Mazda MX5 ND - Fixed the rear end instability!

[@Throttle.Monkey]

So glad I found this. I’ve had my new MX5 for a month and on my local b roads it honestly feels unhinged, the front tucking with the slightest lift and the rear being disconnected. Just started looking at suspension mods and I think I’ll add a rear strut to the list. One of my thoughts was maybe the KPC system (I think it brakes the inside wheel) was doing it’s thing and unloading the outside wheel, though the way to test that is turn traction fully off and it still felt the same to me.

[@AcoAegis]

I know exactly what pop you're referring to. Mine is left-hand drive for the US and does this on left-hand turns, so I'm thinking it has to do with seating position. That leads me to believe it does it on both sides regardless, but it just feels dramatically different depending on which side. Similarly, I've had passengers say "did you feel that?" when I didn't feel a thing, and vice-versa. It was one of the first things I noticed when I bought the car. A shock tower strut is likely helping by reducing chassis flex. From what I've gathered from professionals, flexing in the chassis makes it difficult for suspension parts to work properly. Hope that helps, either way, I don't think you're crazy.

[@Smart451-ut6df]

Hello. How about going to the Mazda dealer and test driving one of their MX5? I also think I have an issue with weird rear end stability, I havent fine diagnosed the conditions as much as you but I run a completely standard car and have the "problem" which makes me keep the traction control on in perfect dry conditions. I will be completely redoing the rear end suspension with new and uprated bushes, all of them, its hugely expensive and powerflex and only just this week made the bushes needed for the whole hub carrier/knuckle, before you could get other brands to get the 2 per side spherical bearings, but that still leaves all the others in the carrier/knuckle. Anyway I will try that and all new either OE or uprated link arms etc. I will be keeping standard dampers and springs. I had the rear brace like you fitted but realised I didnt want to cut the carpet or fuel pipe shield, so returned it. I should have tested it. I have put on 15" wheels and smaller tyres for weight saving. Acceleration feels nice, way too small diameter at moment but using up tyres before I fit bigger ones. I have a lot less grip now overall, but I think this is actually much better to discover the balance of the car, I can lose the car at very much lower speeds making it safer to test if you know what I mean. The behaviour of the rear is the same. My mind is focused on the bushes until I get them all fitted and still have the problem! We will see. Just and idea, lets say your rear brace has somehow given you more rear grip by spreading the loads more evenly, this might mean you still have the problem but its now at higher mph it will suddenly bite you. Try fitting some cheap nasty budget thin small tyres on spare wheels and see if the same overall balance is there at the lower speeds.

[@senseye1977]

Could the sensation you're having be more related to how the diff works? With this car, on a fast corner at high rpm, if you suddenly lift off the throttle the rear end would come loose or seem to come loose. This is something the ND3 was trying to fix. I have an ND2 and this is not an issue for me. I just know it behaves like that. If you want to check for chassis deflection you can just put a laser pointer on one of the shock mounts, raise the opposite end and see if the point where the laser is changes.

[@justaddafan]

You didn't mention alignment. That's the first thing I thought of when you mentioned a difference between left and right turns. In a Miata, the suspension loads are transferred to the pick up points of the arms. The forces at the top of the shock are much less significant to handling than they are on a car with a strut suspension. It's hard for me to see that the bar that just supports the top of the shocks could make much difference to handling, especially at the rear where the "tower" is really not present. Did you ever try swaping the right and left rear wheels? Are you sure everything is tight and in good shape on both sides of the car?

[@DirtyHabit_1ofMany]

@@justaddafan hey. Yea it had this issue with the oem alignment. It’s now got appropriate alignment/geo for the coilovers. No difference. New rubber all round (on my 3rd set), came with OEM, then I got new rubber and went up to 215/45 all round. And now I’m onto the snow tyres. No difference. The issue I’m describing isn’t types, alignment, or the ‘obvious’ suspension components or bushings… they’ve all been changed already 😂

[@DirtyHabit_1ofMany]

@@justaddafan in terms of geo… most likely (I think based on the current test results) that it’s probably the dynamic geo, and not the static geo.

[@senseye1977]

@@DirtyHabit_1ofMany having winter on would likely mask the issue you're describing because with them you can't load up the tires more. They would start slipping before.

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