Might as well pile on this. I had these installed 2 weeks ago along with some Megan Racing adjustable rear camber arms. After about 5 days, started to get some rear rattle. The pre-load wasn't set high enough. I noticed other companies recommended upwards of 30mm of preload on the springs/shocks.
Contacted Riaction, they gave some suggestions. Threw it back up on the rack and added about 20mm plus the 5mm it had. Riaction recommended upward of 40mm depending on the drop. Basically, they say 10mm of preload for 10mm of drop it seems or just a bit higher and that will fix any issues.
Dropped it about 1.5" all around, 25mm total preload about, there are no rattles now, the ride is really good. These coilovers, with aftermarket wheels and falken tires are just as quiet as the 18" aero stock wheels/suspension IMO.
Have the dampening set to 16 clicks, half-way of the 32 total. Ride is firmer than stock, yet with the dampening set, is still less jarring than my stock BMW 435i MSport suspension setup I just sold. It isn't annoying at all, feels just right to me.
I would say for the money, these Riaction coilovers along with the camber arms and alignment is one of the best setups for the M3 for your average person. Glad I didn't waste money on springs and be stuck with the ride height and the stock shocks. It's a quality setup and product. I spent less money on these coilovers with installation and alignment than a set of MPP Comfort coilovers alone. And you can get delivered in 5-7 days.
Riaction is actually five8industries, who have been around for years out of CA. Of course, they are likely just Taiwanese setups they have spec'd built to fit the car etc...really happy with the setup and ride, and the height can be set just perfect.
