I'm more of a dirt bike kinda guy so forgive my ignorance on the subject, but from what i've seen the majority of car suspension is really, really, really cheap and crappy in comparison. Stock suspension is little more than a spring with zero preload adjustability, and a single damper rod with fixed settings controlled entirely by oil flow, with some of them having nitrogen as well. They're calibrated by engineers and then mass produced in a 'good enough' way

Coilovers appear to me to be a step in the direction towards what a dirt bikes rear shock is. In that it has adjustable preload as well as adjustable compression and rebound dampening. I'm not sure on the servicing aspect, whether you can adjust valving, oil weight etc.

Now talking to car guys, the general consensus seems to be that coilovers are a 'performance' option fitted to cars, and overall they make the car ride harsh and aren't great for typical road use. My question is why? In my mind a coilover = dirt bike rear shock, albeit a cheaper version. And a properly setup shock can be tuned any which way you want, whether you want a super plush ride for trail use or to take massive impacts like motocross. More importantly, it can do both. A really well setup shock will be plush and controllable over all types of ground if set correctly for the weight and riding style
Is it not possible to both improve the handling AND ride quality with coil overs? I find it difficult to imagine they'd be worse than stock suspension in any way. Especially since the variation in vehicle weight is a far smaller percentage than a bike - which requires a lot of tuning between riders. Unless whoever makes the coilovers does a rubbish job with 'thatll do' valving, wrong oil weight etc

I think its mostly the spring rate that makes the ride "harsher", compression/rebound dampening also as it is (or should be) matched to the spring rate installed.

For example, the standard spring rate on a Magna is around 140ft/lbs, or 2.5kg/mm. A baseline coilover spring rate is 7kg/mm.

Other factors include the bearing used in the top of a coilover usually is not rubber mounted.

Yep it's purely spring rates, due to the smaller 60mm spring diameter. That's the only difference between stock susupension and performace 'coilovers'.

The smaller the diameter spring, the more coils required, therefore say a 4kg/mm rate x 60mm spring will have a lot more coils, and much less travel. Install in a magna and it will coil bind when you hit the first bump - I know because I've done this!!!

To put 60mm performance coilovers in a car you have to jump to 2-3 times the stock spring rate as a minimum, hence a pretty brutal ride...