What's the best way to transport groceries on rough roads without breakage? (My town has a generous budget for potholes.) I currently use a 2-wheeled cargo trailer, but it there anything I can do to cushion the more delicate items (i.e., eggs)? What about items like milk, where every pothole causes the liquid to slosh around?
Delicate items would probably survive best in a small backpack. Your body acts like a natural shock absorber so anything strapped to your back should get the smoothest ride, especially if you're out of the saddle for the bumpiest sections. Remember to keep the pack light though.
Put heavier items like milk on a rear rack, rear panniers or ideally on a trailer. On your back they can get really tiring and on a front rack they can really destabilize your front wheel (even worse for something that sloshes around).
Fragile and heavy? (e.g. jars, glass bottles) Put them in a carrier on the rear rack, but make sure they're well padded from both the bike and each other.
I don't transport a lot of groceries, but physics tells us that we really shouldn't worry about going up and down so much, but that we should worry more about things getting knocked around. An egg in the carton shouldn't break simply because you accelerate it quickly, it's going to get broken when it takes flight and then falls back down. Uneven pressure is the problem here. Remember, the back of a truck probably isn't any smooter of a ride than your bicycle. You should make sure that your groceries are tightly packed, so that they can't move around so much, and maybe even use bungy cords with a nice soft foam on top and on the bottom to ensure they don't bounce up and down when you do hit a pot hole.
How do you feel about modifying your trailer?
- adding some suspension could absorb some of the bumps
- bigger wheels and high profile (i.e. lots of rubber) low pressure tyres would also go a long way towards smoothing out bumps in the road, though a warning: if they're too wide they might reduce your manoeuvrability with the trailer attached
- some permanent padding for your trailer (and maybe a waterproof cover to keep said padding dry if you don't already use one)
Otherwise maybe just a padded bag for the delicate items (and if there's only a few, definitely stick it on your back as darkcanuck suggests for maximum suspension).
Something like the Bob trailer could be useful. It has suspension.
The BoB trailer is a one wheeled trailer so probably modifying yours to work like the Bob would be impossible. However if you were to build a new one making something like the bob could be a good idea.
My understanding is that one wheel trailers are better for rough conditions.
Edit: The other benefit may be that you can weave around potholes more easily. I have a two wheeled trailer right now too but it is tricky to avoid potholes with three wheels at different spots on the road. This may be easier with a single wheel trailer that tracks directly behind your bike.
I've had experience transporting a laptop, which I also didn't want to jostled. The best padding for it was not an official "laptop sleeve", but wrapping it in bulking fleece jacket, and then stuffing that into my pannier, which made a tight fit. I would be inclined to take the same approach with a carton of eggs: wrap them in fleece jacket, stuff that in a container, and strap it tightly to the trailer.
Also, let a little air out of the trailer tires for some free shock absorption. ( I used that trick today when taking my 3 month old on his first bike ride, in a rear-facing car seat strapped into a bakfiets ).