Roadster roll bars
 

I've been playing with some tube latly and I've asked every body who walks through the door what they think a rollbar should look like and what size tube it should be. Considering the rollbar is mounted to a 16 gauge chassis 3mm ERW seams to be over kill, 2mm CDS is ££££ so 2.5mm wall ERW in either 42mm or 48mm dia? Which of the three designs you would be interested in although I will be making all three in the next week or so and will be in my ebay shop soon.

Personally I like the third one but I already have the second one thanks to AshG.

How much are we talking?

Looking to be £80-120 ish but the lower bar would be fish mouthed on the lathe and fully welded with the base plates in place , 7/16 unf inserts fitted for either 4 point belts or inertia real belt top mounts. The rear support bars would be supplied over long with both ends fish mouthed one at 90' to join to the horizontal bar and the other at 40' (ish) to join the vertical.

i don,t wish to sound negative to your thoughts/idea of supplying a roll bar but,

i,m not sure i agree with the above, having been a semi pro bike racer (sorry i know i,m boring) i was always happy to spend extra on a helmet that i felt would offer me the best protection for my head in a crash, & yes i crashed a few times in my career :o :D but have never had a serious head injury, & i was always thankful that i didn,t buy the cheapest helmet on the market.

my point being....... i don,t think you can have "overkill" when the roll bar is the last safety device to protect your head in a roll over crash.

My own roll bar was supplied via one of Ash g,s group buy & my back stays are of the same material/thickness, & feel happy with the safety it offers.

said in a polite way i assure you.
cheers
andy

Full cage is the best option for paranoid folk and I fall into that bracket as up front the only thing hard enough to keep your head off the ground is the engine if you only have a rear roll bar.

Fair comments Andy and yes you get what you pay for. I come from making NASA Autograss rollcages. Mid mounted engined full space frame saloons and theres no point in making a very strong rollbar if it connects to a tissue paper base. It'll just snap at the weakest part which will be the 16 gauge tubing. I can make FIA spec roll bars and even full rollcages in 38x2 CDS but it's £52 per 5mtr lengh and the idea of the Roadster is 'budget' is it not?

i do understand your points tho i must say i,m in no way qualified in structural strength of chassis designs of any vehicle, as Fabby has suggested, a full roll cage is the "better/safer option" if the car builder wants total piece of mind etc, i was just using my own personal experience of "head safety" to be able to offer ( i hope ) a credible personal point of view.
As you say the Roadster is "to build a sports car on a budget" but doesn,t give a budget figure & so the safety aspect is one area i believe is worthy of spending more rather than less if the individual builder wishes/can afford to.

on a lighter note i prefer the middle diagram of roll bar design :cool:

again said in a polite & hopefully constructive discussion manner.

cheers
andy

i was thinking of the third option for my roadster & have cad drawings for 50mm pipe & was going to use stainless but but now also have the second one thanks to ashg:D
if onyone wants a copy of the cad drawings just let me know.
cheers
samy

I may be able to do some FEA Analysis for you if you want only quick and dirty but will give the general principles

There is a difference between safety and budget.

Safety is never expensive.

There was a required spec in SVA for roll bay size and thickness so i assume it still applies for IVA

I can't find anything in the IVA regarding this.

Well, not the thickness, it only really mentions that the roll bar will be subject to testing for exterior projections

as far as the iva is concerned you dont even have to have a roll bar period. if you hae one they just check it for sharp edges

Thanks Ash that was a question I was going to ask
Ray:)
p.s. id like a double hoop but not like the one above im waiting till near the end of my build to do the roll bar if i put one on

A question,assuming the bar is not fitted they cant test it obviously,does the same apply to a passenger seat and it's seat belt for IVA purposes.
In an MOT if it's not fitted you cant test it ie seat missing/belt missing,Someone who has read and digested the manual will know the answer.
On the suject of roll bars, I rightly or wrongly bored the center of the plates for the bar to go through to give more of a surface to weld to,thoughts or comments ?

Cheers

There's nothing wrong in cutting a hole in the mounting plate as long as you have welded it inside and out so that it does'nt cut through the shock mount plate. I personaly would have ground a 45 deg 1.5-2mm weld prep (as you should be doing with all your thicker plates!) all around the edge and welded solid with about 160amps. Reguardless of what any body says on here by the time the rollbar has hit the ground hard enough to punch a 40-50mm hole through the 3mm plate the 'I told you so' will be the least of your problems.

It will be welded in and out and it's 5mm not 3 and has a chamfer on inner and outer edges of the hole (I started my working career as an apprentice welder in a shipyard )the rear bars may end up on the diff cage for more strength.
All thought's and comments are gratefully recieved.

And while I am in here can one of you nice gents tell me what size or diameter of the the slots in the rack support plates are.

Thanks.

Talon's point about what the rollover bar is atached to is a good one, and nobody seems to be picking up on it. It's all very well having a really strong bar made with all the best and most expensive materials, but look at what it is attached to!

Safety maybe ought to be priceless, but it isn't. We all balance our safety with other considerations every day,and safety frequently loses out to convenience etc. And if we really really wanted to be really safe, would we be driving this kind of car anyway?

I get your point,Stay safe, stay at home and don't drive at all.

Heck of a lot of accidents happen in the home, mind!

I knew that was coming !!!!!!!!!!:p

i noticed that the roll bar didnt attatch to much, as a result i made the rear hoops of the body support out of 20mm x 3mm seamless tube and braced it down to the diff cage to add extra stiffness

Im using a fibreglass rear end from saturn and this is where i anchored my rear roll bar stays, they are bolted in from underneath with m14 bolts through 6mm support plates plates.

Before anyone says it yes i did put one on the other side aswell :D

how gooder fit are these rear ends. i have a prefabbed aly tank that sits about 1" in from were the skin would sit, willl this contact with the pannel??

Unfortunately you need to modify the rear end a little to make them fit and a book spec fuel tank wouldnt work.

But a few simple mods gets them fitting perfect and they really look the part.

Andy is about somewhere and will read this,wouldn't it be sensible to make the rear support tubes to match the rear Saturn/Triton tub,this would make the rear end more structrually sound once again as per the book and offer a little rear end protection also for the fuel tank,can someone enlighten me as to why it was removed other than to fit the Fabby tub.

i may be wrong but the original rear tub tubes were there to support an ali rear tub which isn,t needed for a GRP tub, personally i think that the way Mark has done his rear brace bars offers a stronger anchorage/triangulated point for the roll bar strength.
Then again there is nothing to stop a builder adding some additional 25mm box tubes to create a fuel tank protection cage which could possibly be attached to the diff cage.

andy
ps, in my opinion of course :)

I forgot about the mods for the tub :p

Anyone who has built the rear end to book spec with the round tubes and then chopped it off :rolleyes: to fit grp (like i have) will probably agree that the design i have used is a much more sturdy alternative, that coupled with the fact that my rear stays are of a larger diameter and thickness than the book spec should be more than strong enough.

I am in the process of making my tank at the moment and once that is in i may consider some extra protection in that area but im trying not to over engineer things too much as i dont wanna end up at 700kgs on the weighbridge :eek: :D

Mark

I did exactly the same as you, and my stays go to the same place. Looks good, and after a bit of stress analysis (I used to be a 'proper' engineer) turns out to be a fair bit stronger than original, as stresses are dissipated over a greater area.

Cheers

Adrian

I thought that would be the case, however its good to know that someone who actually has a backround knowledge about stress analysis can confirm it, rather than me just thinking it :o :D