Legendary Bose Magic Carpet Suspension Is Finally Going Global

Citroën pulled out of the North American market in the 1970s, due to US regulations that required headlights maintained a consistent height. Since their suspensions allowed them to raise and lower their height, there was no way they could be compliant without massive changes to their system. Besides, the Citroën network was not big in the US anyway, and since the DS had few facelifts in its 20 years in production, it was falling out of favour with US consumers who didn't want to be seen driving yesteryear's car.

Their build quality is fine, at least contemporarily to the rest of the market; of course today, we would find its steel pitiful. It's not without reason that people who maintain Citroëns of that era tend to replace the panels with fibreglass ones.

Additionally, as Citroën pulled out, the maintenance network in North America began to falter, as the suspension system required significant know-how. There are still a dedicated group of Citroën fans in North America (albeit small), and I met a lot of them when I drove from coast to coast (and back again) back in 2017 in a 1998 Citroën Xantia. A car that may not seem particularly interesting to Europeans (although it was the Activa V6 model), but it was extremely rare in North America.

Just yesterday I was remembering the ride on a Citroen XM in the 90s which has the full blown hydropneumatic suspension (https://en.m.wikipedia.org/wiki/Hydropneumatic_suspension) . Decades later I haven’t been in a car with such a smooth ride

I can confirm. Was driving for a while, impervious to any sign of having a flat tyre before someone on the street signalled me to stop. And that was on a Citroen Saxo, which I don’t think had the suspension of C5 etc. Amazing car, lasted for 15 years with me, with only battery and frankly inconsistent oil changes. The lady who bought it when we immigrated still runs it 15 years later. Build quality is a hit and miss per model I think.

It's not the same.

For a simple example, let's say you are simply driving in a circle. The car wants to lean toward the outside. The linear motors can provide a countering force, lifting the outside, lowering the inside, so the car stays level. Variable damping can only control the rate that it rolls. It will still roll in sub-second timescales, unless it completely locks down the suspension, which is terrible for both handling and comfort.

For another simple example: going over a speed bump. Linear motors can lift the front wheels over the bump, and then the rear wheels, so the body stays level the whole time. An active damper can go full-soft the moment the wheel hits the bump, but the compressed spring will still start lifting the front of the car. An active damper can do a better job managing the rebound on the far side so it doesn't oscillate, but it can't entirely prevent the bump from pitching the body up and down in the first place.

That's not to say it's worthless. Very fast active dampers can improve both handling and comfort. It's just nowhere near the level which is possible with linear motors.

It's easy to underestimate just how slow digital systems are in many real time scenarios compared to analog systems.

Consider it in the context of camera based self-driving cars, it's tangential to this discussion but it's an easy to visualize metaphor:

- A car traveling 60mph is traveling at 88 feet per second

- Assuming a 60hz camera, there would be a 16.67 ms gap between each frame

- The car is traveling 1.5 feet between each frame interval

- A certain amount of exposure time is necessary for the camera to generate even 1 frame or it will be blurry

- High framerate cameras often work around this by staggering/interlacing multiple sensors, but doing this implicitly increases the latency of each frame

- A 120hz camera might deliver double the frames per second, but each frame could be arriving 4 frames late in exchange

- 4 frames would be imperceptible to humans, it would be 3 feet for the car

- You haven't even processed any of these frames yet.

- Your off the shelf library introduces a random 1 second delay for some reason and costs you 88 miles in processing time

- The car can drive as fast as 120mph

All digital sensors implicitly have a sampling frequency, and the fundamental disconnect is always high sampling frequency =/= low latency. People constantly make this mistake over and over, and by the time you notice you are already too deep into development to make a change.

Decreasing latency is expensive, and requires specialized knowledge. Often you get expert software engineers who end up bottlenecked by the hardware limitations they can't even comprehend or the reverse, hardware guys bottlenecked by the software they can't introspect. The latency is only truly understood when you get to integration testing.

Nearly every step of the way you discover you need specialized hardware, software, operating systems, sensors. Every part of the chain each costing you more latency. It's like it's own ecosystem where almost everyone writes everything from scratch and doesn't share anything. It's gotten better in recent years though.

Full disclosure: I work in medtech and don't actually deal with cars, but it's a very similar problem space. We often use the same hardware/software cars use for this reason.

Precision, repeatability, responsiveness.

I would guess this feels quite a bit different, the clearmotion tech puts electrohydraulic actuators in every corner of the vehicle and is proactively pushing and pulling wheels. MagneRide isn't even active (maybe semi-active, not sure) - never mind predictive and proactive.

Adjusting damping rates is very different from proactively lifting a wheel just as it reaches a bump.

At one point, Bose was a few scientists who happened to have a consumer tech company.

that was the joke

Which is exactly why you want that suspension.

Both this and the Bose linear actuator one lift just the wheel that needs lifting, just enough to clear the obstacle, keeping everything perfectly steady, it's incredible.

The fact that it can also do silly jumps for marketing reasons is a different topic.

> While cool as a shower thought, in reality, having a 1200HP car jump and go airborne while you're swerving to avoid a pothole is just about the last thing you want it to be doing.

Surely the system takes cornering into account. Having a suspension that can use predictive motions to compensate for a pothole would ideally produce better handling by minimizing the disruption of a pothole imparting a massive disturbance to the vehicle.

Even though they're the cream of the crop of a country of over a billion people, those silly engineers at BYD don't know what they're doing. We'd all be better off if they took tips about this problem they've spent years developing from random guy on the internet.

They just tried something like this in some city in Minnesota (I think) and had to revert after a month from the public outcry.

> so you can hit them at significant speed and not damage anything.

That’s the point. They’re not supposed to damage the car. They’re supposed to be a little uncomfortable if you’re going too fast.

It’s more reminder than a physical stopper.

> In fact the faster you hit them or the more load you're carrying the better the suspension handles it because you open up the high speed compression valves.

This is a case of knowing just enough about a topic to be dangerous.

Entering the higher shaft velocity part of the damper curve doesn’t mean the suspension is handling it “better”. The high speed behavior of the valving simply means the damping forces aren’t increasing linearly with shaft velocity. They trade extra travel for reduced peak forces.

Make no mistake, though. The faster you go, the higher the forces. The high speed valving (if the OEM dampers are even digressive) isn’t changing that.

If the speed bump is tall enough and the bump stops get completely compressed you could bottom out the damper, which is not good for it.

> I'll often hit them at 30mph+ with no issue.

Just because nothing immediately breaks doesn’t mean you’re reducing the life of the OEM dampers. Repeated high speed impacts and will shorten the life. Getting the wheels bumped up into the range where you’re compressed bump stops transfers a lot of energy into the bushings and other components.

> Rolling over them at a slower speed where your shocks stay uncompressed forces your whole car to go up and then down again, instead of absorbing the energy in the shocks.

That’s the ideal way to do it. This is better than the sudden sharp impact of high speed crossing. You’re not doing your car any favors by driving quickly over speed bumps. Fortunately for you, OEM replacement dampers aren’t too expensive but replacing prematurely worn bushings is kind of a pain.

Properly built speed bumps are most comfortable to traverse at posted speed, but are very well felt when you're speeding. In my experience they build them well in Northern Europe, less so in Eastern.

If it's the posted speed that's exactly how the bumps are designed. You aren't supposed to brake.

Speed bumps are much rougher in my idiot monster truck than they are on my Mercedes station wagon, idiot monster truck spring rates and damping are engineered to tow heavy loads/carry heavy payloads so especially when unloaded speed bumps are quite jarring compared to a passenger car.

timing chains at the back of the engine

Smallblock Chevys have a timing chain at the front but it's basically never a failure point. I agree with your other points, however; the trend is to optimise for short-term efficiency and cost, resulting in complex and relatively fragile designs.

> CVT transmissions

Well, you can take money out of an ATM machine to pay for that. Just try to remember your PIN number.

Yeah, I'm adding Audi to the list. Car just totaled for a blown engine with no determining reason a few months out of warranty. Audi won't touch it. Not worth the engine replacement cost.

Not sure it would make sense to design cars to fail right when they get them back from the lessee?

The first few roundabouts I encountered were terrible. One was next to a school, yet it was too small to be navigated by the school bus. One had stop signs instead of yield at every entrance.

As a result, I hated them until years later, when I encountered one that was done correctly. After that, I completely flipped my opinion. Done right, they can completely beat a traffic light for wait time and throughput.

A general reason: they take up a lot of space. Not a problem in most of America, but that'd be a deal killer in Japan. If you're not familiar with Japanese neighborhoods, I'd recommend spending some time on street view - it's actually kinda cool. Make note of the parabolic mirrors at the intersections.

For America specifically: they're not a great fit for places where everything is spread out and the road system is sensibly designed. I can drive from one side of Tulsa to the other (on streets, not freeways) in a fraction of the time I could drive across a similarly-sized European city. That's because the city itself is designed for cars. It has straight major streets with 40-45 mph speed limits that form a grid. Neighborhoods sit inside the grid and the streets in them curve with the landscape. In most of the city you have maybe 3-5 traffic lights per mile on the major streets, so unless it's rush hour you get minimal slowdowns. Sometimes I can drive several miles without hitting a red light.

The ideal situation is to have a straight road with no traffic directly between you and where you want to go. Obviously, that's not possible. So you have to compromise. Roundabouts suck, but they're better than almost any other option in places that have twisty narrow streets and lots of pedestrians. Many (most?) American cities aren't like that (at least to the extent European cities are), so roundabouts don't make as much sense here.

> I've heard they aren't common in America

They're getting more popular in the Puget Sound area. We have been re-engineering streets to include roundabouts all over the place. I think they're a great thing, but too many people still stop at the wrong time.

They take up a lot of space and they can be inconvenient and potentially unsafe to pedestrians. Unsafe for the same reason that right turns on red are unsafe: drivers are looking to their left for traffic and not to their right.

They were rare in the US before, I want to say, 15 or 20 years ago but I see them all the time now and new ones are always being installed. Good traffic devices, with the above tradeoffs in mind.

> I've heard they aren't common in America.

They are in the Northeast. But they don't always keep bad drivers away.

Yes, there are some cross intersections that are turned into very tight roundabouts as speed control. They essentially just plonk an island in the center, and maybe cut the corners a bit to sort of round it out. Most people slow down when crossing them.