Originally Posted by K&M
One problem, as you can see from reading this thread, is that people have a tendency to get things backwards and say the opposite of what they mean when discussing trail.
Actually, I believe the problem is one of semantics surrounding the word stability and a failure to put that term into context when describing how bicycles handle, followed closely by the same ambiguity that exists around the expression "fast steering". Since I'm at home now I have access to some of the columns that I've written, to include one dealing with this topic and an illustration that also ties in with this discussion that summarizes my views on how sematics muddies the water.
Originally Posted by Me in RTR #16
As for how short (conservative) or long (aggressive) fork trail feels, that's often times where the terminology and expectations can also create confusion. Based on my experience, the following is how I like to sum up how conservative and aggressive fork trail affect the steering and handling of tandems:
Conservative fork trail on a tandem (under 2") favors low speed maneuverability by providing lighter steering effort and faster steering responsiveness to handlebar inputs. Many teams will describe this as being "more stable" because, at least at slow speeds, it "feels" that way. Tandems with conservative fork trail take less effort and attention to steer in a straight line at slower speed and are resistant to inadvertent movements by the stoker, aka (stoker induced steering). However, conservative trail tandems also tend to understeer in aggressive or high speed cornering maneuvers which is not always desirable.
Aggressive fork trail on a tandem (more than 2") favors high speed cruising and aggressive cornering. This is because of their inherently greater straight line stability and smooth responsiveness to leaning inputs, noting that at speeds above 15 -20 mph all directional changes on two-wheeled cycles are accomplished through leaning the bike in the direction of the turn and countersteering with the handlebars. Many teams will describe tandems that handle well at speed as being "more stable" because, at least at higher speeds and for aggressive cornering, it "feels" that way. However, at slower speeds, steering tends to be heavier and less responsive which is often described as being twitchy. Moreover, for teams with stokers that are exceptionally tall, or who tend to move around along or "rock" when they ride, a tandem with long fork trail can make steering control a laborious task that can also be undesirable.
However, despite everything that's been written about steering trail and how well most people understand what they've read an studied in those writtings, tandems tend to defy logic since everything is backwards... instead of the "racing models" having shorter steering trail than the models favored for touring or less aggressive riding, they have longer steering trail. Again, from my column:
Originally Posted by Me in RTR #16
[after looking at steering geometry numbers for solo bikes]... you might logically conclude that high performance steering should be assigned to the tandems with shorter trail numbers instead of the longer ones since the racing bikes in Table 1 have the shortest trail numbers. Unfortunately, while tandems with short trail benefit from the more neutral handling in some performance areas, the long wheelbase and significantly higher gross weight of a tandem creates a point of diminishing returns for more aggressive riders. The long trail tandems, on the other hand, trade off that low speed maneuverability and neutral steering for better responsiveness in those more aggressive riding situations. So, in some respects, expectations about how changes in fork trail "should" effect the handling on solo bicycles can't be extrapolated into how fork trail actually affects the handling on a tandem.
Finally, I included the following illustration and summary of my perspective on tandems, steering geometry, and how they handle: feel free to disagree; after all, we are talking about steering geometry.