Functional roll bar.

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boustrophedon
Joined: Thu 01 Oct, 2015 21:29
Posts: 34

  Z3 roadster 2.0

Functional roll bar.

Post by boustrophedon » Tue 20 Oct, 2015 21:47

There are lots of threads on here on roll bars or hoops, but which are actually functional in terms of roll over protection? And how difficult are they to fit to a '99 model that never had them?

What I would actually like is something like the Hard Dog bars on sale in America, has anyone any experience.

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Robert T
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  Z3 roadster 1.9
Location: Cheshire

Re: Functional roll bar.

Post by Robert T » Tue 20 Oct, 2015 22:14

The BMW hoops are the real deal. You can see photos of how they fit to the car here: http://www.zroadster.net/forum/viewtopi ... 81#p198981

In order to be functional, they need to be made of a certain thickness of steel, and properly secured to the car. The BMW hoops are attached to both the inboard and outboard mounts and when fitted the car actually feels is stiffer. They can be fitted to all cars from 01/97 onwards, with the requisite fitting kit/parts.

There are number of alternative hoops that fit to the BMW mounts, and I would have thought all these should all be functional. As said, it depends upon the grade of steel used.

There are also a number of hoop designs that fit to the outboard mount only, with the inboard leg essentially floating. These are definitely not functional.

There is one kind of bar which simulates a pair of hoops, but they are actually joined in the middle. I suspect that these would fracture where they are joined in the event of a roll.

I'm not sure what is available in terms of single bars, but for these to be functional, they tend to have additional bracing bars that also bolt to the chassis, more like a cage than a simple bar.

Cheers R.
Arctic Silver '99 Z3 1.9 & Black '59 Frogeye 1275cc
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pingu
Joined: Fri 30 Apr, 2004 17:01
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  M roadster S50

Re: Functional roll bar.

Post by pingu » Wed 21 Oct, 2015 14:20

Roll-over hoops only protect you in the event of a roll-over, or the car being placed on its roof. These are very rare events. Most cars are also moving forward when they roll and there will be a rearward thrust on the bars and windscreen.

The collapse of the screen is limited by its strength and to a much lesser degree by the quarter light frame. Early Z3s didn't have rear hoops and I suspect that they were only added as a confidence measure because customers thought it was unsafe.

The strength of the spot welds and the metal surrounding the hoop support brackets would be the limiting factor of the strength of the rear hoops. I wouldn't expect the bar to bend or break before the mountings were ripped out.

A fully protective roll-over bar should have bracing to the front hoop, not a near vertical brace to the floor as in the image.

I would expect any roll-over with forward momentum in a convertible to be a life-changing experience. If you are that worried about a roll-over, fit a full cage. Personally, unless I were racing, I would be happy without hoops (in fact my 2.8 didn't have them).
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deni2s
Joined: Mon 25 Mar, 2013 22:02
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  Z3 roadster 2.8

Re: Functional roll bar.

Post by deni2s » Thu 22 Oct, 2015 09:04

The only roll bars which are functional and certified by German TUV are BMW OEM roll bars and AC Schnitzer roll bars. I believe most aftermarket roll bars on ebay are neither functional nor certified. I have ACS roll bars and compared to aftermarket roll bars from ebay they are at least twice as heavy, so most aftermarket chrome roll bars have only decorative purpose.

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Jonttt
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Re: Functional roll bar.

Post by Jonttt » Thu 22 Oct, 2015 15:26

Schnitzer did not make the roll bars, they are made by another company I forget the name of now, something like alumex in Germany. They are tuv approved as are the OEM hoops. It worth noting the windscreen and seat backs are the main rollover protection.
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billysally208
Joined: Sat 11 Jul, 2015 13:53
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  Z3 roadster 1.9i

Re: Functional roll bar.

Post by billysally208 » Thu 22 Oct, 2015 17:29

Jonttt wrote: It worth noting the windscreen and seat backs are the main rollover protection.
That worries me a bit as my head sits slightly higher than the top of the back of the seat! :shrug

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Robert T
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Re: Functional roll bar.

Post by Robert T » Thu 22 Oct, 2015 19:37

billysally208 wrote:That worries me a bit as my head sits slightly higher than the top of the back of the seat! :shrug
This is precisely the reason I fitted hoops to mine. Took me about 10 years of ownership to get round to fitting them, but hey ho. :D

Cheers R.
Arctic Silver '99 Z3 1.9 & Black '59 Frogeye 1275cc
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deni2s
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  Z3 roadster 2.8

Re: Functional roll bar.

Post by deni2s » Thu 22 Oct, 2015 19:55

Robert T wrote:
billysally208 wrote:That worries me a bit as my head sits slightly higher than the top of the back of the seat! :shrug
This is precisely the reason I fitted hoops to mine. Took me about 10 years of ownership to get round to fitting them, but hey ho. :D

Cheers R.
Do you really think you will still not fall out of your seat when car is upside down? I don't think the roll hoops will be much of help in such situation even if you are wearing helmet and using seat belts.

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Robert T
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Re: Functional roll bar.

Post by Robert T » Thu 22 Oct, 2015 21:35

deni2s wrote:Do you really think you will still not fall out of your seat when car is upside down? I don't think the roll hoops will be much of help in such situation even if you are wearing helmet and using seat belts.
That depends very much on whether the seatbelt pre-tensioners work after 16 years...

Cheers R.
Arctic Silver '99 Z3 1.9 & Black '59 Frogeye 1275cc
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deni2s
Joined: Mon 25 Mar, 2013 22:02
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  Z3 roadster 2.8

Re: Functional roll bar.

Post by deni2s » Mon 26 Oct, 2015 08:52

Robert T wrote:
deni2s wrote:Do you really think you will still not fall out of your seat when car is upside down? I don't think the roll hoops will be much of help in such situation even if you are wearing helmet and using seat belts.
That depends very much on whether the seatbelt pre-tensioners work after 16 years...

Cheers R.
I don't think that even with working pre-tensioners one belt over the shoulder can prevent anyone from damaging the head. There is 5-10cm "clearance" for head till roll bars - a-pilar line. Maybe with soft-top up roll bars might help something.

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Robert T
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  Z3 roadster 1.9
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Re: Functional roll bar.

Post by Robert T » Mon 26 Oct, 2015 12:54

deni2s wrote:I don't think that even with working pre-tensioners one belt over the shoulder can prevent anyone from damaging the head. There is 5-10cm "clearance" for head till roll bars - a-pilar line. Maybe with soft-top up roll bars might help something.
It is not the shoulder part of the belt that pulls you into the seat, it is the part that goes across your lap. Have a watch of some videos of airbags deploying, and you'll see how the dummy is pulled down into the seat by the pre-tensioner as the airbag deploys.

I think I'd rather have roll hoops than not, as between the windscreen and the hoops it creates a survival space, which might just make the difference. Though the better rules is to "keep it shiny side up!"

I don't have any kind of bar/hoops on the Sprite, and the windscreen on that wouldn't do anything. I do have racing harnesses in it, but that is because there is no high-point to attach a conventional three-point belt. The harnesses are anchored at a single point behind you and this helps to keep them in the correct position on your shoulders. As it doesn't have crumple zones either, the best rule is "just don't crash it".

Cheers R.
Arctic Silver '99 Z3 1.9 & Black '59 Frogeye 1275cc
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Jonttt
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  M roadster S54
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Re: Functional roll bar.

Post by Jonttt » Thu 29 Oct, 2015 19:41

billysally208 wrote:
Jonttt wrote: It worth noting the windscreen and seat backs are the main rollover protection.
That worries me a bit as my head sits slightly higher than the top of the back of the seat! :shrug
Duck
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