Hi King!
My, that is a lovely setup you have! Thanks for sharing a photo of such a nicely equipped tourer; it's a beaut!
I have limited time at the moment and my handling tests are not complete, but I can quickly say this:
The handling of the Extrawheel trailer is very much dependent on load distribution, and it is happiest to have the load placed as low and as far forward as possible. High and rearward is not good, and can cause the handling to decay quickly. Pavement is a more severe test in this regard than off-road or on dirt, because there is no loose surface to provide a degree of "slippage" at the tire contact patch and the surface is more consistent. On this last point, there are some paved surfaces that made the trailer feel less stable and I did see it tracking from side-to-side. In my case, this was on a highway shoulder that has been sloppily overlaid in a repaving, so it may well have been not the surface itself but the varying camber of the surface imparting a twisting moment to the trailer that resulted in momentary sway.
I saw a video a gentleman was having a hard time controlling the bike, and trailer down a hilly dirt path.
<nods> Yes, I have seen that too. I think what happened to him is much the same as forum member Pete (Il Padrone) encountered on his recent tour of Australia's Red Center: Ruts in the road caught the wheels and steered the bike. I tried the trailer by riding across an empty field that had been plowed, where the tractor's tires created ruts that then sun-dried into hummocks. I had no problem going
across the ruts, but found going lengthwise, the trailer was "steered" independently -- just as the front wheel of my bike tried to do. The difference on the trailer was, I had no handlebars to correct it.
Another factor is the tires used, their pressure, and their mounting on the rims/trueness. Remember, the tires aren't supporting anywhere near the same load they would on a bicycle with load and rider, so pressures must be dropped according. I decided to see what would happen if I ran my 26x2.0 Duremes at the same 45psi/3.1bar pressure as on the Nomad, and the results were not good at all -- the trailer bounced wildly when hitting small bumps like driveway lips and such, and the tracking and stability were poor because of it Dropping the pressure to the 15-20psi/1-1.4bar range brought a real transformation on pavement and off-road. The trailer's tracking improved tremendously and the bouncing on small obstacles was largely eliminated; the trailer rode smoothly and silently. I am beginning to think less pressure yet may be the route to go, but I need to measure actual rim "drop" under various loads to hit the ideal of a 10-15% drop, then adjust from there. Counter to what one might think, rolling resistance remained low. Remember, these comments apply to a 26x2.0 (47mm actual section width/height) tire with a lot of air volume. If one equipped the trailer with, say, a 700x35C tire, then pressures would have to be raised accordingly to prevent impact damage to the rim. I also think an out-of-true tire or rim would be more apt to "steer" the trailer than it would a bicycle, but I want to investigate this further.
The reason I can't answer your question definitively at this point is I have not completed all my load testing with the variety of weights I will be carrying. I can say the unladen trailer tracks as if it isn't there, and this holds true with lesser weights also. Truly heavy weights approaching or at the trailers limit impart more influence on the handling, but I am not sure if it is simply that I am hauling more weight or if the weight directly affects the trailer's handling.
There is another factor as well, and one worth investigating further: The trailer's kingpin/pivot point is inclined, much like a bicycle's head tube, providing what amounts to "trail". It may seem obvious on reflection, but I think it is important: I think the trailer's handling will be best if equipped with the same tire width/profile as used on the bicycle so the kingpin head angle remains constant. If the trailer was equipped with a tire that varied largely from that of the bike -- say a bike with 26in wheels/tires hauling the trailer equipped with a 20in wheel or vice versa, then I think handling would be far less predictable.
The trailer is also sensitive to left-right load distribution, as noted by Extrawheel. I found the best results came from loading the trailer evenly, as Extrawheel instructs -- certainly within a kg or so from side to side. This keeps the weight effectively centered. If too much weight is carried on one side, there is a tendency for the trailer to impart a "lean" by loading the bicycle unevenly as well, and things get worse from there. This is where the containers of water have been so helpful in my trials; they are adjustable loads, and can be moved around in the bags to see how they affect handling.
I have built my own trailers in the past with success (they were two-wheel trailers with a cargo box and 16in wheels; max. capacity 57kg), and I put the most design time and effort into axle placement, since this largely determined hitch loading. If the hitch carried too little of the total weight, then the trailer wanted to "turkey trot" -- sway or shimmy from the pivot point of the kingpin or hitch. The same holds true for car-towed trailers. I have not yet induced that handing behavior in the Extrawheel, but I think this is the reason why the handling improves with weight low and forward; it is a reasonable assumption. It also shortens the moment arm between the mass (cargo) and the lateral/vertical pivots of the kingpin and rear q/r hitch.
As far as downhill performance goes, the acid test for me will be a downhill at various speeds on Green Hill here in Eugene, Oregon, my usual "test road" for such things. It is steep -- 12%-15% in places, and long enough for extended observation. I can look down and rearward in my eyeglass-mounted rearview mirror by tipping my head up, or I can affix my GoPro HD Hero2 camera to the rear of the bike or the trailer and review the footage after. This is still on my schedule, but I am turning my attention at present to the electronics and spoke-airfoil design. Overall, this is a big project and time-consuming.
I must note Extrawheel strongly suggest limiting downhill speed, and this seems like a Very Good Idea to me. I know from trials with my own trailers, at a certain point going downhill at high speed (in my case at nearly 100kph), they became markedly less stable and this stability was in part speed-dependent and also load-dependent.
Remember, like most bicycle trailers, the Extrawheel has no brakes, and there is a surge or push-surge effect caused by any unbraked trailer. Smooth pedaling is rewarded and so is smooth braking. For example, when I attached the Extrawheel -- loaded to capacity -- to my unladen Nomad, the bike didn't "feel" as burdened as it usually does when carrying the same weight in panniers on racks and handling was much less affected. The bike retained most of its unladen (nimble) handling characteristics. However, I was still accelerating and stopping the same overall mass, so the effect could be felt in slower acceleration and in extended braking distances/effort compared to the bare bike.
I don't think you'll have clearance problems using the Extrawheel with your Tubus rack. I am using mine with Thorn's 5mm-to-6mm rack adapters, so the rack supports are wider than yours will be and I have no clearance problems; the hub quick-release/hitch extends 30mm from the dropout face on each side; the trailer fork or tongue then snaps over it and is retained by spring tension (the fork width is adjustable and is set so it is 30mm less than the overall width across the hitch faces). If you have a new "Evo" design Tubus rack with investment cast lowers, there may be less clearance, since the eyelet mounts are effectively wider at that dropouts than with Tubus' earlier designs. The rear rack in your photo appears to the older "Klassik" Tubus Cargo design, so you should be fine.
I hope this helps.
All the best,
Dan.
