Thomas Offset Reduction Concept - T.O.R.C. 50/50 Steering System

Up until now, bicycle fork offset has been typically 1.5 - 2 inches mainly to allow some inline flex of the material for shock absorbtion. But in the last 10 yrs. the proliferation of stiff effective suspension systems have extended the capability of the vehicle and eliminated the function of bending as shock absorbtion. Both situations combine to allow the evolution of steering geometry as we know it.

The universal 1.5 inches of fork offset as it now stands is a holdover from a bygone era that does not fit the "trail" requirement of today's mountain bike. A general purpose mountain bike typically has about 2.35 inches of "trail", (the distance between the steering center as it intersects the ground and the tire contact patch center which trails behind it). With too little trail, the front wheel cannot climb out of ruts easily and is too easily deflected by rocks and other hazards. The increased capability for velocity of today's sophisticated fully suspended bikes in rough terrain now rivals that of small motorcycles so it follows that trail requirements are similar, (typically 3.5 inches or so).

With a traditional 1.5 inch offset, trail can only be increased by reducing the head angle which slows the steering. Dramatic reduction of offset is the only way to increase trail enough and still retain steering response. In fact decreasing the offset by 50% enhances the response so much that a 1 degree reduction in head angle balances the the added quickness of the steering and adds more trail to arrive at a figure that is 50% greater than a conventional setup, (50/50... get it?).

The result is a front end that does everything well. It can be pushed harder through bumpy turns and still hold a precise line. It can drop down sketchy tech sections with a calmer more controllable attitude. It even has increased stability when standing and hammering the pedals requiring less upper body strength.

The secret of increased trail is that the center of mass of the bicycle-rider package works with the rider to overcome the tendency of the front wheel to deflect on uneven surfaces. Too little trail and your hands become overloaded with this function - every rock or rut becomes a struggle for control of the front wheel. This means that the rider has to tiptoe through the challenging trail conditions instead of blasting through as todays stiff well suspended chassis would allow. "If the bicycle is to have suspension, it must also have the geometry that supports the type of riding that suspension inspires.", is what I said in an article about downhill equipment published in 1995. (3 inches of travel was all that existed then!)

That was also the time that I had a Lawill fork custom made with 30% less offset to go with a frame that had a 1 degree steeper head angle. The idea at the time was to increase steering quickness while retaining a normal amount of trail. It was quick alright and wandered all over the place! Since '98 I have used a Hannbrink fork with inverted dropouts to yield .5 inch offset, on a conventional frame modified only by the longer length fork which slackened the head angle by 1 degree or so. The perfected design is .750 inch offset with .750 inch longer fork length, (adjustable). A longer toptube and shorter stem are also recommended depending on the rider's needs.

The feel of the T.O.R.C. 50/50 steering requires some getting used to though. In a simple parking lot situation the feel is heavier with a slight initial input necessary to stay on the line. But on a twisty single track, the steering becomes effortless as the increased trail pays off its benefit. now the adjustment asks that you apex the turns soonre and push the front end harder. Tricky transitions, (where most crashes happen) become good places to be creative with your lines and make up time. The harder you ride, the better this front end works.

Maybe it's a bold statement, but in my opinion, all mountain bikes will use this concept sooner or later.