Although viewed by most racers...
Although viewed by most racers as safety equipment, a well-conceived seat and restraint system is a key asset toward reduced lap times.
When I put my first race car on the track back in 1958, race seats and even mandated rollcages and seatbelts were far in the future. It did not take too many high-speed, road-course-type corners to make me realize that unless I was at one with the car, I really wasn't in full control.
The fix? What appeared to be an old parachute harness from an Army & Navy surplus store was used to make a homemade restraint system. With some plate reinforcement at anchor points, the whole system looked good to go. Back on the track, things looked a lot better, but one factor became painfully evident: Much of the potential benefit of the seatbelts was lost because the seat frame was flexing. Cutting through the upholstery and tying the seat frame into the chassis worked like a charm, and lap times showed just that.
Two weeks previous, my lap times had been in the mid 1.25s around my home track (Silverstone's 1.5-mile road course Club Circuit, located 80 miles from London). With no other change, the times dropped to the low 1.23s and actually resulted in a second-row start instead of the back half of the field.
Our custom seat helped achieve...
Our custom seat helped achieve better results, including a front-row starting spot, faster laps, and two Second-Place finishes. ChrisRevis.com
All this taught me a valuable lesson that carried through to this day. Namely, it is very important that the driver wears the car, much like wearing a glove. Some years later, I read a paper by some learned group, the name of which escapes me, but the point that stuck in mind was the best drivers gauged their limits to the point just shy of breakaway by feeling the g-forces experienced by the body. What this means is that we really do drive by the seat of our pants, and if those pants are not firmly planted in the car, part of the signal is lost.
The question here is, can we afford to give up a little of that seat-of-the-pants signal? In a sport as competitive as motor racing, we really cannot afford to give up one iota of any potential advantage. I found that the driver who fit tightly in the car performed better on a road course than one who fit loosely, but here's the kicker. On a banked paved track, the difference between being at the limit and being over the limit, to the point of loss of control, is much finer. Because of the higher g's produced by the banking, the tires let go over a much smaller speed range, thus making it harder to stay in control at the very moment all the control possible is needed to stay out of the wall.
Let us not forget that a driver needs to accumulate points to win a championship. If that driver misses an event due to an injury that could have been avoided, points are lost. Having broached the subject of safety, let's delve a little deeper.
Here, Brian Butler starts...
Here, Brian Butler starts the seat-sizing procedure with a series of driver measurements, using a table as the datum source.
Many years ago, a photographer friend of mine took a shot of a spectacular accident at a round of the British Touring Car Championship. This photo made the inside front page in a big national newspaper. The car was about 30 feet in the air, and the driver's head and one shoulder were out of the window, which had just lost its glass. The corner worker, who was first to arrive at the wreck, later told me that the seatbelts were still tight on the driver when he got there.
That experience and others show that the human body moves far more than you may imagine. This point was graphically demonstrated when I watched a video, shot some years ago, that was shown at the University of North Carolina Charlotte by then NASCAR tech director Gary Nelson. A camera mounted in an ASA car driven by Johnny Benson showed the effect an impact of relatively moderate proportions has on a driver considered very well supported and restrained. The video showed that Benson was thrown around like a rag doll. It is an accumulation of visual instances such as Johnny Benson's and almost certainly the death of Dale Earnhardt Sr. that has spurred the safety aspect of seat development to a greater intensity.
By now it should be clear that a stout seat and a well-retained driver is a major move toward reduced lap times and safety. The importance of all this became even greater when I got involved with Nick Losito's Late Model Stocker. In 2005, Nick was dominant in a pro class of karting and walked away a clear champion. But at 17 years old, he had zero oval track experience and almost zero car driving experience. The goal was to get Losito up to speed as quickly as possible. Part of this exercise was to optimize the seat, pedal, and steering wheel locations relative to each other.

Seat angle for driver positioning...

Seat angle for driver positioning in relation to the steering wheel and pedals is a major factor. However, too much seat angle can increase the chance of severe groin injury.

The shoulder restraint needs...

The shoulder restraint needs to be close enough to respond in the event of an impact but far enough away to allow shoulder motion when steering inputs are made.

Head motion containment is...

Head motion containment is a critical factor, especially for a side impact. As a result, the head cradle side plates have become much stronger over the last few years. Also, note the position-the driver has to be able to see over the side plate.