S650 steering and handling is night and day difference compared to S550 Mustang says Chief Engineer Ed Krenz

[Hack]

I look at the following criteria:

• On-center feel:
-how wide is the deadzone before the front end responds
-how well does it hold a straight line (which from my understanding largely comes down to caster angle)
-how busy is the front end or how much does it tramline

Really good post and I'd like to discuss.

These first things you mention make me think about the GT350. I loved how that car really wanted to turn. The dead zone was very small, the car would respond and turn really quickly, and you could feel imperfections in the road.

The EPAS was not set up to be numb. I understand the EPAS can prevent most feedback from reaching the steering wheel. The GT350 is one of very few modern cars I've driven where I could actually get feedback from the road.

• Resistance/Load:
-when does resistance kick in; does it kick in early or does it start too late
-does it increase in load proportional to the amount of lock dialed in
-does it build up and lighten intuitively based on the front tires reaching or exceeding their friction circles
-is it over/under boosted, making the front end too heavy or too darty/floaty

A lot of modern cars feel artificial. The effort to turn the wheel never changes by much. But older cars with manual steering have very heavy steering when the car isn't moving but excessively light steering at highway speeds. I think I prefer the modern steering over an older manual steering car (or at least the ones I've driven).

• Texture/Feedback:
-does it transmit road bumps and textures; can you tell what general surface you’re driving on based on said feedback
-does the wheel provide sufficient bump/rebound/deflection feedback

I'm not sure I've noticed this kind of feedback. I can tell in my inner ear when I'm on gravel and the car is moving around without touching the steering wheel, but I don't think I've noticed much else - other than the wheel gets "lighter" on gravel.

Transmitting bumps and textures sounds like cowl shake and bump steer. Please correct me if you mean something else.

•Accuracy:
-does it go exactly where you expect it to?
-is there a ton of slack in the input/response?
-do you have to saw at the wheel or make micro-corrections to hold a line

Slack is a pretty obvious one that modern cars don't have, but most 60s and 70s cars do. Are there some notable old cars that don't have slack?

•Ratio:
-is it linear?
-is it fast (eg 11:1) or slow (eg 17:1)?

Are some cars not linear? Example?

Wheel:
-diameter and thickness
-are the 9-and-3 ergonomic or is it shaped like one of those aftermarket monstrosities that people stick on their GTIs and Mustangs

The main things affected by HPAS to EPAS are the resistance and loading characteristics. EPAS systems tend to be extremely linear, to an artificial degree, with less proportional and intuitive loading based on what the front tires do. On the flip side, they provide massive levels of adjustment, don’t make fluid-pumping noises when crawling around parking lots at full lock, and are more fuel efficient too.

I'm sure they cost less and save fuel, which is why they are on most cars. It's too bad that almost all companies prioritize cost and fuel savings over the driving experience.

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[OppoLock]

I'm not sure I've noticed this kind of feedback. I can tell in my inner ear when I'm on gravel and the car is moving around without touching the steering wheel, but I don't think I've noticed much else - other than the wheel gets "lighter" on gravel.

Transmitting bumps and textures sounds like cowl shake and bump steer. Please correct me if you mean something else.

I could’ve worded it better, but it’s more to do with how the suspension is engineered and tuned and how that translates to confidence behind the wheel. Ideally, your suspension will absorb bumps and control vertical motions by maintaining as close to constant contact with the ground as possible when driving over irregular surfaces. You want to know what’s happening at the front without having to fight and wrangle the wheel back on track. Too soft, you don’t know what’s going on. Too stiff, and your car’s skiddish and the wheel will get deflected and pulled out of your hands, say whenever you hit a bump or kerb.

Cowl shake would typically be a sign of poor chassis stiffness. Bump steer is directly tied into one of the aspects I briefed just above.

Slack is a pretty obvious one that modern cars don't have, but most 60s and 70s cars do. Are there some notable old cars that don't have slack?

A better way of putting it is that select modern cars are more rigid and accurate than others. The only cars that have noticeable slack are riding on large sidewalls with soft suspensions and loads of unsprung mass. It’s almost unfair to use this as an example, but a Wrangler for instance, and to a lesser degree, something like an F-150. If you’ve rented or driven one for any period of time (or any like vehicle), you’ll get it.

But in the context I’m providing, if you’ve driven a few examples of modern performance cars, you’ll note that some have very little play in the steering and the front end more or less responds 1:1 with the tiniest of inputs. Almost any larger German performance car (and I’ll use Audi as an example because I’ve driven several and they really exemplify this), like an A4-A7, has zero feel, is heavily boosted, but is laser accurate with “tight” video-gamey steering.

But there are plenty of them that aren’t so hot. If you ever drive an F30 3-Series, for example, it has floaty, light, numb steering. It’s like the worst of all worlds.

Are some cars not linear? Example?

A ton of modern cars have variable gearing steering ratios, and often it’s an option. Usually this adjusts ratio based on road speed and is subtle unless you’re in extreme scenarios (crawling in a parking lot = super fast rack where you can fully maneuver without crossing hands/shuffling, or going very fast and having a slow ratio for subtle inputs/corrections).

But that’s not even really what I’m referring to. Some cars have darty off-center turn-in and it’s half to do with the rack as much is it is to do with the way the suspension’s setup. Last car I drove that bothered me in a noticeable way was a W204 C63. Darty nose, but it didn’t feel linear as you continued to dial in lock, so while the steering was accurate, felt good, and had very little slip, you were constantly making corrections to hold a line—say on something like a decreasing radius on-ramp—because the lock didn’t dial in the way you expect it to.

I’m sure there’s a bunch of professionals that would check my opinions, but this is just what I’ve come to observe over the years.

 

[Ericc B]

When a Ford engineer calls something a night and day difference compared to a previous version in my experience that usually means it is about 1% better than before.

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