Wheel alignment Specs Question

Depends on the system, some use a self centering steering rack or have valving in the steering box to assist. On FWD vehicles the engine torque to the wheels also helps as the differential tries to even the tractive effort. Doesn't take much caster when any of the above are used.

Steve W. wrote: "4:35 AMSteve W.

- show quoted text - Depends on the system, some use a self centering steering rack or have valving in the steering box to assist. On FWD vehicles the engine torque to the wheels also helps as the differential tries to even the tractive effort. Doesn't take much caster when any of the above are used.

Are you saying you can't adjust it to have some SAI? If it's adjustable just dial a little bit in. It's your car.

I thought you needed small scrub radius with electric power steering as less power is available than hydraulic. Of course you could use electohydraulic servo valve, but that would get expensive.

Ashton Crusher wrote: "Are you saying you can't adjust it to have some SAI? If it's adjustable just dial a little bit in. It's your car. "

Perhaps I didn't phrase my question clearly enough. I was asking that, if Mazda speced 0deg SAI(kingpin angle), and only +2deg caster for that particular model, what else might they be using to assist steering return and straight-ahead stability on it?

Camber, caster, and kingpin inclination are the three factors. However, although toe has nothing to do with wheel return, it can make the car walk around when trying to go straight. Some cars - and drivers - are sensitive to even smallish changes in toe. If you are constantly correcting in both directions it might be toe. I missed the beginning of this thread, though, so I have no idea what your main concern was.

now that everything is computer controlled there is no reason they can't be reading sensors for steering rack position, wheel angle, whether the wheel angle is changing or being held constant, the angle of the car centerline, etc,etc and using any or all of them to control what the steering box is doing. A lateral accelerometer can sense if the car is moving sideways and that signal could be compared to whether the driver has turned the steering wheel to cause it. If the steering wheel was not turned the system could make the steering box counter steer to stop the lateral movement of the car. Once this stuff gets computerized and senorized there's just a ton of stuff it's possible to do.

Ashton Crusher wrote: "now that everything is computer controlled there is no reason they can't be reading sensors for steering rack position, wheel angle, whether the wheel angle is changing or being held constant, the angle of the car centerline, etc,etc and using any or all of them to control "

Which leads me back to my original premise: Why can't all this be done simply with more aggressive doses of the directional alignment cues: SAI, Caster, Camber. Save the computer stuff for ESC(electronic stability control), but keep good old fashion physics in charge.

And someone here mentioned the relationship between scrub radius and electric power steering, perhaps that's why my first experience with electric(2005 Chev Malibu) was less than satisfying. Icrave road feel, being able to sense the differences in road surface composition, and being able to feel weight build up when I'm turning the steering away from center.

So again, in the Mazda MPV example, is it possible that electro- mechanical means are beiing used, in conjunction with conservative doses of caster, etc, to center the steering from turns?

To your most recent question my guess is that the more aggressive doses of directional stability result in greater rolling resistance and consequently lower gas mileage. Years ago I would have thought the notion that they would deign a car with "tricks" to gain some trivially small amount of reduced "drag" to be just absurd... why would you worry about the added expense and complexity of "active radiator shutters" to gain 0.0x more mpg. Yet they are looking at all those tiny things hoping to coax another 1% greater fuel economy from the NEW car. So my guess is letting the steering system ACTIVELY work at keeping the car stable creates less drag then making the car inherently stable. That's not to say that the car is unstable if the system "goes out" but they think its worth doing the "hard way", i.e actively/electronically to get the extra mpg then doing it the easy (old) way where the car is just naturally stable.

As an anecdote from a friend of mine who was working on sound issues... he was talking with someone at GM and they said they monitor the wind noise generated by the air over the top of the cab and they can tell when the dies that stamp out the cab tops are worn out because of the increase in noise from the no longer perfectly correct/most aerodynamic shape that they are supposed to be stamped to.

Ashton Crusher wrote: " So my guess is letting the steering system ACTIVELY work at keeping the car stable creates less drag then making the car inherently stable. "

Interesting.

Alright, let's take this thread in a slightly different direction based upon that premise:

That combining minimal directional parameters(Caster, camber, SAI) with a computer stabilizing the car increases fuel economy vs high doses of those traditional parameters.

Let's start by asking the question, do higher amounts of caster & camber reduce the fuel economy of X vehicle, all other factors being equal?

"Let's start by asking the question, do higher amounts of caster & camber reduce the fuel economy of X vehicle, all other factors being equal"

Hmmm.. Nobody?

Must be a lot of cats in this NG.

I would have to think they would. Here's a physical explanation... When you put caster/camber in one of the reasons it makes the car stable is because as the wheel deviates from straight ahead the turning movement of those parts actually raises the front of the car a small additional amount. This upward movement is what creates the centering downforce that tries to make the car wheels stay straight. It takes energy to raise the car, and raising the car makes the shocks work to dampen the movement which results. Some of that energy winds up being dissipated as heat in the shock absorbers. There is also the friction in the ball joints, etc. There is no free lunch.

Ashton Crusher wrote: "small additional amount. This upward movement is what creates the centering downforce that tries to make the car wheels stay straight. It takes energy to raise the car, and raising the car makes the shocks "

Still, I trust gravity and built-in stability over electronic means any day. I recently drove a friend's 2012 Mazda CX-7, expecting some of the feel from a 6 or Miata. Nope! While I didn't have to correct all the time, the steering on that CX-7 felt just TOO SOFT. That's what you get when you let servos & microchips do a job more suited for traditional alignment parameters.

Guess I'd just better stick with older cars where I can add as much caster or SAI as I like - or replace the power steering with a lower-pressure system.

The ideal system would be where you could hook up a laptop and dial in your own settings for the electric steering, transmission shift points, shock settings, spring rates, etc.

- show quoted text - The ideal system would be where you could hook up a laptop and dial in your own settings for the electric steering, transmission shift points, shock settings, spring rates, etc. "

No thanks! I'd rather drive a CAR, not a computer. This is all just reinventing the wheel for the sake of reinventing the wheel.