Steering Feel & Other Delights

[RyDeFly]

Alright, I want to bring something up that often seems to fall by the wayside in our community and others; steering feel.
More specifically, the MKIII's seeming lack of it.

I know we have old cars, that bushings wear out, steering racks explode, etcetera, but I'm not quite convinced that's all there is to it.
During perusal of ye olde Motor Trend articles, I noticed that various pre-production supras were tighter and more responsive than those sold. It seems Toyota experienced some drama over the Supra's final designation - sports car or numb GT. (I'd guess that's where the .5 delay in 1986.5 came from.) Numb won, leading to a "second-guessing" of Lotus' specs.
Bastards.
Timed laps were similar, but the mags report that the "sportiness" was destroyed in the process.

What I'm getting at is the Supra had superior "crispness" at one time, despite technical performance being generally the same.

But why? What attributes affect steering feel, and how are improvements/detriments even noted?
Unlike, say, damper operation, steering feel lacks both a method of measurement and specific nomenclature. I'm positive this is a multi-faceted phenomena, yet I'm met with the same vague descriptors: "lacking" "adequate" and "improved". I never hear things like a porche's steering being a couple degrees more "snipid" than the last model, or a BMW that has a marked decrease in "cromulent bias". There's entire books on how to set up handling and suspension, but Feel is relegated to the "black arts" category of tuning.

Steering feel is possibly my favorite aspect of motoring, even over handling; though the two often arrive in the same package.
Both are fun but definitely distinct. Compare the original rabbit GTi, which had good handling but lousy feeling in the wheel, to something like the Lotus Elan, which had an incredible amount of information and sensations coursing through the wheel, but its handling wasn't as incredible as the wheel told you it was (second hand info).


And so, I've started this thread with the intention of compiling knowledge of Feel; what it is, how to change it, how to improve it on the MKIII.

I'll take a shot at defining some individual characteristics of Feel:
Play in the steering
Steering effort
steering accuracy
Steering feedback
I'm sure accuracy and feedback especially can be broken down and defined even further.

I've also gathered some properties that seem to affect feel (but not necessarily handling):
king-pin inclination
castor angle
pneumatic trail
bushing compliance
tire sidewall stiffness

Those are all well and good, but its the application I can find little info on. Sidewall stiffness seems incredibly important, but can I assume increased stiffness will improve steering accuracy and feedback? What specific effects do kingpin inclination and castor cause?
I've read that BMW's traditionally good feel comes from their use of MacPherson struts. But is that because of properties of the strut itself, or simply because they've used the layout for so long, and have a method?
Increased chassis weight is always detrimental to handling, but is the same true for feel?
Loads of questions, but hopefully we/I can figure it out.


Feel free to add or subtract from the terms, expand and explain. As I do more research, I'll dump info I obtain.

 

[Wiisass]

Well this is a very good topic. It's going to be a long response, so I will add more to it a little later.

But before that, does anyone know what Toyota changed before the car was released?

One of the things that could be numbing steering feel is power steering. The tires and wheels will also play a lot into this. Wheel size will determine scrub radius and the tire determines a lot about how things will feel, cornering stiffness, spring rate, pneumatic trail, etc. Caster angle also has a lot to do with it. As are compliances in the steering system itself. In the steering column or rack bushings or tie rods. Also other suspension bushings will contribute.

I will explain everything a little more later.

Tim

 

[popemobile]

Steering "Feel" in my car is improved. I've got solid mounted subframe, polys everyplace, Eibacs and Tocico blues. The LS7 RX7 got dramatically imroved "feel" by cutting a few coils off of the spring (pressure regulator?) in the rack. I don't know if there is an equivalent on the MKIII rack, but may be an idea.

Oh and by the way, the Golf "feel" is similar on the scale (dramatically different, but similar level) it rides on Soft sport springs (not so soft) and Bilstein HD's.

P.S. TIRES TIRES TIRES

 

[Asterix]

You forgot steering offset. It's the distance from where the steering axis hits the ground to the center of the contact patch. Increasing the steering offset, say with different offset wheels, will increase the return-to-center force. It doesn't really affect handling, just feel.

You also forgot Ackerman Angle, which affects both feel and handling. Smith suggests it's hard to have too much.

Carroll Smith talks all about this type of thing in his Prepare to Win and Drive to Win books, which is where I get my info.

The current trend I see is to have these front suspensions with two ball joints bottom, and sometimes top, which increases the return-to-center force dramatically. I've not had a chance to analyze what that does to castor and SAI, since both change with steering angle.

My opinion is that the chassis designers of the Supra designed a race car which was then crippled by management with soft springs and squishy bushings, because they wanted to sell the car to old fogies.

Asterix

 

[Wiisass]

Asterix, steering offset and scrub radius are the same thing. As long as you mean front view when you're talking about steering offset. It has more of an effect under braking than turning. It will affect turning though to some extent, but pnuematic and mechanical trail have more to do with turning than scrub radius does. But of course, they all work together, but for small steering angles and lateral loading of the contact patch, scrub radius doesn't factor in that much. But you're still just looking at the same point from different views. Mechanical trail is determined by the kingpin axis intersection with the ground and its distance from the wheel center longitudinally and scrub radius is deterimined by the same two points but it's a lateral distance. So it's really the actual point that the wheel rotates around when being steered.

But generally, you can attribute scrub radius to feedback under braking and it can cause problems when braking over rough surfaces. And you look at trail for handling and steering force and feedback while cornering.

Ackerman does affect steering. And I would not agree with Carroll Smith on that it's hard to have too much. I don't think there are many people that really understand ackerman. For some reason, it's not as simple as it sounds. And the old way of determining ackerman percentage doesn't account for steering rack position which will change ackerman. The percentages that they use don't make sense in any logical manner either. But this discussion would be better served if we stayed focused on variables that are easily changed. Moving the tie rod point on the spindle or relocating the rack and not on that list.

What are you talking about with two balljoints? One on the top and on on the bottom like any non-strut car? Or are you talking about two on the top or two on the bottom? Maybe I just haven't noticed that trend or the way you described it just didn't sound right, but that doesn't sound like it would work for a front suspension. I have seen and dealt with the virtual ball joint on rear suspension. Unless there's something I'm not seeing, it sounds over contrained for a front setup. Do you have any more information or is it just some random passenger car trend that has no bearing on anything performance related?

If the supra was only changed with softer springs and bushings then that's not a big deal at all. Everyone's stock suspension and bushings are crap at this point and should be replaced anyway.

Tim

 

[jmanbball]

What are you talking about with two balljoints? One on the top and on on the bottom like any non-strut car? Or are you talking about two on the top or two on the bottom? Maybe I just haven't noticed that trend or the way you described it just didn't sound right, but that doesn't sound like it would work for a front suspension. I have seen and dealt with the virtual ball joint on rear suspension. Unless there's something I'm not seeing, it sounds over contrained for a front setup. Do you have any more information or is it just some random passenger car trend that has no bearing on anything performance related?

BMWs, some eclipses and the new ford fusion all have double lower ball joints. It allows the the bottom pivot point to change location.

http://en.wikipedia.org/wiki/Dual_ball_joint_suspension

 

[Asterix]

What are you talking about with two balljoints? One on the top and on on the bottom like any non-strut car? Or are you talking about two on the top or two on the bottom? Maybe I just haven't noticed that trend or the way you described it just didn't sound right, but that doesn't sound like it would work for a front suspension. I have seen and dealt with the virtual ball joint on rear suspension. Unless there's something I'm not seeing, it sounds over contrained for a front setup. Do you have any more information or is it just some random passenger car trend that has no bearing on anything performance related?

My '04 Nissan 350Z has two ball joints on the bottom of the front, and a third on the upper arm. The G35 has the same suspension. The Audi S6 (I think) has two ball joints on the top in the front, so there are two upper links instead of one wishbone. I'm also fairly certain than the Lexus IS300 has the two lower balljoints system like the 350Z.

I had to ponder why for a while before figuring the best reason for two lower ball joints in the front is simply for stronger return to center. My 350Z has steering return like a FWD car. Without analysis, this is simply an educated guess.

Obviously, I'll have to review Smith's descriptions of Ackerman angles. He was certainly talking about open-wheel race cars, like the Formula Ford or Atlantics, but I figured much of his information would be applicable to the Supra. Sure, we can't change that easily, but is good to know what Toyota was thinking when they decided where to put the rack.

I guess I was talking more about mechanical trail than a simple front-view steering offset. Your description jives with my understanding; I must not have presented that well.

Asterix

 

[toyo4life]

the biggest changes to the car before release were ride height, spring rates and shock valving. Steering feel is most affected by the steering rack and how it is geared and valved. this is why toyota went to variable asist in 89. Also unsprung weight is a big factor.

On an other note steering feel is a very subjective matter. I think it really needs to be looked at from the point of "what do I want this car to feel like to me." I wouldn't want to drive a Miata with the steering feel of a LS460. Or vice versa. On a personal note I love the feel of the 350z light but connected. Unlike the MKIV which feels great at speed but can feel clumsy and ponderous around town.

As to the MKIII, My first one an 86.5 back in 89 felt nicely asisted without feeling numb, but the heavy stock rims and tires did little for feedback and accuracy. My current 89 needs some attention before I cansay I'm happy with it.

 

[Wiisass]

Oh ok, I see what you're talking about now. I forgot that the Z had that weird setup in the front. I haven't been able to find much information on the design or why and it's really hard to look at a picture of it and see how things move. But from what I've found, one arm is loaded in tension, the other in compression, it seems this would act like a spring in a way and try and get the wheel back to straight. I would be really intersted to see the actual effect on mechanical trail, kingpin angle and caster angle throughout steering travel with that setup. But I doubt anyone is going to be putting a 350Z or other dual ball joint front suspension on a Supra anytime soon, so that can be put off for another time.

So if the biggest changes to the car were ride height, spring rates and shock valving then that's all stuff that's easy to change and get back some of the feel to the car. This will affect overall response and how the car feels. But that makes sense if that's all that really changed. I know they pushed back production, but changing suspension geometry and such would cause a lot more than a 6 month delay in production.

The steering rack plays a small part in steering feel. It actually just scales down the force at the wheel to what you feel at the steering wheel based on the ratio of the rack.

So the things that are easy to change to get a better feel out of the car are shocks and spring, wheels and tires, alignment settings. On my brother's supra with nothing done to steering besides the TIP spacers and the only thing on the suspension was the TIP Motorsports setup, the steering felt good. The car was point and shoot, the feedback at the wheel was good, I didn't really have any complaints about the steering from driving it on the street, at Pocono on the road course or drifting at englishtown.

A better spring and shock setup will definitely tighten up the car and make it more nimble, or as nimble as it can be for a 3500lb beast.

Wheels and tires will also affect how the steering feels. Different tire spring rates, lateral compliance, tire curves, etc. You will also want to properly size a tire on a wheel. Stretching a tire can give a little better steering feel with the possibility of less available grip due to a smaller contact patch. A ballooned tire will give sloppy feedback, running too wide of a tire on a smaller rim would be a bad idea for steering feel. I like to go slightly smaller than the manufacturers suggested sizing, or at least stay on the larger end of suggested wheel sizing for a given tire. If a tire says that it is meant to fit 8"-9.5" wheels, I would at least go with a 9" wheel, usually a 9.5" or bigger. The feel is better and depending on sizing, you won't be losing much available grip with a slightly smaller tire. But that also depends on a lot of things.

Scrub radius will increase from changing offsets and this will factor into steering feel as I have mentioned before, but it's main effect is under braking on rough roads, so it is not as much of a concern for handling. It has it's biggest effect on lateral manuevers at high steering angles, but this is also slower speed stuff. Also changing offsets will change your track and the amount of lateral load transfer. Lower offsets will lower the amount of lateral load transfer for a given lateral acceleration. There are also other effects of changing tracks. But we can get into those later.

Alignment settings are also easy to change and will effect steering feel. More caster, up to a point, is good. More caster will increase steering force and the self aligning torque about the steering axis. The front end will be more stable. But more caster can also wash out the effects of pneumatic trail. Pneumatic trail is a function of the tire and is combined with mechanical trail, which is determined by your caster angle, to give your moment about the steering axis. Pneumatic trail peaks low in the slip angle range and falls off as the tire approaches its peak slip angle. This equates to a decrease in the moment about the steering axis which becomes a reduction in force felt at the steering wheel. With too much mechanical trail, this effect is a very small percentage and is hard to feel by the driver. This will not warn the driver when the front tires are approaching their limit.

Obviously, there's more that will affect steering feel. But with suspension, there isn't much you would change that wouldn't affect anything else. These are the things that you will see the most change in steering feel from and if anyone thinks I've missed anything just say so.

Bigger changes, such as changing pickup points on the chassis or spindle will effect steering feel, but that is out of the range of most people to do or to do right, so I think it's out of th scope of this discussion.

Tim