example, has identified at least three broad posture categories — erect, normal and slouching — each of which presents different design challenges.

Cushions: The biggest challenge in designing cushions is combining initial plushness with the underlying firmness required to prevent muscle and joint fatigue. Designers often handle that by putting a thin pad of soft foam underneath the cushion-trim material, then layering that over a denser base consisting of hard foam, springs or a combination.

Thigh support is the peskiest aspect of cushions. "If your thighs don't have enough contact with the cushion, you create a pressure point where you're actually sitting on your tailbone, and your weight isn't distributed," explained Sweers of Toyota. "An hour or two along, you get 'tailburn' — a lower backache. Most people associate that with not having enough lumbar support, but it's really the pressure on your tailbone."

So seat designers can make cushions longer or wider, or make them electrically movable. But they also have to watch out that the calves of shorter drivers don't come into contact with the longer cushions. That's where adjustable pedals come in especially handy.

Bolsters: More American consumers want bigger and more stylish bolsters, as in many high-end and performance vehicles. But bolsters that are substantial enough to make you feel snug in your seat also pose some very practical problems. For one thing, having to slide over them makes it more difficult to get into and out of a car seat. Plumper bolsters also limit the amount of "leg splay," or room for your legs to move — a certain amount of which you need to be able to operate the pedals freely.

And because people are wider, more aggressive bolsters are making seats uncomfortable for individuals beyond certain widths. "The trick with bolsters is to have different zones of stiffness" within the bolster that get firmer with distance from the legs, said Terry O'Bannon, a principal engineer for Lear. Using foam with various thicknesses, densities and compression properties, "you can almost separate the look of the seat from how the bolsters are going to feel."

Designing the Seats
Designers take these disparate concerns and integrate them into comfort targets for a seat system. The main tools of their trade include the polypropylene and polyethylene foams that they layer horizontally or vertically, at various densities and flexibility levels, to form unique seat contours.

Adjustment hardware is another key part of designers' arsenals. Most midmarket and upper-segment vehicles offer electric controls that move seats front and back, and up and down. High-end models also provide separate electric adjustment of back and cushion angles, as well as lumbar supports and even electrically adjustable bolsters. Carmakers also are paying more attention to factors other than seat construction and adjustability that contribute to comfort or discomfort. Heated seats, for instance, now are available in just about all high-end and midmarket vehicles. An increasing number of vehicles are offering seats that cool as well.

Some cars, such as the 2007 Cadillac DTS, have even harnessed the technology for explicitly therapeutic purposes by offering heated seatbacks only. "It's like taking your heating pad with you," said Mark Grajek, GM's lead engineer for human vehicle integration. At the same time, GM recently discontinued a previous DTS option of a massaging driver seat. "It was hokey" and didn't work well, Grajek admitted.

It's a Different Ballgame Past the First Row
Car seat designers are turning more attention to second- and third-row seats, in part because of the increasing versatility that many vehicles require in their space behind the first row. "The front row is where the owners sit, so we used to mainly be concerned about that," said GM's Grajek. "But the challenge now is to allow people in the other rows of seats to get comfortable and have good posture, too."

In second and third rows, body types and sizes vary even more than in the front row, because kids often sit in the back. Rear seats routinely must fold, split, stow away and be removable — yet also provide comfort over the course of a long ride. Another recent wrinkle is the need to design around the battery packs of hybrid vehicles, which typically reside under rear seats.

While innovations such as Chrysler's Stow 'n Go seats in minivans have made rear seats more flexible, there's now more emphasis on comfort. The 2008 Chrysler minivans, for example, offer swivel seats in the second row that make entry and exit easier. And the second row of seats in the new Toyota Tundra truck offer cushions that slide forward to give passengers more of a reclining position, even though the seatbacks are fixed.

Seats as a Brand Differentiator
Seat engineers also are working more closely than ever with vehicles' chief designers and stewards of brand equity to better match comfort characteristics with each model's personality and the preferences of target demographics.

As GM's Grajek explained it, "We're making sure the character of the seat matches the customer. So that could mean, in our high-performance vehicles, going after a high-bolstered, BMW-type seat, to producing more of a Lexus-type seat for an older crowd."

And Nissan's seat contours tend to be aggressive, just like its design-first brand mentality. "You get direction from the ergonomics standpoint, and then from your actual brand-identity statement. You have to add in what the personality of the seat is going to be so it meets the personality of the vehicle," said Lawrence Smythe, a senior project engineer for Nissan. "You balance those two things to create an experience that is consistent with the entire vehicle experience."

Because seat comfort is ultimately such a personal preference, it's difficult even for Edmunds.com to come up with an overall list of the "most comfortable" vehicle seats on the road today. Generally speaking, the high-end brands like Lexus and Mercedes-Benz offer highly adjustable driver seats, and that alone increases the likelihood of finding a comfortable position. Many Edmunds editors feel that Honda and Volvo seats are generally comfortable, but exceptions exist there as well. (Some taller staffers have been unhappy with the seats in the Honda Fit, for example.)

In the end, every car shopper would benefit by keeping seat comfort top of mind during a model's test-drive.