Tracker Tidbit

TRACKER TIDBIT

The belt final drive on the Lawwill Street Tracker (CW, April) has made people ponder why belts aren't used more commonly on sportbikes Even compared to low-mess modern 0-ring chains, a belt is lighter, quieter and needs no lubrication.

The Lawwill twin-arm setup constitutes a four-bar linkage, tunable for anti-squat or anti-rise geometry. But Mert Lawwill himself confirmed that his design-one he originally applied to mountain bikes-exists primarily to keep the rear axle at a near-constant distance from the engine sprocket, because a belt must maintain a set tension in order not to slip. This is

why the Buell XB series’ conventional arm has a large tensioner and carefully manipulated rear-suspension geometry. Lawwill tuned his setup to be “neutral,” so the suspension reacts minimally to throttle input. Because power is not consumed by compressing the rear suspension, Lawwill’s bikes show a rear-wheel horsepower “gain” over normal Sportsters.

This is a clever solution on a sporty, air-cooled street standard, but belt width would likely be prohibitively wide if applied to a 160-horsepower racerreplica. So for now, it’s Lawwill’s advantage. -Kevin Cameron