Anti Sway Bars 101 (LXi and LX)

[davidbrady]

Here's a document with a good drawing of the anti-sway bar (#7 in the drawing) that came standard on my LXi:


  0024707.pdf (Size: 165.15 KB / Downloads: 841)

[davidbrady]

Here's some interesting reading on TRW's active hydraulic sway bar.
  TRW Hydraulic Active Stabilizer Sway Bar.pdf (Size: 965.72 KB / Downloads: 882)

[mhughes01]

Are the bars solid steel, David, or castings?

If solid, would be interesting to see how much they would have to be turned down to get the spec to where you wanted. I guess one could calculate that from dimension D in your earlier drawing providing the 500,000 factor wasn't specific to a grade of steel ???

I notice ours rides like a brick sh*t house on expansion joints on interstates. But it don't roll much - actually very good on tight curve mountain roads in BC! It's bad for porpoising though sometimes on badly engineered roads. There is one short stretch just entering the south of Edmonton that damn near bounces me out of the air seat every time I go over it.

[ernie ekberg]

haven't some folks taken those off with good results?

[dentmac]

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.

[pgchin]

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. Between 95 and 2003 there are "several" iterations of chassis setups, cradles, bars, no bars, etc........ so do your homework and make changes as appropriate. Mike, the older LXI's are more like the 95-97 WB's, than the newer LXI's. - yes brick houses to quote ole Lionel like you did..... David already posted the chassis #'s and suspension styles / generations to help you and other members decide how best to improve your ride and if his work will help your particular LXI.Bottom line one size does NOT fit all, even in the LXI line............

[davidbrady]

(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.

[mhughes01]

This is an absolutely fascinating thread. I am learning so much.

David, are you a Mechanical Engineer by trade? I find your knowledge of physics and ability to turn it into plan English very inspiring.

[davidbrady]

Thanks for the compliment Mike, I appreciate it!

My foundation is 2 degrees in electrical engineering, which I was driven to because I enjoy math, plus I wanted to delay the real world for as long as possible... (more time to drink beer)! My advice to my nieces and nephews (despite their parents angst) is to delay careers, marriage, and children for as long as possible. LOL!

Growing up my brother and I could always be found at the local autocross track with our Triumphs and MGs while our friends did the straight line thing in their muscle cars. Later as my career developed it was Porsches and BMWs and track days with local clubs - Lime Rock to Thunderhill. I've always had a passion for suspension tuning and handling; I can't get enough and continue to be a student of it. I'm very happy to contribute what I can, in plain English if possible! :-)

[mhughes01]

Cool, I guess circuits can oscillate like springs to. Lol.

Was in Engineering Physics myself for a bit, but I never finished. 13 courses a term was just too much and left ZERO time for fun.

Always wish I had done Mech Eng and completed.