Why change the suspension in an MX5. To be, or not to be

ckleanth · 2 January 2022 18:51

Note that I’m not an automotive specialist, I’m a systems engineer working at an aerospace landing gear manufacturer. These are simply my personal thoughts regarding ownership of an mx5 NC and a platform for discussion with others similar minded people perhaps more familiar with the subject. I see this thread as an attempt to summarize the reasons why would one perhaps want to change the stock suspension in their mx5.

First of all some suspension fundamentals…
What is a coilover
Another good video about coilovers in an mx5 from Good-Win Racing
A video explaining the antiroll bars in an mx5 from Good-Win Racing

After reading various threads about people swapping the stock springs or wanting to change the suspension coilovers altogether in a perfectly working mx5, I’m sat here just wondering why?? and whether I’m missing the point?

And If I’m honest I could not really find a single point of reference for a definite answer so in order to understand what’s going on I have to figure this out on my own…

Basic principles:
The whole point for reducing the height of a car from the ground is to lower the centre of gravity. That reduces the weight transfer both during braking and during cornering (reduces the moment generated during body roll in respect to the car CG).
However reducing ride height you are reducing available shock absorber travel. If you reduce shock absorber travel you have to increase the spring stiffness (because you don’t want the car suspension to bottom out) if one assumes the same maximum loads will be applied through the suspension. However you also have to increase the antiroll bar stiffness. This is because the car suspension wont be balanced if you simply just arbitrary change the springs in the suspension. Also if you lower the car the end links that connect the wishbone to the antiroll bar also technically need to change. This is because the stock end links that come with an mx5 are fixed length so the moment arm transferred through the antiroll bar will be different from what the antiroll bar was designed to, if the car is lowered.

A good video on the principles discussed above can be viewed here.

In addition, Jason from Engineering Explained explains the difference between Soft and Stiff springs in a car and why a stiff suspension is used in race cars.

As explained above, a stiffer suspension should be great on track use because you keep the wheel and steering geometry firm. But compared to normal roads there far less bumps on a track therefore a track focused car will be twitchy if driven on normal roads as the bumps are larger and you will bottom out the suspension. And the other fact is that if we change the spring rates and mess with the anti roll bar spring rates we are effectively changing the handling of the car, which the mx5 is known to be great fun, easy and forgiving car to drive.

So I keep asking myself why would I want to change the car stock handling, Is there a problem I cant see? And to find my answer I need to ask myself, what do I want from my car? Where will I use my mx5?

Note that before you even think about changing any suspension components if your car is not handling right, check tyre pressures. You dramatically can change the handling of the car by setting the wrong tyre pressures - so if you haven’t bothered to check and ensure your tyre pressures are correct you shouldn’t be looking at making any changes in the suspension system.

Your tyres is a part of your suspension. So if you have a 17" or a 16" wheel it will make a difference how the car handles and absorbs bumps. If your tyres are old, change the tyres.

Now lets look at the requirements for a Track car:
I completely understand if you want to have a track focused mx5 to go through the expense of getting the roll cage, chassis stiffening braces as well as a fully adjustable coilover system where you can adjust the ride height, change the damping, have the ability to swap the springs if you need to. It wouldn’t be unusual to have different suspension settings for each track. But if you have a fully adjustable suspension you should also change the antiroll bars and links with the adjustable type, as well as changing the stock rubber bushes (that may be too old and have too much play thus need changing anyway) to something with less compliance - this will help ensure the wheel/steering geometry is retained at the expense of comfortable ride.

Note that this implies that the owner/driver or someone competent (either paid or team resource) would be able to understand and make the necessary changes to the suspension as needed.

On a side note if you are thinking about modifying a car for track use “Car Throttle” did a somewhat interesting video series on the effect of changing tyres, suspension, brakes, reducing weight
and various other modifications on to a car and their effect of reducing lap imes
https://www.youtube.com/playlist?list=PLzleYhq4aqPuY3FJ2d52KuefWbO00juLw

Now lets look at the requirements for a Road Car with the occasional tack day use:
I believe most of us will be in this category. This solution may involve a suspension system somewhere between stock and a fully adjustable coilover system and antiroll bars.
I would argue that for some people leaving the car as is may be a valid solution. “if it ain’t broke don’t try fix it” sort of speaking.
For others you could get away with an non adjustable coilover system with suitable spring and damping characteristics and perhaps make the necessary adjustments to the antiroll bars and links to suit the suspension. Because the changes would be fixed and non adjustable I would expect this work to be done by someone that knows what they are doing - to reduce expenses and the pain having to go through further purchases and modifications on the long term. On the other hand I would also expect to hear that some companies will happily sell you a fully adjustable expensive suspension upgrade to someone that don’t really need it/are not going to use it…

So what is the conclusion…
As an engineer I am a member of the “if it ain’t broke don’t try fix it” cult. So I am extremely reluctant to go modify something unless I know exactly what I’m doing or the reasons why I am doing it.

So I think it depends on the individual. I believe I have summarised the requirements above; think what you want from your car and what you want it to do. Personally I would encourage you before buying anything to find a reputable mx5 suspension specialist and make an appointment for a chat. I believe knowing the fundamentals and understanding what you want from the car you can make an educated decision on what you should be doing - if anything really.

I hope this helps…

Edit 09/04/2022. An attendum to this article/post.

I came across an interesting talk about aftermarket suspension - not specifically aimed at a particular brand but more about the design principles that went into some brand offerings and how their adjustable coilover designs work and goes into the why some adjustable coilover designs will be compromised by using off the shelf standard damping chamber components matched with various bottom housing compared to adjustable coilovers made specifically for the mx5.

I highly recommend anyone who is interested about car suspension to watch this.

I also believe not enough is being said about the importance of swing bars and how they can influence your car handling. Again for the same reason as above i highly recommend watching this video to explain the reasons why one should look into adjustable swing bars.

TOGs_driver · 2 January 2022 19:28

Hi, nice summation.
I can see your logic and agree with everything that you’ve said.
Pushing things further on the discussion, where do we think things become adversely affected?
I openly admit that I have compromised the feel and handling of my car. With stock suspension my car drove better. It felt more compliant over bumps and rode better. So why did I go for a set of coilovers? Aesthetics, simple as that. I wanted the car to look right in my eyes. The stock ride height of a standard 1.8 NB is too high for me leaving too much of a gap between tyre and arch.
So, I purchased a set of coilovers to be able to adjust the ride height a bit. The fact that I chose a cheap set that don’t adjust for height has made things worse as I am forced to firm up the springs too much, especially at the rear, for the exact reason you explained above.
At some point in the future I may be able to buy a proper set. At that time I hope to gain some of the OEM compliance back.
The drop links and anti-roll bar is also worth considering. Mine runs on standard items which must be negatively impacted by the different ride height. The car seems to run a bit of camber at the rear too. Possibly a result of the mismatched geometry?
With all of this said I still really enjoy driving my car. She goes round corners well and still gives plenty of feedback so it’s not the end of the world but I’ve written this as a possible cautionary tale for others.
Cheers and HTH,
Guy

PDQ · 2 January 2022 20:58

Interesting thoughts - i think people avoid doing another major contributor to ride comfort/feel and that’s the suspension component bushes.

They are on my list to do - but I did fit coilovers first (because that’s easier)…I chose them because they allow me to control the ride height rather that just a preset height, and I like tinkering with the damping on track days.

ckleanth · 2 January 2022 21:23

I don’t think changing the suspension height for “aesthetics” is a valid reason to do so (at least not in my eyes). If one reduce the suspension travel one has to increase spring stiffness there is no way around this. If you operate the car at designed conditions the max load does not change so if you use less spring travel the stiffness has to increase to match the load otherwise the suspension will bottom out. So if one just change the springs from stock to something with less travel (so the car sits lower) they have to be stiffer (assuming its the same material the coil should be thicker diameter compared to the stock spring) and the ride will be firm; this is a consequence of reducing the suspension travel.

If you swapped the stock suspension with an aftermarket adjustable coilover suspension the spring stiffness (and shock travel) should be matched to be suitable for the car. An adjustable coilover suspension should have an adjustable bottom part that holds the spring in place. That primarily changes the preload but it also changes the ride height - needless to say these should be matched and adjusted evenly per side. As you found out with some more premium adjustable coilovers you can change the ride height independently to the preload by adjusting the bottom part of the suspension. The second video about coilovers from Good-Win Racing goes into that process.

May I ask what brand of coilovers did you purchase?

Davy_F · 3 January 2022 09:05

ast · 3 January 2022 09:45

“Dual Adjustable” shocks (whereby the shock body length is “adjustable”) have the same travel irrespective of adjustment, but it will always be less travel than a factory-specification shock. Less travel= more time on the bump stops= jiggly ride over bumpy surfaces. Some manufacturers attempt to address this by extended top hats. Some of the aftermarket extended top hats are truely appalling, and bordering on dangerous.

It is virtually impossible to lower any generation of MX5 without some sort of compromise.

First_rider_off · 3 January 2022 10:24

I changed the “stock” springs fitted to my ND Sport GT to the “Mazda spec” Eibachs which are 30mm lower. These springs are available through Mazda dealers and can be fitted by them. The Sport GT ND (Sim to the Sport NC versions) is factory fitted with the uprated Bilstein shocks and the general opinion is these are better matched to the lower Eibach springs than the standard springs. The handling in my opinion is greatly improved (with a good suspension set up), rolls a lot less and comfort is minimally affected with the Eibachs fitted. Indeed, the car feels a lot more comfortable than many so called sports saloons that I have driven. I have only bottomed out the car once on a very big compression and that was fully fueled and loaded up with luggage and a passenger. I don’t know how the Eibachs would perform on a car fitted with the standard non Bilstein shocks. It is possible that it would bottom out easier as the standard shocks will have a lower damping ratio. I think that it may be possible that Mazda designed the Bilstein shock equipped versions for the lower Mazda spec Eibach springs but for homologation and legal requirements fit the “normal” standard springs knowing that many customers would modify the cars using the Eibach springs. As a footnote I have a friend who owns a Lotus Exige which is set up for track racing and track days. This car is very competitive on track surfaces but is a complete nightmare to drive on public roads. Not only is the suspension very harsh but the thing reacts badly to every small bump and requires constant correction. Even he admits that it is extremely tiring to drive it any distance on public roads. I drove it once and couldn’t wait to hand it back!

ckleanth · 3 January 2022 10:57

I have to say that my NC also comes with the sport package and since I bought it used I tried to understand whether it has been modified or not (which thankfully it wasn’t). The ride is excellent with the stock springs with the Bilstein shocks. Its firm but not uncomfortable.

Now as I explained earlier if you decide to lower the car by using shorter springs, you reduce the suspension travel. So you have to use springs with increased stiffness to match the maximum designed loads so the suspension wont bottom out under the same loading conditions. This will result to stiffer suspension if compared with the stock springs however there are a few caveats.
a) Do these shorter springs have increased stiffness? They should, because if they don’t the chances of bottoming out the suspension are higher as you have reduced the suspension travel and potentially in this case have not changed the spring stiffness.
b) is the 30mm decrease in vehicle height actually noticeable to the average driver or is this a placebo effect?

TOGs_driver · 3 January 2022 11:07

Hi, thanks for the explanation.
I bought an early generation MeistrR Sportiv. I asked if the components were height adjustable and was told there was some height adjustment but they are not. I’ve had this discussion elsewhere and explained that the set I bought does not have the adjustable lower section and third locking ring. The only way to adjust height is to firm up the spring by adjusting the top ring. I originally had the springs quite soft which rode better but the car was way too low and caught on bumps all the time plus the tyre was level with the arch meaning she sat 4.r.5.e end down.
Firming up the spring lifted the rear but of course affected ride quality. Not ideal but I can live with it for now.
I agree that lowering a vehicle purely for cosmetic purposes is not a priority but my car is not used hard. I don’t ever envision using her on track and I certainly don’t thrash around on public roads. I do however sit and look at her on the drive.
So for me I am happy to compromise ultimate road manners for an improved ownership experience. I don’t necessarily expect everyone to feel the same.

Cheers,
Guy

DickieRltd · 3 January 2022 11:11

As far as I am aware the Mx 5 has always had coilovers fitted from the factory !!!
So fitting coilovers as an upgrade is Bull Poo.
Fitting adjustable dampers with moveable spring platforms and changing the spring rate can be of use.
As you lower the suspension the steering rack has to be moved to suit.
The R package cars had a different track control end to sort out bump steer as they were a bit lower from the factory.
You can go for the slammed look !!!
You can go for the I want it lowered a bit look !!
You can go for the Monstertruck raised ride height if classic trials is your thing. !!
Mx 5s are begining to appear in club rallies which require a different suspension set up.
Or you can actually alter it to suit your driving style for track days and motorsport.

My personel choice is running factory stock Bilstein shocks and springs with mildly uprated anti roll bars. and stiffer rubber bushes in the suspension.
My 1994 car is compliant enough to use on the road and is balanced enough to do sprints and hillclimbs.
It is still running at the same ride height it came out of the factory with.

There seem to be two choices
Fashion and looks.
Motorsport performance.

Happy New Year

TOGs_driver · 3 January 2022 11:13

Lowering springs was an avenue that I explored but I wasn’t able to find any that gave me the drop that I desired.
I felt that 30mm was too much otherwise I would have gone with the Eibachs.
My car isn’t 30mm lower than stock but speed bumps are still my nemesis

DickieRltd · 3 January 2022 11:38

Most shocks have a fixed spring perch.
My Bilsteins have a spring ring in a groove.
The old fashioned way was remove spring ring and spring perch then fit an tube over the top with threaded adjustable spring perch. Demon Tweeks used to sell them
This allowed the use of stock shocks and springs but allowed the ride height to be changed.
Modern aftermarket shocks can come with adjustable spring seats as well as adjustable bump and rebound damping.

ast · 3 January 2022 11:42

Certainly for the NA, the cheap way was an adjustable coilover tube kit; you cut the spring perches off, and fit over the shock body a threaded tube, with a spring seat (perch) that can be adjusted up and down. So standard springs can be retained. Of course lowering this way does reduce shock travel, but without an uprated shock (unless you revalve). The perch on the Bilstein shock is designed to detach, and some Bilsteins will have alternative positions to refit the perch.

So you end up with something like this:

Jitsuka · 3 January 2022 16:28

Seems to me there are several considerations as to why, which combine to differing degrees for each owner:

Most drivers over rate their ability behind the wheel.
Most drivers spend >90% of their time driving slower than desired, in traffic, and on dull roads.
Many drivers are unaware of the difference caused by sub-optimal chassis geometry.
Most drivers love the way their car looks and seek to make the already attractive car more lovely in their eyes.
Those who can tell their handling is reduced may choose to sacrifice outright performance in favour of a perceived improvement in aesthetics.
Because race car.

In short, every owner will prioritise characteristics according to their own tastes which means that some will choose handling over looks, some vice versa and some few will spend proper money to get both.

MickAP · 3 January 2022 16:41

I can’t really agree with any of that.

Jitsuka · 3 January 2022 16:49

You can’t agree with:
“Most drivers love the way their car looks and seek to make the already attractive car more lovely in their eyes.”

Or that most spend the majority of their time driving slower than desired on dull roads, only occasionally getting out for a blast on good roads?

Or that all owners will choose their own priorities on the various characteristics and make their decisions accordingly?

None of it?

MickAP · 3 January 2022 17:09

"Most drivers love the way their car looks and seek to make the already attractive car more lovely in their eyes.”

It’s the word most, I can’t agree with.

“Or that most spend the majority of their time driving slower than desired on dull roads, only occasionally getting out for a blast on good roads?”

Again most is the word I can’t agree with.

“Or that all owners will choose their own priorities on the various characteristics and make their decisions accordingly?”

The word all, you are assuming all drivers/car owners will want to do the above.

These are assumptions you are making.

Jitsuka · 3 January 2022 18:40

Not looking to argue so I’ll leave all the other points and touch only once more on the final one.

If someone considers aesthetics, handling considerations, costs, etc., and decides not to do anything, have they not definitively made a decision based on those considerations?
In any case, it’s become a discussion on semantics on how many people might do so rather than whether the points themselves were cogent, so I’ll say no more.

Couper · 3 January 2022 19:03

I’m new to MX5s so accept I maybe shot down for this…

It is very easy to get carried away when you find a car you connect with. You want to make it your own and enhance the elements you enjoy.

Cars are also an extension of self and identity.

Most modifications narrow the scope of a cars ability and if that narrower scope matches what you use the car for that’s great!!

However, over time the compromises (with mixed use as a everyday road car) can grate.

I have 3 fiat coupe 20VT’s. For all circumstances standard is best. Lowered, hybrid turbos and the search for more power is brilliant on the right road on the right day. 303bhp is great but less drivable.

Speaking to one of the best Coupe experts in the UK I was advised the best mods for the road were a live map (about 255bhp), good tyres and fresh suspension was best. (I wanted 400bhp)

My ancient red block volvo has 270bhp and a 60mm drop. Epic but flawed…

My 2p is:

Be realistic about what you use the car for
Accept that modifications compromise a road car
Consider the cost and if it would be better to start with a different car? Modifications are expensive

Then do what you want. It’s a free country!!

I did 200 miles in my NC Sport today and was amazed how it worked on the motorway, A roads and muddy narrow lanes. I appreciated its breadth of capabilities. That is a real talent!!!

ckleanth · 3 January 2022 21:30

The whole point I was trying to make with my original post is that its not a simple matter to reduce the ride height of a car. There will be consequences and trade-offs, some consequences you may have not realised. This is why I tried to be thorough, and tried to explain what might be affected so at least you have an idea.

If you want to take away just one thing… I would encourage you before buying or changing anything on the car, find a reputable mx5 suspension specialist and make an appointment for a simple chat.