Comfort Drive, A Steering Innovation

April 20, 2008

Comfort Drive, what is it, and is it all they say that it is? First, it is actually ColumnDrive, and was designed and built by the world leaders in hydraulic steering systems and electronic steering aids, TRW. The name Comfort Drive is what it is termed by Newmar, the only motor home manufacturer that has to date been able to offer it. This was the result of an exclusive arrangement for a given term between TRW, Spartan and Newmar. It is believed that this contract will expire sometime in July of 2008. For reference, going forward, I will use the term CD which is the initials for either Comfort Drive or ColumnDrive.

The CD product is an electronic steering aid that is located between the steering wheel and the steering gear. It is not connected to, nor does it directly affect any portion of the hydraulic system. It is a software-driven computerized device that utilizes an electro servo motor to react to user steering input, steering gear feedback and self centering predictability. The steering input energy is substantially reduced requiring less force from the operator. The needed input force is slightly increased as the vehicle’s speed increases, but still remains lighter than normally experienced. More about this will follow a bit later. Steering wheel kick from the road is virtually eliminated for the user and is totally handled by the CD. Computing both the operator input and the steering gear feedback, the CD automatically predicts and corrects the steering center. Once this is accomplished the steering weight does not favor either direction regardless of road slope or wind forces.

So, basically that’s what happens, but how does it feel to the operator? Well, when I first drove a demo Essex in California in the spring of ’06, I had mixed reactions. The demonstration run was primarily through an urban area with speeds limited to 30 or 35 miles per hour. The first thing that is really apparent is the super light feel of the steering, especially when the vehicle is stopped, or hardly moving. There was little to no wind and the roads were relatively flat without much crown slope, therefore pretty well eliminating the need for the steering to self center. Upon returning to the parking lot where the demo run started, I had the opportunity to turn and back it in a space between two other coaches. This was a pleasant new experience. I turned sharply as I backed toward the space. Once the coach was nearly lined up with its parking place, I released the steering wheel. It automatically tracked to center and guided the coach straight down an imaginary course line. It was pretty impressive. Even stopped I found the steering wheel would automatically turn to center if turned in either direction, even from a full hard over position, and released.

So, was it a must have after such a demonstration? I my opinion, it was not. It certainly was interesting, but I was not yet fully sold. In some sense I wondered about such a steering, as it substantially reduced road feedback. That is, assuming that in fact road surface feedback, is a good thing. It must be, we’ve always had it, so it must be needed, right? Well, as I later learned, may be we don’t need it. In fact, perhaps it would be better not to have any steering feedback. After all, what exactly am I really doing with the “feel of the road” feedback? That sudden steering wheel kickback, as you cross an uneven section of road surface, may be well worth being rid of.

Well it seemed pretty good so I purchased a coach that came with this new innovation called Comfort Drive. I soon found the answer to the feedback question.

While driving on an uneven road surface, as a result of a contractor doing some repaving, the front tires met a multi-ridge pavement distortion at about 60 miles per hour. This led to a quick coach body movement to the left and then back again. No steering wheel pull was experienced using the CD during this event, and the coach sailed on without driver input or any noticeable change in lane position. This was a far contrast to my previous coach, which, while it was an excellent driving motor home, steered about 8″ or so left to right when presented with the same challenge in similar circumstances with nearly identical tire deflection. In analyzing it now, it would appear that the steering kickback felt in the standard non-CD equipped unit caused an unconscious reaction which led to instant driver input. This, certainly in my case, and quite possibly others, displayed symptoms and results of over steer.

Over steer, seems to be the most common mistake of new CD drivers. This is certainly not caused by steering gear feedback, but more than likely a reaction of the reduction thereof. This may be amplified when a driver first drives a CD equipped unit. There is absolutely no way it feels like a conventional motor coach steering system. It feels far lighter, perhaps at first, too light. It does take time to get accustomed to driving with CD, but it’s a full control feeling, and as the name applies, it is Comfort Drive.

I had additional positive results using the CD equipped unit in varying weather and road surface conditions. High winds, even gusty ones, required little or no steering wheel pressure as it automatically compensated to create a new wheel center. Likewise, high sloped road crowns were corrected automatically centering the wheel and alleviating any driver input pressure. An increase in safety margin in the case of a blowout is a feature that is not talked about, possibly due to liabilities involved of making such statements. But, just think about it. External forces of such things as road surface ridges do not cause any steering feedback pull. A front tire blowout would have little affect on the steering wheel as the CD servo motor would deal with the majority of the steering pull involved.

After a number of trips, totaling several thousand miles, a great appreciation and respect grew for this unique feature. So much so, that it was questionable that I would want anything less than CD on my next coach. This feeling seems to be common among those that have this innovative steering aid.

The CD on Newmar’s 2009 coaches, are, and will come with an additional feature, an adjustment knob to vary the power sensitivity. Personally I do not see the need for this add-on, however it may help some potential buyers overcome that “I need more road feedback” syndrome. Hopefully, this is not used to partially defeat the benefits of this great automatic electronic steering aid product.

Note: This article covers the basic operation and application of what we know as Comfort Drive, and is based on the opinion and product experience of the undersigned and that of other like owners. Applications and results herein stated may vary do to many factors. Those factors include, but are not limited to, coach weight and load, tire pressure, road surface profile, speed, curve radius if turning, etc.

Keeping It Between The Lines Lug_Nut Peter Mercer