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Hi everyone,

Do roll bars stiffen the chassis, specifically in an NB?

Or is the main flex the twist between front and rear because of the lack of roof?

I can't answer scientifically but I can say when I fitted my roll bar to my NB8a there were few squeaks and the car felt a little more direct on turn in.
So my gut feel is that it did stiffen the chassis.
Second best mod to help with this was replaceing the rubber door buses with Drelin ones.

Yes, they do. Instantly noticeable.

Two stock front sway bar mounts ripped off the chassis with the use of a big bar suggests no it doesn't stiffen the chassis wouldn't it?

NA/NBs suffer from chassis twist. This one one of the big issues that the NC addressed.

You will get some very knowledgeable guys here on the forum who claim they do nothing for chassis stiffness but when I added a Twin Hoop MX5Plus rollbar to my MSM/SE, which already had the must bracing of all NBs, the difference was immediately noticeable when turning, even at slow speeds.

The MX5Plus rollbar has a built-in torque box that sits above the seatbelt towers and essentially close off the U-shaped seatbelt tower brace, reducing its abilty to twist and stiffening the car.

Other rolbars do not have this torque box but do close-off the U-shaped seatbelt tower brace so they too will improve chassis stiffness to a lesser extent.

slug_dub wrote:Two stock front sway bar mounts ripped off the chassis with the use of a big bar suggests no it doesn't stiffen the chassis wouldn't it?

No, it suggests that the flimsy front sway bar mounts are too flimsy to handle the additional torque of the larger sway bar - that's why Racing Beat aluminium block and braces were created, and about 5 other stronger sway bar mounts.

Yeah I think my example is wrong actually
I guess to answer the OP's question, yes the flex is from body related stiffness (or lack thereof) and not sway bars.

A little bit, but in an area where it's not really needed anyway.

The bit that flexes most is the door areas, since they've got bugger all structure there due to the door openings.

If you have a full cage, that ties the windscreen and/or front footwells to the rear bulkhead, then it will help a lot.
Until you need to get in or out of the car and do some rollcage yoga to do it.


As for the normal bar behind the seats, not really much.
it braces a thin parcel shelf and the seatbelt towers, neither of which carry any hard suspension loads etc.

Unless the car has done a lot of kms or been beaten silly over rough roads you would not expect a lot of flex in the NB. The car was designed as a convertible and a certain amount of flex is not a bad thing. You actually want to car to move a little. If you attach roll bars made out of substantial tubes and bolted down of course it will reduce movement - afterall the things are there to protect in a roll over. You would not put roll bars in to stop the car flexing ... or would you?

Sirois I don't know why I read rollbar as sway bar this morning... hadn't had enough coffee I expect.

Improvements in vibrations/flex in my NB SE have been felt from fitting the torque box twin hoop roll bar as Lokiel mentioned, delrin door bushes and chassis rails. Each made a difference in their own way but the chassis rails was the biggest improvement for me - maybe because I had already fitted the roll bar.

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Mr Morlock wrote:.......and a certain amount of flex is not a bad thing. You actually want to car to move a little.

I totally disagree.
You want zero movement of the chassis, then the suspension can do as it’s supposed to, and not be affected by the mount points moving around it.

rascal wrote:

Mr Morlock wrote:.......and a certain amount of flex is not a bad thing. You actually want to car to move a little.

I totally disagree.
You want zero movement of the chassis, then the suspension can do as it’s supposed to, and not be affected by the mount points moving around it.

Yep, it would have been better if they built our cars out of carbon fibre. Dammit that they didn't. Still fun enough though for what they cost.

No, roll bars do nothing.

rascal wrote:

Mr Morlock wrote:.......and a certain amount of flex is not a bad thing. You actually want to car to move a little.

I totally disagree.
You want zero movement of the chassis, then the suspension can do as it’s supposed to, and not be affected by the mount points moving around it.

I would have to agree with Mr Mortlock. While of course in a perfect world it would be like you say. But envelually nothing is built strong enough. It would become too heavy. Anchoring points of suspension will fail. Engineers go to a decent amount of trouble to incorporate a certain amount of flex to prevent other parts while designing cars.
Suspension working perfectly? No such thing. Only compromise.


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