Ride Height and Ride Quality and Ridewell

[davidbrady]

I find myself thinking about something Bennie Collier told me a long time ago. He said the LXi rides better when the steer axle ride height is set lower than the drive axle's.

When setting the axle ride height I've always blindly followed Ridewell's recommendation of 8" +-3/16" at both the steer and the drive axles. This seems reasonable because both axles use essentially the same air springs. The air spring part numbers are different but that's mostly because of differences in the air fitting location and mounting bolt holes. The bellows and the pistons are the same parts on both the steer and the drive axles, so I've always set my ride height to their recommendation, basically 8 inches.

We often talk about the Blue Bird Bounce or as some call it, Porpoising. We all know what it is because it's something all Ridewell suspension equipped Wanderlodges do.

The technical term for Porpoising is Pitch. Pitch is vertical displacement of the bus body on it's suspension but in opposite directions at each end. The front goes down while the rear goes up. At some point between the axles there's no up or down movement, that point is the pitch axis.

It turns out that pitch isn't dependent on the center of gravity location or the suspension geometry, it's dependent on the spring rates at the drive and steer axles.

Imagine an extraordinarily stiff drive axle suspension and a soft steer axle suspension. In pitch all of the motion will be at the steer axle and the pitch axis would be the drive axle. Alternately, we can imagine a stiff steer axle and a soft drive axle, now the pitch axis will be the steer axle and all the vertical motion would happen at the drive axle.

Without having "yet" done any experiments, I think our pitch axis is way back close to the drive axle. After all, the springs are stiff on the drive axle as compared to the steer axle. The effect of this is a lot of vertical motion at the steer axle as we all feel through our captains seats.

What does this have to do with Bennie's advice? Well lowering the steer axle ride height has the effect of stiffening the air spring. Now we've moved the pitch axis forward. In theory, we've reduced the vertical motion felt through the captain's seat.

Remember, this is all theory - I haven't yet experimented but I will! I'm going to play around with lowering the front in very small amounts followed by test drives. I seem to recall Bennie suggesting 3/4ths of an inch. I wouldn't go any more than that. In conjunction we could raise the rear slightly to soften it.

[Arcticdude]

So what does the math say the spring rates will change from/to with a 3/4" lowering of the front?


Another question might be how would adding a ping tank to the front bags change the rate? It would seem to me to soften the rate, so maybe we really just need pings on the rears only?

[davidbrady]

John,

I'll have to check the charts, that is if I can find curves for the loads that we see on each axle. Bennie never said lower the front; he said their should be a 3/4" difference, so we could set the drives to 8 3/8" and the steers to 7 5/8", just for grins. That's only 3/16ths of an inch outside of Ridewells settings. We still want soft in the front but we want it stiffer than the rear relative to the weight it carries. Wish I had numbers to throw at it. I'll see if I can come up with some charts. The easiest thing is to just give it a try.

I'm leery of ping tanks on our buses after seeing what Prevost does to make them work on theirs. They added tanks but then they added conical bump stops inside the bellows that dramatically stiffen the suspension at full jounce and sway bars to stiffen up roll. I'm afraid that we may simply bottom.

I'm resigned to working with what we have, and like I've long said, what we have is good. I'm looking for that last 5 to 10 percent. So I'm going to forget ping tanks and instead work with sway bars, shocks, ride height, tag pressure, and tire pressures.

[Arcticdude]

Sounds like a good plan! Raising the rear would definitely offer some advantages. It's not like its going to see full extension often!

[al perna]

good roads GREAT RIDE , bad roads SCARY RIDE . I think keeping up on all components, will assure the best ride our coaches can provide . I found the removal of the sway bar BB installed to be the greatest effect on poor roads. she absorbs the shock , as opposed to resisting it . On the 29 th I plan to have George M replace my drive and tag shocks . we will also determine why I am lower in the steer curb side . I also will go to Michelins on the steer . when these repairs are addressed I will have the ability to compare the ride over the same 2000 mile run I make monthly . so those miles provide the good, bad and ugly of our nations road system for a good comparison .

[davidbrady]

Thanks Al,

When you visit George have him set your steer axle adjustable Koni's to full soft and take it out for a spin. I think you'll be pleasantly surprised. George can also help you with the ride height of the steer axle relative to the drive axle. He's been around Wanderlodges long enough and has listened to folks like Bennie Collier and the BB engineering staff to know that subtle changes in ride height, shock settings, tag axle pressure, and tire pressures can make a big difference. Have him lower the front relative to the rear - this may require picking up the rear a smidge (3/8ths of an inch or so). The coach is capable of great things if set up right! Please keep us informed.

Your coach leaning to the side up front needs to be addressed and George is the man to do it - it could very well be a bad bushing in a torque arm or transverse link (panhard rod).

I'm very happy that eliminating the sway bar has worked out for you. The legions who've done it all agree that it is the single most important change in improving ride quality.

[al perna]

I agree small adjustments here and there will make a world of difference . I also will address the knock sound if I apply the brakes firm on a stop at slow speed . the strange part is while at Josams they did not pick up on any issues during the shake test . you should have seen Lola during that test lol ..

Looks like we have a big project in Ashville in a few weeks , looks like a good time to write off a foliage trip !! I will keep you posted

[Bob Johannesen]

(10-19-2013 11:59)al perna Wrote:  I agree small adjustments here and there will make a world of difference . I also will address the knock sound if I apply the brakes firm on a stop at slow speed . the strange part is while at Josams they did not pick up on any issues during the shake test . you should have seen Lola during that test lol .........

Al,
You might check the bushings in the front suspension arms....they will load up (try to pull backward) during heavy braking. If they are worn, the bushing "slop" will allow the links slap against the bolts and make the bumping sound. I have to do mine soon.

.

[al perna]

thanks Bob , that sounds like a " BUSHING RALLY " ha ha ha . strange they didn't pick up on this when tested . the sound is coming from the curb side . when I am back in Fla in Nov, I will have this looked at again and get er done