Setting up FCM coils to run low ride heights
 

I bought my Miata from an older guy who primarily used the car for autocross. It came with FCM coilovers, which I've generally been very impressed with, they ride and handle better than any other suspension I've experienced. However, I quickly found out that once this suspension gets below stockish ride heights the ride quality really starts to suffer. I'm not looking to slam my car, just get rid of wheel gap and run around 12"F/12.5"R or a tad lower if possible. I've given some thoughts to the ISC tophats and possibly running a stiffer and/or shorter spring (currently at 550/350). Can anyone comment if the ISC's would improve this issue with FCMs? Is it even worth the effort of trying to make them work at lower ride heights? I'd rather get xida's but since I already have the FCMs I thought I'd try and make them work if I could.

Sell FCMs and buy xidas. After you buy ISC top hats, ang 6" springs. You're damn close to the price difference between selling your FCMs and buying xidas with NB mounts.

You could contact FCM and let Shaikh advise you. May be only a change in bump stops or something like that will get you what you want.

That's kinda what I thought after thinking about it for a while....

I considered that, except they charge $75/hour to talk to you about setting up suspensions.

Really? Did you actually call him? Shaikh never charged me either before or after I bought my FCMs :dunno:

I'm just going off what this page says. Sounds like it is new for 2014. And I was mistaken, it is actually $150/hr.

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I've spoken with Shaikh a few times this year about my plans. He tried to pull that $150/hr on me once but I just remained persistent and bugged the shit out of him...I've got $840 worth of FCM vouchers, you're god damned right we're going to talk on the phone, lol.

He's good people but as you know, when you're good at something, don't do it for free.

Sounds like you're transitioning to the bump stops earlier than intended. When Shaikh sets up a coilover, one of the things he wants to know is your intended ride height. He sets them up so the transition to the bump stops isn't abrupt (i.e., spring compression force approximately matches the beginning bumpstop hardness). If you go lower than what he setup, then the spring won't be as compressed and the transition becomes much more abrupt -- like how the stock cars are. More than likely, all you need are shorter bump stops.

I'd give him a call. I think that consulting on suspension engineering (for national-level auto-x guys) is a different animal than resolving a perceived problem. He's a good guy and concerned about his reputation. I really like the FCMs on my silver car, BTW. Really neutral and progressive. And they handle 30 minute track sessions without any issues whatsoever. It's been a while since I set them up, but pretty sure I'm running 12.25" front and 12.5" rear on 550/325s (give or take a bit for the corner weighting).

Cut your bumpstops to the length matching whatever ride height and bump travel you want to run.
You can even trim them while they are still on the shocks, takes 20 minutes at most for all 4 corners.
Problem solved.

+1, I run my FCM set up fairly low too at 4.5" from the front pinch weld and 4.75" from the rear without issues.

Take them out and put the lower pivot in a bench vice (pad it!). Take the spring off and compress the shock with the top hat. You're most likely hitting the spring isolator or top hat to the shock, threaded collar, or bump stop. This is probably what's causing your shitty ride experience at low ride heights.

ISC top hats in the back will allow the bump stop and shock body to travel into the top hat before bottoming out. Make sure your threaded collar is short enough that you won't hit it when the shock body goes into the hat though.

Start with the rears, your fronts are probably fine. But your butt is closer to the rears, so that's probably the bumpy ride you're feeling: rears bottoming out.