Swing arm linkage for a mid-wheel drive wheelchair

A swing arm linkage for a mid-wheel drive wheelchair comprising a first caster wheel, a second caster wheel and a drive wheel, comprising:

• a first swing arm having a first swing arm pivot point and a linkage member first mounting point,
• a second swing arm having a second swing arm pivot point and a linkage member second mounting point,
• a linkage member configured to be connected to the linkage member first mounting point and to the linkage member second mounting point, to enable force transfer between the second swing arm and the first swing arm, wherein the linkage member has an elongated shape defining a linkage axis extending between the linkage member first mounting point and the linkage member second mounting point,
• a first straight line being formed between the first swing arm pivot point and the linkage member first mounting point, and a second straight line being formed between the second swing arm pivot point and the linkage member second mounting point,
• wherein the linkage member first mounting point and the linkage member second mounting point are so arranged relative to each other that the sum of an angle α between the linkage axis and a line perpendicular to the first straight line and extending from the linkage member first mounting point and an angle β between the linkage axis and a line perpendicular to the second straight line and extending from the linkage member second mounting point is constant or increasing with increasing ditch angle,
• the ditch angle being the acute angle between two planes of which a first plane is tangent to both a second caster wheel contact point to ground and a ground contact point of a drive wheel, and a second plane is tangent to a first caster wheel ground contact point and a drive wheel ground contact point.