Anti Sway Bars 101 (LXi and LX)

[dentmac]

Back to the sway bars.... The CG is moved laterally with the roll. So keeping the roll to a minimal is paramount. With air suspension ,both IFS and solid axle, exhausting the inside and airing the outside has to help. Perhaps not so much in emergency maneuvers but most of us are not at the track.
With IFS ,especially multi link (over "king pin" style ), are the effects more pronounced? Possibly with the geometric differences -- ie Scrub steer?

I would think that IFS suspension requires something-- either solid metal sway bars or "Active Air".
Interesting NHTSA recall here, possibly giving validity.

Ross

Report Receipt Date: JAN 28, 2014
NHTSA Campaign Number: 14V020000
Component(s):
Potential Number of Units Affected: 452
All Products Associated with this Recall expand
Details close
2 Associated Documents expand
Manufacturer: Spartan Motors, Inc.
SUMMARY:
Spartan Motors Chassis, Inc. (Spartan Chassis) is recalling certain 2010-2014 model year MM motorhome chassis manufactured December 11, 2009, through January 30, 2013, and equipped with a sway bar and model 1253 front suspension. This front suspension design has increased rebound travel which may result in a binding condition of the sway bar end link which could lead to the breaking of the sway bar end links.
CONSEQUENCE:
Broken sway bar end links may result in poor vehicle handling, or sway, which increases the risk of a crash.
REMEDY:
Spartan Chassis will notify owners, and dealers will replace the old end links with new end links and an improved mounting, free of charge. The recall is expected to begin in February 2014. Customers may contact Spartan Chassis at 1-517-543-6400. Spartan Chassis's number for this recall is 12012.
NOTES:
Owners may also contact the National Highway Traffic Safety Administration Vehicle Safety Hotline at 1-888-327-4236 (TTY 1-800-424-9153), or go to http://www.safercar.gov.

(11-06-2013 16:18)davidbrady Wrote:  

(11-06-2013 04:36)mhughes01 Wrote:  Are the bars solid steel, David, or castings?

Mike, The roll bar is made by Addco and it's a solid mild steel, low carbon. It could be turned but it might be easier to simply bend a new one. IDB, Addco, or Roadmaster can make up any bar we'd like and we can use a high quality spring steel if we prefer.

I think the ride is intolerable with the bar that Blue Bird used, but that's my coach with my OEM 2.125" diameter bar. Some coaches have a 1.75" bar which is better but others have reported an improved ride by removing it too.

I also run my tag air pressure at 55 psi, my steer tires at 95 psi, and my Koni adjustable shocks set to full soft. The ride is fantastic - I search out bumps on the road just to marvel in the suspensions ability to soak them up! No more dentures jarring or heads banging the ceiling. Even the porpoising is vastly improved. The soft shock setting lets the steer suspension recover quickly morphing porpoising into a gentle heave. It's really very good but as Pete points out your coach and your preferences are probably different.

(11-06-2013 09:20)ernie ekberg Wrote:  haven't some folks taken those off with good results?

Bill Mattocks, principal engineer at Ridewell, and the man who designed our suspension told me that the bar isn't needed and the suspension works just fine without one. Wanderlodge has a long history of using his Ridewell suspension without a sway bar.

(11-06-2013 10:08)dentmac Wrote:  Interesting. Probably too sophisticated for a solid axle in an RV but for IFS the response/change speed would be far better then active air since RV's have high roll and understeer. The article refers to safety aspects of controlling roll and pitch.
Sadly , the Hadley modifications done to the 450 removed the "Sway bar" type function of the active air.

Ross, your coach with its independent front suspension is different from the Ridewell that Blue Bird used on their earlier Wanderlodges - big surprise :-). Our Ridewell equipped coaches have a horizontal roll axis. Your coach probably has an inclined roll axis. Your steer axle probably has a roll center close to ground level. The drive axle's roll center is above the differential. Your roll axis starts off low and inclines upwards as it moves to the rear. On my LXi the roll axis is at about frame rail height and is level from the steer to the drive axle. In a turn your seat-of-the-pants feel is much different from mine. My coach rolls. Your coach rolls and yaws. The front of your coach yaws out of the turn. Because of this you probably feel more movement in the driver's seat than I do. I can see how you might want more roll control.

The safety aspect is interesting. In a high G turn the limit that automobiles approach is loss of grip and a spin-out. The limit that buses approach is a tip over. We all know this is due to the higher center of gravity of our buses. It turns out that if the CG is higher than about half the track width then the limit is tip over; otherwise, it's spin-out. But, we hardly ever hear of buses tipping over. If they do it's usually due to hitting a curb or an embankment or running off the road. All of these things can tip a car too. I think this is due to a bus's CG not being quite as high as we think it is - it's probably closer to half the track width or around floor level. This is why I don't feel that much roll in a turn.

In a turn the CG rotates outward on the roll axis - there's a lateral shift of the CG. If the CG shifts out enough then the bus tips over. The trick with active sway bars is to keep the CG from shifting. This is something that a passive sway bar can't do. An active sway bar can actually roll the bus inward towards the center of the turn to displace the CG to the inside. This creates stability and further removes the risk of a tip over. I don't think HWH Active Air or Hadley SAMS are capable of this; a high G turn will simply pick the bus body up off the exhausted inside air springs. An active sway bar will force it back down.

Incidentally a big advantage that the wide bodies (102") have over the narrow body (96") birds is tip-over resistance. The wide bodies are more stable in a turn.

(11-06-2013 11:08)pgchin Wrote:  FWIW please keep in mind most of the info David posts about LXI suspension changes he's done applies to "his" generation of LXI's, one of the last years with the latest chassis upgrades.

Very true Pete. Each bus is different and needs to be custom tuned and every owner has his preference.