Four-Wheel Driving = Power goes from the engine to all four wheels Four-Wheel Steering = All four wheels turn to steer the car
In a car, your greatest transfer of energy from wheel to ground is when their vertexes of motion at the contact point are exactly matching. When you have all four wheels turning to steer, even if the rear ones only turn half or a fourth as much as the front, that should still mean that at any given time each tire is closer to the center of the line, rather than at an odd angle to the vertex of motion. Or is my mental visualization of that off?
Why doesn’t this technology seem to be used in racing?
I am not an engineer or a mechanic. This is only my conjecture here…
I think that existing steering mechanisms seem to do a pretty good job of getting the car around a corner, and the added complexity and possible failure points aren’t worth any added benefit. The car might turn sharper, but is that good? Any decent race car now is engineered to be able to handle the side load imposed by the turn. Turning sharper would mean a higher side load. You might cause the car to oversteer or even spin out. Counteracting this might mean re-engineering the entire vehicle, and the costs of that would be a lot more than just adding some steering linkage to the rear wheels.
Then, think about the driver whose skills are tuned to a regular steering system. A quarter turn of the wheel pitches him maybe another 30 degrees more around the turn than he expects. So instead of setting himself up for the perfect exit from the turn, he’s ears deep into a wall of hay bales, heading for the infield. Or worse - the grandstands.
Race car chassis are pretty well tuned as is. Tire temperatures are monitored so that each tire does the same amount of work; spring rates, tire pressures and alignment are adjusted so that the cars track well through the corners.
Four wheel steering would effectively move the center of gravity inward a little, but that can also be accomplished by moving things around in the car for circle and oval tracks and it doesn’t seem to be a major concern for road racing.
Saying that it’s well tuned for what it is doesn’t much negate that it could be better tuned with an alternate underlying methodology.
I guess the main question is just whether anyone has even done any research on whether my idea that it will achieve more efficient transfer of energy is correct, let alone whether it’s ever actually been put to practical test for racing purposes.
Racing cars are traction limited in turns. Being more efficient doesn’t buy you anything, because you can’t use all the power you have without skidding out anyway.* And you don’t really gain any effiency anyway: A car normally steers such that the two rear wheels remain tangent to the turn. or said another way, the radius passes through the rear axle, and the front wheels are ahead of the radius.
That said, the rear suspension is often tuned so that there is some rear wheel steering due to body roll. This is done to help counter oversteer or understeer tendencies the car might have, so in some cases the car steers like a skateboard (as you propose) and in other cases the rear wheels turn toward the inside of the turn, so the car crabs a bit. The goal is to make the front and rear wheels skid evenly and predictably, so that the driver can manage the resulting drift with steering and power changes.
Some higher end sports cars use this as well.
*Except for NASCAR, where the curves are gentle and steeply banked. Your change would be against the rules there, and unlikely to be accepted unless it could be shown to make the cars cheaper, or the races safer, or more appealing to the fans.
The goal isn’t to turn more tightly, it’s to not lose power whenever you angle the tires away from the direction you are traveling.
I imagine that this is my answer. Perhaps my mental visualization is wrong and there isn’t a gain to be made. I guess I should work it out on paper first.
I don’t think there is any gain to be made by aligning the tires with the turn – the contact patch is static, and especially with slicks, will give pretty much the same friction no matter which direction the force is coming from.
In any case, the differential is what keeps the longer path taken by the outside wheel from causing traction loss. Turning with all four wheels wouldn’t affect that portion of it, and I don’t think it will affect overall traction, which is really the main consideration.
Probably because it’s not allowed and nobody really wants it. Different racing series have different specs the cars must adhere to whether its Nascar, F1, Cart, Formula, etc. If you just showed up on race day with a 4-wheel steering car they wouldn’t let you in.
If they changed the spec to allow it, and it was beneficial, then everyone would do it. But you’re kind of adding an extra expense to everyone that nobody really asked for.
The Benetton Formula 1 team built a car with four-wheel steering capability in 1993. It hydraulically altered the steering angle of the rear wheels by a maximum of about two degrees, according to this article.
They tested it late in the season, and neither driver (Michael Schumacher and Riccardo Patrese) found that it helped so the system was never used in a race. From that same article:
They did all of this development in 1993 knowing that four-wheel steering would be banned in 1994 (along with a host of other whiz-bang technology) - which it was. I believe it remains illegal in F1, so I guess it is still unclear whether the idea is fundamentally unsound or if Benetton’s implementation was the problem.
Yep. 2010 Formula One Technical Regulations (PDF), Article 10.4.1: “Any steering system which permits the re-alignment of more than two wheels is not permitted.”
First off, kudos to brad d for knocking this out of the park. There’s a LOT of room for improvement in every racing series, but the rulebook is there to keep speeds in check and costs down. If F1 allowed active aerodynamics and lifted the rules on engine technology, speeds would get ludicrous in a hurry. I’m not sure if 4 wheel steering would ever pan out to be worthwhile in the long run, but I wouldn’t be at all surprised if, given a few years of development, it proved beneficial.
That said, some street cars employed 4 wheel steering in the early 90s (Prelude comes to mind, and I know Nissan had a similar system), but it ended up not being a big selling point. Just about every car on the market is designed NOT to rotate at the limit, and 4 wheel steering is at odds with that notion. Plus modern traction control systems can do a much better job at pointing the car using existing technology (electronic differentials and ABS).
That said, most cars are designed with some amount of dynamic rear toe, which has been called “passive rear steering.” The idea being that as the suspension compresses the outside wheel, the toe changes to help steer the car through the corner. I imagine this design idea is present in every racecar rear suspension. It’s not quite the same as active rear steering, but since it’s not prohibited by any rulebook and it doesn’t involve any extra components, it’s a much more attractive alternative.
I’m struggling a bit to grasp your terminology, but if I understand correctly, you’re saying that some of the wheels are not rolling on a perfect tangent to the center of the turn. Thanks to Ackermann steering geometry, this is not the case; with the inboard front wheel turnign tighter than the outboard front wheel, all four wheels are rolling on a perfect tangent to the center of the turn, even with the rear wheels at a fixed (straight forward) orientation with respect to the chassis.
Interesting to note that (according to the Wikipedia article) race cars employ reverse Ackermann geometry for other considerations.
Have I got your concern right, or were you talking about something else altogether?
Oh, I know. I just think it’s fascinating that somebody tried that, and was able to make it work. These days, they quibble over a few millimeters on the rear diffuser. Back in the 70’s, those guys were really using their noodles.