eliminating chassis flex creaks.

[slidetaker]

roll cages in street cars usualy increase the chances of serious injury in road accidents are are highly not recomended by people who investigate colisions.

Question is on the balance of how bad and your attitude towards chassis flexing VS how often you will cause an accident which require the attendance of crash site investigator...

[Muzz]

the crash site investigator has nothing to do with what im talking about. Im saying its been proven time and time again that there is a MUCH greater chance of serious injury, in not so serious accidents. Eg, guy died in a very minor accident from cracking his scull on the windscreen bar. without a helmet and harnesses, roll cages are dangerous, even with good padding.

When i say people who investigate colisions, im not talking about the people who work out what happen in an accident, im talking about the people who design safty systems (harnesses seats cages etc. etc.) for race cars and road cars alike as there day job. All professionals in this industry have the same opionion - if its a road car and not used as a track car at all, having a roll cage is a very very bad idea.

if youd like i can post up a seminar from justracing.com regarding this exact issue, from a racing safty designer.

[chef_32]

Do It!!!

[Muzz]

http://www.justracing.com/seminar_ar...wtopic.php?t=5

the saftey devices in your car are designed as a system, you cant just pic and choose what you want to add, you need to upgrade as a hole system.

eg. You remove the air bag steering wheel - that requires you to use harnesses to keep you from smacking the wheel with your head.
using harnesses - that requires you to add some sort of rollover protection eg a rollbar or cage. With ur stock 3pt seat belt, in the event of the roof crushing down, they allow ur body to be pushed out of the way, where harnesses will hold you upright, perfect if ud like spinal compression or a snapped neck. Very dangerous in a rollover without rollover protection.

Having a cage, padding or no padding, requires a helmet!
Using stock seats with a cage or rollbar? u should get a seat back brace to keep safe in a rear ender accident, most oem seats are designed to flex, some to break at the hinge, better yet, get a racing seat. Also harnesses cannot be saftly used with oem seats, unless they have the holes specifically for harnesses. Finally using a cage with oem 3pt seatbelts is highly dangerous.

Ignore any of these points and ull end up less safe than if you left the whole system stock.

For chassis flex, get a rollcage...

Saying "get a rollcage" when the OP asked what he can do to decrease chassis flex creeks is some very bad advice and also very ignorant. Too many people get cages for the COMPLETLY wrong reason

[Muzz]

oh crap, that link speeks nothing of the roll cage in street car delima- still a good read though!

[slidetaker]

Certainly a good and insightful read indeed. But from argument seek, a newie view, there is really about 2 inches of different between a person’s skull cracking on the roll bar or cracking on the chassis frame??? And when you are talking about skull cracking, which is caused by a great force, that couple of inches would not make a difference in the sense of the reduction of force with respect to space???

In situation of rollover or roof crashing down, I still cannot see why could a roll cage harmful instead of helpful against the impact with transferring the forces more evenly across the chassis given that it is installed in a professional manner?

Definitely agree on the point of having the complete race spec with bars, racing harness and seat and helmet. Surely it is the safest opinion. But in reality, there are still lowered car out there without an upgrade of shocks shows that everyone will mod their cars for different purposes. They might lower their cars for aesthetic reasons, not performance, just as a roll cage for chassis flex, not to comply real racing safety standards.

Please understand I am not trying to start a quarrel, but merely trying to get more information and learn more.

[bennjamin]

(on a road car) also in an accident situation ~ the forces usually ABSORBED into the cars bodywork and chassis would actually expel the car further away IE "bounce" off the impact area. This would lead to massive damage to occupants inside and also possibly throwing said vehicle into more danger ( ie off a cliff , into other cars etc)

[Muzz]

Certainly a good and insightful read indeed. But from argument seek, a newie view, there is really about 2 inches of different between a person’s skull cracking on the roll bar or cracking on the chassis frame??? And when you are talking about skull cracking, which is caused by a great force, that couple of inches would not make a difference in the sense of the reduction of force with respect to space???

I totaly understand where your coming from here. I am definatly no expert, just somone who is very interested in racing safety and trying to learn lots about it. So i cant give u a proper answer, only my opionion, which may very well be wrong.

Say u have a hard accident, and your head meets the halo bar running across the windscreen. All of the impact energy will be experianced by your head, you wont make a dint in the bar at all.

So your head may be moving at 30kph and come to complete stop in 0.5mm, to do this, the amount of deceleration would be extremly high.

using physics equation (Vf^2=Vi^2+2A(Xf-Xi)) You'd find that the deceleration your head would experiance in the above situation would be 69,723m/s or 7715g’s of force! No head could survive that!

Nearly everything around the cockpit of a car is designed to flex a little Eg. steering wheel, dash, door trims rooflining etc. incase of an impact.
(The windows are an exception to this, however if you hit the windscreen with the same force as in the above example, it wouldn’t decelerate your head that quickly, it would simply shatter (absorbing a little energy), and your head continue go through it. Your head would experience lots of damage and cuts, but it wouldn’t experience the MASSIVE g forces from instant deceleration (id say you’d still end up dead)).

So lets say your head hits something like the trim which allows your head to decelerate from 30kph to 0kph over 5mm (id say most trim pieces deform well over 5mm when hit hard enough), the deceleration would be 6970m/s or 711g’s. So if your head hits at 30kph, on the cage it would experience 7715g’s of force, where it may experience 711g’s of force or less if hitting the trim at the same speed. That’s a difference of over 10x the force your head is subjected to.

It’s hard to imagine, but picture yourself relative to the car during an impact. The interiors all perfectly still around you, and in the moment of impact your body’s thrown forward inside it.
In an accident harnesses/belts are designed to stretch an inch or so, and keep your body from experiencing sudden deceleration inside the cockpit (the cockpit is also decelerating as the nose is crushing up). Id guess that when your head is up near the top of the windscreen area the belts are in high tension and well into doing there job of pulling you up inside the interior. They do this very quickly, over maybe an inch or two? So one minute you could be moving forward at 50kph relative to the interior around you, and two inches later be moving 0kph relative to the interior. (that’s not to say your not moving, the nose of the car would still be crumpling & absorbing energy, so you, and the interior as a whole would be decelerating as one). So as you can see, the speed at which you decelerate inside the cockpit (as the cockpit decelerates aswell) means only a few inches can be the difference between hitting with full force, and just a little bump.

[Muzz]

In situation of rollover or roof crashing down, I still cannot see why could a roll cage harmful instead of helpful against the impact with transferring the forces more evenly across the chassis given that it is installed in a professional manner?

I totally agree with you there ur exactly right, if you dont dammage yourself on the cage, having it there in a rollover would be a huge benifit!

I think you just misinterpreded me saying that to be in a rollover, with harnesses but no cage or rollbar, is a very dangerous situation, due to the harnesses holding you in an upright position as the roof crushes down (stock 3pt belts are designed to allow you to be pushed out of the way by the roof)

[Muzz]

They might lower their cars for aesthetic reasons, not performance, just as a roll cage for chassis flex, not to comply real racing safety standards.

Your exactly right there too, i just hate to seeing people make there street cars dangerous for asthetic reasons, or cus the driver want less flex for a car that he has no plans to take out on track.

If it is used on the track, then yeah i can see why one might want one put in for the other benifits, apart from safety

Please understand I am not trying to start a quarrel, but merely trying to get more information and learn more.

yeah its cool mate, and iv been feeling like a bit of a ass after saying -

Saying "get a rollcage" when the OP asked what he can do to decrease chassis flex creeks is some very bad advice and also very ignorant. Too many people get cages for the COMPLETLY wrong reason

it was a bit harsh there, im not usually like that. i was having an absolute shit of a day. I parked at the shops next to a commodore with three dodgy lookin teenagers inside, when i came out i see my drivers side mirror is ripped of, and those dickheads gone

[Muzz]

(on a road car) also in an accident situation ~ the forces usually ABSORBED into the cars bodywork and chassis would actually expel the car further away IE "bounce" off the impact area. This would lead to massive damage to occupants inside and also possibly throwing said vehicle into more danger ( ie off a cliff , into other cars etc)

yeah the stiffer the car is, the greater the g forces experianced by the people inside it.