Strut Brace discussion

[Magpie]

This topic, strut brace adding stiffness, started in another part of the forum.

The issue is in a road designed car the type of suspension you have (Double Wishbone or MacPherson Strut) will dictate how much benefit the strut brace will give.

For an expalantion on Double Wishbone and MacPherson Strut have a look here:
http://www.team-integra.net/forum/blogs/michaeldelaney/153-double-wishbone-vs-macpherson-strut-i-basics.html
http://www.team-integra.net/forum/blogs/michaeldelaney/154-double-wishbone-vs-macpherson-strut-ii-compared.html

Interestingly Racing Beat makes the following statement
On the Miata application, the tops of shock towers are subjected to primarily vertical loads from the upward movement of the springs and shocks. Adding a brace between the tops of these towers has not shown any measurable handling benefit during our testinghttp://www.racingbeat.com/mazda/performance/faq/miata-shock-tower-brace.html

As stated in another post I'm intending to find some bonded strain gauges (http://www.sensorland.com/HowPage002.html)to mount on my strut brace to measure the forces, but this will take a few months as it is not a priority.

Do strut brace on your car add to the stiftness? If so can you please advise what other mods you have done to the chassis as this may also determine the struts effect (perceived effect).

Not sure if I really want to do this as if I remove my strut brace for an airbox and prove that it does not (in my case at least) add much stiftness then it will be difficult to sell the said strut brace...

[Magpie]

Copied from my garage thread.

Mark, and everyone else reading this thread, the strut brace will make a difference.

As the brace does more than just help with forces put through the suspension. The double "A" arm design the MX5 uses looks suspiciously like the early Ford suspension used in Mustangs and Falcons from the 60's. A lot of the Mustangs had bracing from the strut towers installed by the factory.

The bracing of the strut towers is not just for the suspension it is for stiffening the whole chassis.

My explanation may ramble a bit so be patient. I am also not an automotive engineer but have been racing cars since the late 80's, so I hope a little knowledge in car preparation has rubbed off from various very smart people who have helped and mentored me over the years.

To start at the beginning, good chassis preparation will make sure that the suspension works as intended. That is the chassis geometry will behave as intended by the designer through its full travel, body flex will not introduce twisting or changing of the suspension mounting points relatively to each other which then change geometry unexpectedly and then the performance of your suspension.

Have a look at race car chassis, open wheelers and sports cars plus touring cars, NASCAR, DTM and the V8 supertaxis. The chassis are built to be as stiff as possible to provide the best platform possible for the suspension.

Open wheelers and sports cars started off as "space frame" chassis, think the Maserati bird cage cars, Lotus 7 cars and so on, plus the Siver Arrows of the '30's.

I personally had a Turner Sports 1300 as my first proper race car. A space frame chassis that was very stiff and not a lot of consideration for the driver over the other more important bits such as suspension mounts and engine, gearbox. The suspension was simple double wishbone on the front with proper coil over dampers and a 4 link rear end, again with proper coil over damper units, in may case Spax brand. The car could be jacked up at the front corner on the chassis and the diagonally opposite wheel would be the only bit still on the ground.

As technology advanced the chassis construction of race cars moved away from space frames to monocoque tubs in the 70's made out of aluminium and aluminium honeycomb. Even today the principle is the same, just the materials are now more exotic and stronger, ie carbon fibre, and exotic alloys. The advantage of this is the stiffness is a lot more than a space frame. Also it allowed constructors to use the engines and gearboxes as stressed members in the car, again aiding chassis stiffness. In fact in some cases the cars were too stiff and it may be argued that the construction may have contributed to injuries suffered by drivers in some crashes.

In the world of touring cars, NASCARS have morphed into very thick space frame chassis that a silhouette of another car shape is draped over the top of it. DTM cars are basically carbon fibre tubs that have the suspension bolted onto. Our V8's are again a space frame to which a body is glued and riveted to. The last generation of cars were built up from the roll cage. The only production bits used were a heavily modified floorpan, heavily modified firewall, a pillars and modified roof. An example of the "kit car" nature of this is when the Queensland MX5 club toured 888 racing just after they announced the switch from Ford to Holden. They had a ride car that was just completed and were in the process of converting it to a Holden. All they had to do was replace body panels. The only way you could pick that it wasn't built as a Holden was to have it parked next to one of the Commodore race cars and it was 50mm taller. All this is done to get the chassis as stiff as possible to provide the best platform on which to bolt the suspension so it will work the best it can.

Another example in chasing chassis stiffness in V8 supertaxis is the "Larry bar" used in the earlier generations. The bar diagonally across the windscreen, so famously shown at Bathurst when Craig Lowndes had the tyre bounce through the windscreen, was not there for driver safety it was there to stiffen up the chassis, which it did, a lot. If it didn't then no one would have added the extra weight to the car, especially that high up in the chassis. The benefit in having that piece of pipe added to the car would have to have outweigh, excuse the pun, the penalty of the extra weight and fractionally raising the centre of gravity of the car for every manufacturer to incorporate the bar into the cage. Remember this was in the days when the chassis still had some freedom in construction.

So now, onto why chassis bracing is important to an MX5...
Basically the car has a few things going against it to be a good platform for a race car.

First an NA is over 20 years old, any NA chassis can be basically said to be worn out, it has 20 years worth of fatigue in it.

Second, the body is a convertible, there is a big bit missing that adds a lot of stiffness to the car.

The technology of the time when the chassis was designed is very different to what is available now and is shown when comparing the stiffness of an early model to the latest model.

In simple terms, spending a bucket load of money on the best suspension available for your 20+ year old car is of no benefit unless the chassis is prepared to make use of it. If the chassis is as floppy as Raggedy Andy's flaccid penis then the suspension is going to flop around with the chassis and not provide the improvement to performance it should.

That is why there are so many solutions for bracing the MX5 chassis, some work better than others. Even the factory made strut braces for the car and when the NA6 was updated to the NA8 extra bracing was fitted by the factory.

On my 5 I have done the following to improve chassis stiffness, front struct brace and torque bar roll bar. It makes a bit of difference to how the car handles, but I could do so much more to make any changes more effective to the handling of the car. To do the job properly, I would look at a full welded in cage, seam welding and also some under body bracing to get the basic car as stiff as possible so the suspension can do its job better.

If you look at most MX5 race cars built, how have they been done, especially for 2F? Basically get the carpet out of the car, remove some trim and bolt a half or full cage into the car.

Does anyone strip the car down to an absolute bare shell and then take out all the sound deadening clean all the seams out and then weld them up?

When the cage is built is any consideration given to making sure the elements in the cage are tied to suspension mounting points? Again this aids in stiffening up the chassis and minimising the movement of the suspension mounting points allowing the suspension to work better.

As an example of what I would consider reasonable chassis preparation here is what I have done to my S14 in building the cage and also seam welding the shell where required.



This is a basic overall view of the ROPS being built in the car. The rear legs tie into the rear subframe mounting points. The rear stays also tie into the strut top mounts in the rear parcel shelf structure.



The cage is also tagged to the a and b pillars to add to the stiffness of the shell.


On top of the cage work, as the rules for Production Sports cars don't allow me to have the cage through the fire wall to tie in the front suspension, I have had the front seam welded, plus the two seams in the floor pan running across the car. I will also be fitting a front strut brace as allowed by the rules, so unfortunately I won't be able to triangulate to the firewall.




The end result of this work is a car that will respond to suspension tuning a lot better than most. Rather than the body flexing preventing the springs and dampers from doing their job or the suspension geometry changing in unexpected ways with the change in shape of the body and the twisting of suspension mount points I will have a nice stable base for the suspension to work.

This means that when I make a change I know what will happen and I can actually fine tune the suspension to the point where very small changes will make a difference.

As another example of how chassis preparation makes a big difference is to compare the two Datsun Zeds I owned and raced.

The first was a 260Z 2 seater, built fior rallying, I bought it after about 3 seasons at State championship level events. It had a half cage tied into the rear rear strut towers, but no other real preparation. After three years of rallying the shell could only be described as tired, some would say well and truly flocked would be a better description. I raced this car in what was the precursor to 2F in the early 90's. It was a horrible handling car that taught me a lot about about driving and how to drive around a problem. When we jacked up the car at either the front jacking point under the sill or by the lower control arm only that front wheel would be raised. If the bonnet or doors were open they couldn't be closed and vica versa. There was no tuning the suspension you threw what shocks were known to work and slightly stiffer springs and away I went.

The second Zed was a 240, an early light weight shell, but it had a full cage and seam welded throughout the engine bay. This car was a world of difference in behavior on the track. The suspension could be tuned for damping and also spring rates. I could make a 20lb/inch change in spring rate and you could feel and quantify the difference in handling. The damping could be changed and again you could feel the change and also quantify the change against the clock. Because the chassis was stiff and the suspension worked properly, consistent times could easily be achieved when testing and making changes to the car.

When jacking up the car in the same locations as the 260, the doors could be opened and closed. The bonnet was a fibreglass bonnet held on by 6 pins so no comparison there. All wheels bar the one opposite the jacking point would lift off the ground at the same time as you jacked the car up.

In summary, for mine it doesn't matter what suspension is used, proper bracing and preparation of the chassis for stiffness is essential to get the best performance from the suspension. As most time is made on the track through the chassis, in Mark's car I would sacrifice and drive around the torque dip caused by the intakes to get the more beneficial performance and better times that comes from having a stiffer chassis.

[NitroDann]

Absolutely nothing Matt wrote has anything to do with the question.

Will a piece of kinked aluminum mounted between the strut towers alone do anything for performance on an mx5.

No.

Dann

[Magpie]

I actually think it does Dann. From the perspective that it is all about preparation of the car, whilst few with road going cars would do what MattR has done it does show that just adding a kinked piece of aluminium mounted between the strut towers (which is what I did with no real thought apart from everybody else does) is only part of the solution.

However I do disagree, at least at the moment on keeping the strut brace over longer trumpets.

The data I collect will be interesting as it will be specifically for my vehicle alone but hopefully it could be indicative.

[RS2000]

I don't know if a strut brace is beneficial or not in an MX5, but I'd bet that the Racing Beat one shown in that link is useless - it has pivot joints at either end!

The Mazda brace as fitted to later NB's would be much better.

Cheers

[NitroDann]

Part of what solution?

thats like asaying an exhaust tip bigger than stock is part of your exhaust flow solution. It's just not. It's not the right way to go about it and is completely ineffective in improving actual measured performance.

If we were talking about a full cage that ties to the strut towers and even has a crossover bar between them made of rollbar material and welded on, sure, I might agree.

Dann

[Trackphotos]

I want a 3 point brace, not to help with chassis stiffness for handling, just to try and minimise that damn scuttle shake

[MattR]

Absolutely nothing Matt wrote has anything to do with the question.

Will a piece of kinked aluminum mounted between the strut towers alone do anything for performance on an mx5.

No.

Dann

It will, but with a standard car you won't see the benefits to anywhere the same degree as a fully prepped chassis. You will still see benefits as the load through the top of the damper will have somewhere to go and the body won't be as creaky.

Admittedly some brace designs are a lot better than others.

The response was to the blatant disregard of any benefit of a strut brace.

[NitroDann]

Blatant disregard for a regular off the shelf strut brace alone improving meaaureable performance (ie. With a stopwatch).

Dann

[MattR]

Dann, if you are saying that a strut brace on its own won't be quicker, well I would disagree.

It can help a tired chassis a lot in stopping it flop around and you will get benefits with that alone. It won't cure the underlying the problem of the flex, but it can alleviate some of the problems associated with it.

In fitting the factory strut brace to my car with no other changes I went quicker at a track day where most people were slower or at the times of the previous day at the track (QR). I am consistent in my times when driving on the track and I know the brace made a noticeable difference, as it has to the scuttle shake my car gets.

My responses were originally to Phol's post questioning if I would actually forsake a bit of performance from the engine to get a bit more performance from the chassis.

In my opinion I would take an improvement in the chassis anytime. When I was seriously playing weekend warrior racing my car was as quick on tight tea is like amaroo, Oran park shirt circuit and Wakefield as cars with a lot more horsepower because the better chassis allowed me to carry higher speeds through the corners.

With my current 5 I would spend money on the chassis to get better bang for my buck than engine mods for the tracks and roads I enjoy driving on. In my case it would be aftermarket chassis bracing as I am not about to do to the 5 what I am doing to the s14.

[toppertee]

I would think the single point strut brace would make little or no difference.

I.M.H.O. The way I look at, it's just linking the to top mounts of the suspension towers, If one moves the other one is going to move, because it forms a square (with the side movement). It's needs a third, point of contact to mount it, lock it in, solid or in other words triangulate it? I.E on too the chassis/fire wall at some point. Even then, the mx5 has a pretty bloody good set up in the front, can't see it doing much more than adding weight. It's not like it's a mk 1 escort front end
Could be wrong.

[project.r.racing]

doubtful a 3 point will be much better than a 2 point.

the force from the suspension top go upwards when a car is turning. in the triangle would also need to be inline with the forces direction to do anything. the firewall is not in the same direction as the force produced.

the square as you said actually doe help. without a brace, the suspension is like a C shape from the side.

think a cardboard box. open it and exert force on a side, it flexes. close the box and create that square, push again and you need more force to create the same flex.

in the end, with a mx5 you are dealing with a double a suspension, and the pivot points for the suspension are not taking the weight of the car when cornering. hence the suspension geometry doesn't change is any compared to a macpherson strut car in the same corner. so the bracing is hardly required.

[toppertee]

I thought a single brace would only, benefit macpherson strut suspension. Because the strut acts as part of your suspension linkage, so if it moves around the movement will affect the wheel. With our double wishbone suspensions, the linkages are all attached to a rigid subframe so the wheel will move in a relatively fixed manner. Movement, or lack of rigidity, in the shock tower will only be a very small effect acting essentially like a lower spring rate. Chassis rigidity affects double wishbone suspensions when the subframe moves from unibody flex. In this scenario, a 3 point shock tower brace will act similarly to a frog arm in making the unibody more rigid?

[gslender]

Strut brace helps front end chassis stiffness in an mx5. As I said lift the front corner and the distance between the towers change. Qed


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[NitroDann]

What effect does a regular bolt on brace have on that?

What affect on performance does that have?

Dann