SUV ROLL DAMPENING

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Olefud
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SUV ROLL DAMPENING

Post by Olefud » Mon Sep 19, 2016 1:18 pm

I did some thinking this weekend. My grandson, driving too fast (60mph) while under "supervision" with a learners permit, lost control and launched into a terrible end-over crash - crushed roof, cracked block and wheels broken off. Car seat (second grade granddaughter), seat belt and side air bags with very, very good fortune yielded no physical injury. That same evening a young couple with baby in car seat but not seat belts had a similar incident Two adult fatalities.

First thought is; "do SUVs have rather severely underdamped suspensions in roll?" I can twitch my street-modified-suspension Mustang through chicanes and it settles right down. The high CoG SUVs have much less roll dampening in my limited experience with them. Just asking.

And back in the 50s I bolted WW2 surplus seat belts in my Alfa Spider. Why would anyone still be driving without using them?

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Re: SUV ROLL DAMPENING

Post by Splitter » Mon Sep 19, 2016 2:16 pm

Wow, good to hear nobody was injured. Five years ago I drove a Ford Escape across BC, from the Crow's Nest Pass to Tofino on the west side of Vancouver Island. There were some curves where I couldn't keep up with traffic the body roll was so severe. A 4x4 truck has a more responsive suspension and less body roll, but I'm guessing that's because the springs, swaybars and shocks are a lot stiffer, probably because people expect that from a truck but want a smoother ride in an SUV.

Here's an example of good roll stability: a few years ago I went for a ride in a logging truck, drove 3 hours north out to the bush to pick up a load (Google satellite coordinates 54.984420, -101.462371), and on the way back my buddy was running the truck up against the limiter at 65mph on a hilly, winding gravel road. That was a B-train tractor trailer weighing around 60 tons loaded, and you would not believe how well it handled.

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Re: SUV ROLL DAMPENING

Post by pdq67 » Fri Sep 23, 2016 8:58 pm

Anybody remember Fords Explorers and Bridgestone Tire and the crap they both caused because of too high a CoG and lowering the tire pressure instead of lowering the CoG like should have been done.

Tires ran hot because of too much sidewall flexing and then blew out. I think several people were killed because of this.

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Re: SUV ROLL DAMPENING

Post by Splitter » Sat Sep 24, 2016 2:10 am

pdq67 wrote:Anybody remember Fords Explorers and Bridgestone Tire and the crap they both caused because of too high a CoG and lowering the tire pressure instead of lowering the CoG like should have been done.

Tires ran hot because of too much sidewall flexing and then blew out. I think several people were killed because of this.

pdq67
I remember Ford Exploders and Firestone tires. Even people who weren't affected by the recall were getting their tires changed out, on other vehicles...nobody wanted Firestone.

Going back to the original post, I guess the vehicle doesn't lose control from the initial turn, but when the driver tries to correct by countersteering before the suspension has time to settle down?

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Re: SUV ROLL DAMPENING

Post by PackardV8 » Sat Sep 24, 2016 10:18 am

It is good that many of us survived youthful mistakes; I had my share.

No vehicle is idiot-proof. Back when I did a lot of business travel and had to haul supplies, I rented most every SUV on the market. Because I was hauling max GVW at max legal speeds plus, I always carried a tire pressure gauge and verified the tire pressure. When safe to do so, I drove them thousands of miles and often through corners hard enough to scrape the chrome off the door handles. They're not sports cars, but I never found any of them inherently unsafe.

The main problem with current SUV design is the buying public wants them so large and so heavy. Most are in the 4,500 -5,000# range. A lump of that mass doesn't want to stop or turn instantly. As previously mentioned, an inexperienced driver can quickly get behind on his steering, compounding his/her initial mistake.
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Re: SUV ROLL DAMPENING

Post by pdq67 » Wed Sep 28, 2016 1:34 pm

"End and rebirth of Ford/Firestone relations[edit]

John T. Lampe (Chairman & CEO of Bridgestone/Firestone) announced in a 2001 letter to Jacques Nasser (Ford Motor Company chief executive) that Bridgestone/Firestone would no longer enter into new contracts with Ford Motor Company, effectively ending a 100-year supply relationship.[24]"

From wiki, I thought Bridgestone was in on this!

https://en.wikipedia.org/wiki/Firestone ... ontroversy

And I think that the Decatur, IL Firestone tire plant didn't put the tires together right in the 1st place, whatever..

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Re: SUV ROLL DAMPENING

Post by Kenova » Wed Sep 28, 2016 4:01 pm

I think Ford just underestimated the stupidity of the average SUV customer.
They jump out of their Crown Vic and into the SUV expecting it to handle like their car. We all know that never ends well.

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Re: SUV ROLL DAMPENING

Post by Walter R. Malik » Wed Sep 28, 2016 7:33 pm

In the interest of comfort and easy driving, manufacturers of newer vehicles with a high center of gravity use steering which is much, MUCH to fast in a panic situation for a non-experienced driver or people with less talent for vehicle control.

They grab a big handful of the steering wheel when bad situations happen and over correct without realizing what is happening, then over correct the other way and over it goes.
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Re: SUV ROLL DAMPENING

Post by Olefud » Thu Sep 29, 2016 11:31 am

Walter R. Malik wrote:In the interest of comfort and easy driving, manufacturers of newer vehicles with a high center of gravity use steering which is much, MUCH to fast in a panic situation for a non-experienced driver or people with less talent for vehicle control.

They grab a big handful of the steering wheel when bad situations happen and over correct without realizing what is happening, then over correct the other way and over it goes.
Right you are. I pretty much correct for this with “feel” through experience. It shouldn’t be that difficult to enhance roll dampening while maintaining jounce fluffiness.

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Re: SUV ROLL DAMPENING

Post by PackardV8 » Thu Sep 29, 2016 3:29 pm

It shouldn’t be that difficult to enhance roll dampening while maintaining jounce fluffiness.
Not difficult assuming one is willing to pay BMW prices.
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Re: SUV ROLL DAMPENING

Post by Olefud » Fri Sep 30, 2016 1:20 pm

PackardV8 wrote:
It shouldn’t be that difficult to enhance roll dampening while maintaining jounce fluffiness.
Not difficult assuming one is willing to pay BMW prices.
With all the electronic cabin gear we seem to be doing so anyway -except BMWs are now RR prices. But your Hudson twin carb wouldn't have this problem.

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Re: SUV ROLL DAMPENING

Post by pdq67 » Sat Oct 01, 2016 4:05 pm

Walter R. Malik wrote:In the interest of comfort and easy driving, manufacturers of newer vehicles with a high center of gravity use steering which is much, MUCH to fast in a panic situation for a non-experienced driver or people with less talent for vehicle control.

They grab a big handful of the steering wheel when bad situations happen and over correct without realizing what is happening, then over correct the other way and over it goes.
Walt,

Walk down through a boneyard and look at all the front wheel drive cars that have "rolled over" and I think that you will find that the drivers over steered which led them to flip their cars as so doing made them roll around the front heavy CG!!

No more than dropping the right front tire off the edge of the road and "jerking" the car back on the road will cause this!!

Usually you will find that as the roll happens, a pass side rear tire axle will break off as it rolls! The vehicle, "cork-screws", as it flips!!

And don't forget that the EXACT OPPOSITE of this effect was the rear end, "jacking", of the old VW's and the 1st Gen. Corvair's!!

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Re: SUV ROLL DAMPENING

Post by Olefud » Mon Oct 03, 2016 6:54 pm

pdq67 wrote:
Walter R. Malik wrote:In the interest of comfort and easy driving, manufacturers of newer vehicles with a high center of gravity use steering which is much, MUCH to fast in a panic situation for a non-experienced driver or people with less talent for vehicle control.

They grab a big handful of the steering wheel when bad situations happen and over correct without realizing what is happening, then over correct the other way and over it goes.
Walt,

Walk down through a boneyard and look at all the front wheel drive cars that have "rolled over" and I think that you will find that the drivers over steered which led them to flip their cars as so doing made them roll around the front heavy CG!!

No more than dropping the right front tire off the edge of the road and "jerking" the car back on the road will cause this!!

Usually you will find that as the roll happens, a pass side rear tire axle will break off as it rolls! The vehicle, "cork-screws", as it flips!!

And don't forget that the EXACT OPPOSITE of this effect was the rear end, "jacking", of the old VW's and the 1st Gen. Corvair's!!

pdq67
I think we agree. Too much roll couple or too little roll damping is rather the same thing.
I’m only familiar with the swing axle thing regarding completion Porsche 365s. Their problem was poor rear axle location –toe out with trailing brake. Keep the power on through the corner and they were fine and rather fast.

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Re: SUV ROLL DAMPENING

Post by GLHS60 » Wed Oct 05, 2016 1:54 am

The Ford Explorers from around 1991 with the tire problems stated 26 PSI tire pressure!!

Seems hard to believe Ford would recommend such a low pressure on a vehicle that size.

Combined with owners who might not check pressure, many were probably only running 20 PSI.

And Firestone's to boot!!

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Re: SUV ROLL DAMPENING

Post by Brian P » Wed Oct 05, 2016 4:07 pm

Original poster did not state which year, make, and model was involved.

A lot of people buy SUVs because they "feel safe", or some such thing, or they like to sit up high. Wroooong line of thought. A lot of them - mostly the truck-based models - don't have good real-world crash experience compared to other vehicles. A lot of the reason is that they are easier to roll. A car with good safety ratings is a better choice if safety is the real priority as opposed to "feeling" safe.

A lot of compromises are made in the interest of ride comfort. The low specified tire pressure in the older (truck based) Ford Explorer was one such compromise. Too-soft spring and damping rates and inadequate roll stiffness are others.

Modern ESP systems make a difference. But still, the truck-based SUVs are too high, too heavy, are too tempting to drive too fast (being quiet and smooth with a lot of power on tap), and have comfort-oriented tires and suspensions, and it adds up to something that can get drivers in trouble. For that matter, you can say the same things about a lot of pickup trucks nowadays.

You can get away with soft-ish suspension settings if the center of gravity is low. If it's high, the suspension needs to almost stop the body roll from happening in the first place. Look at tractor-trailers for an example. A lot (most?) have air suspension nowadays - but the design of the suspension has very high roll stiffness because you can NOT let that trailer start swaying back and forth. And they don't ride well (by car standards), despite the air suspension - because of the high roll stiffness. So maybe the Explorers should have been equipped with very stiff antiroll bars ... but then perhaps Mom wouldn't have bought it to shuttle the kids around because it rode too rough. Well, maybe she SHOULDN'T have bought it for that purpose.

Not all SUVs are alike (and hence the year/make/model question). Some of them are pickup trucks underneath. Others are (more or less) cars with the body sitting a little higher and the center of gravity isn't appreciably higher than where it would be in a car - they're essentially wagons, but the marketing department calls it a CUV instead.

I have a van that I use for my motorcycle-related activities (hauling bikes to and from track days, etc). I've lowered the suspension ... and had I bought a pickup truck, I would have done the same. They're all too high in the interest of looking macho in some bizarre way, big, brash, in-your-face, etc. Functionally ... I'd rather have it easier to load and unload and that means a lower floor. If that also lowers the C of G and makes it less likely to roll ... bonus.

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