Originally Posted by
cyccommute
I agree with most every thing else that has been posted. However they have all missed why a touring bike has a longer wheelbase. Avoiding hitting the panniers with your feet is important but the long wheelbase lets you carry more of the weight between the axles rather than cantilevered off the (usually) rear of the bicycle. The more load that is behind the axles, the more effect it has on the stability of the bike. A heavy load cantilevered off the back of a bike becomes a tail that wags the dog.
The front center distance (from the center of the bike to the axle) is also longer longer which slows the steering and makes the bike more stable with the load.
Finally, the heavier frame isn't just a strength member. It helps with handling loads on downhills. Road bikes with thin tubed frames can develop a harmonic flexure at certain speeds called a "death wobble". A death wobble on an unloaded road bike will happen, if it happens, at higher speeds of 40 to 50 mph. A load lowers the speed to much lower speeds. The heavier frame of a touring bike can also develop a death wobble but the frame isn't as flexible and it doesn't occur with a load until some really stupid speeds.
Yep.
Having the weight centered is a really big deal when it comes to stability. It's also important to keep the weight low. A pretty common touring set up at one time was heavy rear bags and a pretty large front handlebar to distribute the weight fore and aft. The handlebar bag though rode high and was a negative in terms of handling. Low riders were a big improvement in terms of handling and in allowing you to distribute the weight more evenly over both wheels.
I have no idea at what speed you get a wobble on a touring bike. I do know when touring on my old school 1983 Trek 720 with a 43 inch (!!) wheelbase and low riders, it is solid as a rock coming down mountain passes at 50 mph plus. Low riders really help the bike hug the road as well.