Extremely common. Eibach are more or less the same as any other lowering spring.
The Mk1 has a flaw in its rear shock travel; mthere’s not enough, and on uneven surfaces (UK roads) the car spends a lot of time hitting the bumpstops. Lowering the car exacerbates this (early S-Specials had different bumpstops than standard).
MX5parts and others will do “trim springs”, that are in between Eibach-like springs (which lower, nominally, 30-35mm) and standard spec springs. Autolinkuk used to do springs like this but now only do springs modeled on the 1990-93 factory spec springs (a little different from the later 1.8 springs).
Spring rate is a function of coil length, wire thickness and number of coils. You are not going to get a lowering spring that rides as comfortably as standard on a standard shock.
The KYB AGXs are a decent shock. Most direct replacement aftermarket shocks are slightly firmer or slightly softer(rebound, compression) that standard. There is nothing magical about the OE shocks; Mazda don’t make them, they come from Showa, which is one of the big 3 in Japan (Kayaba (KYB), Tokico).
The AGX shocks are adjustable (the adjustment simultaneously adjusts compression and rebound).
Damping rates:
100 is considered the same as factory.
1990-97
1 = 95 (5% softer than Factory)
2 = 100
3 = 107.5
4 = 115
5 = 143.5
6 = 172
7 = 197.5
8 = 223
Now you will find lots of posts of people’s favourite combinations of settings, front and rear (by the number of clicks), and how they will turn it up for the track, and turn down for the road.In reality, the adjustment allows you to kind of match the shocks to the spring. So for something like a Eibach spring, you turn up, so the shock is better able to control the spring, and a Trim Spring, you back off a bit, and a stock spring, well, you set it to 2 clicks.
The adjustment knob is on the shock, so you adjust you need to crawl on your hands and knees, and essentially adjust blin. People complain that this seizes up after a few years. But, I don’t think that really matters. My current setup is Protec shocks with a Performance 5 pigtail spring (the spring diaiameter is smaller and one end than the other), with Mk2 shock tops, bushes and Superpro bumpstops. On paper the springs are very stiff, double standard, but the ride is superb, well controlled, not at all crashy. I haven’t touched the shock settings in years (the brass adjusters have probably seized), but I’ve no reason to. They’re getting long in tooth now (2008-2009, and a lot of miles and one rebuild).
If fitting lowering (upgraded) springs, fit the right shocks to go with them. The AGX plus Eibach, with bit of time with the settings, can give a good, well controlled ride. Thats not the same as a soft ride. It will be firm, but its possible to be well controlled. Frequently when people complain of a rubbish ride after fitting lowering springs, its usually because the shocks aren’t up to it on poor road surface.
The AGX is OE quality. I can’t recommend retaining Showa springs and fitting lowering springs, to maintain originality (too much compromise); either get better shocks, or stick to factory spec springs.
The “OE” alternative to AGX is the Koni Sport; instead of grovelling on the ground, adjustment is via a top knob (the disadvantage is the top mounts have to be drilled, though it doesn’t really matter, because by the time you have to replace the Konis, the top mounts will have long collapsed). The AGX has fixed adjustments, but the Koni is stepless; what people have found is as the Koni ages, you can slightly turn it up to compensate.
There is also Gaz; the fixed height versions, which are basically equivalent to the AGX (adjustment on the body)
The AGXs are about £420 plus the springs, the Gaz are ~£480 including the springs, and Konis are £650 with springs. Showa are about £350 plus springs plus £140 for the Eibachs. On top of that you need to budget for 4 new bumpstops/gaiters (£40-50 a set, technically the Konis don’t need the gaiters).
If on a budget, the KYB sports kit is good enough (Excel G shocks with KYB’s own lowering spring).
