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Discussion Starter #1
I had a teaching moment recently. All summer, I fought with my car, very frustrated that it was trying to put me off a cliff on a nice twisty road I like to take as a shortcut.

I had done two things very recently, and while one was actually done wrong, it was not the problem.

My first thought was that Midas had put the wrong fluid in my car when flushing out my brake fluid. They actually did. I verified this at a second shop where we heated it to boiling and measured the temperature. Dot 3 does not ever belong in a smart due to the extremely small capacity of the system. Dot 3 cannot absorb the heat into that small volume of fluid. Dot 3 boils under “spirited” driving.

That was not the entire problem, though. Clear of the fluid issue, I replaced my now trashed rotors and pads with some cross drilled very thick, to my eye, rotors and ceramic pads. I was still having issues, although less pronounced.

My instinct here was to suspect the rotors were dragging, and with the way they would buzz when warm, I really thought I was right.

My front track is significantly narrower than my rear, and my belief was that the brakes were dragging, and whenever the front track arc extended outside the rear track arc I was being pulled to the outside of the curve.

That was in fact the science of it, but not the cause. You see, as our cars get stiffer and lower and wider, we depend more on artificially helping the front tires win the fight between HP go straight, and steering go maybe over this way more.

The second thing I did way back at the beginning of this was buying 4 new tires. I do not usually do this. My tire rotation has always been burn the rears to death, buy new fronts, move old fronts to rear. As it turns out, all of my many many modifications have biased traction severely toward the rear.

On advise from a friend, I found a couple used matching tires. I put the scuffs on the rear, and I am back to carving corners and scaring the crap out of tailgaters by taking them into corners way faster than they can hold.

Now, I am looking into the possibility of a rear sway bar. This is exactly what the track cars do to correct the issue I am fixing with used tires.

The moral is that sometimes we need to stop trying to be right and take a step back. Look at the big picture and consider the things that we don’t think are it.

Modifications: smartmadness blue 1x1.7 lowering springs, with upgraded silver madness springs to replace coilbound rears. H&R 50mm track spacers rear + 5mm shim per side. H&R 30mm track spacers front + 3mm shim per side. Rail LeMans rear 15x6 wheels all around with Toyo T1R 195/45-15 tires. All under Panamex fender flares in river silver from Madness. Trailer hitch to stiffen the rear/protect the large oil filter.

Unrelated modifications (for fun): SFR header Cat delete, Solo side exit resonator, silicone intake baffle delete. Chin spoiler, eyelids, led fogs, leather floor mats, leather sand seat covers, fosgate audio, scangage, gps digital speedometer aforementioned large oil filter.
 

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Discussion Starter #3
Although I have worked on a racing pit crew, none of that would really transfer here. I was more talking about the racing smarts. Rear sway bars are added to compensate for the stiffer suspension and the wider firmer tires. Your question feels like an attack, really. Did you have a point you wanted to make? There’s no need for debate set up questions. You can just offer your opinion. What I did solved the problem. What I want to do may solve the problem better.
 

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No attack intended. But in a forum like this, it's hard to know a person's level of experience and knowing that helps me communicate in a way that might be the most clear. Just like if I were a medical doctor and knew you were the same, I'd attempt to communicate differently than if I knew you were an accountant.

Anyhow, I was going to say that a major problem with the smart is the difference in front and rear track. That four inches of difference is pretty significant considering how narrow the car is, and in stock form the smart suffers from that weird lean angle like you get when you turn hard on a tricycle. The narrow front track generates too large of a slip angle at the rear tire, which can cause the smart to oversteer, which is why Mercedes Benz put so much effort into designing huge amounts of understeer into the vehicle. Large slip angles also limit what you can do from a driving perspective to compensate for handling imbalances, unless you are running race tires designed to operate at larger slip angles. So my suggestion was going to be to try to equalize the track before trying other fixes. I think you said you used 50 mm spacers in the rear and 30 mm in the front, which exacerbates the original problem.

A rear sway bar is only available from one source for the 451, from Europe. Depending on the current exchange rate and shipping costs, it would be around $600 to land it here in the US. Sway bars are typically used to tune handling balance, and create other problems when used to compensate for too-low spring rates. From what I have been able to find out, none of the aftermarket springs have anywhere near what would be typical spring rates used in a vehicle of the smart's approximate weight. The most often raced vehicle, a first gen Miata, is within 10% of that weight and there are numerous resources to help choose appropriate spring rates for various types of track use and thus the expected grip levels. What is different is that in the Miata world, camber and toe curves through the suspension's range of travel are well known, and the chosen spring rate has to balance placing the suspension in that sweet spot, with the optimal rates for the level of grip that will be developed. These things are not known in the smart world, but what does seem to be is that as the smart's suspension reaches the ends of travel, binding occurs due to the design, so almost certainly a high enough spring rate would be required that would not possibly be delivered in an over-the-counter spring upgrade set. Custom coils are probably the only way to go, probably around 400 in/lbs up front and around 550 in/lbs in the rear. The commercial sets are in the 200-300 in/lb range, which is at the upper end of what is manageable by the stock shocks and probably why the spring rates are specified as they are - and not taking into consideration the narrow track nor high center of gravity. So optimal spring rates will require custom shocks.

Many, many other factors as well, and I love talking about this stuff and trying to figure it out. My personal hope is to get my smart to handle better by doing reasonable things, without making other things worse.
 

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Discussion Starter #6
Sorry for being defensive.

I actually increased the track difference deliberately to keep the front track arc inside the rear track arc for braking stability. With equal track width, any braking in a turn results in the car heading to the outside. It works better for my driving style.

I drove a 453 as a loaner, and it was scary how bad it handled in braking. I attribute this to the equal track width, but I may be wrong. The thing just refused to go straight while braking.
 

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My 453 brakes straight and true. Granted, mine is slightly lowered from the factory and it has the sport package. I've only ever gotten pures for loaners and they aren't the greatest examples of what the 453 can do. My 451 doesn't handle great, though in its defense I set it up for towing and ground clearance for offroading.

Track width on the 453 is not equal.

https://www.smart.com/en/en/index/smart-fortwo-453/technical-data.html#engine1

From a safety perspective placing worn tyres on drive wheels is a recipe for a bad time. As it is the rears already wear faster than the fronts. I just keep replacing the rears until I also need to replace the fronts.
 
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The loaner was obviously stock, and I'll admit, it handled better than my 451 when it was stock. I honestly don't understand how people tolerate the 451 in stock form. I absolutely hated it for the first couple months. it was so frustrating, rocking and bouncing, and my favorite, sliding the front tires in a u turn. So, yes, much better than the 451 in stock form, but still pretty awful.
 

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Our 453 was pretty loose on Waltkins Glen race track , but I found I had way too high psi’s . The 2015 Brabus seems more settled and I can push it a bit bit more . I’m not sure which is better at this point .
 

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I actually increased the track difference deliberately to keep the front track arc inside the rear track arc for braking stability. With equal track width, any braking in a turn results in the car heading to the outside. It works better for my driving style.

I drove a 453 as a loaner, and it was scary how bad it handled in braking. I attribute this to the equal track width, but I may be wrong. The thing just refused to go straight while braking.
A wider front track leads to more stable braking, especially in combination with any turning. Think of it this way - when you brake, the center of mass has momentum that forms a vector that points towards the front of the car and determines the amount of weight transfer to the front wheels. When this vector is centered between the wheels, the amount of weight transferred to the front wheels is roughly equal. Any amount of turning while braking causes this vector to point towards one side or the other. So for any amount of turning and braking, the closer the front wheels are to each other, the more this vector overloads one tire. Also, if this vector is closer to one side or the other, it creates a torque that rotates the car, and again the closer the wheels are to each other, the greater this rotation effect. So to have a car which minimizes the effect of turning and braking, you want the front wheels as wide apart as possible.

My 451, even without the spacers I used, brakes very well in a straight line considering the narrow width of the OEM tires. Stability problems when braking are usually due to unequal braking force across an axle, so it may well be that the 453 you drove had one glazed brake rotor/pads or some other mechanical issue with the braking system.
 
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