hey.
ive just recorded a little video, as im hoping that will be easier to explain.
once watched (or not) im looking for help on the following:
i have installed this new part i can easily take it on/off. how can i measure and demonstrate the difference this has made?
because i hate anything that ‘‘feels better’’. thats placebo. it has no place in my before and after comparisions but i dont know how to capture this bit in particular. especially as its not an area of improvement i was epecting!
snippet from the video ive just uploaded for a bit of context
‘‘I’ve had issues with my mx5/miata rear end not behaving as expected into corners. I documented this across several versions of the car early on.
I went down the coil overs and sway bar upgrades bit this didn’t fix the issue over 60mph. I thought it was lift.
Lots of others report this issue across the owners forums but the answers are always ‘armchair mechanics’ (check bushes. Tyre pressure. Learn to drive style responses). Point being I’ve not seen anyone say ‘found the problem’ and that being a unilateral fix.
I installed this rear strut by accident (bought it for the sake of it) and it’s completely fixed the cars mid corner instability issue.
If anyone else has one of these fitted PLEASE let me know in comment so I know it’s not just me. Because based on my years of tuning, a rear strut is a vanity part and should have minimal performance impact. Let alone noticeable.’’
Flyin Miata reckon you don’t need a rear shock tower brace as there is substantial material for the rear fire wall. As a matter of interest US MX5 cup cars won’t have one either. I haven’t noticed any mid corner instability when on the track.
Armchair Mechanical Engineer here! The only reason that this strut could work is that the suspension spring rates were previously reduced by flexing of the structure at the top of the damper mountings. The wheel alignment is controlled by the struts attached to the subframe, which is attached to underpan structure. The spring rates would affect the frequency response of the system so the “instability” could be oscillations excited by bumps. Stiffening could increase the frequency so it is not excited as much. In the steady state, there would be less body roll. If the suspension geometry tends to change the camber then there can be grip changes, but I think the MX-5 set up is better than that.
When it comes to measurement, I have measured the spring rates and weight distributions by putting weight beams under the wheels of stands, and measuring the displacements with a dial gauge. I think static measurement should show what is contributing to the dynamic change.
Dynamically, you either need complexity of strain gauges etc. or maybe two sections of tube, sliding inside each other, one fixed to each side so that paint or ink would be scraped off during the “pop” event. Also could rig a phone to record the movement?
Find two rigid tubes, one which will slide snuggly inside the other. Attach one end of each to the turret tops. Rig a phone to film the movement. Go drive with various set-ups.
Possibly the movement is almost too small to see, but a cheap way to have a try.
P.S. I wish I could drive as hard as you, that would be fun!
By the way, what does the suspension adjustment do? It seems to be referred to as “soft to hard”. I presume that it is not changing the spring rates but something in the damper. Does the damper also have some spring function, e.g. gas chamber, or is it just a damper? The latter would mean that the damping is being changed (e.g. by closing an orifice(s)). The term “hard” would then mean higher damping, which would “feel” harder, because a bump would transmit higher forces into the body, but would also lead to tyre “returning” to the road more slowly. At the soft end, forces would be lower, suspension would extend more quickly, but the suspension/body would rebound. In essence there should be an ideal damping, usually referred to as “critical damping” which minimises rebound while allowing good road holding.
I expect no effect on overall torsion related to joining two points across the car. The bar needs to be diagonal (like the video door bars.
My own tests on my MX-5 involved measuring loads while supporting at various body suspension mounts while jacking up one mount with the jack sitting on a load measuring beam. I was just testing the front turret bracing on and off, and the doors open and closed with standard door bushes. I saw no effect at all.
Fitted the same brace to my car, also felt the same change. Chassis feels more “premium” and like the front is actually attached to the back when loaded up. Enjoy.
the two rigid tubes:
i cant quite imagine that in my head as to how i could pull it off. on top of the strut towers i only have 2 bolts (which are holding the shocks on! ). there is some ‘spare’ thread on the top. i might be able to use that safely. but, im not sure where thw two intersecting tubes would come in. got any pics?
suspension adjustment:
so its the YSR coilovers ( i did a review thread about a month ago, thats floating around…). The springs are indeed a ‘fixed’ spring rate. they are somewhere around 2.5x stiffer than OEM if i recall. (its written in that thread, i did the math lol).
The adjustable bits are the ride height (semi-adjustable, because once youve set it you typically wont change it unless for special occasions))
the part im refering too with my adjustments is the strength of the shock. theres a knob on top to make it flow the contents faster or slower against the springs movements.
Your comments about the spring extenson and rebound are correct So ive been playing with many many combinations to see if i could ‘tune out’ this issue with the ability to find a ‘maximum tyre contact’ capability with the shocks.
@SimonT1 thanks for that video. that was a good watch. i immediately saw that bonnet flex visually shown, made me think of the front bonnet i described on my video post-front strut reinstall.
I’m not sure i have the ability to perform the tests he did. but thats a good place for me to start working something out. i dont need the math, i just need to prove a difference really .
what was interesting, was the amount of flex he was getting (and changes) at 160lbs of leveraged force. on full cornering that should be in region of 600lbs a corner i would imagine before tyre traction break. with bursting increasing on bumps. very interesting
@stevegilkes placebo effect + blind testing. that would require me having a friend im a bit short on those… plus its a pig to fit and remove to torque. i cant give it to the wife.
i am wondering though if i could perform this as a test: the strut brace holes are oversized a little to allow for easy fit. (oval shaped)). im thinking of structurally reoving the strut and secure the suspension mounts. then on the remaining thread to overlay the strut on top and moderately tighten on one side. then film the unsecured holes on the other… if theres flex, the bolt threads (unsecured) should be moving inside the oval holes…
@AdamR28 Yes! thats great to hear. so theres a chance its not just me.
@IanH yea its the gravity performance one. i had to get a new front for my shock towers, so i bought the rear ‘for fun’. this whole thing is a happy accident.
At 1g cornering, there is a shift of about 600kg from inside to outside tyres, with a bias (which I haven’t worked how to calculate yet) toward the front due to the geometry. So I don’t think there will be a difference of 270kg between front and back which is what cause the twist
I have always wondered why racing folks don’t bolt the bonnet down if they want more stiffness in front of the firewall :). It could be done so as not to be too much of an inconvenience, there are plenty of quick release fasteners used on aircraft to ensure that doors form part of the structure.
I am struggling to understand what the ‘rear end instability’ constitutes. So what is it , and how does it manifest itself ? MX5s can easily be made to oversteer under power but that’s part of the appeal . And if you trail brake too long and too hard of course it’s going to get lively at the back .
So as oversteer is welcome to the party what else are we talking about ? I’ve never read even very experienced journalists mention it and after 50 k miles of sometimes press on driving neither have I?
Felt to me like, when the car was loaded up mid corner, the back end was “disconnected” from the front end; a general lack of “cohesion” in the chassis. Hard to describe. Don’t recall that sensation being present unless pressing on.
but i dont know how to capture this bit in particular. especially as its not an area of improvement i was epecting!
got any pics?
So ive been playing with many many combinations to see if i could ‘tune out’ this issue with the ability to find a ‘maximum tyre contact’ capability with the shocks.