Originally Posted by cyccommute

You missed the other part of what I said. If you are simply stopping a wheel from rotating, that is not a skid. If you are stopping a wheel from rotating and converting from rolling friction to sliding friction, that is a skid. The contact patch has to be stationary and sliding to be a skid. Front wheels on single bikes in a straight line motion don't convert the rolling friction to sliding friction. Before that happens the center of mass of the system rotates around the handlebars and the rider is thrown over the bars.

The key is the center of mass. A bicycle rider in a "normal" position has a high center of gravity and they can't overcome the coefficient of friction between the tire and the road. Tandem, cars and motorcycles all have lower centers of gravity that are also further from the front wheels which keeps them from rotating around the front center of gravity. (Motorcycles can still be pushed into endos but it takes much more force and speed). Their front wheels can slide under braking but in the case of motorcycles and tandems, the riders will probably fall anyway since they no longer have the gyroscopic benefit of the wheels.

You can increase the amount of deceleration that you can get on a bicycle by a large amount (still not enough to keep you from going over the bars, however) by moving the center of gravity rearward and down when braking. I've used Wilson's calculation to see what the effect of moving 4" backward and 2" down on a bike is and the possible deceleration increases to around 0.9 g. Alternatively, if you move the CG forward, you can skid the rear wheel more easily and get into a nose wheelie more easily...if that is your goal.