Multiple Barrel Roll Crash - No Air Bags!

[RaVolvoR]

Originally Posted by owyn

Pull the other one!, I'll find you some text books that explain the differences between static and dynamic coefficients of friction.

Go ahead... please enlighten me!

[RaVolvoR]

Originally Posted by rippedoffagain

I'd still rather have ABS than not, because with your wheels locked your car is just a big sledge. You have no control whatsoever.

ABSolutely me too (sorry no pun!) ... we don't get the ICE conditions I spoke of so I'd always want ABS on any car I drive.

[opotwiman]

You were quite lucky. Take it easy for a while and thanks to Volvo for saving another precious life.

[Viper_7]

Matt, definitely over 30mph!

So this is where you hang out when not working ;-)

[KATANA MAN]

Glad you are ok and not badly hurt! One hell of a lucky escape!

If i had a roll in my car, a 2001 V70, I would probably get knocked out by the grab handle above the drivers door as im always bashing my head on it on bumpy roads............anyone elase have this problem?

I think I may have to remove the handle!

Katana man

[jackass]

Originally Posted by RaVolvoR

Go ahead... please enlighten me!

Static friction tends to be measurably lower than dynamic friction. Once the wheels are locked you are into the realms of static friction; optimum braking occurs the moment before the wheels lock - this is where cadence braking comes in, the aim is to keep the maximum braking force applied without locking the wheels (this is achieved by increasing braking force and releasing if the wheel locks).

The ice problem is even more complex, if a wheel locks the ice beneath it melts and starts to lubricate the slide (like a sledge or ice skate), so the optimum method for slowing is actually gradual engine braking (which will never lock a wheel).

The problem ABS faces is that it has to continually compare its 4 inputs (the speed of each wheel) and determine if one is about to lock with respect to the others. On ice all four wheel can lock at once and the system has no choice but to release all four brakes - on most other surfaces modern ABS will only release the locked wheel mantaining braking, even the best driver couldn't beat that as he's only got one brake pedal.

The final problem you face is that when the ABS triggers continunously, as it does on ice, the quickly expend the vacuum assist and have to apply some real pressure to the pedal to maintain brake operation.

[RaVolvoR]

To "jackass" this all souds good but the reason this all fails (I argued that the locked wheel would stop you quicker, not safer and not under control as clearly you wouldn't be "in control"). All you say is correct but "the system has no choice but to release all four brakes " is where the problem occurs. What causes the wheels to turn again? This is required for the ABS to become effective again. You've already argued that the fricion is lower in static situation so it takes longer for the wheel to speed up, in that time you have travelled... whilst the static wheel (even though its got lower friction) is still slowing you down. So you have a lower slowing effort applied constantly for longer than the higher slowing effort which is intermittently with longer gaps of no slowing force.

The reply from "grass hoper" is correct, I worked in chassis engineering at Jaguar when the old XJ40 (first modern jag in 1986 after 1969 XJ6) and the frst to have ABS option. This is precisely the result they found, sheet ice is worse for ABS in these terms only. I did qualify my comment saying its relative, if you're on sheet ice like this, then the chances are unless you are on a frozen lake you will probably run out of straightline room to stop, ABS or not, then you rely on the airbags.

I must admit I would like to see this proved again, since modern ABS uses a different technique for sensing wheel lock, inertial differences between wheel and hub or similar. Perhaps James May on Top Gear could do this...

Its a ridiculous situation that should never occur in normal driving, so I said once already ABS is a must on all cars.

[Viper_7]

Regarding DSTC - if fitted why did the backend still step out etc.

~These systems are great and do in the main aid the driver in keeping control - however space is required!

We've all seen clips of tests on sheet ice with other vehicles including Volvo showing how the systems works etc, but in all these clips do you ever see any oncoming vehicles? do you ever see near by trees? do you ever see a road side ditch etc etc.
In the real world and not on some frozen lake no matter how brilliant these systems are, there just is not enough space for recovery in the majority of cases.

Same for ABS/ well any braking systems, it's SPACE and time that is required to avoid disaster.

Secondly modern cars are terrible on the snow/ice due to the wide tyres. Rather than cutting through the snow/ice and building up a small wake, they end up floating on the top,and as said under braking they never get to dig in.
ABS only provides control under braking, it does not necessarily stop you in a shorter distance.

[jackass]

Originally Posted by RaVolvoR

I must admit I would like to see this proved again, since modern ABS uses a different technique for sensing wheel lock, inertial differences between wheel and hub or similar. Perhaps James May on Top Gear could do this...

Fifth gear did test a Jag X-Type on a frozen lake. I don't remember if the car stopped any quicker with the ABS disabled (i'm pretty sure there was nothing in it) - but it did hit every obstacle in its path. I had a quick look on Youtube but it's not there, could probably find it on finalgear if you really wanted.

[mbren30]

Originally Posted by thebigv

Having also attended lots of RTA's (not RTC's, RTA's are Road Traffic Accidents, whereas RTC's are Road Traffic Collisions, no signs of another vehicle here, ergo RTA) in a proffesional capacity i feel that thanks should be given to Volvo for what they have done, whether or not the driver was driving like an idiot is besides the point. Fistly, he had an accident and felt the need to reassure fellow Volvo owners of A) the excellent safety these cars provide, and B) the concern of airbags not going off. Second, Only a few people have indeed answered his concern, yes the car has sensors to decide whether or not to deploy the airbags, in this case it felt none were needed due to lateral movement which has been mentioned.

My last comment for all who have attended in a professional capacity, you guys should know better that there are always two sides to a story and before jumping to an assumption should ascertain facts before publicly flogging and individual. I've been in the position of notifying loved ones and it is not nice, but why should this individual have to suffer because some people intentionally drive like a prat? stereotyping anyone?? If he was, fair enough, but don't assume just because it was unusual he was driving like an idiot. Whats to say he wasn't on a country road, hit mud or diesel, turned sharply and it flipped after hitting a verge!! I know why because driving like an idiot gives us the right to comment. If he'd bumped a wall reversing out of his drive who would have said he was driving like an idiot? He could've been reversing at speed drunk and high on drugs, but no one would've thought that i bet.

As has already been used, some may be offended by my comments and i'll be the first to say i'm wrong if i am, however i'm not going to apologise either. If the individual concerned was driving like a prat and he hurt himself in the process, we should only be concerned if he didn't learn his lesson from this!!!

Too many people get caught up in the ins and outs of what doesn't concern them. He's one less statistic to worry about, we should be thankful, as cars can be replaced, people cant!!

You call them RTA's I call them RTC's, in my opinion there is no such thing as an accident, when vehicles collide it is down to driver error or mechanical fault. This very incident is down to driver error on the side of the other motorist that swerved towards the OP to avoid an animal in the road.

At no point did I suggest the OP was driving like an idiot, i was simply generalising when i said that things like this make people step back and reevaluate there driving methods, that doesnt mean im saying the OP was at fault.

At the end of the day the guy got out alive thats whats important. Like you state, cars can be replaced people cant.