FIA / Replacement Roll Bars

[Richard_W]

Hi All,

I am sure this has been done to death, but I haven't quite got the info I am looking for from doing archive searches.

I am doing some update to my car and as ever things mushroom... Having decided to fit new adjustable dampers and springs all round I decided that with the rear dampers out I may as well change the standard bar currently fitted to one that allows me to run in club track days etc. I have also pulled the rear arches but that is another mushroom effect...

I am in the process of thinking about ordering a new bar and am deciding between a single diagonal and a double diagonal. What are the pro's and con's of each? I never use the hood, I've taken the frame etc out of the car, so hood clearance and bar height doesn't bother me; so which is best to go for? I am angling towards a double diagonal at the moment.

The car is an imperial, De-dion S3 on the off-chance that anyone has a spare bar kicking around!!

Thanks!

[Geoff Brown]

Double diagonal obviously due to its structural integrity.

[SLR No.77]

"obviously" ???

It's rarely quite so simple ... unless you have access to test results! Both bars are FIA approved (with their relevant forward (Petty) struts fitted and are different in more ways than just an added diagonal - shape, dimensions, tube diameter etc. You'll not go wrong fitting either.

Stu.

[Mcalvert]

Hi Richard - there have been some good articles in Lowflying on the subject that you might want to read.  I'd point you to the following:

http://lowflying.lotus7.club/2016/2016_03_05_Rollbars.pdf

http://lowflying.lotus7.club/2018/2018_01_03_ROPS.pdf

http://lowflying.lotus7.club/2016/2016_04_09_Rollbars.pdf

However, I'm not sure that any of these address the actual question you're asking about the single vs double diagonal (sorry!).  My belief (but may be wrong) was that the single diagonal was the design for the imperial chassis, but that when they came out with the metric chassis, they took the opportunity to resesign the rollover bar to the twin diagonals (which has the advantage of being universal for LHD and RHD cars.)

However, I may be talking out of my posterior so do please check .

[Shortshift]

Michael is right.  Rollover bars for imperial cars were made by Arch and have a single brace; bars for metric cars have been produced by Caged and have the double brace. 

Both types are recognised, as appropriate, for use on Club trackdays.

James

Edited to say: this isn't exactly true as both single (Arch) and double (Caged) braced bars were available for fitment to imperial chassis cars.  See #9 for a less hasty, less lazy and more accurate summary!

 

[Richard_W]

Thanks all, those articles are useful.

I guess my question was whether one was inherently better than the other, my initial thinking being that more triangulation seemed like a good thing.

The conclusion seems to be that both are better than what I have and it comes down to what fits best!

By the time I've finished I'll have replaced significantly more of the car than I expected! Good job I've been working at home for three months and not gone anywhere... The fuel savings have updated the car!

 

[Nick Chan]

I suppose from an aesthetics (sp?) point of view, the Caged double diagonal is a more modern look.  Arch have produced a double diagonal but I think they were special request whereas Caged would be off the shelf

[7 wonders of the world]

Had 2 Imperial cars both with double diagonal bars, both made by Caged, the first was supplier by CC in a new kit.

there are a lot of Imperial cars with that set up.

 

[Shortshift]

Well, just goes to show what I know!

Maybe I was relying too much on memory.  In fact, that is definitely the case.  So in an attempt to salvage some credibiliy in this area here's what I believe to be a more accurate summary of trackday (sometimes called 'FIA') rollover bars.

• Until 2003, all trackday bars were supplied by Arch, with the main hoop manufactured from 1.5" CDS tubing in 12g.  These bars are characterised by a single diagonal.  There was a tall bar option available.  All cars were imperial chassis at this time.
   
• From 2003, Caged became the main supplier of trackday rollover bars.  The spec remained broadly the same apart from the double diagonal bracing.  All cars were still imperial chassis at this time.
   
• In 2007, Caterham Cars introduced the metric chassis with trackday rollover bars continuing to be supplied by Caged.

I think it's therefore accurate to say that imperial cars could have been fitted with either Arch or Caged supplier bars, depending on the purchase/supply date of the bar, and that all metric cars will have been equipped only with Caged, double-diagonal types.

James

[TomB]

 Is it possible to fit the FIA cross bar with Tillet seats? 

[bluenose]

Is it possible to fit the FIA cross bar with Tillet seats?  Yes

 

[Geoff Brown]

sforshaw #3 - 'It's rarely quite so simple'-  yes indeed it is quite that simple having seen the test results from the tests that the club commissioned.

The latest double diagonal bar resists collapse from side ways forces more ably than the single diagonal bar.

[Tazio]

But a cage is better.....

[StevehS3]

#3 Rarely that simple. I agree. When I was discussing buying a car from CC they had a different view on roll bars - even a 620R comes with standard roll bar unless a cross braced one is ordered as an extra.

[Ian B]

The OP may also need to budget for a new boot cover, and a different half hood if used.

[SLR No.77]

Good point Ian 

[Shortshift]

" 'It's rarely quite so simple' -  yes indeed it is quite that simple having seen the test results from the tests that the club commissioned.

The latest double diagonal bar resists collapse from side ways forces more ably than the single diagonal bar."

Well, not quite so, and I wouldn't want the Club's work in this area to be misrepresented.

For anyone with an imperial chassis car wondering whether to buy either a single or double diagonally braced trackday bar, rest assured that the work carried out by the Club showed remarkably little difference in performance between the earlier (single brace) and later (double brace) bars.  Actually, having just checked, I'd say to the point of any difference being negligible.

To recap the summary of the Club's investigation - when assessed using an internationally recognised test standard, both examples of trackday bars (single and double braced) performed substantially better than either of the earlier or more recent standard, unbraced bar types that were also considered.

James

 

 

[7 wonders of the world]

Best option is an SLR cage though with lowered floors   even though these cages are like hens teeth