NB 1.8 Sport with KYB AGX

Technical Area Steering & Suspension
2

Hi All,

 

I was hoping one or more of you might be willing to spare a moment of your precious time to help me out please!

 

I am pretty new to MX-5 ownership and have absolutely no experience of suspension tuning (having left every previous car I have had “stock” - although a couple had very aggressive factory sport suspension). I picked up what I had thought was a very standard low milage 05’ 1.8 Sport in October. My first MX-5 . There was no mention of modification to the suspension in the advert or the partial service history that came with the car.

 

The car is much more compliant and handles much better than my last two cars (MG ZR160 and MG ZS180, so that goes without saying) but I suspect that is the case with all MX-5s (even those with badly modified suspension) and I have nothing to compare it to MX-5-wise. On flat twisty roads the car is a real treat…I’d go so far as to say perfect. The car also seems to smooth out most motorway surface imperfections, but proper bumps / holes do make the car “crash” quite hard with a noticeable bang a bolt up your spine. On poor surface or bumpy country roads the car seems to stay flat but can be very “juddery” (and I apologise for my useless terminology on this). My fiancée says that the car makes her feel travel-sick with all the movement. I have also had very loud bangs going over relatively tame tarmac speed bumps at under 20mph. Of course, I have no idea how normal any of that is and I would have just been prepared to accept that this is the way the car handles (especially as it is a sport), BUT…

 

I sent the car in to Julian at Doctor MX5 for a full "do absolutely everything’ service (along with a cambelt change, new underseal (as she is remarkably rust free) and Goodridge braided brake flexi upgrade) at the end of last year and discovered that a previous owner had “upgraded” the stock Bilsteins (which I now understand are yellow) with red adjustable KYB AGX shocks. The car appears not to have been noticeably lowered (confirmed Julian who said ride height was standard), so I assumed this was about providing some adjustment for a more comfortable or sporty ride depending on the application. I declared it to my insurance, smiled at the thought of a free upgrade and shrugged my shoulders!

 

However, after a jolt out on some fairly nasty country roads yesterday with a large mate in the passenger seat (I’m a 5ft5 whippet but this guy has another foot on me and is heavily built) the ride frankly felt awful (and a little embarrassing when trying to show how great my little sports car was at handling!). I decided to do some research here and at MX5 Nutz to work out where I should be setting the KYBs for a good sport / comfort compromise. I think the general consensus was to start on 3 all round and go from there, but as I read into the subject I started to get concerned about what I actually have on my car:

 

  1. I now understand the stock Bilsteins on the sport were about a net 10mm lower than stock and so Mazda adjusted the rest of the geometry of the sport to accommodate. My guess is that putting a regular 2.5 damper and spring on such a car would thus raise the car up a bit and do something funny with the geometry and thus putting aftermarket shocks designed to replace non-sport shocks could also do something funny with the setup. Is this right? I am now wondering if the KYB AGX are actually suitable for the Sport as a result of the different geometry designed for the Billies...
  2. I also understand that the Bilsteins springs are unsuitable for standard shocks are designed solely to go with the Bilstein dampers. My KYBs on the other hand are designed for the standard non-sport spring or modified springs on the same pattern. So I have absolutely no idea what springs I have, but I assume new ones will have been fitted with the KYBs (when I had previously assumed the stock Billies had been used on new dampers) - is there any way to work it out?
  3. I can't find a conclusive answer on what the ride height should be as standard on a UK Mk2.5 Sport (and whether I measure with a full or empty tank of petrol) to see if mine is actually sitting a little high because a regular non-sport Mk2 spring has been used.
  4. I'm now concerned that the characteristics I have noted are not standard to the car but as a result of a poorly matched, shock, spring and geometry setup.
  5. If it's the springs at fault I don't know what I should look to replace them with as I would rather not lower the car and all the ones I have seen recommended for the KYBs (the FM or Eibach ones seem to be the common recommendation) lower by about 30mm.
  6. I still don't know whether the "setting 3" suggestion is right for a Sport or if that is for a standard (or even a Mk1).
  7. Having read around the area I'm now wondering whether stock bump stops were used, and if so whether I should really be upgrading them - and if so, what to. I have seen that both modified Audi A3 and Fat Cat Motorsport bump stops have been used by others, but I have no idea where to start in choosing a bump stop for me, if indeed a modified aftermarket option is a good idea!
  8. I'm now a little worried that the KYBs are actually a downgrade from the stock Mk2.5 Bilstein setup - can someone reassure me otherwise or advise if I would be better off going to MX-5 parts and replacing them with stock Billies when I can afford to do so?
 

I have no intentions of using the car on the track but I would like a fast-road setup.

 

In short, I’m totally lost! Can someone please help!!

Many, many thanks to anyone who took the time to read this - even if you didn’t know the answer!

 

David

 

3

Not a clue, sorry. However what a refreshing change to get so much information in an initial post. Usually posts start with ‘Why does my 5 ride bumpy?’

4

I would suggest you are getting unduly worried. 

The factory suspension settings have quite a large degree of variation permitted to still be in tolerance and aren’t the optimal settings if you were to take an average of all the mx5s that have ever been set up by experts. The mx5 has a lot of adjustability in its suspension geometry and even small adjustments to this can affect how the car drives and the confidence you’ll have in it.

Thing is, you don’t know what you’ve got presumably. And even if your history does show alignment settings, these can alter over time, especially if you hit a few potholes or speed bumps.

With regard to the hardware you are using, you indicate that at one point it felt perfect to you so I’m inclined to say stick with what you have. Find out what settings you are running then take advice based on those findings.

I don’t know where you are based but Wheels in Motion are a highly respected specialist in setting up all sorts of cars but they’ve also done loads of mx5s. There are plenty of other good suspension gurus too but make sure you go to someone known to be good with the Mazda.  Anywhere with a hunter machine can measure your alignment set up but your local members should be able to advise of a good specialist.

 

Ben 

5

The difference in ride height only applies to Mk1 Bilsteins, not Mk2.

AGXs are minimum setting, have a lower rebound rate than stock. These shocks were originally US only, and are a licensed copy of a GAB shock. They are considered at the lower end of the spectrum. There is no telling what springs were fitted with these KGXs. Generally, many AGXs were sold with Eibach springs, but KYB did their own springs as well, which I don’t think have a particularly high spring rate. Eibachs are quite firm. AGXs are supposed to work with stock springs. On the Mk2.5, I think the springs are the same irrespective of model.

NB AGXs only have 4 levels of adjustment (NA versions have 8 clicks). So 3 is pretty stiff. Generally a recommended start is (Brainstorm’s recommendation 2 clicks up front, 3 on the rear. There is no “best” setting, as it depends on your driving style. Some owners are happy with 4/4 or 4/3.

Audi A3 bumpstops was a suggestion related to NA shocks.

6

Hi

I’ve got a similar query and hope someone can help - I’ve a supercharged mk1 on Gaz pro coilovers for fun which is pretty low, set up great and all good. I got a winter rusty 2.5 which I think has Eibach  lowering kit but I’m just going on height being about 30mm lower than my 2.5 s-vt and having black springs - this has been my daily driver over winter and on Toyo Snowproxies been a great winter car but with probably too much rust I’ve bought an immaculate 2.5s-vt instead of restoring it. I now want to get the same sort of handling as the lowered 2.5 (i’m going to keep as a daily) and a 30mm drop would be as much as I would want and I’d like any advice on the pros and cons of going Gaz pro again or getting KYB AGX and Eibach springs to replace the Bilsteins or other options - I’ve not found a way to lower the ride height of the rear of the car keeping Bilsteins but I’ve also 2 MR2 mk2s which are slightly lowered running Bilstein Blacks which i’m really happy with so I would have thought there would be a way. The s-vt will also be turbocharged.

Finally are the current Bilsteins on the 2.5 s-vt B6’s - I have a Fiat panda 100HP which would benefit from the Bilstein B6 conversion and it would be brilliant to know if these are the same shocks - I’ve seen B6’s advertised for MX5s so hoping.

thanks in advance Nick

 

7

Just to follow up seems the 2.5 S-VT Bilstein have a longer piston than Bilstein sports dampers so to lower you need change the whole lot - I’m going with Gaz Gold pro on the S-VT but with the 350/250 springs rather than the 400/300 on my MK1