Handling mods for NB8

[hks_kansei]

I'm interested in the topic of using higher offset rims, ie increasing wheel track - any idea what the reasonable / practical limits are for a factory SE ride height using, say, 225mm wide-ish rubbers?

Just for future (so you don't get confused at the tyre/wheel shop etc) LOW offset is what makes wheels stick out further.


Offset is a measure of how far from centre the mounting face is.

Stock is +40, which means 40mm outwards from centre.
so on a 6inch wide wheel that means the inner barrel is 192mm, and the outer 112mm
On a +0 offset wheel the inner is 152mm and the outer is also 152mm
on a -25 offset wheel the inner is 127mm and the outer 177mm

Just figured I'd let you know so you don't end up buying +50 wheels expecting wider track, only to find it's narrower.

[kazama]

from my understanding roll bars dont do much for rigidity. they mainly just reduce nvh (as well as roll over protection lol). it seems door bars by far do the most. frame rails are pretty cheap from places like omgpham and theyd definitely help as well

door bars
frame rails
fender braces/frog arms

^in that order and call it a day IMO

[alexbwang]

from my understanding roll bars dont do much for rigidity. they mainly just reduce nvh (as well as roll over protection lol). it seems door bars by far do the most. frame rails are pretty cheap from places like omgpham and theyd definitely help as well

door bars
frame rails
fender braces/frog arms

^in that order and call it a day IMO

Yes that seems to be most intuitive solution; adding reinforcement length-wise to the frame (ie. front-rear).

Is a full roll cage structurally stronger than a door bar + roll bar combo, or are they pretty similar? I suppose the latter would look better and be easier to live with.

Who is omgpham? Mind if I grab a contact?

[alexbwang]

EDIT
Oh look, I just said the same thing as Nevyn!

Thanks both of you for your freakishly timed suggestion!

[sailaholic]

If you really want a driving with a roof feel try a hardtop and bolted attachments rather the. The factory latches.

A full cage is illegal in As part of the new code of practise for light vehicle modification. The code was meant to be national. Some states took it to more of less of an extent.

And effective full cage (not a JDM bolt in jobbie) is almost impossible to do and keep road car features like interior fans, easy exit etc.

Increasing chassis stiffness isn't needed for increased handling. It's not really a deficiency that exists short of a full race car. Sure it might help creaks and grones but it's not low hanging fruit for reduction in track times.

I have a mx5 plus bar, fm frame rails and butterfly brace.

The roll bar was in when I bought the car but a friend noticed a big increase in chassis stiffness when installing his.

Frame rails are good, and I would get again purely for protection and jacking.

Butterfly brace....yah I THINK it makes a difference but it's expensive, and bitch to install. Given the money again I doubt I would bother. I'd spend the money on better suspension for car comfort or track time of reduced lap times.

If it's track times you want to improve then track time is the cheapest / lowest hanging fruit to achieving it.


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[sailaholic]

Note; stiffness added from a roll bar depend on the design. Look at the design of the mx5 plus bar. It's impossible it couldn't increase stiffness.

Omgpham is a forum sponsor. http://omgpham.com/products

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[Lokiel]

:
Even with all the factory upgrades over the stock NB, the car scuttles at speed and creaks when driving over humps, leading me to believe that the chassis flex needs to be addressed to enhance the performance, as well as the safety and perceived quality of the car.
:
I'm currently looking into the MX5Plus roll bar - how much stiffer would installing one of these make the vehicle? I would imagine it would increase the side-side rigidity but what effect, if any, would it improve front-rear rigidity? Would a 7pt full frame with hard top achieve that "I'm driving with a roof" feel?
:
Apart from that, are there any braces worth getting? I've seen several MX5 specialist websites who highly recommend the butterfly brace - has anyone had any experience and could recommend me one?
:

Frog Arms will reduce the car scuttles/creaks you mentioned and are the 2nd biggest chassis stiffener IMO that I could genuinely observe/feel.

The MX5 Plus roll bar was by far the best chassis stiffener, I noticed it even at slow speeds while turning. This roll bar has a "torque box" built into it so I think this makes it much more effective than some other roll bars.
NA/NBs suffer chassis twist, something that the NCs addressed, and the roll bar goes a long way to eliminating this.
There is some debate about the effectiveness of roll bars on chassis rigidity but mine felt immediately obvious. The argument goes something along the lines of "The roll bar is just attached to the seatbelt towers which are already very strong.". The amateur structural engineer in me tells me that since the seatbelt tower structure is U-shaped, it can be strengthened even further by putting a brace across the top 2 points AND two additional anchor points in another plane.

A roll bar should be your first chassis stiffening mod - the fact that it's a rollbar too is just a bonus.

I also have the FM frame rails. You can't fit the FM butterfly brace to a MSM/SE so forget about the butterfly brace.
I had the frame rails before the Frog Arms and didn't really notice any difference when driving.
I did notice the difference when jacking up the car, the other tyre on the same side as the corner I was jacking got airborne much earlier than it used to so it definitely does add to chassis stiffness.
They make a great jacking point too, it only takes me 15 minutes to change to track tyres + brake pads (Willwood brakes make pad changes a breeze) with my rattle gun and a jack under the centre of each frame rail.

So how effective are all 3 of these modz?
NitroDann actually commented on how stiff my car was when he had it to build the manifold+exhaust.
Unlike many of us, he's dealt with quite a few MX5s so his taking note of this indicates to me that they're effective.

I also have a 3-point front strut brace. The OEM MSM/SE already had a front strut brace which is very good according to Keith Tanner from FM and I can't really say that the 3-point brace makes a difference to the factory brace. There's some debate too whether or not a front brace is even needed on our cars.

[Lokiel]

from my understanding roll bars dont do much for rigidity. they mainly just reduce nvh (as well as roll over protection lol). it seems door bars by far do the most. frame rails are pretty cheap from places like omgpham and theyd definitely help as well

door bars
frame rails
fender braces/frog arms

^in that order and call it a day IMO

I strongly disagree with that first paragraph, as would most people with an MX5Plus roll bar (see my previous post).

Door bars will improve chassis rigidity but in an MX5 are a real pain in the arse because:

1. You have to hurdle them to get in and out of an already difficult entry/exit car
2. They take up room which is something you can't afford to lose in an MX5
3. They will restrict even further the already limited track seats you can fit to the car.

[alexbwang]

The argument goes something along the lines of "The roll bar is just attached to the seatbelt towers which are already very strong.". The amateur structural engineer in me tells me that since the seatbelt tower structure is U-shaped, it can be strengthened even further by putting a brace across the top 2 points AND two additional anchor points in another plane.

A roll bar should be your first chassis stiffening mod - the fact that it's a rollbar too is just a bonus.

If that's the case, couldn't I just get one of those braces which attach themselves to the seatbelt pillar, in a similar way to the MX5Plus (and numerous other roll bar designs)? This is an example of what I had in mind: http://www.mx5parts.co.uk/ultra-racing-cabin-brace-mk1225-p-3308.html



Conceivably it would offer similar stiffness minus the added weight, $$, and disadvantages that you mentioned above? Your thoughts appreciated!

[Lokiel]

My ex-housemate has an NA with one of these type of bars on his '97 and it does make a difference.

[sailaholic]

The tower brace is better then nothing (hence why it's factory fitted in a Na) but not as good as a full bar.

Does the NBb not come with one?


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[hks_kansei]

Does the NBb not come with one?

Has a windblocker instead.

Hard plastic centre, folded ~3mm steel mounts.
Not sure if there's a steel bar inside the plastic, but I doubt it.

[alexbwang]

Just for future (so you don't get confused at the tyre/wheel shop etc) LOW offset is what makes wheels stick out further.

Cheers, duly noted Kansei san!

[kazama]

from my understanding roll bars dont do much for rigidity. they mainly just reduce nvh (as well as roll over protection lol). it seems door bars by far do the most. frame rails are pretty cheap from places like omgpham and theyd definitely help as well

door bars
frame rails
fender braces/frog arms

^in that order and call it a day IMO

I strongly disagree with that first paragraph, as would most people with an MX5Plus roll bar (see my previous post).

Door bars will improve chassis rigidity but in an MX5 are a real pain in the arse because:

1. You have to hurdle them to get in and out of an already difficult entry/exit car
2. They take up room which is something you can't afford to lose in an MX5
3. They will restrict even further the already limited track seats you can fit to the car.

doors bars try to address the mx5s biggest structural weakness. the lack of a roof. its a compromise but from what ive read its not enough to turn me off them.
id go as far to guess that doors bars will make a larger overall difference than frame rails, roll bar and a front tower brace combined.

[hks_kansei]

id go as far to guess that doors bars will make a larger overall difference than frame rails, roll bar and a front tower brace combined.

Except that a lot (cusco) are made to brace nothing to nothing.

The Cusco ones for example brace the front of the seat rail to the seatbelt mounts, and then a bolt through an arbitrary section of floor.




Door bars will make a bigger difference if they're braced well at both ends, a lot aren't however (talking separate bars some are integrated into a rollbar, but I can't comment on them since I haven't seen them)