Howard Center Steer

[Just Plain Jeff]

There are some rather strange handling characteristics of heavy vehicle tracking over the road, particularly those of a bus. If you envision a school bus, for example, or a semi-tractor, the driver sits behind the front wheels and the front wheels actively control the direction of the vehicle. In a Prevost coach, for example, there is a 'castering' effect, that is, the front wheels do control the direction of the vehicle, but they also follow the line of direction of the vehicle. It sets up a rather odd physics problem.

One of the ways that people have rigged up their Prevost conversions is with the use of a Howard Center Steer. These rather expensive rigs promise that if a bus blows a tire, the bus will automatically track to center and perhaps more importantly, improve steering characteristics.

I 've had some time to be thinking about some things and I think it is a bad idea to try to re-engineer Prevost coaches, particularly suspension systems and steering systems. This is the one area which Prevost has done a truly amazing job with their own parts and off-the-shelf parts and getting into the front suspension/steering system of a Prevost shell seems to me to be a pretty bad idea.

Drove a Howard equipped coach a number of months ago and it didn't seem to make much difference in handling; maybe guys are just looking to find a place to put some money.

Hmmm.

[Kevin Erion]

Jeff, I am not an engineer but I don't think there is any difference between a bus and a semi other that about 2500+ lbs more on the front axle of the bus. I also am not sure how the wheel base effects the steering but I am sure that the long wheel base of the bus helps to soften the ride and also slow down any input that you give the steering wheel.
Kevin

[MangoMike]

Jeff,

My bus came equipped with the Howard Steering. I usually don't engage it, it's air pressure adjustable, unless I have a strong crosswind then it's a big help as you can "trim" the wheel like a rudder on a plane to compensate for the the wind. Luckily I haven't had a blown tire to experience its effect.
Mike

[lewpopp]

Jeff

You praise Prevost for the perfection they have put into the Conversion front ends.

Why is it they cannot locate my problems.

Someone suggested the Howard system, but I to believe it would mask what the real problem is.

I said before that I have to set up an appointment with Jacksonville on my way home in May. Robert Hitt, the Eastern Area Service Mgr. will meet me and I hope not to donate just to the Prevost fund as I have many times before.

It would be so nice to head for a destination and have the trip a super pleasure, but it isn't the way my front end acts.:confused:

[Just Plain Jeff]

Kevin: The point I am making about the difference in handling is 'castering' the same effect that one finds in the front of a grocery cart. The wheels 'trail' and wobble. That is why the grocery cart tires wobble as they trail the leading edge of the front suspension. And I am certainly no engineer either.

[Jon Wehrenberg]

I'm not a professional driver so my skills at evaluating subtle changes in handling between vehicles are somewhat lacking. I have put almost 280,000 miles on two coaches (combined) and neither had any handling characteristics that were remarkable.

We have now driven some other coaches and all of a sudden I have sensed a change. The last XLII we drove did not track straight down the road. It did not pull, but if I did not concentrate and make constant minor adjustments it would have been all over the road. In other words I had to work at keeping it in my lane of traffic at highway speeds, unlike my coaches that just seem to track straight and require minimal correction.

That could be related to alignment or tire issues, but I now know why someone would consider adding something to their coach to minimize that characteristic.

[pognumber26]

My 2000 H-3 Marathon came with this system and I used it all the time...It was especially helpful in high crosswinds situations...My '06 H-3 is a driving dream come true!!! I can literally drive all day with one hand on the wheel...There is NO COMPARISON in the handling charecteristics betwee the two coaches!! Night and day difference...A top service tech pointed out to me while doing the undercarriage inspection on my new coach that Prevost has developed their own version of the HPS option and installed it on their late model H series coaches...It works MUCH better in m my opinion... Another good idea that was mentioned to me by a couple of the professional Nascar drivers and several multi owner coach owners, was to take my coach to Prevost/Nashville and have them perform a triple axle alignment asap on my new coach...One of the drivers had tracking problems for years ,until he head this procedure done and they ALL went away, according to him...For what its worth...

[Just Plain Jeff]

Here's a demonstration of the problem. Go to Home Depot and get a four-wheel metal cart. Push the cart empty at high speed down the aisle and you will find the front wheels flopping wildly. Put two 5-gallon buckets of joint compound on top of the leading caster wheels and you will see the handling characteristics of the cart change dramatically.

For shells, the XLII is supposed to be the finest riding coach on the market; that according to a Sr. VP at MCI (who is chasing down some Prevost business). The difficulties come when converters 'load up' their stuff into the shell and the handling of the coach changes markedly. If the conversion is well balanced front to rear and side to side, there should not be a reason why any kind of additional suspension or steering aftermarket parts needed.

The trouble begins when the trailing front wheels are unbalanced, just like the cart at Home Depot.