Smart car Suspension Mods

[Loren]

Yeah, you knew it was coming. I'm thinking of modifying the suspension on my Smart (2019 Smart Fortwo EQ).

I'm not looking to do anything major, but I don't like how the nose of this car dives under braking... and when I drive the Mirage after driving the Smart, I definitely feel like the Smart has too much body roll. It's not bad, really. Just not super-fun and confidence-inspiring. Not trying to make it an autocross car or anything, just a little more fun.

The first thing I notice when looking into mods for this car is that the Miata community has spoiled me. This is more like working on the Mirage, I guess. Not a lot of aftermarket support. Perhaps more than the Mirage, but still not nearly enough.

There are several choices of simple lowering springs (which I might do, just to see if it helps anything because they're cheap and easy), but absolutely none of them give any indication of spring rate, just the amount of "drop". Yay. Of course, I'll never find the OE spring rates, either. As I said, this ain't no Miata!

There are Bilstein shocks available! They're pricey, but they are out there. That might help with the nose dive, but I have a hard time spending a ton of money to replace shocks with only 2500 miles on them. Maybe.

There are coilover kits available, because of course there are! All it takes to make a coilover kit is to design a couple brackets and fit them to some generic threaded shock bodies that are valved something close to acceptable for the spring rate. That's pricey, too... but, I've had good luck with cheap coilover kits. And at least they're adjustable. (that's what's on the Mirage)

What really strikes me is that there are NO swaybars available for these cars. I guess it doesn't have a rear one, which makes sense. Shouldn't really need one. But, it has a front bar, and absolutely zero aftermarket options!

I might look at modding the front bar as a first course of action. See how much that can tighten up the body roll situation. It's interesting modding a car for pure street use. For autocross I'm always thinking how will this affect the ultimate handling ability of the car? This car will never be pushed much past 90%, if that. The concern is more "feel". Front bar should make the car understeer more, but I'll never get there! If it makes it feel better, it might be just the ticket!

So, I can either drill new end link bolt holes in the ends of the swaybar to give the bar ends less leverage and make the bar stiffer... or, I can cut the middle of the bar and fit maybe a 10-12" hollow tube around the middle of the bar to effectively make the middle of the bar more rigid and stiffen it that way. Either method would make a difference, I've done both before.

I'm just at a thinking phase, currently. I'll probably do wheels and tires first, anyway.

Hmmm... another fresh thought. I could leave the shocks, maybe even leave the springs, and just put some longer progressive front bump stops on it. That's always a fun thing to play with.

[Native]

Lol... well that didn't take long.

[Loren]

Decided to go super-simple first. I just took some measurements and ordered spring spacers for the front.

They're cheap, easy to install, and effective. They just fit between a couple coils, and when compressed, they effectively take that coil out of the equation, making the spring a bit stiffer.

[Loren]

Got the spring spacers installed the other day. They're a loose fit, so they aren't active until the suspension compresses about a half-inch. But, I can tell that they are there. Definitely less nose-dive under braking. That transition to greater regen when you first get into the brake pedal is more evident now... as what it is. Before, you couldn't really feel what was going on, just that the nose suddenly dove.

In driving the car around the other day, I was thinking about the shocks. They're really not bad. They do their job. No double-bounce over the local RR tracks. Good control overall.

Thinking seriously about ordering a set of lowering springs. Not so much for the lowering, but just for the stiffer spring rate. Will look at the front swaybar while I'm under there and see how easy it would be to modify to make it stiffer. I'm just trying to make the handline a little crisper. Less body roll, less nose-dive, more control and precision.

[CaptainSquirts]

Feels like the Mirage all over again lol. Sway bar and custom end links here we come.

[Loren]

The difference is that here I'm just going for feel rather than ultimate grip. And the starting platform is actually very good.

[Loren]

6 months later...

I finally ordered a set of H&R springs from UK. Who knows when I'll see them?

I still don't drive this car a lot. But, what I'm finding is that I'm sort of getting used to how it feels under braking, but some moderately stiffer springs should still help with that. I thought seriously about getting a coilover kit, but that would cost between about $1500 and $2200, and I just couldn't justify it. (I used all of my justification credits just on the purchase of the car) So, I'm trying a good set of springs... and then maybe upgrade the shocks if needed. With only 4k miles on the stock shocks, I'd like to leave them.

The other reason I opted for some springs is to lower the car. These will take it down about 1.25". I'm really not worried about the aesthetics, the car just feels too tall for me. It's designed to feel that way, I guess. They're trying to make it feel like "a normal car", where I'm used to a sports car, and want it to feel more like that.

The other aspect of height is the seat height. I noticed this the very first time I drove it. The factor seat position is about 2" higher than it needs to be. I can't even get the rear view mirror adjusted right to properly see out the back window, and I'm only 5'9"! I'm sure there's a factory seat upgrade with height adjustability. I'm also certain that if I could even find it, it would cost $800 or more to get. I'm thinking seriously about customizing the seat brackets to lower the seat a bit.

I still haven't found anyone who makes a swaybar upgrade for this car. Weird. It has no rear bar, the rear is an interesting variation of a beam axle, or something like that. I have found that I've started pushing the car enough to get the slightest bit of a rear slide when cornering hard. Maybe the springs will take care of it? If not, I may be back to pondering customizing the front bar.

Aside from all that, the only other thing I expect I might do is put a set of Miata wheels on it and wider tires.

[Loren]

So... it seems my H&R spring order evaporated along with the company I ordered from. I couldn't find anybody else to get the H&R's from, so I went to plan C. There's an outfit in TX that big into aftermarket Smart stuff. They have an house brand lowering spring set. Supposed to be designed and made in Germany. (I'm betting that they are rebranded Eibach springs)

These "Smart Madness" springs are fairly cheap at under $300, and claimed to lower the car 20mm front and 35mm rear. I can work with that. I've spent more money on stupider stuff.

The springs were delivered promptly, and we just installed them today. After a drive to settle them, here are the numbers:

Front Fender Height: Was 25", is 23.5"
Rear Fender Height: Was 25-5/8", is 23.75"

Center of front lip height: Was 5.5", is 3.75"

So, that's 1.5" lower in the front and 1-7/8" lower in the rear. (no, we didn't get the springs backwards, they are very different front vs. rear)

Looks like it's 1.75" lower at the front lip due to the rake. If that proves to be too scrapey, the bottom 1.5" of the lip is a rubber flap that can be trimmed or removed. I'll try leaving it in place.

Converting to metric: 38mm lower front, 47mm lower rear.

That's a lot lower than it's supposed to be, but it looks good. Properly low, nice "stance". So far, everything feels like you'd expect a lowering spring to feel. Firmer response, flatter cornering, a little rougher over bumps. I'll need to spend some more time with it, but so far I like it!

[Loren]

Dammit, Ben was right. I'm going to have to do something more to this suspension. Not sure what yet.

So, the springs.

On the good side:
Solved the nose dive under braking, which was my biggest complaint about driving this car.
Improved the handling. (to the point that I'm regularly squealing tires on curves... might need to address that)

On the bad side:
Ride quality over bumps is harsh.
Ride quality over bumps is HARSH.

Cathy can't stand to ride in it now. And driving across the Bayside bridge where it gets humpy... at 70 mph, was somewhere between comical and dangerious! The car has a serious "pogo" problem.

What to do?
I think the problem is mostly in the rear. My guess is that when the front hits a bump, weight transfers to the rear, settles it on the bump stops, and then when the rear hits the bump... BOING.

I have a set of poly spring spacers that I used to have in the front of the car. I might slip those into the rear and see if it helps.

Other possibilities:
Take it all apart and trim the bump stops, or replace them with something more progressive.
Fit better shocks. I'm not sure that this will solve the problem, really. Could help, I guess.
Ditch the springs and buy a Bilstein coilover kit that's designed to work properly.

I'm going to try the easiest/cheapest options first.

[Native]

"Somewhere between comical and dangerous" - what a fantastic description! Completely paints the picture.

[Jamie]

.

On the bad side:
Ride quality over bumps is harsh.
Ride quality over bumps is HARSH.

Cathy can't stand to ride in it now. And driving across the Bayside bridge where it gets humpy... at 70 mph, was somewhere between comical and dangerious! The car has a serious "pogo" problem.

What to do?
I think the problem is mostly in the rear. My guess is that when the front hits a bump, weight transfers to the rear, settles it on the bump stops, and then when the rear hits the bump... BOING.

Is it pogoing (is that a word?) all the time, or only on the bumps? What are the rear shocks doing? Not enough compression/too much rebound maybe?

[Loren]

The ride is fine on smooth roads, and it handles curves like a champ! Any kind of sharp bump will cause the rear to bounce. And stuff like those repeated undulations on the Bayside, it just gets stupid. It's not completely uncontrolled. The shocks are WORKING. But, whatever the spring rate of that bump stop is (probably upwards of 1000# when you get fully into it) is way more than the shocks can handle. They're a pretty firm bump stop.

The shock damping is weak. Definitely soft compression, but likely not too much rebound. Just all around soft damping. Firmer damping might help a little. The bigger problem is that the springs lowered the car a LOT more than they were supposed to.

As with a Miata, trimming the bump stops by a half to 3/4" would surely help a little. Or, fitting a more progressive bump stop that engages less harshly.

But, I'm going to plug in the rear spring spacers first. See if that gets things up off of the bump stops far enough to take care of it.

The problem with replacing the shocks is that the only thing available other than stock replacements seems to be Bilsteins, which is fine... but, they tend to be a little harsh with their compression damping. (great for steering feel, bad for ride quality) I always love Bilstein shocks for autocross, but not for street. I bet they wouldn't pogo, though!

If Konis were available, I'd have already ordered a set! "Power is nothing without control."

[Loren]

Got the spring spacers in the rear today. They are very firm polyurethane, and they fit fairly snugly between the coils of the spring. Meaning that they are not actually compressed at static ride height. Meaning that they sort of add some progressiveness to the spring. As the coils get closer together under compression, they bind against the spacer, and progressively remove a full coil from the spring rate equation. That makes the spring rate higher. (I could calculate approximately how much higher, but I'm lazy and I don't much care in this instance.)

Because the spacers isn't bound at rest, it didn't change the static ride height.

So, the only benefit here is a stiffer spring rate that might keep us from crashing into the bump stop as hard. That does seem to be what I feel from it. A little less crashy over big bumps. Otherwise, not much different. Mind you, I didn't have my wife in the car (150# makes a difference in this car), and I didn't drive over those annoying humps on the Bayside Bridge.

I'll let this rest for a couple weeks. Spend some more time with it, see what I think. The car HANDLES quite nicely and behaves well under braking. All I'm fighting now is ride quality and uncontrolled bounciness. We'll see.

My gut right now is saying "just spend the money and buy the Bilstein PSS coilover kit". But, that's about $1100 plus shipping, and I'm not sure I want to go there.

Looking at the PSS coilover kit instructions. They use the stock bump stops. Interesting. That means that they're either not going as low, or they're using much firmer shock damping. (likely both) And those shocks are not adjustable, only the ride height is adjustable.

With that, I might be better off just getting a set of Bilstein shocks. I'd have that teeth-rattling Bilstein ride, but at least it probably wouldn't be bouncy.

I'll take some time to make the next decision. Trimming the bump stops is still an option.

[CaptainSquirts]

Why take half measures when you can go full on 4 way adjustable coilovers. Adjust for Low high speed compression and rebound . Im surprised bilstein has a coilover kit for that car. What springrates do they come with and whats the springrate of the lowered springs? My rear had kinda annoying bouncing that I never really got fully rid of. We'll see if being able to adjust compression and rebound now will hopefully cure that. Anywho, time to throw the bouncy bugger in an autocross

[Loren]

I did some more digging and found a semi-custom coilover company that does a kit for this car. It's "only" about $1500. But, they would help me choose spring rates to suit my needs, and set up the dampers accordingly. Height and damping adjustable. And they have great reviews out there. It's certainly worth considering.

FWIW, bounciness is due to either too much spring rate or not enough damping. Two sides of the same coin. If you've lowered the car a bunch, you need more spring rate to keep from bottoming out. More spring rate requires improved damping. I'd think rebound damping would be the most important. But, compression and rebound are most important. Koni shocks have fixed compression (based on the spring rate) and adjustable rebound. That seems to work well for me most of the time.

In this case, I don't think the springs are all that stiff, really. The stock shocks should be fine for them. They've just lowered the car onto or near the bump stops, and the bump stops are progressive (somewhat... they are stepped and somewhat conical), but VERY stiff. So, as soon as you hit a bump, the spring rate goes through the roof, THEN there's not enough damping.

I really should get in there and trim the bump stops before I get crazy and spend a bunch of money on a coilover kit. I drive the car like twice per week. Silly to spend that kind of money on it.

[CaptainSquirts]

Who’s the coilover company, sounds like the ones I have, fortune auto. You get to choose the spring rates and they valve it according to the rates. I’m assuming the adjustable damping is mostly the rebound and a tiny bit of compression. How big are the bumpstops and how much bump is available before they got hit?

[Loren]

Ceika