KYB AGX and standard spring combo feedback

[[Will]]

Hi,

I bought an NB8A MX5 with this combo and I find it unacceptably harsh for the street as a daily driver. I know this is a sports car and I'd say the best handling car I've owned, but I still think the ride compromise of this combo is still unacceptable for what it is. I think it also exacerbates the scuttle shake problem that MX5's suffer from too. I drive down relatively flat roads with small undulations and if I set the AGX's to '1', the car will almost be in a constant wobble over every road ripple (even ripples you can barely see). I've had to firm things up to '3' front, '2' rear at a minimum to stop the wobbles and crashiness.

I'm after some comments from people who have run this combo compared to stock or compared to AGX/King or AGX/Eibach. I've been living with this setup for a few months now and constantly tinkering with the settings on the AGX but I've concluded that I either need new stiffer springs for the AGX's (such as King or Eibach), stock shocks to suit my stock springs, or I go the whole hog and go Tein SS.

Bushes on the car appear OK when inspected with a pry bar. I've added a Brown-Davis rollbar which has helped a little with chassis rigidity, but that's a whole other discussion ;)

Just to give some perspective, I've owned a few modified cars such as an AE86 with Koni/King combo (bearable, but quite stiff), a VR4 Whiteline/Koni combo (similar firmness to a stock 350Z believe it or not) and both stock AW11 and SW20 MR2's and found them quite comfortable in comparison. Perhaps a bit foolish, but I never got to drive a stock NB8A when I was shopping around for the MX5, so I don't have this as a point of reference.

Any feedback will be appreciated and will help make up my mind which way to go.

Will

[fundies]

Yo Will. I have had my NB8A 2000 model for about 5 months now. It has 75,000km's on it with standard springs and shocks. I drove the car back from queensland and on some of the rougher stretches of the Highway to Sydney, my impression was the same as yours, with heavy crashing over potholes and shimmying/scuttleshake over rippled sections of road so bad it nearly put me into another lane! I ditched the \"heavy\" 16 inch mazda upgrade rims first of all for something lighter, then experimented with a few different tyre pressure combos, settling on 34 front 33 rear. I was tempted to go AGX/standard spring combo, but after hearing your story I think I'll think again. I'm pretty happy with my ride now, although its far from plush over rough surfaces, but I can live with that as it's only a weekend driver now on mainly smooth roads.

Oh, and the rattling passenger seat when you dont have a passenger in it will drive you mad on these rough roads!!!!!

[[Will]]

Thanks for the comments fundies, good to know that I'm not that far off the stock setup. BTW. I'm on standard 15\" wheels and I've experimented with tyre pressures too. I settled on around 28 - 30psi, but its only a marginal improvement.

Some roads like Old Windsor Rd from Windsor to Parklea are perfect with my setup with almost no perceptible scuttle shake and no crashiness over bumps. But often at slower speeds like 60km/h over road joins where old tar sections join new, the harshness of such a small bump amazes me. It feels like flogged out bushings, but with about 135000km on the car together with the pry bar check on the bushings, they should be OK. I'm happy to be corrected here on the condition of the bushings. Do they have to show signs of wear before they need changing, or is this one area I should be looking more closely at?

[manga_blue]

Will, I used to have the AGX/OEM shock/spring combo on my car. The AGX shocks for my earlier model (NA) car had 8 standard settings where stock was setting 2. On 2 my car was nicely damped and still soft and compliant for day to day driving.

For your NB model I can't remember whether 1 or 2 is stock rates on AGXs but I repeat that they should give a good ride - they're not rubbish, at least not when new.

Depending on car history the bushings last up to around 160ks but it wouldn't be unusual to find shagged bushes at 120ks. It's nigh impossible to detect when they're shot by inspecting or levering them unless one is really disintegrating. New bushing, even poly ones, replacing shagged ones will soften the ride, quieten the whole car and improve handling precision dramatically.

Stiffer springs are a whole step up again for driving experience. You can play around with all sorts of combos with Konis, Kings, Whitelines, Eibachs, Bilsteins, KYBs, etc or you can go out and buy Teins and just smile and never have to worry about it again.

[[Will]]

I got nothing against the AGX's, just thinking that my combo isn't working for some reason. I do have a slight clunk noise in the rear left every now and then, so that might also be an indicator of bushes starting to go off. Its not the sway bar as I disconnected it and the clunk was still there.

Sounds like there is no easy answer, but to try new bushes first and then get Teins after that if the results aren't what I expect.

Is $600 still the going price for a full kit of Super Pro bushes? I noticed that they're no longer listed on the N*POWER site which has been mentioned in previous posts.

[manga_blue]

I do have a slight clunk noise in the rear left every now and then

Check the tightness of the top centre nut of the AGXs. Be very, very careful not to overtighten, it's not hard metal and the threads are shaved off each side to make the flats to allow you to stop the shaft itself from turning. A second nut on top of the first is good insurance and stops them from loosening themselves.

Can't remember where but the price of a Superpro set has dropped below $500 recently.

As far as crashing over bumps goes, hard wearing passenber car tyres with names like Michelin Energy or Bridgestone Turanza or Yokie S306, etc will do that on an MX5 with any suspension.

[fattima]

I paid $400 for my bushes recently, that was without roll bar bushes. Not a quick job to install.

[[Will]]

I do have a slight clunk noise in the rear left every now and then

Check the tightness of the top centre nut of the AGXs. Be very, very careful not to overtighten, it's not hard metal and the threads are shaved off each side to make the flats to allow you to stop the shaft itself from turning.

Already checked and tightened.

As far as crashing over bumps goes, hard wearing passenber car tyres with names like Michelin Energy or Bridgestone Turanza or Yokie S306, etc will do that on an MX5 with any suspension.

I'm running Bridgestone Grid III on the front and now BF Goodrich on the rear. I did notice slight improvement when I put on the new BF Goodrich's that replaced the rear GIII's. The harshness I'm experiencing reminds me of my old KA Laser that I once owned

[[Will]]

I paid $400 for my bushes recently, that was without roll bar bushes. Not a quick job to install.

Super Pro? Do you remember where you bought them from?

[fattima]

Probably not much help to you. Autobarn Eltham they give a discount to MX5 club members, they were very helpful.

[[Will]]

Results of my ring around led me to buy from Wholesale Suspensions in Blacktown. I paid $400.

I've installed them already and there is a definite improvement, but I think I will still change over to Tein or B.C. coil-overs. Anyone used the B.C. coil-overs?

[franjae]

I fitted AGXs to my previous NB8B with stock springs at around 100k kms. Found setting 1 was about the same as stock. Position 2 stiffens up noticeably and I couldn't use any higher than 2 for normal use. I ended up with 1 up front and 2 for rears. From memory I had 30psi all round.

[Slugoid]

Another solution would be getting shortened bump stops. Fat Cat Motorsport sell them to suit all sorts of shock absorbers. Problem with stock bump stop is that they are too long, and the fact that MX5 shock bodies are fairly short, so amount of travel is very little. With lowered springs, or insufficient damping for the springs, you'll bound to hit the bump stops.

If you want a quick fix, I suggest trying them first.

[[Will]]

Another solution would be getting shortened bump stops. Fat Cat Motorsport sell them to suit all sorts of shock absorbers. Problem with stock bump stop is that they are too long, and the fact that MX5 shock bodies are fairly short, so amount of travel is very little. With lowered springs, or insufficient damping for the springs, you'll bound to hit the bump stops.

If you want a quick fix, I suggest trying them first.

I don't have lowered springs, but guess what? You're still right on the money. I went outside and pulled back the dust boots to find the front shocks are resting on the bump stops, and the rears were about 8 to 10mm away. It appears my stock springs have drooped quite a bit. Wheel centre to guard distances are 334mm front, 345mm rear. Car doesn't look lowered at all, but I guess the amount of droop is still enough to erode the little suspension travel that is available.

Also explains why my settings of 2 rear, 3 front appeared to help with the ride, whilst setting of '1' is completely useless. I was using the shock to minimise the bump travel!!

According to http://www.virkki.com/jyri/miata/bumps.html, at those wheel centres, I should have more travel before contacting the bump stop, but I have KYB AGX's, so that might explain the slightly shorter travel.

I've also read on the Miata.net forum that standard spring/AGX should not require bump stop mods, but I think the droop factor has been overlooked. So there is a lot of confusing information out there, but I think I'm close to sorting this out. Thanks to everyone that has contributed so far.

I might consider new springs and the shortened FCM bumpstops. As a test, I think I'll cut my stock bump stops first to check if this makes a huge difference or not before replacing these parts with the proper parts.

BTW. The new bushes have fixed a few alignment issues I've been having. I now have my lower control arm adjustments all on the centre adjustment and the rear toe is perfect (just a tiny fraction of toe in) and the car now tracks perfectly straight. I used to have my rear control arm settings all over the place to get the required toe and the car used to pull a bit left, but inconsistently.