I don't understand coilover spring rates.
 

According to this thread, the stock spring rates are about ~130 - 210 lbs/in. So that's anywhere from ~2.3k to 3.75k. Most coilvers are sold in 6, 7, 8k and up? So are they really three times as stiff as stock?

Yes. Lowering springs (RCE, Swift, Eibach, lots of other options) and dampers like Bilstein or Koni Yellows land in between OE and aftermarket suspension kits with rates typically under 300# and seem like they're closer to what you would want. 6k is just enough rate to prop up the super sticky 200TW tires and support a good amount of lowering, good damping can keep those rates well controlled and comfortable but that's >$2k investment, likely closer to $3k-$4k.

It honestly depends on the damping, i not long installed coilovers with 6k front and rear and they feel exactly like stock when fully on soft damping if not softer. There are coilovers out there that will ruin the car ride if you buy a cheap set or not doing any research on the company that makes them and what cars they specialise in. There are companies out there that sell top notch coilovers for cheap, its just a matter of researching.

Here's a good read about selecting spring rates: http://speed.academy/how-to-choose-s...koni-marcor/3/

Springs are measured in lbs/in or kg/mm. If you lower a car, it gives the wheel less space to travel. So you need a stiffer spring to stop the suspension from bottoming out. Thats the main reason for coilovers to increase spring rates so much.

Extreme lowering coilovers designed to drop a car around 3-4 inches will have rates in the 12-20kg/mm range. No suspension travel means a really hard spring. On the other end of the spectrum is the (*in development) 949 Racing coilovers. Designed to run only about 1in lower than stock and managing to keep a 175/150 lbs/in spring. Or about 3.1/2.7 kg/mm respectively. These coilovers are made to run over apex curbs without upsetting the car in the middle of a corner. These are also capable of handling a 200tw tire. Dont ask, I dont understand how they do it either.

If youre not running any serious downforce, 6/6 kg/mm seems to be the most popular. A few are 7/6, maybe 5/6. What you decide will depend on tire size and grip. Stickier tires on a racetrack will lean toward stiffer in the front, while street tires doing autocross will want a soft front end.

949 Racing can do that due to their valving, with that said if you talk to them they are not going to recommend those rates for that kind of tire. It's not going to be remotely ideal, and if you are serious about running a super-200tw tire like the RE-71, you need a lot more spring rate. There is a reason the race spring pack is around the 9kg/500lb range.

I ran 6kg for quite some time on my AST5100 and while it can "do it" with the 200tw tires it is not enough. I just bumped up to 8kg on my MCS 1WNR shocks and this is really the starting point for modern performance tires. With more spring rate and proper valving, the car is way easier to drive too. My wife went from hating the car on the 6kg spring set up to loving it with the 8kg springs and dropped the gap between us significantly at autocross.

With anything less than around 8kg you are just going to spend the entire time cornering on the bump stop, which unless you have a really good shock like the 949 Racing Xida, good luck with that. The second you hit any imperfections the car will react poorly. Regarding ride quality, I really agree with 949's approach. I think you either want to get something that is track/autocross worthy or designed for street use.

I've spent so much time with my cars being in this awkward middle space and at the end of the day they never end up being as good as they should be. Commit to the performance if you truly want it and intend to use it that way or rock the street pack for ultimate winning on your trip to Starbucks.

6 kg front
4.5 kg rear

MCA street performance coilovers.

Ride height: 350mm front and rear, measured from centre of the wheel to the guard.

Sway bars: stock.

Rims: 17 x 8.

Tyres: 235/45 17 ((currently running Bridgestone Potenza RE003, previously run Hankook RS4)(yes RS4 are much better than the RE003 in the dry, but, the RS4's are much worse than the RE003 in the wet)) = compromise because street car.

IMO it's an excellent setup for street and the occasional session.

Handy maintenance advice from MCA > https://mcasuspension.com/technical-section

I'm not sure how much the shocks matter when the suspension is bottomed out and basically not moving anymore.

If it takes 450 lb rates to keep the car off the bumpstops the entire time, you've pieced together your suspension poorly.

I'm not saying it is ideal, the Xidas are just going to behave BETTER than the competition in that scenario. Shock behavior while bottomed out IS important. You can adjust that with bumpstop rate, length, shock valving, etc.

Take any modern Super-200TW tire, install a 245 or 255 on a 17x9 and pair it with soft suspension (ex. Flex-A). Enjoy cornering on bump stops. These cars need way more spring rate to support a sticky tire, it's not rocket science. I've tested a bunch of spring rates from 4k-9k and anything less than 8k you are into the bump stops a lot more than you realize.

The tire width must make a massive difference.

Ohlins R&T 4K - 3K on 205mm RS3’s. I’m not on the bumpstops. I do bottom out the rear occasionally on the street with a passenger. Rarely driving alone. It is a soft setup. I did have Ohlins 7k 7k briefly but the overwhelmed the tires IMHO

So given that a particular damper is manufactured to match the spring rate, then theoretically the spring rate could be irrelevant? After lowering I am seeking to keep the handling as close to stock as possible. Without getting to scientific it looks like I should start with a stiffer rear than front, according to the stock fr-s numbers.

I'm very hesitant to go too stiff because of a thread that Dadhawk posted here. I can't find it but he mentioned that the platform requires lots of suspension travel and that lowering will reduce the already narrow travel range. I'm not sure if that was in reference to dampers/springs as a whole though.

I'm running Lincoln's old AST5100 (whiteline tuned MAXG) on square 6kg's on Kumho's v720 super 200

and I agree with him. But at the same time I am limiting myself to 225 width and I enjoy this car on a daily status. not hyper wide 17x9 super 71r's and going for fastest pax

if I where the Xida's on 245's would be my goal

I have a set of 5k front and rear swift springs if you want to go to a semi softer set up and add a helper spring.

I like my 6k as a compromise between street use and track use and yess you "can" race on them at the track. but they are compromised.

for me Im enjoying it thouroughy! it forces you to drive the chassis and not tire


I dont give starbucks my money though .

According to this https://www.ft86club.com/forums/showthread.php?t=8739

...the Cusco and RS*R coilovers have a near stock or comparably softer rate. Stiffer rear and under 6k