Spokes?
 

Which is harder on spokes, loaded bike or trailer?...........Sam

I guess I can't say for sure, but I would bet a beer that the loaded bike is tougher on the spokes.

I agree - the spokes aren't supporting the weight of the trailer - it rides on its own wheels. More weight supported by the wheel = greater stress on the spokes.

I have read that BOB-type trailers do exert some lateral forces on the rear wheel, forces that they are not really designed to take, however probably not as hard on the spokes as the weight of loaded panniers.

I'm going to do some major hand waving and guessing but I'd say that a pannier loaded bike is a bit harder in the spokes than a trailer. On the other hand, I'd suspect that the trailer is harder on the frame than panniers are. (I have ridden with both panniers and trailers.)

For panniers, the loads tend to be more vertical with strong lateral forces as the bike corners. This would make compression of the rims higher (although adding a touring load of around 50 lbs isn't that much more weight to add). As the rims flex more and the spokes loosen, movement of the spoke head in the hub would lead to spoke fatigue and failure more quickly.

With a trailer, the wheels aren't compressed as much and the lateral forces are different since the frame will spread the force of the load into the frame rather than the wheels. That's why I think that the trailer would be harder on the frame. Now, instead of flexing the wheels, you are putting a lot of lateral force on the rear triangle. I think it would take a long time for the frame to fail but it could eventually.

One of the other problems I have with trailers and Old Man Mountain type racks, is that you are depending on a pretty small diameter piece of metal to take a lot of stress. I have an Old Man Mountain that I no longer use because it never felt right and eventually the skewer bent even though I never rode with a load on the rack. And, yes, I kept the skewer tight.

It depends. the easiest on the wheels is a two-wheel trailer.

A single-wheel trailer (a.k.a. BOB trailer) is very hard on a bike with a lightweight rear triangle but doesn't put too much stress on a bike with a very rigid rear triangle. The BOB seems to sway at high speed but not at very low speed. IOW you won't break spokes while climbing but you may break some while going downhill.

Panniers make the bike wobbly if you have a weak triangle and narrow rear wheel. To illustrate my point, I recently replaced the 126-mm-wide rear wheel of my commuter with a modern 135-mm one (I spread the frame). What was a flexible frame, even wobbly with loaded rear panniers suddenly became a relatively rigid frame. With panniers you may break spokes going uphill, especially if you stand on pedals and/or have a swinging rack.

I have read quite a few cross-country ride reports on Crazyguyonabike and other web sites and when groups cross the country, most of the people who break spokes – sometimes many spokes – are those who ride with a BOB trailer. But then, one may wonder whether they carry more stuff because the trailer contains more, or whether they chose a trailer because they have a racing frame that can't accept racks.

At the risk of side tracking the thread...my apologies up front....you guys are saying that the lateral forces of a trailer are hard on frames, and I'm wondering if that is enough of a concern to change my mind about what I was thinking of doing. I want to take a week long tour next spring, and I have a carbon fiber bike. Obviously no braze-ons for attaching a rack, so I was think that a BOB was really the only option I had since the burley trailers hitch uses the frame. I know that would not be wise, but figured that since the BOB attaches to the QR, it would minimize stress to the carbon fiber frame.

Would you guys use a BOB on a CF frame?

It's the twisting forces of loaded single-wheeled trailers that are hard on spokes and rear triangles, especially noticable when pedalling out of the saddle. Depending on the mounting system, a two-wheeled trailer would be a lot less stressful on your CF frame.

I suggest you have your LBS ask the manufacturer's rep if they recommend using your bike to tow a BOB and if they will warrant the frame if it's damaged while towing the trailer.

If the answer is no to either question, then use another bike.

My experience with a older Burly (with the metal spring hitch) agrees here. Don't think the newer rubber hitch will flex as much, but it does "give" a bit even when pulling up hill, loaded, out o' the saddle! Plus it'll twist when you rock the bike from side to side, where a single wheeled trailer or panniers will excert forces side to side, which does happen even when riding the flats.

Do remember that the lateral load isn't just taken up by one side of the rear triangle, but both sides. Such a structure is probably pretty strong.
For the most part, you're probably riding along with very little load on the frame.