Roll bar or chassis brace?

[Dweezle]

A small obsevation.

On my brothers na when jacked up from a corner you could not open the side doors.
Once he installed a BD bar we noticed that they opened almost without hindrance. Still a slight notchiness but much better.

Not sure if this equals stiffening the car though?


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[sweep77]

Interesting points guys. I checked tyre pressures as they are new and were set at 34 which is a bit high for street use so I set them at 28 and now seems much better. I'll see how it goes. If it still annoys me I might look at new bushes as there 13 yrs old still.

[yem11n]

A small obsevation.

On my brothers na when jacked up from a corner you could not open the side doors.
Once he installed a BD bar we noticed that they opened almost without hindrance. Still a slight notchiness but much better.

Not sure if this equals stiffening the car though?


Sent from my GT-I9100T using Tapatalk 2

+1

There is definately additional chassis stiffness. Over the weekend I had to swap the track wheels back to the OEM wheels and also to raise the height on the COs. The rear wheel easily get lifted as soon as the front wheel is off the ground a few inches. I had to move the wheel stopper to the rear wheel on the other side of the car. This was not the case before...

yem11n

[Guran]

Why don't you do an easy test. Jack up the corner of the car, measure the twist with and without the roll bar. Free fastbacky to the winner.

Yep ... and then triple or quadruple the measurement. A static test will not give you a true indication of the amount of body flex you'll get when it is subjected to an impact load such as when you hit a bump or pothole mid corner. But don't take it from me. Where's a mechanical engineer when you need one???

Gotta admit that I have no idea what my car feels like without a BD rollbar. I fitted the rollbar within a couple weeks of buying it ... almost four years ago. I do remember that it eliminated most of the scuttle shake. I'm not about to remove the rollbar either! I want a little rollover protection in case things go pear-shaped on the track.

[lee]

I would be intersted in this experiment too, My car currently has no extra bracing or a roll bar, so if you want a car that has nothing added as a test car you can use mine.It may save a heap of time removing anything from your car to start with.

Thanks for the offer, but I'm thinking that may reduce the validity of the experiment, as my chassis may be inherently tighter or looser than yours. I don't have a lot of chassis bracing on at the moment (only OEM NA8 rear and Cusco 2-point front), so it won't be terribly difficult to get them on and off as required

[Lokiel]

You guys that sit in a car and notice a difference by throwing on a roll bar are, ummm, well. Put it this way, that is a very strong part of the car. Tell me what the roll bar is doing to stiffen anything except what is between your legs?

Jacking up car up won't demonstrate how the chassis deals with short-sharp jarring motions.

The MX5 Plus roll bars mount on the seatbelt pylons which are very strong. How can you argue that mounting a strong brace (eg. torque box) across them has no effect whatsoever with regard to minimising chassis-twist? The roll bar essentially completes the "bracing box" provided by the chassis and seatbelt pylons - without it, it's just a "U-frame".

FYI: The NC chassis has significant chassis-twist stiffness built into it since it was a recognised deficiency of the NAs/NBs.

[Hjt]

Regardless of all the above, I don't believe this is the OPs problem or the correct way to fix it.

[deviant]

Another non-believer in roll bars making the car feel stiffer or handle better.

I have an NB8B that saw track time in stock form and then again with a twin diagonal MX5+ bar. Same circuit, same driver, same tyres....SFA difference. I noticed zero difference on the road and no reduction in scuttle shake. I have dríven enough MX5's hard on track and dríven this particular car enough in competition situations to know when there has been even a slight change.

The weakest part of the car is the hole in the middle where you sit, not across the rear bulkhead.

Agree with Hjt, usual advice with these things...get the basics in to good condition and then work on modifying the car.

[nbse2]

Hey guys, I'm thinking of either getting a rollbar or butterfly brace to strengthen up my nb8a. Over rough roads my car seems to have an annoying amount of shaking which may be just normal for an nb as I've only had an na8 before which had the seatbelt brace but never seemed to shake as much as this nb. I thought maybe the shocks are bad but they seem firm enough. Maybe it's just old bushings? Cars only done 80k though. Chassis rails seem in good nic with only 1 slight dint from bad jacking. Maybe just a seatbelt brace would be enough? Thoughts?

why is it that some cars have more scuttle shake than others in standard form? Is it possible to attribute this to a particular part of the car? Can you narrow it down?

[zephyrus17]

Speaking for the MX5-Plus bars, what would be the difference between the "Tall Boy" or Single Hoop?

[plohl]

I think there are much better options then the BD bar.

The tall boy gives up seat travel for extra height by moving the roll bar forward. Not a major issue if you have a bucket seat.

Hjt is probably right though - you should get the suspension checked.

Where's a mechanical engineer when you need one???

Laughing at some of the posts in this thread

[superfluous2]

Installed my MX5Plus bar today (tallboy diagonal).
Big difference IMO.

Don't know if it will help OP's issue with shaking/rattling, but feels 100% tighter than before.


I don't know if roll bars without the torque box would provide as much of a change - if any.

[Hjt]

I don't think that roll bars without the torque box won't provide as much of a change - if any.

the metal fills the gap, creating the illusion it's holding it all together.

[zephyrus17]

I think there are much better options then the BD bar.

The tall boy gives up seat travel for extra height by moving the roll bar forward. Not a major issue if you have a bucket seat.

But I thought one advantage was that the BD bar allows the rear window to zip down?

Anyway, OP, you should look at it this way, get the roll bar for roll-over protection; chassis brace for stiffening. The roll bar has some stiffening effects (maybe 1%?), but it's just not the point of it.

[plohl]

But I thought one advantage was that the BD bar allows the rear window to zip down?

Pretty sure you can still do this with the Plus bars, but you should double check with them.

Anyway, OP, you should look at it this way, get the roll bar for roll-over protection; chassis brace for stiffening. The roll bar has some stiffening effects (maybe 1%?), but it's just not the point of it.

Have you got an references for this 1% improvement? I would love to have a read of how they tested it. Was through testing or simulation/calculations? Or is it just speculation/a guess?