Variable air suspension
 

I've been thinking about lowering my suspension a few cm, to get less drag at highway speeds, but I'm afraid of being too low. The roads here have potholes deep enough to swallow your wheel, plus parking in the city usually involves climbing high curbs. Some cars have a hydraulic suspension system (many old Citroens, some SUV's), but those are heavy and tend to leak. While reading Mike's Insight I saw he added air springs and a small compressor to handle the weight of extra batteries. I wonder how hard and how expensive would it be to install air suspension? I'm thinking about a setup for all 4 wheels, which will let me lower the car 5-10cm on the highway and jack it up an extra 5cm when maneuvering in the city.
Would a project like this be worth the trouble? What kind of parts would I need, would I have to modify the suspension I have? How heavy would everything be?
I've seen jumping ghetto-mobile low-riders
Jumping low-rider
but let's just say I don't want to go that far...

I suppose it would depend on the vehicle but you should be mindful of suspension and steering geometry, wheels don't raise up and down on suspension in a straight line typically.

I had an Isuzu Trooper on which I had installed air shocks on all 4 corners, all of which were cross-linked (shared common air) so that on highly uneven terrain the contact pressure to the ground would be more equal - a dramatic increase in available traction for an independent front suspension vehicle. Because of the air pressure, I had to lower the vehicle from stock height so that when the shocks were pressurized, normal ride height was restored. I had an engineer friend build me a 4-way ball valve so I could simply reach down and isolate all 4 shocks for road travel. The ball valve leaked.... so after 2 or so days the 4x4 looked like a lowrider - but this had a frustrating side effect of dramatically changing the front wheels' camber since Troopers use unequal-length control arms. The top of the tires stuck way out, the bottom sucked in, and the edges of the tires saw most of the vehicle's weight. Obviously not a good thing.

So... lowering your vehicle for aero has merit, but be careful that you've thought it all the way through to make sure it's the right mod for your vehicle.

Piwoslaw -

I've heard you can do it, but it's a lot of $$$. I definitely think it's the best of all worlds if you can afford it. Doesn't a model of Lexus "auto lower" at freeway speeds? Is that an air-suspension-tech solution?

CarloSW2

Me -

Here's one, but I can't find the price :

AccuAir - Air Suspension

Here's one for Pontiac Firebirds, $1100 (US) front and rear :

Firebird Air Suspension Kits to customize your Pontiac

CarloSW2

My mark VIII did this, "for highway fuel economy" it was a big thing apparently in '93

BUt the effect was never quantified. I know a lot of people end up ditching the air compressor and going to regular springs because of the hassle. I wonder if they notice the difference?

That's the thing, I think. Lowering at speed is likely to help fe... but is your fe savings going to pay for your fancy, complicated suspension adjustment system? Probably not.

Coming from someone who has an air suspension for a totally different reason, they are a pain in the arse. Expensive, especially when you consider that in order to control it you will need some sort of valves and switches with air pressure gauges.

Many high end set ups have memory settings where its a simple function of pressing a button to reach a pre determined pressure. But over time the maintenance becomes the hassle. The bags rarely break, but the valves freeze, it is nearly impossible to get a leak proof system and of course the air compressor is noisy, not to mention you need space to store it plus the air tank.

Some have done dive tanks which have 2000 psi and it lasts quite some time with minimal hassle except for the ocassional trip to the dive shop.

So unless it is an oem application that is currently trouble free, all you are asking for is something really cool that requires constant vigilance.

Cost Depends HEAVILY on the vehicle.

I got a used airbag setup for my dad's E-350 for $150 it was ok, ended up spending another $100 on a replacement bag.

You would be amazed how low you can get away with; all of my cars are "slammed" and I go off road more than most SUV's do.

Piwoslaw ,

Google "air bags" for a heap of sites and prices.

Most are Firestone (the largest maker by far) air springs and still require separate dampers.

Basically you will need to re engineer most of the suspension of the car if you go this way.
Expect to provide space for the air tank reservior as well as the compressor. Then the lines and gauges and finally the sir springs and fittings them selves.

Many large trucks and buses use air springs so check out a few of them as well.

The air adjustable dampers available as an accessory for many cars here to give a temporary change in ride height typically of around the + / - 50 mm range may be easier to do.

You will still need a four way adjuster to lower the front at freeway speeds and raise all corners for curbs.

Good luck , Pete.

Most luxury sedans have this, most are automatic, those who don't have one
the owners might install it.

Why, if you don't mind not being so fancy, I used to have regular air shocks in
the back of a Thunderbird, however these are used more to adjust for stiffness
of ride than anything else, such as when carrying a load...

The point I am making, however, is these air shocks are inflated and deflated
like a tire, via a tire valve that the installer conveniently placed inside the trunk.

All it takes is a little planning, and adjust the pressure before going on a trip,
also it has to be checked about once a week or so, like tires.

How hard they are to install, I don't know, spending this kind of money I had it done.
The rear I hear say isn't so bad, which also that's the only place I had them...
Most folks wouldn't dream of putting air shocks in the front, I am not even sure
it can be done.

But I am doing front struts on another car right now, and I can honestly not
recommend this as a DIY procedure... It is somewhat technical but there is a
considerable danger factor involved, and you need special tools.
Also the amount of labor, specifically some parts have been together so long
they are real tough to get apart, even with pneumatic tools this has been an experience.

Several things to consider:
The price, I think I paid $400 installed and all...
But will the meek gains in FE outweigh even that?

Also, like I said, they're mostly used to adjust for stiffness, not height.
So I suspect the reason is hardly FE, why would someone owning a Lincoln
Continental Mark VIII care, there's a dog gone 5.0 V-8 under the hood...

Wow, you guys are going hardcore on this...

Piwoslaw - Just use normal adjustable airshocks that will fit in your vehicle. Someone somewhere will be able to cross reference them for you.

I used to have adjustable air-struts on my first Honda (not for Fe reasons) and I just kept a 20lb CO2 tank in the trunk, the struts were hooked up to valve blocks with schrader valves in them.

Hmmm. Let's see. your typical air ride needs the following parts:

Air springs- $65-75 each and you need 4.
Air tank- 5 gallons about $50
Compressor- Few hundred depending on what type you get.
Valves- $35-60 a piece, 2 for each spring
Airline- pretty inexpensive
Misc wiring and other stuff- $$$

All in all, it's going to be pretty expensive. I plan on doing a full air-ride, but only because it's awesome. :)

Those don't allow any significant lowering do they? Stock springs will keep it up in the air.

The air-struts on my Honda were for highway/road use, and they actually replaced the strut/spring assembly altogether.

Air shocks won't allow a full lowering, like replacing springs would, but they do allow for *some* lowering, by using less pressure in them.

My Sunbird had airshocks on the back (I had a hitch/trailer and needed the shocks to keep it stable) and I could raise it up 3" or lower it down about 1.5" from stock with them, but I'm sure part of that was worn springs.

Oh. See, I replaced all the struts on my car once, and one was completely, 100% blown out. Yet, that corner was no lower.

FWIW, I lowered my truck 4 inches and did realize a 1 MPG improvement. My truck was fairly tall, so potholes and high-centering were not issues to me and my lowering is static.

It does work but whether or not its worth the hassle and expense is a value judgment.

air suspension
 

All the low-drag concept cars of the last two decades have active- variable-height suspension to lower the car for highway travel.So your instincts are correct.As other members have touched on,suspension geometry and durability are big issues.------------------------- The low-riders in the past,used hydraulic suspension,with belt-driven pump and slave cylinder rams at each wheel.The front wheels camber would change radically through full range of motion,and I'd never consider that safe for high speed highway travel.----------------------------------------------------------------- After Ford's development of the PROBE series of concept cars,they offered an air suspension on Lincoln cars.The front suspension incorporated a special air strut with linear ball-bearings,which would maintain perfect wheel alignment at all positions.------------------------------------ The front of the car seems to be the challenge for retrofits.Modern supercars feature active suspension.The Bugatti Veyron comes to mind.I'd look at sucessful modern setups and see if they offer clues to technology you can safely borrow.

Just one point more related to the practical side of lower the car.
A number of years ago I had some idiot following way too close to me in a car much lower than mine on the freeway at around 65 mph (the legal limit here) or so.

Ahead was a truck carrying rubbish from a building site I guess. Doors , window frames , sheet rock for interior panelling, bent guttering etc.

The inevitable happened and two brick concreted together fell of the back and landed on the roadway.
My car just went over the top and no problem.
The car following smacked right into them and there was some considerable damage done.
Anecdotal I know but worth keeping in mind we do need to live in the real world out there.

Pete.

How about lowering the car static, then putting helper bags to raise the car when needed. Far less expensive and simpler to setup. Because you would only need one fill and one dump for all four air bags or shocks. imo

That's probably the best way to go. Lower the car in such a way that the geometry and everything is cool, then jack it up only at low speeds, so handling won't be much of an issue.
Thanx everyone for the advice :)
- Adam

For what it's worth, I have otherwise identical versions of the same model car, one lowered about 1 1/2" and one stock. FE is pretty much the same between them.

Piwoslaw - Get an alignment done for the height that you plan on spending most of your driving time, obviously.

Also - keep in mind that when you "jack up" your suspension, you just might go higher than your springs extend, which will unseat them. This can cause serious problems. This would normally happen only if you have coilover springs, which have been shortened to accommodate the vehicle being lowered, or in any case where the springs don't actually get fastened to both perches.

Also keep in mind that lowering your car isn't really getting rid of that much frontal area, either. The only thing you're really getting rid of are the front/exposed areas of the tires that you're now covering, and any suspension components that might get hidden in the wheel wells or behind something.

The real benefit comes from less air being able to make it under the car, but there are much cheaper/easier ways to accomplish this as well. See: belly pans/Air dams.

They don't necessarily stop the air from getting under there, but if you can clean up the flow, who cares how much gets under it?

Aesthetically, it might look like you've accomplished something major, but MPG-wise, I don't think you'll be satisfied with the result of all your work.

http://www.youtube.com/watch?v=eSi6J-QK1lw
My two cents. . .
Bose® Learning Center - Bose Suspension System
So yeah the idea with bose is you have a very fast EM-motor that allows it to expand and cotnract quickly and fluidly(not to mention dynamically).

If you could find a set of those it would be relatively simple. . .send a signal to expand or send a signal to contract. No leaking problems.

I saw this in PM a few years back. I think the reason it has not been developed is because the components are too long. They are about the same length as uncompressed springs. . .but they don't get much shorter once weight is applied. Causes the vehicle to ride too high.

<edit> which would not be a problem if you pick a chassis with the mounts high enough into the body to set the wheel wells just above the tires. If you were to build a chassis for these you could put the mounts very high on the frame as opposed to a few inches below.</edit>