Sway bar selection – the dump truck story

Stories are my favorite way of conveying ideas. This story is relayed as accurately as possible.

In March 2006 two of my co-workers had a very close call here is their story.

The driver, in his early 40s, is a traveling salesman in France. On this day he was driving his Audi A6. His beloved weekend toy is a 300kph (186mph) super-bike he drives 8,000 miles per year. He is a very experienced high speed driver driving his car 30,000+ miles per year for business. In the passenger seat sat another highly experienced driver and former 120mph go kart racer.

On their way to a customer visit they came up to their exit on the A86 outer ring road of Paris. As there was a large dump truck in the left lane the salesman decelerated from 80mph (130kph) to about 50mph (80kph) and tucked in 150 ft (50 meters) behind the dump truck as it was too tight to pass before the exit. At that moment there was a loud crash as the several hundred pound steel dumper door (tailgate) fell off the back of the truck and started cart wheeling towards the Audi. Acting on pure instinct our salesman said he hit the gas and the brakes at the same time and veered sharply to the left and again to the right. The passenger, a Scotsman, who is more inclined to understatement then overstatement, said the dumper door passed within one inch of his side view mirror.

Without talking they drove to the customer’s parking lot and sat silently in the car for 2 minutes thinking about how they had just cheated death.

At dinner that night the visibly shaken salesman raved about the handling of the Audi saying that it had saved his and his passengers life. What aspect of the handling – I enquired? His answer: The fact that even under extreme evasive maneuvers the car did not over steer – had the car over steered, even a little, the dumper door would have sliced through the passenger door at a 90 degree angle with devastating consequences.

When I asked him if he could have evaded the accident as well on his motorcycle he looked away momentarily and said he had asked himself the same question. He said his motorcycle would have over steered with such a sharp steering input probably resulting in a crash with the dumper door. He said he didn’t know if he could ever ride his motorcycle again and he may have to sell it. (I’ve said similar things after really close calls but this feeling goes usually away)

Lessons to learn:
1) don’t follow too closely
2) pay attention
3) always be ready
4) In an emergency, at speed, with no time to think, under steer is better that over steer – this is why all cars come from the factory with a tendency to understeer. Keep safety in mind when choosing a sway bar for your car. The larger the bar the greater the tendency to over steer and the smaller the margin for error. The stock MCS 17mm rear sway bar is inherently safer than a 19mm bar. And a 19mm bar is inherently safer than a 22mm bar – all things being equal. Apparently JCW even thinks a 19mm rear bar is too much as they don’t offer a larger rear bar.

 

The smaller bars may be safer for a driver in a unique situation, as described by you, but I think the rationale isn't an "inherent" safety issue. It is a driver experience issue. A vehicle that begins to oversteer, requring counter-lock to control, is more difficult to keep facing the correct way on the road/track compared to your Chevy Lumina style understeer built for the masses. As many tuners will suggest, after even modest suspension and driveline upgrades, tighten the screw behind the wheel. Get yourself enrolled in a class or course, such as Phil Wicks, to learn how to handle your car at the limits in a controlled environment, prior to getting in emergency situations on an open carriageway!

And to JCW, who cares what they "think". They are only one, albeit well regarded, tuning shop.
Thanks for the story, and for your opinion.

BTW your buddies Audi, Quattro right?

 

The JCW suspension really does dial out a lot of the "inherent" understeer. Still run my H-Sport Comp, though.

 

Hhmmmmmm.....reminds me of the story a little old lady was telling me as I was writing a damage estimate on her car. She said she had to swerve to the left & rt. several times before final hitting the other car. {made me wonder if she really needed to swerve at all}
But I know what you are trying to say. I run my rear sway at the softest setting on the street. I enjoy a spirited drive on the street, but hold a lot in reserve for the unexpected. The track is the best & safest place.

 

I fully agree, but run my H-sport comp rear bar at max stiff on the street. Here's why: my MCS, and probably that Audi, has DSC and I do not turn it off for street use. The DSC even seems to control lift-throttle oversteer reasonably well by braking the outer wheels forcefully. Not smooth, not the fastest way around... but safe.

Yes, the DSC is a reactive system while the driver is proactive. But in an emergency situation such a setup should allow for more rapid turn-in; just need to learn to place your faith in the computer to save your hide afterwards.

 

This should be fun.

 

BFG9000,

You bring up a good point. I forget about DSC because I don't have it. The underlying condition to these handling anecdotes is individual driving style, car setup, and, venue.

I'm running my new setup this weekend with all the stock bars in place. I prefer high speed understeer. I think I can coax the Mini's backend to rotate enough thru the only left hander at LRP for eample - enough to satisfy my level of enjoyment. I don't think I can do the same thing on an autoX course...even if I could the clock would be ticking away as I waited for rotation.

Remember, a rear bar works by transfering weight and it does so by removing weight - traction - from the rear. I'm not suggesting this is bad, rather, it is what happens. It may desirable or it may not be. A comfortable driver in a viseless car is faster than the same drivier in a car with higher, but spooky limits. I hate spooky I know myself...I'm not Hanns Stuck.

 

Good thing his car didn't understeer - if so, he'd have apparently plowed right into the object!
Here's to neutrally handling vehicles!

I'm not sure of the consequences of hitting the brakes and the gas at the same time - if a RWD vehicle, it would load up the front tires significantly (inducing understeer.) If FWD, you're just fighting yourself and, I would think, slowing down any reactions. AWD would be something in between, though the bias tends to be toward driving the fronts.

 

That was my thought as well.....plus the last swerve was to the right....with the dumper door just missing the passenger side
Sounds like a little luck, as well as expert driving.


Wooops....I guess they do drive on the other side of the road over there don't they.

 

Hmm. Ancedotal stories are interesting but here's another one, first person and I was very thankful for OVERSTEER.

The following is a true story, only the names have been changed to protect the innocent

In 1991 my wife and I drove xcountry in our brand new, mid-engined MR2 Turbo, RWD. We were on a mountain road doing BELOW the speed limit ... about 40 mph. To the right was some dirt and a huge granite mounstain side. to the left was some dirt and a 3000 foot drop, no guardrail, two lane road.

There was loose gravel on the road, very small, couldnt be seen. The tail end started to come around so I did what was NOT instinctive unless you are used to RWD and engines in the rear and clutch in, brake in, steered into the skid ... no surprise, full turn 4 wheel drift followed by sharp spin INTO the wall. ... At that moment I figured, totalled new car and us injured. Everything going in slow motion ...

Car continued into a 180 scrubbed off speed but now heading toward the cliff ... now I thought ... oh well, its been fun ...
The car stopped after a full 360 facing forward on the dirt, literally 2 feet from the edge. I walked around the car, no damage, very little rubber on the road (mostly gravel skid). Drove away in complete silence and then we laughed. ALIVE!

I see two really bad scenarios that could have happened if the car didnt oversteer.

1. Builit-in understeer? No question, smack head first in to the granite. Totalled car. Thats going to hurt.
2. Thinking FWD, turn away from the skid .... don't even want to think about what would have happened as I had visions of a counterclockwise out of control spin for being stupid and over the cliff.

Lesson learned???? Be afraid, very afraid of 3000 foot cliffs

Seriously though, the car was about inherently neutral to oversteering and I'm convinced that if the tail hadn't come completely around we would have understeered or plowed right into that wall. Ouch.

BTW, there was no time to thing, it was just clutch in, brake in, cut the wheel all the way around, and hold on. Who knows, maybe I did the wrong thing ... been known to do that too.

I think in an emergency, know what the car will do first ... try it out in some snow and see how it skids but who does that these days anyway.

 

I once knew a girl who was in a bad car wreck, and because she was NOT wearing her seatbelt she was thrown from the car and managed to survive an accident that otherwise would have killed her. Even though her lack of seatbelt saved her life, it is still very much the case that you are safer wearing a seatbelt. There are exceptional circumstances that can happen in any situtation, you just have to try to do the best you can to be safe in MOST situations. Considering the benefits of my rear swaybar, I will not remove it in the off chance that a dump truck door will come at me on the highway.

my 2 cents

 

I'm with Eric and chows4us, and certainly do not think that understeer is safer at speed than a car which has more neutral handling characteristics. Personally I think that a stock MCS understeers quite noticably when pushed at all, and I believe that that my car is safer, and also way more fun to drive, with a stiffer rear sway bar.

For example, think of a quick right hand bend - would you rather have your car (A) push/understeer into oncoming traffic (and in this case more steering lock causes more understeer) and hit a car, or worse a motorcycle or cyclist, head on, or (B) turn consistent with the amount of steering input you put in and follow the radius of the curve?

I choose B.

 

Understeer scrubs energy

Oversteer gains energy

Nuetral steer is, well, between the two.

But there are degrees of each and every car reaches these characterisitics in a different way.

 

Meh. Exact same situation happened to me in my old A4 which was tuned very neutrally. It had a Neuspeed 19mm rear bar set on stiff and a 425#F/625#R spring rate differential.

Anyway, I was driving down the highway behind a truck which dropped a 2x4. The 2x4 was bouncing end over end right at me. I instinctively braked, and then swerved around the 2x4 while on the gas. The *** came out a bit but I was able to avoid the 2x4 - can't say I would have if I tried to pull the same maneuver without the rear bar.

I think the moral of the story should be to know how to do an avoidance maneuver in whatever car you drive, whether it's neutral, or biased toward understeer or oversteer. It's all about driver training.

I would make the argument that n00bs with no track experience should not be driving cars equipped with hefty rear bars.

 

Huh?
I understand the 'scrubs energy' part, as pushing tires sideways will scrub off speed (though I wouldn't use the former term).
But you lost me on the 'gains energy' part. Oversteer turns forward force into lateral force (just like understeer, but on the other end of the car), but no energy is 'gained' - though it certainly feels like you're moving faster when swapping ends!!

 

Like them NASCAR boys say......loose is fast

 

E=mass*(velocity*velocity)
somebody said that once.

Mass is constant, velocity is constant(or decreasing due to friction in a slide). Whether it be rotational/lateral (i.e. over/under steer) or linear it can't increase unless you step on the gas. You neither gain nor lose "energy" in the truest sense.

 

What did some NASCAR guy say?

"understeer means you hit the wall headon. oversteer means you hit it from the rear"

 

The original story has abosolutely nothing to do with understeer/oversteer/whatever. This story reminds me of the stories on motorcycle forums where people insist that the "had to" dump the bike to slow down in time.

What would stop faster - a cart wheeling steel dumpster door or a car with four very sticky rubber patches? My $'s on the car. Memory does funny things - I'm guessing the 2 in the car were much closer to the truck than 150 ft and didn't react as quickly as indicated.

 

Quattro * (Brake + Gas) = 100% throttle cut

just ask my R32....

this story sounds like an email I got from a African prince, but I can appreciate where its coming from and why it was posted....

 

The throttle cut-off actually has nothing to do with Quattro whatsoever. It's the ECU programming of the Drive-By-Wire cars, both Quattro and FWD.

The cable throttle Quattros do not cut the throttle if you're on the brake and the gas.