Handling mods for NB8

[alexbwang]

Hi folks, hopefully this is the correct place to post my query...

I recently purchased a 2004 SE and while I appreciate the improved handling over the regular NB chassis, I feel there is still room for improving the stiffness of the chassis. The goal is to make the car behave closer to a car with a "roof" without spending too much and adding unnecessary weight. Preferably mods which don't require complex body work and can be "bolted on" by regular joe like me :-)

I've searched this topic and come across a multitude of roll bars, braces, etc - however, I haven't found a resource that quantifiably rates each mod. For example, I'd like to compile the following information (mod name, manufacturer, URL, cost inc shipping, installation complexity, what it enhances and by how much) - I reckon a prioritised list would be helpful to fellow forumers as well...

Any inputs and comments are most welcome, cheers

[tescoking]

Search mighty car mods mx5

[davekmoore]

Proper rollbar, coilovers, lower ride height, alignment. Not necessarily in that order. Nothing else needed for the road.

[Lokiel]

Proper rollbar, coilovers, lower ride height, alignment. Not necessarily in that order. Nothing else needed for the road.

I'd insert 15" rims after the roll bar in that list - SE's factory 17" boat anchors are detrimental to handling and performance.

[davekmoore]

Proper rollbar, coilovers, lower ride height, alignment. Not necessarily in that order. Nothing else needed for the road.

I'd insert 15" rims after the roll bar in that list - SE's factory 17" boat anchors are detrimental to handling and performance.

Yup, I forgot that. Also, if you go for Tien coilovers, remember to have them set fully or nearly fully soft for the road otherwise you'll think your newly acquired 15s are no good.

[alexbwang]

Proper rollbar, coilovers, lower ride height, alignment. Not necessarily in that order. Nothing else needed for the road.

I'd insert 15" rims after the roll bar in that list - SE's factory 17" boat anchors are detrimental to handling and performance.

I would've thought that bigger rims would require lighter tyres, so they compliment each other to a degree? The lower sidewall on larger rims would enhance turn-in stability and road feedback - I wonder what is the benefit of having "fatter" tyres using smaller rims?

Having said that, I find the current setup (factory 17x7 Racing Harts with KU39 205/40R17) a little harsh, "floaty" and "pokey", but I'm not sure if that's largely attributable to the wheel or the fact that the factory "lowered" springs and Bilstein shocks are to blame (getting on 100,000 kms)...

Regarding unsprung weight - what is considered a "light weight" wheel set up (tyres and rim) that's still affordable and comfortable for every day street use?

[alexbwang]

Proper rollbar, coilovers, lower ride height, alignment. Not necessarily in that order. Nothing else needed for the road.

Roger that, I'm leaning that way... regarding coilovers - any particular brand you could recommend in terms of value for money? I wonder how much of an improvement it will offer over the stock SE springs and Bilstein shocks, which are both stiffer and lower than a stock NB anyway.

What about the underbody re-inforcements such as butterfly brace (I hear that's quite cost effective as well, as per the MCM video)?

How about replacing polyurethane joints and bushings? I wonder what the cost would be for that and if there are kits floating about the internet...

Lastly, does anyone notice that the car likes to track with the road undulations, the feedback is amplified at speed through the steering wheel - I understand this is the nature of the car's suspension and mechanical steering design, but I find it can get pretty tiring driving on uneven roads. Any tips on "neutralising" this issue?

Quite a few ideas here - feel free to dissect

[davekmoore]

Proper rollbar, coilovers, lower ride height, alignment. Not necessarily in that order. Nothing else needed for the road.

Roger that, I'm leaning that way... regarding coilovers - any particular brand you could recommend in terms of value for money? I wonder how much of an improvement it will offer over the stock SE springs and Bilstein shocks, which are both stiffer and lower than a stock NB anyway.

What about the underbody re-inforcements such as butterfly brace (I hear that's quite cost effective as well, as per the MCM video)?

How about replacing polyurethane joints and bushings? I wonder what the cost would be for that and if there are kits floating about the internet...

Lastly, does anyone notice that the car likes to track with the road undulations, the feedback is amplified at speed through the steering wheel - I understand this is the nature of the car's suspension and mechanical steering design, but I find it can get pretty tiring driving on uneven roads. Any tips on "neutralising" this issue?

Quite a few ideas here - feel free to dissect

My car had Tiens when I bought it so don't know how much they were. They're adustable for shock rate and for ride height and for pre-tensioning of the coils. When set fairly soft they are more comfortable on the road than the standard SE setup and remove the feeling of being on stilts the standard SE has.

The consensus is there's no need for butterfly braces as the SE has every bit of extra underfloor bracing an NA or NB ever had.

Dunno about poly joints and bushings. It may depend what you want to use the car for. The only similar item changed on mine so far is to replace worn and split original rubber engine mountings with stiffer bushes and way stronger mounts. They significantly increased NVH but equally stopped the engine rocking as much especially when changing down coming into a corner on the track.

Yes, these cars do follow road undulations and yes, they're supposed to. Jinba ittai. If it's doing it too much, there may be an alignment issue.

Others here will be more expert than I on some or all of these matters and will no doubt chime in. In particular, I wonder if your steering issues might be partly due to worn bushes allowing changes in steering input as the suspension moves up and down?

[sailaholic]

You would be looking at atleast 1000k for bushes fitted, maybe 1500.

Plenty of people are happy with BC coil overs.
you can get better bilstiens (PSS 9)
MCA are about to release their red and blue series which should be very good
Ohlins are also very good.

Which is best depends on your demands on them and how wide you wallet will open.

Personally I think yellow speed are complete rubbish. I've dríven a NA on ohlins and it's the gold standard so far. Noticeably better in a short drive then anything else I've dríven since.

Tires need sidewall flex to generate grip so they don't just bounce over things. Have alook at the various serious race car designs, most run a decent but not huge sidewall.


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[hks_kansei]

Regarding unsprung weight - what is considered a "light weight" wheel set up (tyres and rim) that's still affordable and comfortable for every day street use?

If you're looking for the lightest, cheapest, strongest wheel, then buy a set of NB8A factory 15s.


But, I'd say don't bother getting too hung up on weight, lighter is better yes, but the difference from the driver's seat won't be night and day.
Just buy the wheels you think look good, and are within your price range.

[MLR]

A good wheel alignment and good rubber is paramount, some side wall is your friend, have a look at some track day guys who run on good street rubber, the difference in side wall can be a second here or a second there.

I have seen a lot of guys buy bigger diameter rims only to put the smaller rims back on, from my research you don't want anything bigger than 16" with 15" being optimal.

Large diameter rims are for the people who care more about how their car looks sitting in a car park rather than how their car performs being dríven.

Also offset isn't all about stance, the wider the wheel track the more stable the car is, you can even play with oversteer and understeer characteristics of your car in this fashion, though for that purpose I would not recommend the hassle.

And looking under a few MX5 track cars there seems to be a lack of the aftermarket under body braces that are available, as stated above its more, roll Bars, Coils, Sways, correct Rim size and offset and GOOD RUBBER.

One guy I was talking to had the rail braces, but he said the only reason he got them was due damage to the rails from a previous misadventure.

[alexbwang]

A good wheel alignment and good rubber is paramount, some side wall is your friend, have a look at some track day guys who run on good street rubber, the difference in side wall can be a second here or a second there.

I have seen a lot of guys buy bigger diameter rims only to put the smaller rims back on, from my research you don't want anything bigger than 16" with 15" being optimal.

Large diameter rims are for the people who care more about how their car looks sitting in a car park rather than how their car performs being dríven.

Also offset isn't all about stance, the wider the wheel track the more stable the car is, you can even play with oversteer and understeer characteristics of your car in this fashion, though for that purpose I would not recommend the hassle.

And looking under a few MX5 track cars there seems to be a lack of the aftermarket under body braces that are available, as stated above its more, roll Bars, Coils, Sways, correct Rim size and offset and GOOD RUBBER.

One guy I was talking to had the rail braces, but he said the only reason he got them was due damage to the rails from a previous misadventure.

Agree on the smaller wheels but that's a cost I can put off for now; I'm going for the low lying fruit... Besides, I've chucked on some fairly sticky rubber (Kumho KU39) on the factory 17" rims and done an alignment already.

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?

[alexbwang]

Thanks to all for your comments so far, but I'd like to take us back to my original post: I was wondering how I could improve the stiffness / rigidity of the chassis...

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.

Many of your responses talk about improving the handling through suspension upgrades (a significant cost!) and that's before we get started on the braking upgrades, which I've also been researching :-)

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?

I've had the car inspected at a MX5 specialist, the car is straight, there are no leaks and everything appeared to be in order, at least that's what the mechanic said haha.

I'm sure I'm not being unreasonable... While I accept roadsters are inherently weaker than cars with roofs, I am not interested in masking these deficiencies but would rather address them using proven mechanical solutions.

[Nevyn72]

As Lokiel advised me recently with regards to chassis stiffness.....

Roll bar first, then fender braces, then frame rails if more rigidity is required.
Probably no real benefit in replacing the strut tower brace with a 3-way unit.

Having just installed the MX5+ roll-bar I can certainly vouch for it's effectiveness!

[ManiacLachy]

I recall Lokiel mentioning in his garage build that adding a roll bar (MX-5 Plus Twin Hoop in his case) added the most structural rigidity, and also that adding Frog Arms to the front fender really helped settle the scuttle shake. I think that was a while ago, perhaps his opinion has varied over time?

From that though, I'd say those two mods sound like the best approach to improve the issues you're concerned with.

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