Air Ride Struts - Opinions

[tfreer85]

Okay there is nothing I love more than a low Z. Now this may seem a little rice to some of you, just don't flame. Coilovers are a great setup, however I don't race autoX or drag for that matter. My Z is going to be a just a very fast street car. So to the question I'm like the idea of having on the fly adjustability of my ride height. I was looking at Air Ride suspension setups ( http://www.ridetech.com/productinfo/shockwave79.asp ) and starting thinking about modifiying the strut assembly to accept something that looks like this.

 

Now a guy has used these on his Porsche and using a design similar to this:

 

 

Another design using "the adjustable struts rather than shocks:"

 

Some more pics of actual creation:

 

Fully installed:

 

For more pics of the setup you can go here and scroll down to Air Ride suspension. http://hypertec.ws/todd_porsche/

 

So would something like this be able to be done on a Z? I have very very little suspension experience so I would be having a professional do it if I were to ever try and do it. But I wanted some opinions on the setup and design and what you guys think of it in general.

 

Tyson

[OlderThanMe]

well the suspension design is similar to a Z's suspension. it is certainly possible with a bit of welding and fabrication...but if you mess up new strut tuves are not cheap...you could have someone experienced build them or someone here do it...it is a little ricey but if you could solidly mount the bottom of the strut to the the spindle then it might be worth the conversion...

[spork]

I had seriously considered doing the same thing, but they didn't seem like they want to help me any and wouldn't give me dimensions of struts that they had so I could source something that would be close enough to work w/ new bracketry. I decided to go a different route. They wanted way too much for their products anyways.

[tfreer85]

Yeah their products are pricey, but I'm used to air-ride and such prices. Have bags (not fast bags) on my custom truck and my dads work truck both for actual purpose. Like I said just trying to think of something unique to give me the lowered when parked and not scrape the hell out of my underbody when driving, I already know what its like its not fun bottoming out your car, you pucker up trust me. Any other opinions for alternative options or anything? Thanks for the replies.

 

Tyson

[Guest nitr0]

The biggest problem with airbag suspension is that it rides like a boat - which would feel ok in a z, but it wouldnt be handeling anywhere near as good as it could.

 

I thought long and hard about this one, and thought the best option for the front would be to secure mounts onto the chassis and Lower Control arms (box the arms for strength) , and get airbags about the size of a standard coke can. The first problems that would arise are alignment and you might be able to mark out some nice alignment specs for different heights on adjustable strut tops.

 

This way (i think) if you pump the bags up a little bit (1-2 inches) the cars ride will be softer when going over speed bumps / driveways etc, but when the bags are empty (2-3psi) the car is getting supported by the springs and the ride will be firm.

 

One of those airstruts on the rear should be pretty easy to adapt and but you might want to put a support spring somewhere in there to help with the load of people in the back and a full petrol tank. - And try to keep a firmer ride. Plus bigger rear sway bars.

 

Just an idea....

[Cruez]

I was watching a show that tested some type of air ride setup that performed BETTER than it did stock, on a track.

[Mike kZ]

I too have thought about this. For me the rear would be easy, I have coil overs on my shortend chevy rear end. It was the front strut, there was nothing out there for it. But with this guys ideas, it could work. The other problem is where to put the tank, and pumps. Not a whole lot of room in a Z to hide those. The Air Ride systems are pretty pricy though.

I have read that these systems improve handling, not make it feel like a boat.

[johnc]

An air bag is just another spring. Your car already rides around on four of them with a rate of about 40 lb. in. per psi. Increasing or decreasing pressure in the bag changes the spring rate and, surprisingly enough, affects ride height and response.

 

One unfortunate side affects of this is: lowering the air pressure reduces ride height but it also reduces the spring rate - which is exactly what you don't want to happen as the car gets lower to the ground.

[Guest PROJECTRB240SX]

Some Companies Make Independantly Ride Height Adjustable Struts And Also Dapening Adjustable Struts. This Is So You Can Increase And Decrease The Ride Height Without Effecting The Spring Rate.

[tfreer85]

The ride with bags can be bad if you have them in only one area i.e. the back. My truck on the freeway is whiplash central, however I've ridden in cars with all around bags and the feel isn't that bad. What I was thinking would be a setup something similar to this, with large sway bars. The only purpose for me would be movement up and down and maybe front and back. No pancaking, or rocking, just basic up and down functions. The only problem I see is with the manual adjustable struts is that its manual. If I had to deal with that I would just go coilovers. I think having a couple of presets would be good, parked, street, and race setup, then you could adjust the pressure accordingly. I think somewhere along 3-4 inches of travel would be the most needed. Thanks,

 

Tyson

[tube80z]

An air bag is just another spring. Your car already rides around on four of them with a rate of about 40 lb. in. per psi. Increasing or decreasing pressure in the bag changes the spring rate and, surprisingly enough, affects ride height and response.

 

A friend wanted to try these on his vehicle. A number of companies were called a few basic questions were asked. Like what is the spring rate of these bags. Long conversations about pressure were given to us but at the end of the day nothing about how pressure changes the rate or any ballpark figures.

 

So I'm not really convinced these would be useful unless you're just wanting to set the car on the ground in a parking lot 'cause it looks cool. And as John mentions they seem to be backwards to what you'd need.

 

Cary "self adjusting my ***"

[Guest nitr0]

tfreer85 i was thinking about exactly the same thing with my setup, 3 settings :

 

Track/Strip (2-4psi, ~85mm ground clearance)

Street Legal (??10-12 psi, 103mm ground clearance - used 90%)

Speedbump/driveway (?18-28psi, 130-150mm ground clearance)

 

Most of the time it will be set to Street Legal height and the car should be aligned like that, you also have to keep some saftey precautions in mind, like when the car reaches a certain speed the pressure should drop top aligned height so if one airbag fails you wont loose as much control. These are all saftey regluations here in Australia.

 

As for tanks and compressor, hmmmmmmm good question. Boot? I have a 280zx 2+2 and i was going to tear out the back seats to make space for water storage / toolbox, fan belts, hoses/ bigger fridge / computer so a small air tank shouldnt be too hard, and a compressor should be able to fit somewhere in the engine bay.

[Ed260Z]

Mercedes has an air ride suspension hybrid set up in alot of their AMG performance cars. It also has 3 positions, but there is only about a 3" movement from lowest to highest.

[tfreer85]

Minimum ride height isn't an issue here or at least not one anyone abides by. I figure most of the setup will be just like a coilover setup, just an air controlled coilover system. The 3 presets I figured on (though you could modify the presets to how you wanted to) would be parked 0psi, driving (optimum ride comfort), then a racing based one. I'm searching for other style air-struts besides air-ride that have a good reputation for quality products. I refuse to use firestone, I've seen too many failures at truck shows. I could be completely wrong but I don't think it would be a hard install or modification to perform, either by a shop or for an experienced fabricater to do. I think cost and the fact that its not performance based is why I've never seen it on a Z. I don't think I'm crazy but let me know.

 

Tyson

[gwheeler]

An air bag is just another spring...

 

One unfortunate side affects of this is: lowering the air pressure reduces ride height but it also reduces the spring rate - which is exactly what you don't want to happen as the car gets lower to the ground.

 

The first sentence is spot on. People claiming that air springs make their momma's Mercedes ride like this or their Uncle Bob's truck handle like that are missing the point. They're just springs. You can get them in all kinds of rates' date=' and all kinds of rate [b']curves[/b]. They must be selected very carefully for each vehicle and intended application. There is one change that always applies though: one less mechanical noise transmission path - all other things being equal means less road noise.

 

That brings us to the second sentence. Many luxury/sports cars use air springs that do get stiffer at lower ride height (lower air pressure). They accomplish this by designing specially shaped "pistons" that increase the volume change for a given displacement change at lower pressures. If you search around Firestone's site you may find some cross-section pics of the progressive rate systems showing the funny shaped pistons (kind of a cone).

 

Bridgestone makes an aftermarket system called Praxxis for Subaru WRX and BMW 3-series that uses this concept. You put it in track mode and the car drops AND firms up significantly.

 

In my opinion this is quite a cool invention since it is contrary to common sense. I hope someone does figure out a HybridZ installation.

[tube80z]

That brings us to the second sentence. Many luxury/sports cars use air springs that do get stiffer[/b'] at lower ride height (lower air pressure). They accomplish this by designing specially shaped "pistons" that increase the volume change for a given displacement change at lower pressures. If you search around Firestone's site you may find some cross-section pics of the progressive rate systems showing the funny shaped pistons (kind of a cone).

 

That's very interesting. I wonder why no one could give me rate versus pressure info then. I wouldn't put these on a car until someone can answer basic spring rate questions.

 

Cary

[Ed260Z]

I was trying to link this info, but you would need a password to get in. May be this can give someone an idea of how to make a compact Air Ride system. This is a lot more complicated than any of us would ever need, since it also incorporates an anti roll feature.

 

 

ADS dampers

 

The ADS dampers are basically similar to the 220 series. At the front axle, they are integrated in a spring strut, while at the rear axle they are located separately parallel to the air spring. The gas pressure dampers are friction-optimized by using a step-seal. The gas pressure has been lowered to achieve good roll control and response, which necessitates an additional valve.

 

 

40 Left front axle ADS shock absorber y1 Front axle solenoid valve 1Y51 Damping valve y2 Front axle solenoid valve 2

 

 

 

 

The adjustment of the damping forces is controlled in the damping valves (Y51, Y52, Y53, Y54). A damping valve is installed at each wheel between the upper and lower chamber of the single-tube gas pressure shock absorber integrated in the spring strut. Each damping valve features two electromagnetic valves (yl, y2), which, depending on how they are operated by the SAS control module with ADS, permit four different damping force stages.

The extremely short reaction time (in the milliseconds range) ensures that the optimal damping force stage is available with practically no time lag when a sudden change in the vehicle state occurs, such as an avoidance maneuver.

 

Pressure supply

 

The electrically driven compressor is positioned in the left of the front end and comprises an electric motor (400 W), an electronically actuated outlet valve and a pressure relief/residual pressure valve. An air drier stores the moisture contained in the inducted air, and, when the moisture is drained, the air drier is regenerated by the dry air of the system. A paper air filter is integrated in the air intake passage.

 

With the aid of the compressor it is possible to produce the air pressure required for raising the vehicle. The load current of the compressor motor is switched through a relay. In particular operating states (wake-up, central reservoir empty) the compressor is also permitted to run when engine OFF. The compressor is operated provided the charge state of the battery permits subsequent engine start (engine start has priority). For this reason, the control module monitors the on-board voltage before the compressor is switched on and during the time it is operating.

 

 

Power of compressor motor 400 WPeak current consumption <100 AContinuous current <35 ACurrent consumption if system free of faults approx. 25-30 A

A9/1 Compressor unita Intake air filterb Pressure relief/residual pressure valvec Air drierg Plastic linem1 Electric motor

 

 

 

 

 

 

Level valves

The level valve output stages are dimensioned as follows:

* The solenoid valve must reliably operate within the specified nominal voltage range.

* In the function mode a maximum of 2 level valves, or 1 level valve and the central reservoir charging valve, are actuated simultaneously.

 

 

Switching valves for additional air volume

* The switchover valves for the additional air volume, located at each wheel, are integrated in the spring struts.

* It is possible, by switching over the valves, to influence the spring characteristic curve.

* Large volume -> comfort

* Small volume —p sport

* The basic setting of the valves is opened (large volume)

 

Note:

* A further two additional air volumes are engaged at the rear axle.

* At the front axle the air volume is split within the spring strut without an additional air volume (additional air reservoir) Sequence for actuating compressor unit A9/1

 

Component

N51 SAS control module

K67 compressor unit relay

f74 4OAmax.yellow

A9/1 Compressor unit Installation position

Passenger footwell/below supporting plate

Driver-side SAM rear right (green)

Passenger-side SAM

Left front wheelhouse

 

 

 

Valve unit (Y36/6)

 

The valve unit (Y36/6) is installed on the same mounting plate as the compressor, offset to the left side.

 

It comprises the air distribution for all the components connected to it.

1 connection left front axle

1 connection right front axle

1 connection left rear axle

1 connection right rear axle

 

 

 

Pressure sensor

 

The pressure sensor is located between compressor (pressure outlet side), the level valves and the central reservoir charging valve. The pressure sensor measures the central reservoir pressure and, if necessary, ensures that the reservoir is replenished. The position selected for the pressure sensor makes it possible with “skillful†actuation of the valves, both to measure the central reservoir pressure, as well as to detect the individual spring strut pressures. Central pressure charging valve

 

The central pressure charging valve is required for charging the central pressure through the compressed air compressor. Once the desired pressure is reached, compressor and central reservoir charging valve are switched off. The top cutoff pressure for charging the central reservoir depends on the ambient air pressure. This is obtained over the CAN from the engine control module. If the connection to the engine control module is interrupted, the ambient air pressure is set to a fixed value in the control module.

If the compressed air reservoir is used for raising the vehicle, the central reservoir charging valve and level valves must be opened. Assuming an adequate pressure difference between central reservoir and spring bellows, the compressed air is able to escape into the spring bellows. The vehicle is raised.

 

 

Pressure reservoir

 

The aluminum pressure reservoir has an air volume of 3.8 liters and is located in the right of the trunk. The task of the pressure reservoir is to store the air volume and to make it available to the system as necessary. In addition, it is possible to achieve post-control processes using the air volume, in which the compressor either does not run, or starts.

[Ed260Z]

Here is a better shot of it.

 

Design

 

40Front suspension strutmRubber mount rebound stopaRubber mount jounce stopnSuspension strut support bearingbTop wiperoHydraulic pipecTop spring platepTop guide sleevedPiston rod tubeqHigh-pressure sealeAustenitic piston rodrSteel springfPosition magnetsProtective bootgHydraulic cylindertHydraulic cylinder bottom stophBottom guide sleeveuShock absorber piston rodiBottom wipervShock absorberjInner bump stop822/4 Left front suspension strut motion sensorkk Outer bump stopB22/5 Right front suspension strut motion sensorlBottom spring plate

 

41Rear suspension strutnSuspension strut support bearingaRubber mount jounce stopoHydraulic pipebTop wiperpTop guide sleevecTop spring plateqHigh-pressure sealdPiston rod tuberSteel springePiston rodsProtective bootfPosition magnettHydraulic cylinder bottom stopgHydraulic cylinderuShock absorber piston rodhBottom guide sleevevShock absorberiBottom wiperwLower mountjInner bump stopxHigh-pressure sealkOuter bump stopB22/1Left rear suspension strut motion sensorlBottom spring plate822/Right rear suspension strut motion sensormRubber mount rebound stop

The suspension strut forms a unit comprising hydraulic cylinder, steel spring and shock absorber. The suspension strut motion sensor is integrated in the hydraulic cylinder.

 

The shock absorber is a twin-tube shock absorber with gas preload.

 

[gwheeler]

That's very interesting. I wonder why no one could give me rate versus pressure info then. I wouldn't put these on a car until someone can answer basic spring rate questions.

 

Cary

 

While selecting air springs (but not for small automotive applications)' date=' I've had good luck getting detailed specs from Firestone's web site. Here's a link to one of their catalogs/guides with lots of good info for techies:

Engineering Guide

 

I also got good support from their engineers over the phone. I suppose if you buy through a reseller (of whatever brand) they wouldn't know any engineering details.

 

Here's the Praxis: http://www.praxissystems.com

 

By the way, that Mercedes system with an external auxiliary volume is a similar concept as I was describing - but more complex. Typically German. After owning an Audi 4000CS quattro for a while, I promised myself I'd never buy a German car again. But dang they make some neat stuff...

[Ed260Z]

Yehh they do tend to overcomplicate their creations a bit. But they do have some cool stuff.