Instability of single wheeled trailers

PortlandJim said:

I'm looking for a good cargo trailer for a long, unsupported trip. I've tried a single wheeled trailer (Kool-Stop Wildebeast), but thought it had horrible instability when running downhill at anything over 23mph.

Is this a characteristic of single wheeled trailers, my lack of cycling skills, or poor loading techniques?

Some folks say that single wheeled trailers should be used primarily for off-road work...and I should just get a Burley. Many of the roads that I ride have very narrow shoulders, so I hesitate to invest in something that forces me more into the car path.

The new Bob Ibex (with suspension) look really interesting. Has anyone run one loaded at higher speeds?

Any ideas?

I have used both BOB trailers and found them to be stable. Ibex shock helps take some of the bounce off when you hit obstacles. I have ridden at over 50 MPH with both of them. You must make sure the load is securely tied down and can't move around at all. It does take some getting used to.

If you're setting up for a long trip and aren't going to be taking the trailer off a lot, you might consider splitting your rear brake cable and rigging a brake to the trailer. You can adjust things so that the brake on the trailer engages first. It should keep everything nice and straight.

Have you done that? Sounds like an interesting idea. How did you mount the brake grabbing onto the trailer's wheel? And what did you use to split the rear cable cleanly?

artmichalek said:

If you're setting up for a long trip and aren't going to be taking the trailer off a lot, you might consider splitting your rear brake cable and rigging a brake to the trailer. You can adjust things so that the brake on the trailer engages first. It should keep everything nice and straight.

artmichalek said:

If you're setting up for a long trip and aren't going to be taking the trailer off a lot, you might consider splitting your rear brake cable and rigging a brake to the trailer. You can adjust things so that the brake on the trailer engages first. It should keep everything nice and straight.

That's a good suggestion, but my instability problem is not while braking. It feels like my front wheel is drifting as my speed increases. As I approach 23-24 mph, I begin to feel a slow quake. Both symptoms disappear when I apply the brakes and reduce my speed below 20.

daveornee said:

I have used both BOB trailers and found them to be stable. Ibex shock helps take some of the bounce off when you hit obstacles. I have ridden at over 50 MPH with both of them. You must make sure the load is securely tied down and can't move around at all. It does take some getting used to.

Hmmm....so it sounds like you're saying that my problem is strictly in weigh distribution...side-to-side distribution or front-to-back?. Interesting that I've only seen this problem at higher speeds.

While I didn't try for a specific balance point, I used the "problem trailer" on several week-long trips. I'm sure I inadvertantly packed it a number of different ways, but I still had the same instability symptoms.

50 mph is mighty fast without a trailer...I usually start to lose my nerve at 35 or 40.

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Have you had any problems shipping a BOB on an airline?

jasong said:

Have you done that? Sounds like an interesting idea. How did you mount the brake grabbing onto the trailer's wheel? And what did you use to split the rear cable cleanly?

I haven't tried it yet, as I haven't taken any tours long enough to warrant a trailer. They make brake cable splitters for tri bikes that allow two levers to control one brake. They can also be rigged to control two brakes from one lever. As for mounting, you can probably drill into the underside of the trailer frame and mount a bmx caliper.

My Bob has been bad when I've loaded it wrong. Note: fault is in the user not the trailer. I find that overall it is very stable when I load the heavy to the bottom and front with lighter items top and back. I've hauled very heavy (over rating) loads that were compact and didn't move around without any difficulty, ie sacs of flour. Other loads, not so heavy but more bulky, were nearly impossible to work with - kept jacknifing the trailer and there was no amount of repack that would fix it. I had to split it into 2 loads. The only problem I find is that I have to be very careful when I stop at a traffic light with a heavy load because if I tilt the bike, everything wants to fall over. It takes a bit of getting used to when hauling groceries in traffic but I'm forever amazed at how much I can carry and how little it impedes me. I figure I lose about 2 kph when fully loaded, which isn't so bad.

This is very cool - I didn't even know these trailers existed. It sounds like the perfect thing to take on a bike/camping trip we're thinking about in Arizona.

Is the BOB Ibex from the Ibex bike people? I thought they went out of business? Can you give us a link to find one?

Thanks!

I own a Bob Ibex, bought for a cross-country trip this past spring. Two weeks before departure, had a bad crash on dry asphalt road due to a severe wobble while going downhill (estimate speed at about 30 mph+/-). It was probably my own fault. I loaded the Bob with two 25-pound weights in a plastic storage container; the weights were not tied down. Prior, I had gradually increased weight from 25 to 35 (tied down) with no problems. Got cocky and paid. I did some observations later on "tongue weights," i.e., weight on rear wheel with different distributions (my guess as to cause of control loss was force on rear wheel caused front wheel uplift and loss of road contact) :

[font=Arial]All Weights on Rear Wheel unless stated[/font][font=Arial][/font][font=Arial][/font][font=Arial][/font][font=Arial][/font][font=Arial][/font][font=Arial][/font][font=Arial][/font][font=Arial]W/Trailer[/font][font=Arial]W/O Trailer[/font][font=Arial][/font][font=Arial]Normal position[/font][font=Arial]138[/font][font=Arial]130[/font][font=Arial][/font][font=Arial]30-deg pitch forward[/font][font=Arial][/font][font=Arial]120[/font][font=Arial][/font][font=Arial]Off seat, pitched forward +[/font][font=Arial][/font][font=Arial]110[/font][font=Arial][/font][font=Arial][/font][font=Arial][/font][font=Arial][/font][font=Arial][/font][font=Arial]25-lb weight, front of cage[/font][font=Arial]34[/font][font=Arial][/font][font=Arial][/font][font=Arial]25-lb weight, rear of cage[/font][font=Arial]24[/font][font=Arial][/font][font=Arial][/font][font=Arial]50-lb, rear[/font][font=Arial]38[/font][font=Arial][/font][font=Arial][/font][font=Arial]50-lb, split frt/rear[/font][font=Arial]42[/font][font=Arial][/font][font=Arial][/font][font=Arial][/font][font=Arial][/font][font=Arial][/font][font=Arial][/font][font=Arial]Me on bike[/font][font=Arial][/font][font=Arial][/font][font=Arial][/font][font=Arial][/font][font=Arial]25-lb Wt in rear[/font][font=Arial]50-lb, rear[/font][font=Arial]50-split[/font][font=Arial]Normal position[/font][font=Arial]143[/font][font=Arial]156[/font][font=Arial]164[/font][font=Arial]30-deg pitch forward[/font][font=Arial]134[/font][font=Arial]140[/font][font=Arial]143[/font][font=Arial]Off seat, pitched forward +[/font][font=Arial]123[/font][font=Arial]129[/font][font=Arial]138[/font]

Anyhow, the main advice I would give is, do plenty of trials on varying inclines, with gradual weight increases up to what you expect to transport. Good traveling.

Could you describe how the wobble started? Did it feel like the weight began to shift around? I'd probably respond immediately by braking, but maybe that's not the best answer. What did you do?

Does the Bob also state a low maximum speed? I have a Yakima BigTow that seems to be an almost identicaly design, and can't believe they'd recommend an 18mph speed. That's impossible downhill and would probably rule out a large number of hills because one wouldn't be able to continue braking for such a long time without risking rim damage/heat up.

jfbtown said:

I own a Bob Ibex, bought for a cross-country trip this past spring. Two weeks before departure, had a bad crash on dry asphalt road due to a severe wobble while going downhill (estimate speed at about 30 mph+/-

The wobble began as I approached the bottom of the hill (probably max speed). No, I had no sense that the weights shifted. I did try braking, but it happened so quickly it didn't help. I've since read some on the physics of this phenomenon. As would be expected, there are many variables: frame geometry, wheelbase, wheel loading, et. al. No simple answer. As to a recommended max speed for the Bob, I don't recall a number; however, they recommend practice, which I heartily endorse. Lots. At different loads and on inclines, especially, with care until confident of limits.

I apologize for the jumble of numbers in my first reply. I copied a table from a spreadsheet I compiled; it didn't transfer properly. Anyone wishing the numbers can write me: [email hidden].

I've also experienced wobble on a normal road bike, which is probably what the articles you've read address. On your same bike, sans trailer, have you had the same problem? Things that seemed to contribute to my wobble have been having too much weight up front, like a handlebar bag, or being too far over the front of the bike. But, as you've probably read, it's not well understood and difficult to isolate what's contributing to it because it's often not repeatable under similar circumstances.

But a lot of that doesn't come into play when you've got something behind you that's pushing the bike down the hill.

I'm curious as to where one might estimate the effect of the trailer to be, in terms of a free body diagram. One a level surface (and at rest), all of the tongue weight is stuck on the rear axle. But incline the surface, add some speed, and realize that the front wheel is connected through the frame, and it's more complicated.

jfbtown said:

braking, but it happened so quickly it didn't help. I've since read some on the physics of this phenomenon. As would be expected, there are many variables: frame geometry, wheelbase, wheel loading, et. al. No