Hello, I know this topic is old stuff, and I get the info for what's fast at the track, but not so sure about street.

Some context of what I'm looking for:
Street mostly. I do autocross but I skip the hot months, so I'm not 100% dedicated. My GF likes riding in the car and although she doesn't complain, I like to keep the ride somewhat enjoyable.

I consider myself a newbie when it comes to AutoX still and although drifting looks cool and fun, I recognize that whenever I encounter unexpected oversteer I don't feel too comfortable. I think I would drive the car harder if I knew the tail is not about to get loose on me unless I ask for it. Mid corner stability is important for me and I rather it be a bit pushy than too tail happy, at least for now. I also think this would help me push the slalom a bit harder than I do now.

My setup:
I have these Bilstein B8 for NBs:
https://www.summitracing.com/parts/BSN-24-065504
https://www.summitracing.com/parts/BSN-24-065511

Paired to 375/250 springs. 1.5F/R

Stock 1990 sways. No other suspension mods.
Tires are 205 NT05s
I don't remember the alignment, but I think I maxed camber, got all the caster I could get, and toe is pretty much 0 all around.

My problem is that the rear is just weird in a few ways.
First of all I don't know when the car is going to oversteer. Entering a corner is plenty responsive, sometimes I think too responsive, but mid corner I just don't trust the car. This is definitely partly my fault, but I try to be smooth and the rear is always the first one to give up, I have never ever felt this car understeer. I've been thinking of disconnecting the rear sway, or buying stiffer front springs, but now comes the second part.

The front is fine, but the rear seems to not be able to hold the tail of the car on big bumps. It seems to go all the way down to the bump stops and then bounce back up past the resting point and then settle back down. Makes me think it's under dampened. Someone told me to raise the spring rate so it holds the car more on its way down, but I'm concerned I will get an even worse effect on the way up
.
If I go over those parking lot short speed bumps, the tail just falls down hard unless I brake while the car rolls down. The front doesn't do it, feels like any normal car. the rear feels as if I dropped the car from the air.. Makes me wonder if the spring is too short too, but a longer spring would just raise the car because I don't have adjustable perch.

I don't keep the car stupid low I think, I need to measure the pinch weld height, but I've seen lower cars at AutoX be faster.

Anyway, so I'm confused. Other people use this spring combo and claim is really nice on the street, but Idk, maybe compared to a track setup is very plush but something doesn't sit right with me.

Do I have the wrong shocks?
Do I just buy a set of 400lb front springs and try that? But this won't help with the rear.
Do I raise both spring rates to 500/300? Will this be a kidney killer on the street? Will this help with the rear? Idk.

I guess I could live with the problem in the rear if someone confirmed it's somewhat normal for the setup, but still feels odd.

Anyway thanks for reading my rant.

 

Springs are WAAAAAYYYYYY too soft. Don't fall into the trap of thinking that stiffer springs is automatically a bad ride. It's all about having dampers and springs that are matched.

What happens with soft springs is that they compress easily to the bump stops and now you have really stiff springs (basically the compliance of the bump stop). The result is a shock and instant oversteer. TBH, it's dangerous. You can easily lose control in a sudden evasive maneuver.

Also, rear spring travel on NAs is really short and with soft springs you bottom out to those bump stops easily.

500/300 with matched dampers (I run 550/325 on the silver car which is almost 100% street) gives a nice ride. The Miata should have come that way from the factory.

 

Those things are wet noodles compared to any typical setup you'd find on an autocross/street car. Even like a 600/350 combo would still behave nicely on the street.

 

Even if you go off the extremely simple and not very accurate gravity reaction by adding up all your spring rates, you only get 1250lbs, just a little more than half the weight of the car. Granted its 375/250lb per inch of travel, but that might give you a perspective of how overburdened the springs are, they're probably sagging well over an inch more than what they're supposed to on a car with already short springs. Its no wonder you hit the bump stops coming off a speed bump. If you choose a much normal spring rate like 500/300, its much closer to the weight of the car, maybe you can visualize how the suspension will moves over bumps and in corners.
Keep in mind a few things: in a corner the weight shifts to your outside tire, in a drift your rear tire is following a larger circle, the inside spring will create an upward force as it is unloaded and your sway bar will only compensate so much, and the car is relatively 50/50 split in weight plus or minus a few lb per corner, but deceleration will throw some of that weight up front. You probably don't feel like you are in control because the rear outside suspension/tire is completely overloaded, probably without any assistance of torque. With a too light spring in back the outside spring is probably fully compressed as far as you set your suspension to go, this is probably undesirable in your case as I doubt you have set your bump stops to anything specific. Since we are only suggesting you go up 50-100lbs in the rear the affect of changing springs may not be as dramatic as the change you will experience from the front springs, I assume it will help, but I can't gauge what you will feel as in control. This is why bump stop tuning is important, I highly suggest you look into it, buy new bump stops and some wafers and see how it feels. I do want to mention that I am not saying you should always ride on the bump stop, if you're hitting it a lot and it feels right in a drift, it might feel bad with the tires gripped and vise versa, same with slow corners, fast corners, etc. It is a rabbit hole, but you can tune one thing that is easy to adjust such as your bump stops, or damping and ride height if you add coilovers to the mix, then try disconnecting your swaybar and seeing if it feels better worse (if you need more stiffness try a solid bushing, adjustable end link), add/remove a stack of bump stop wafers, check it, then move on to a new spring rate.

 

B8's aren't gonna take much more spring at all. That works well enough on nice flat autocross or track pavement, but completely overloads the shocks and goes completely uncontrollable on any large bumps. You might be getting a lot more suspension travel running soft, but that's what it takes to let the shocks do work when they are weak.

 

Other important parameters:
Ride height
Sway bars
Did you use NB or extended top hats on the rear?

You are fairly low sprung for what you could be. Conversely, common wisdom re: B8's is that 500/350 is as high as you should go, and Emilio would say even that is too much.

Read the Better Bilstein DIY thread for lots and lots of options.

 

I'll be getting ride height today.
Sway bars are stock '90
I have NB tophats in the back yes.

I must have fucked reading the bilsteins thread because I asked back then if these shocks were OK I got a yes, that's why I'm here, because seems like they aren't. You live, you learn I guess.

I thought the shocks used in Spec Miata were not ideal either because they are too slow?

I'm open to changing the rear shocks if needed. is the NA B6 what I'm after?

Seems like the consensus is for me to go up to 500/300. Am I reading that right? Or would that still be weak and not worth the investment?
I don't think I can afford xidas but if there is something else worth it like the Feals 441 I can think about it.

Thanks all for your input.

 

You should think about putting in extended top hats in the rear. I use these Goodwin extended rear shock mounts and like them.

 

Or if you are poor like me, but like high-quality parts:
¥Ï¥¤¥¹¥È¥í¡¼¥¯ÍÑ¥¢¥Ã¥Ñ¡¼¥Þ¥¦¥ó¥È¡Ã¥í¡¼¥É¥¹¥¿¡¼¥×¥í ¥·¥ç¥Ã¥× ¥Þ¥ë¥Ï¥â¡¼¥¿¡¼¥¹ Maruha Motors

The budget bilstein topic is your friend.

 

I have a set of old (circa 2012) Tein springs - 400/330 - that came off a Street Advance setup that hasn't been on a car for 10 years. They aren't rusty, just a little dusty. I have no idea if they'll fit around a Billie and I think they're "good" for a 2-inch drop.

If you want them, they're yours for the cost of shipping. Hey, $50-20 for a "Try 'em and see" test...why not?