I was working on my web site the other day and found some data from a suspension lowering module I did for MB's active air. Like Tesla, MB uses Continental springs and potentiometers on all four wheels.
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Active Air - Small bit of nerd candy
- Thread starter lolachampcar
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- Driving Dynamics Model S
Tesla sent following email to lolachampcar, a member of this forum, in response to the same question:
"Bill,
Thanks for bringing this up but this statement is actually correct. Air springs by
their nature automatically adjust stiffness in response to load. This means that the
ride frequency remains constant even with large loading changes. This is why you now
often see air springs on the back axles of heavy trucks. The reason for this is that
in order to maintain ride height, the spring must adjust the air pressure inside the
spring. This change in pressure also gives a change in spring rate. Since the ride
frequency is governed by:
2*pi()*sqrt(K/M)
Where K = spring rate and M = sprung mass,
If you change K and M in equal measure, the frequency stays the same. This is one of
the cool things about air springs.
The spring will also change stiffness slightly with ride height since the spring is
now riding on a different portion of the piston which will almost certainly
correspond to a different stiffness since it is almost impossible to make an air
spring truly linear.
Please feel free to pass this along to the other forum participants."
"Bill,
Thanks for bringing this up but this statement is actually correct. Air springs by
their nature automatically adjust stiffness in response to load. This means that the
ride frequency remains constant even with large loading changes. This is why you now
often see air springs on the back axles of heavy trucks. The reason for this is that
in order to maintain ride height, the spring must adjust the air pressure inside the
spring. This change in pressure also gives a change in spring rate. Since the ride
frequency is governed by:
2*pi()*sqrt(K/M)
Where K = spring rate and M = sprung mass,
If you change K and M in equal measure, the frequency stays the same. This is one of
the cool things about air springs.
The spring will also change stiffness slightly with ride height since the spring is
now riding on a different portion of the piston which will almost certainly
correspond to a different stiffness since it is almost impossible to make an air
spring truly linear.
Please feel free to pass this along to the other forum participants."
ra-san
Member
You know, just as an aside, I really treasure the responses we sometimes get from Tesla that are straightforward and full of information, whether they are a proper technical answer to a technical question, or a straight-talk, no marketing or legal speak straightforward, plainly spoken answer to a policy question, feature discussion, whatever.
While I see occasional non-answers come out of them, and each of them slightly erodes the bond I feel with them, it's the other type that have thus far characterized my interactions with them, and are what really built the bond in the first place and continue to strengthen it.
If anyone from Tesla is reading this, I hope you take it to heart and pass it around that that investing in really good answers and carefully cultivating that as a company habit pays real and lasting dividends.
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Should also add, Lolachamp, I've really appreciated your contribution to the forums and have especially found your suspension, wheel, and tire posts very helpful. Thanks for continuing to contribute.
While I see occasional non-answers come out of them, and each of them slightly erodes the bond I feel with them, it's the other type that have thus far characterized my interactions with them, and are what really built the bond in the first place and continue to strengthen it.
If anyone from Tesla is reading this, I hope you take it to heart and pass it around that that investing in really good answers and carefully cultivating that as a company habit pays real and lasting dividends.
- - - Updated - - -
Should also add, Lolachamp, I've really appreciated your contribution to the forums and have especially found your suspension, wheel, and tire posts very helpful. Thanks for continuing to contribute.
Well you should expect engineer-speak from them as opposed to market-hype. What's neat is that they are allowed to speak to us directly.
@LCC: re those charts: Is there ever a speed where the MS Active Air is fast acting enough to actually level out the ride as the car goes over a 90 degree speed bump, for example? The 1968 Austin America's HydroLastic Suspension was able to do that passively thru tubing and fluid suspension cylinders (rubber bladders).
Yes, the ride in Very High around the ranch is quite firm with reduced compliance (not the best term perhaps).
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@LCC: re those charts: Is there ever a speed where the MS Active Air is fast acting enough to actually level out the ride as the car goes over a 90 degree speed bump, for example? The 1968 Austin America's HydroLastic Suspension was able to do that passively thru tubing and fluid suspension cylinders (rubber bladders).
Yes, the ride in Very High around the ranch is quite firm with reduced compliance (not the best term perhaps).
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ra-san,
I fear that the quality communication will decrease with time as Tesla gets bigger (can not possibly talk with all the customers that want to talk with them) and some of those customers act like children and "bite the hand that feeds them" by bitching or otherwise causing trouble with the information they are given. For my part, I too really appreciate the ability to ask questions and get honest answers. I try not to ask too many for fear I will wear them out
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I think the Tesla system is just like the MB system in that all it can do is pump air into the springs and bleed it off. I believe there is only one speed which is that which you see when you raise and lower your car.
I fear that the quality communication will decrease with time as Tesla gets bigger (can not possibly talk with all the customers that want to talk with them) and some of those customers act like children and "bite the hand that feeds them" by bitching or otherwise causing trouble with the information they are given. For my part, I too really appreciate the ability to ask questions and get honest answers. I try not to ask too many for fear I will wear them out
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I think the Tesla system is just like the MB system in that all it can do is pump air into the springs and bleed it off. I believe there is only one speed which is that which you see when you raise and lower your car.
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