9 replies to this topic

[TopCatCustom]

Hi, does anyone know what size tubing should be used for a full weld in cage? I keep hearing conflicting information- perhaps this is because people mis-interpret the MSA blue book?

I was under the impression that the main hoop and legs should be 45mm (1.3/4") 2.5mm thick (12g), and the rest could be smaller, then I was told it should ALL be 45mm 12g, but looking on websites that sell cages there seem to be loads at what look like 38mm (1.1/2") which I also heard was ok if fitted before whatever year. Also the safety devices and similar cages can not be 45mm surely?!

I'm a very competent welder and am going to TIG the whole lot, but I want it to be as light as possible. I'm just going to be doing very small scale club rallying, and not sure what they all look for. At the end of the day I will be making it plenty strong enough and I know exactly what needs to go where, just not sure on the "requirements" if I want to enter any other events.

Also I dont see why a 600kg mini should need the same size tube as a 1200kg car with 3 times the power!

[Kerrin]

If you don't already have one get a copy of the current MSA blue book. There is minimum size to each of the reinforcement plates under each leg as well as other things you need to consider.

If possible befriend an MSA licenced scrutineer and discuss it in the pub.

[mini93]

i cant remember fully, but thinking the OD is dependent on wall thickness and material. T45 is stronger so can get away with thinner sidewall for a given OD.
as said, have a look in the newest version of the msa rule book

[ANON]

i've got a fabricage cage and off the top of my head there are about 4/5 diffent tube sizes all in all.

[Chris C]

http://argent.fia.co...-11)-080910.pdf

[mcduff2]

If you don't already have one get a copy of the current MSA blue book. There is minimum size to each of the reinforcement plates under each leg as well as other things you need to consider.

If possible befriend an MSA licenced scrutineer and discuss it in the pub.

Heres the link to the blue book http://www.msauk.org.....or Safety.pdf

It is possible to have cages with smaller diameter tubes but these will have a ROPS certificate whereby the cages will have been tested and engineering calculations supplied to the MSA who then issue the certs.
Roll cages are a bit of a minefield at the moment as a number of current rally cars that are fitted with non compliant cages and are being turned away at scrutineering - even though they have been using the same cages for a number of years, it seems that the rules havent changed recently but the scrutineers have been asked to pay particular attention to roll cages (mainly the down leg from the windscreen top to floor which I believe can only have 1 bend in it)

[TopCatCustom]

Thanks for the replies and the link. It states 45mm 2.5wall or 50mm 2.0wall. I guess the other cages must be tested ones which can get away with smaller tubes?

[MRA]

Also don't be tempted to use welded tube, which is only cheaper if you don't crash or roll always go for seeemless steel tube.

Welded tube in certain circumstances call fail dramatically.... almost explode, with the corresonding sharp edges

[TopCatCustom]

Yep I'm aware of that, I use the damned cold heavy sharp stuff every day! Well I'll have a last chat with a couple of rally guys tomorrow before ordering the material.

[ibrooks]

Also don't be tempted to use welded tube, which is only cheaper if you don't crash or roll always go for seeemless steel tube.

Welded tube in certain circumstances call fail dramatically.... almost explode, with the corresonding sharp edges

This one always gets me. CDS is stronger thickness for thickness than seamed tube but if you stick with the MSA regs then it does allow for seamed tube as long as it meets BS1387 (I think that's the number). BS1387 is seamed tube but much thicker than the equivalent CDS. On a race car that means that CDS is better because it's lighter.

When using these tubes in off-roaders where the cages were often external to the bodywork and regularly used in anger we found that (in as much as you could compare like-for-like incidents):

The CDS cage would deform and whilst it would protect the occupants it was now permanently distorted.

The BS1387 tube would move by the same amount but it would come back to it's original shape again afterwards (repeatedly).

If you use the proper MSA approved British Standard seamed tube then it's just as strong as the CDS and more resilient with the downside that it's heavier. If you do end up in a heavy enough crash to actually break it then all bets are off as we're looking at a massive impact and you wouldn't be any better with the seamless stuff.

Iain