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Discussion Starter #1
Has anyone purchased or had installed and driven a Smart Fortwo 451 with KW Variant 1/2 or 3 Coil Overs. I would like some real insight on the experience of Smart's reaction to having these installed vs the stock Smart. So far I have been unable to find Smart owners who have tried these. So it's a hunt these, so far, mythical Unicorns. Again this is a call to actual owners or drivers of these equipped cars. Thanks, I want to give them a shot.
 

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Bilstein coilovers on mine made an enormous difference. The stock spring rates are too soft all around, which leads to bottoming and harshness, in addition to too much pitching and body roll.
 

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Discussion Starter #4
Ok. On the Bilsteins, are they springs variable rate?. Did you also make a tire change? There are two things I am looking to change two driving issues tell me if your current set up would get me there. First, I would like to protect my rims. When the city digs up a street they often place large metal plates over the hole. At only about an inch in a half thick the generally carry no warning and when I hit then at speed that feels like it compresses the time enough to bend the alloy rim. I want to soften that blow. The second is at low speeds I want a soft ride and have firmer spring for higher speed body roll reduction during cornering. What were you looking for when you swapped and did you get there.
 

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Yes, I did wheels and tires at the same time. Four 15x6.5 rims, four Falken tires to suit. I stayed with 15" rims in order to keep tire sidewall for handling potholes and broken pavement better.

You are not going to get a "soft" ride. It doesn't work that way. The better-quality aftermarket dampers have better internal valving - firmer low-speed damping for better control of pitch and roll (bulk motions of the bodyshell) but which "blows off" at faster suspension movements to take the edge off large suspension movements. Note here that "low speed" refers to the speed of the suspension movement, not the speed of the car.

Springs with a higher spring rate give a better ride in this car, which sounds odd ... until you realize that the front suspension in particular doesn't have much travel available. Higher spring rates do a better job of keeping it off the bump stops. By the way, although the Bilsteins are height adjustable, I set the front at stock ride height and the rear at 20mm lowered, for two reasons - one, it levels out the appearance, and two, lowering the rear by 20mm comes very close to leveling out the lateral control arms for less rear bump-steer. Front was stock ride height in order to preserve bump travel before it hits the bump stops.

Steering response, in particular, was much better with this setup. And it lost most of the annoying pitching on gear changes. Overall, it transformed the car into the way it should have worked.

One thing that this will not improve is the impact harshness when driving over imperfections. The design of the front suspension on these cars does not allow much cushioning of bump impacts transmitted through the lower control arm pivots. (The 453 fixes this.)
 

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Ok. On the Bilsteins, are they springs variable rate?. Did you also make a tire change? There are two things I am looking to change two driving issues tell me if your current set up would get me there. First, I would like to protect my rims. When the city digs up a street they often place large metal plates over the hole. At only about an inch in a half thick the generally carry no warning and when I hit then at speed that feels like it compresses the time enough to bend the alloy rim. I want to soften that blow. The second is at low speeds I want a soft ride and have firmer spring for higher speed body roll reduction during cornering. What were you looking for when you swapped and did you get there.
It sounds like what would work best for you would be to get taller sidewall tires all around, and then stiffen up your suspension in both spring rate and roll resistance. Only problem is that there is one sole manufacturer of a rear roll bar and that will cost about $600 US to get it purchased and imported from Great Britain.

I think what you're looking for is a lot easier than what I initially thought you were looking for, which is to increase the handling capabilities. As a decades-long track junkie, I've played around a fair amount with at-the-limit behavior of my 451 ED and there are two significant problems. The more common one is that the traction/stability control systems are too intrusive and trigger at times when the car is still under full control. The second and seemingly impossible problem to resolve is that on the ED, that same stability control system cuts engine regen during times when near the limit but when still under full control. This causes a **loss** of control as the understeer suddenly increases, and this regen-cutout cannot be shut off even if the stability control systems are disabled.

Anyhow, I've given up on trying to make a true go-cart of my smart and instead am now pursuing what you're after, which is to get much more neutral handling with sharpening response and minimizing body roll. I think to fully get there, I'm going to reduce the tire size stagger, increase front and rear spring rates, and increase front and rear roll stiffness. Overall, it's about a $2000-$2500 proposition to get it done in a way that I think would be pretty optimal.
 

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Discussion Starter #7
I find what you say about the higher spring rate to apply to the tire pressure. I feel a better ride on rough pavement with my stock 175/60 15 front Conti's tires at the current 39psi and my also stock 195/50 rear Conti's at 36psi. It seems to force the springs to do more than the springs do with softer tires. I would like to know what tire size you are running. I have the stock 15inch 6.5 inch wide 6 spoke rims in the rear and 5.0 inch wide 6 spokes up front. These are the painted silver ones. I will be running the same style but they will all be 15inch 6.5 inch wide Chrome versions. I want to do all I can to protect the rims from being bent when I install them, in all likely hood after winter. Now the 453 if it has seemed to resolve some of the harshness, an in depth look at what areas of focus brought on the change may clue us in. If it is not a complete redesign but some more subtle changes, maybe some reverse engineering could find its way back to the 451 model. If it turns out to be a doable and affordable retro fit, there seems to be a ready market for it.
 

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Hey "Injured Again", now you are talking my desire. I would have to then be more clear in what I want. I don't want a soft ride, I want a less harsh ride on the low speed driving. I also don't want a full blown auto cross runner. I want a capable feeling in corners when I do find a nice curvy road and push it with a little spirit. A nice little sporty feel on a nice country back road that doesn't rattle my teeth loose on my drive to and from work. If you have set that price point at 2-3 thousand dollars I'm in, although I think this more clear description of what I want may lessen that price point. You have a lot of valuable knowledge as to what not to waste effort and expense on. So I would love to get your guidance in tweaking this absolutely fun car to something even more fun.
 

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Discussion Starter #9
I am looking too "SmartforYouRacing" to describe a variable rate spring option for their Road Set of coil overs. "Injured Again" would the roll bar SmartforYouRacing has interest you.
 

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twcom, here's a sort of rambling diatribe of my thoughts that I typed up throughout the day as I had time, so as to give you some perspective of where I'm coming from. I see that you posted a couple of messages since I started this, and I'll address those tomorrow. I do love thinking about and talking about this stuff, and love the tinkering aspect of it. Some of the things you subsequently posted I write about below, but I'm too lazy now to edit it so I'll just let this roll and see where the discussion goes!

Anyhow, as far as my history, I have a track-modified Corvette and traded in a 1995 Miata that I owned and daily drove for five years to buy the smart. My Miata was set up to maximize driving response, to feel nimble turning, and to have a neutral handling balance while being able to cope with our rough roads. As such, ultimate grip was pretty low on my list of priorities. To accomplish this, I decided to run 185/55-15 all-season tires rather than the usual 205/50-15 or 225/45-15 tires that most owners use who want maximum grip. This tire choice would give me the comfort for daily driving, and I'd have to modify the suspension to accommodate the extra flex in the tires to get the driving response and handling balance I was after. In the end after a lot of fiddling, I stuck with the stock springs, used a high quality and longer than normal bumpstop (since the Miata on stock springs rides on the bumpstops most of the time), and used high rate adjustable sway bars on their stiffest settings. I used alignment settings and tire pressures to fine tune the handling balance. This gave me the low stock impact harshness over about the first inch of suspension travel, with the effective spring rate at each corner then rapidly but smoothly ramping up from there on. With the flex inherent in the tires, it was cushy on sharp pavement breaks yet had minimal lean once that initial compliance was taken up. I had a number of people drive my Miata and say that it had great balance, feedback, responsiveness, and comfort for a daily driver.

So with my smart, I realized there were a number of hurdles to getting this same behavior.

Lack of information - I've asked here and on other smart forums or pages and no one has any information on spring rates or lengths for the various models, nor information about things like camber or toe curves during suspension excursions (in the case of the smart this would be for the front only). Knowing this information is important as it can help predict suspension behavior and prevent needing to physically try things to see their effect. As an example, here's a page showing basic Miata suspension information and effects of changes in spring rate and roll bar size in suspension bounce frequency, roll stiffness, and front roll couple:

FCM_MSDS_TUTORIAL.xls

Lack of parts availability - There is only **one** source of a rear roll bar, and that's from a UK based shop which sponsors a smart racing series. To get it here to the US is about $600:

Rear anti-roll bar - Smarts4you Smart car parts shop UK

There's no information on whether or not this bar is hollow or what the lever arm length is. There are various sets of springs available, even like take-offs from Brabus models, but there's no information about what their spring rate is or what their static length is.

Lack of adjustability - The deDion rear is not adjustable at all, other than loosening bolts, moving the wheel to the limit of the slack in the parts, and tightening bolts. It's basically set at around -1.8 degrees negative camber, and slight toe-in. That's not bad, generally, but it makes using alignment to alter behavior difficult to impossible. Especially since the front suspension only allows changes to toe and not to camber.

Intrusive stability control - I don't know what the behavior is on a gasoline 451, but on the ED the stability control system cuts regen on the electric motor when it thinks a crash is imminent. The thresholds are low enough that it cuts regen even at times when there is no loss of traction. At higher speeds and near the limits of traction, this sudden freewheeling is enough to CAUSE a loss of traction. I don't know of any way to disable this effect, so my goal would be to make the smart as fun to drive below this threshold.

So, with all this being said, this is the approach I was going to take. These first three items need to be done as a group to establish a new baseline:

Even up the tire size - there's only a slight rearward weight bias so there needs to only be a slight rearward tire size bias, if any. Since you can typically increase grip at one end by increasing the amount of negative camber, and since the rear already has more negative camber than the front, I feel comfortable in predicting that the same size tire at both ends will still have more grip at the rear, roughly proportionate to the amount of rearward weight bias. I ran 185/55-15 on my Miata that weighed about the same and had about 0.85-0.88G of grip, but I could also run 175/60-15 for a bit more shock absorbing sidewall. Either size should provide more than enough grip to make the traction control system grumpy. These sizes will almost fully correct for the optimistic speedometer, and these sizes are available in many different tire models.

Install spacers up front to more equalize front and rear track width - the front track width is about four inches narrower than the rear, and this is compounded by the short wheelbase. This creates some weird lean vectors and increases slip angle at both outside wheels, which hurts grip. I'd go with 20-25 mm on each front to about half the track width disparity.

Install the rear sway bar - I don't see any to get more neutral handling balance without using really high rear spring rates that would probably make my teeth rattle.

At this point, I would evaluate what the handling balance and driving behavior is like. I'd be somewhere around $1400 or so into it by this point (tires/wheels, spacers, rear roll bar).

From there, I'd address the brake dive and acceleration squat by removing the four springs, having them measured to determine their spring rate and static length, and then having custom springs made with spring rate increases to get the handling balance I want, while simultaneously trying to balance ride height, suspension jounce frequency, and front roll couple. That's probably $600-800 depending on how much labor costs are.

I'd then try to fine tune using tire pressures.

I believe I can get it to the point where I have neutral handling balance (taking into account the regen) and be very fun to drive, though only up to about 8/10ths to make sure the stability systems don't cause me to crash. This would still be a very high rate of speed considering how narrow the smart is and how much room there is to maneuver within a lane.

That's it. About $2000 and some experimentation and I'm pretty confident I'd be successful. Next up is to convince the boss that this is money well spent, which may be the most difficult thing as I just started the paperwork to buy another new car that will have used up my discretionary spending money for probably the rest of my life. But you only live once so I'll approach her, timidly, some time after the weather starts warming up again.
 

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Crickets....... The elusive Unicorns remain mythical.
On e90post there were complaints/mentions about squeaking issues with KW coilovers, at least the original ones. Kind of turned me off from the brand..... (Like I've ever lowered any car in the household anyways...)
 

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Discussion Starter #13
Great Info. Now since there are already shops with take off original Smart springs laying around (I imagine) it may be a way to get one of them to give the spring rate of those take off. Could save time and cost to get that info instead of removing your own.

As I thought what could a rear rim front rim swap do for the spacer issue due to the rim offsets. So 5.5 rims in the back with the same 185 tires and the 6.5 rims up front again with the same 185 tires. I might actually go with a wider tire on back even if slightly over sized for looks. But this is just about your thought on rear rims up front front rims out back.

I am going with 205/ 55 or 60 series Out back. 195/60 or 205/55 up front. These choice have no mathematical or scientific basis. Just where my visual mind has lead me.

But I'm now under standing that and adjustable height coil over coupled with the right spring is the hunt for me now. So what the stock Smart spring rates info must be found out.

The hunt for the Unicorns may change to becoming Unicorns ourselves.
 

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I find what you say about the higher spring rate to apply to the tire pressure. I feel a better ride on rough pavement with my stock 175/60 15 front Conti's tires at the current 39psi and my also stock 195/50 rear Conti's at 36psi. It seems to force the springs to do more than the springs do with softer tires. I would like to know what tire size you are running. I have the stock 15inch 6.5 inch wide 6 spoke rims in the rear and 5.0 inch wide 6 spokes up front. These are the painted silver ones. I will be running the same style but they will all be 15inch 6.5 inch wide Chrome versions. I want to do all I can to protect the rims from being bent when I install them, in all likely hood after winter. Now the 453 if it has seemed to resolve some of the harshness, an in depth look at what areas of focus brought on the change may clue us in. If it is not a complete redesign but some more subtle changes, maybe some reverse engineering could find its way back to the 451 model. If it turns out to be a doable and affordable retro fit, there seems to be a ready market for it.
twcom, I'm still running the stock sizes right now (15X4.5 front and 15X5.5 rear). In my experience, running the lightest wheel provides the best feedback and the lighter unsprung weight also helps minimize impact harshness. And from playing around driving the smart at and near the limit, there seems to be a point beyond which more traction doesn't help - even when steady state cornering at some point the stability control system kicks in even with no loss of traction and no bumps to make it think something bad is happening. Again, this manifests for me in the regen being cut off so a gasoline 451 may be different.

But because the smart, with a narrow track and high center of gravity, will never be a big grip vehicle, I'd rather shoot for making it fun to drive and eager to turn in up to 0.75G, rather than have something that fights me all the way to 0.85G.

So for me, I'm looking to go as light in the wheels as I can, which means no more than a 15X5.5 at each corner, and as narrow of a tire as I think I can get away with. Certain no more than a 185/55-15, which weighs about 17 pounds, along with about a 12-13 pound rim. That's right at 30 pounds, which is pretty heavy for a narrow 15" wheel. Miata wheels can run as low as 26 pounds or so, and the extra four pounds per corner is transformative in the way the car feels. I'm probably looking to either purchase another set of 15X5.5 stock rears, or go for 15X5 Genius Newton or Darwin wheels at each corner, and 185/55-15 or 175/60-15 (which are only 15 pounds).
 

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Great Info. Now since there are already shops with take off original Smart springs laying around (I imagine) it may be a way to get one of them to give the spring rate of those take off. Could save time and cost to get that info instead of removing your own.

As I thought what could a rear rim front rim swap do for the spacer issue due to the rim offsets. So 5.5 rims in the back with the same 185 tires and the 6.5 rims up front again with the same 185 tires. I might actually go with a wider tire on back even if slightly over sized for looks. But this is just about your thought on rear rims up front front rims out back.

I am going with 205/ 55 or 60 series Out back. 195/60 or 205/55 up front. These choice have no mathematical or scientific basis. Just where my visual mind has lead me.

But I'm now under standing that and adjustable height coil over coupled with the right spring is the hunt for me now. So what the stock Smart spring rates info must be found out.

The hunt for the Unicorns may change to becoming Unicorns ourselves.
Our smart is the third car for my wife and I, so we can afford to have it down for a week while I have the springs removed, sent to be measured, and have new ones made. I'm a fan of this place:

Coil Spring Specialties

I had them make some custom springs for me in the past and they were great. If the cost weren't too great, I'd probably get a shock dyno graph as well. I like them with a lot of rebound damping but with near stock levels of compression damping. However, getting a custom shock made is probably going to be prohibitively expensive.
 

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Discussion Starter #17
I emailed them with you as the referral. I will see what they have in mind to couple with a height and rebound adjustable shock.
 

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Good luck! Let me know how it turns out!

I'm going to start on modifying my ED in the spring as my other vehicle isn't good in rain nor snow. I'm keeping a daily eye out for a second set of rear rims!
 

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...Even up the tire size...Install the rear sway bar...
IA,

I now have a pretty neutral car at the limit with the Brabus Bilstein shocks and springs kit, Smarts4YouRacing sport bushings, and 175/55R-15 front and 195/50R-15 rear tires. I considered the rear sway bar from Smarts4YouRacing, but the ForTwo Cup cars that race with those bars run 175/50x16 front and 225/35x17 rear tires, considerably more rear tire size bias than I have now.

I think adding a rear bar without correspondingly wider rear tires is a recipe for oversteer.

Peter
 

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IA,

I now have a pretty neutral car at the limit with the Brabus Bilstein shocks and springs kit, Smarts4YouRacing sport bushings, and 175/55R-15 front and 195/50R-15 rear tires. I considered the rear sway bar from Smarts4YouRacing, but the ForTwo Cup cars that race with those bars run 175/50x16 front and 225/35x17 rear tires, considerably more rear tire size bias than I have now.

I think adding a rear bar without correspondingly wider rear tires is a recipe for oversteer.

Peter
Peter,

Do you know what the spring rate is of the springs that you are using? And this is on a gasoline fortwo, correct?

I've primarily look at the video of the cup cars and did noticed some tire stagger, but at least in what I saw, it didn't look like a 175 and 225. At least from this promotional video:

Promotional Video | smarts4you racing

Handling balance still looks like some amount of understeer, even with what amount of tire stagger that can be seen. Since I've done practically all of my track time here in the Pacific NW and often enough in wet conditions, I'm used to oversteer and don't mind a handling balance just on the oversteering side of neutral if it can enhance the feeling of agility during turn-in. I don't think I'll ever solve the riddle of the stability system where it cuts regen near the limit, so I'll shoot for maximum nimbleness up to 9/10th and leave that last 10th alone.

But even with the 19mm bar, there may be things that can be done to modify its effective stiffness. Back in the day when I was tracking our BMW, there were two main aftermarket bar sizes available for the rear. The smaller bar still gave some understeer and the larger bar gave some oversteer. Most drivers ran the larger bar but put a couple of spacers underneath the sway bar bracket mounts. This created slack in the mounting that allowed some initial compliance before the bar fully compressed the bushing. Yes, it wore away at the bushing and they needed to be replaced every year or so, but it did soften that bar enough to noticeably alter the balance. Two 1-mm think spacers were pretty much the standard practice.

I'd love one day to drive a Brabus and see what the ride and handling balance is like. Doing so will help me a lot in figuring out where I can go and where I can't go.
 
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