Active Air Suspension: Reliability?!

[dmckinstry]

Even metal coil suspension can have different settings (changeable by a service center). Not sure if that is common, though.

Probably not necessary, because variation of total weight with different number of passengers will far exceed difference in weight with different pack sizes.

 

[SuperCoug]

I asked the reps at the Bellevue store about the different weights of the various battery sizes and they told me on several occasions that there is NO DIFFERENCE IN WEIGHT between the 40, 60, and 85 Kwh batteries because they have artificially weighted the empty chambers on the smaller battery packs to preserve what they claim is "almost a perfect 50/50 balance front to rear". While it is odd that an EV would choose to carry extra dead weight it makes sense that all cars would need to weigh the same in order to ensure ideal handling without the need for modified suspensions.

 

[doug]

I asked the reps at the Bellevue store about the different weights of the various battery sizes and they told me on several occasions that there is NO DIFFERENCE IN WEIGHT between the 40, 60, and 85 Kwh batteries because they have artificially weighted the empty chambers on the smaller battery packs to preserve what they claim is "almost a perfect 50/50 balance front to rear". While it is odd that an EV would choose to carry extra dead weight it makes sense that all cars would need to weigh the same in order to ensure ideal handling without the need for modified suspensions.

Might be more for the crash testing. With three significantly different weights, they might need 3x the crash tests for safety verification.

You'd think that if they are using fewer cells for the lower capacity battery packs, they could place them in such as way as to maintain the weight distribution.

 

[VolkerP]

Yes, adding dead weight to a partial empty battery pack to keep the 50/50 weight balance seems completely hilarious to me. We are talking about a marvel of engineering here, right?
The point with constant weight for crash testing purposes might be of substance. But many other cars come with different weight e.g. 4cyl vs. 6cyl ICE or gasoline vs. diesel engine. Neither would require to repeat crash tests, right?
If there is dead weight in the 40kWh pack, that's one more reason to upgrade to the 60kWh pack.

Edit: We're talking about a difference of 20kWh between 40 and 60 on a 18650 cell with 9Wh and 46g weight, that gives 2222 cells weighing 102kg (223lbs). Add some weight for packaging into ESS bricks, I arrive at 250lbs.

 

[jerry33]

I would have thought that they would just shift the cells to the centre of the pack to preserve the weight balance.

 

[Doug_G]

For crash testing they probably have to maintain the same overall weight and distribution.

 

[ckessel]

there is NO DIFFERENCE IN WEIGHT between the 40, 60, and 85 Kwh batteries because they have artificially weighted the empty chambers

Heh, way back I mentioned I thought they might do this and was told I was crazy.

 

[zdre]

there is NO DIFFERENCE IN WEIGHT between the 40, 60, and 85 Kwh batteries because they have artificially weighted the empty chambers on the smaller battery packs.

Since I am getting 40kWh pack, this is very concerning. Having dead weight in a car is not acceptable to me. I can't imagine that Tesla would go this route since the rest of engineering is so elegant.

 

[VolkerP]

I see the point that shedding some estimated 250lbs near the bottom of the car might invalidate the results of the "rollover probability" crash test.
But adding dead weight in a car which was engineered for lightweight construction just won't fit easily into my brain.

 

[ckessel]

But adding dead weight in a car which was engineered for lightweight construction just won't fit easily into my brain.

The advantages of modularity and consistency apply in almost any mass produced item. Cheaper on various counts (machinery, crash testing, etc) if the batteries all appear identical in form factor.

 

[stopcrazypp]

The 60kWh and 85kWh packs will use the same amount of cells, so there would be no need to add dead weight for the 60kWh pack. (The cells in the 85kWh pack are slightly heavier at 45.5g vs 44g, but if I remember correctly, the resulting pack weight difference is only ~25lbs).

The 40kWh pack is a different story though. But it still seems less than ideal to add dead weight. It should be possible to spread out the modules to even out the weight distribution, without adding dead weight.

People would reservations should ask their customer rep (not just store reps, which may or may not have an accurate picture of engineering details) to verify how they are handling the different battery weights.

 

[doug]

The 60kWh and 85kWh packs will use the same amount of cells, so there would be no need to add dead weight for the 60kWh pack. (The cells in the 85kWh pack are slightly heavier at 45.5g vs 44g, but if I remember correctly, the resulting pack weight difference is only ~25lbs).

Do we know that for sure? At the October event, it was yet to be decided if the smaller battery packs would be using different cells or simply a fewer number of the same cells as in the 85 kWh pack.

I agree that the weight distribution issue has less to do with front versus rear, but rather above versus below the belt line. I.e., the vertical position of the center of mass. As point out by Peter Rawlinson in one of the videos, the Model S (by design) is using some uncommonly thin (anti-) sway bars.

This is reminiscent of a conversation we had about the Tango.

 

[SuperCoug]

Can someone knowledgable on suspensions compare and contrast the two types available on the Model S? (Adjustable Air vs Traditional coil) For example, this is what is listed on the Model S Specs page under Suspension: "Double wishbone, virtual steer axis coil spring front suspension and independent multi-link coil spring rear suspension". This sounds like they are describing the traditional spring suspension but perhaps I'm wrong and these components are common to both types. Please advise. Thanks to all who reply.

 

[gg_got_a_tesla]

The Specs page lists the standard ones so, yes, that describes the standard coil suspension.

 

[spatterso911]

Can someone knowledgable on suspensions compare and contrast the two types available on the Model S? (Adjustable Air vs Traditional coil) For example, this is what is listed on the Model S Specs page under Suspension: "Double wishbone, virtual steer axis coil spring front suspension and independent multi-link coil spring rear suspension". This sounds like they are describing the traditional spring suspension but perhaps I'm wrong and these components are common to both types. Please advise. Thanks to all who reply.

You are reading the traditional coil suspension, which is the base suspension for the Model S. The Active Air suspension uses 4 wheel air bladders and a compressor system to inflate/deflate the bladders. This allows the car to self-level, and be raised/lowered by commands or computer input. The air bladders function as the "springs" present in a coil system. The suspension geometry remains the same for both cars, however, with double wishbone, virtual steer axis joints up front, and multi-link joints in the rear, just replace coil spring with air bladder.

Either way, the car should handle well, but with the air suspension, expect a more supple ride, plus the added benefit of the ability to lower the car for loading, raise the car for steep driveway access or weather conditions, and allows the computer to lower the car a bit during highway driving.