TECH WATCH

How much ef­fort goes into seat com­fort?

Motorcycle News (UK) - - Garage -

Seat de­sign sounds easy: make it comfy. But thereõs more to it than that. The first is­sue is shape. Shape de­ter­mines the type of sup­port the seat of­fers and the free­dom it gives to shift po­si­tion, for com­fort or to en­hance con­trol. So a dirt bike has a long, thin seat for room to shift body­weight fore and aft.

On sportier bikes the rid­erõs weight fo­cuses through two bones called the is­chial tuberosi­ties (the bones you feel if you sit on your fingers), so the seat is wide at the back to sup­port, ta­per­ing at the front to get feet down Ð a clas­sic sad­dle shape. Yet de­spite us­ing arms and legs to sup­port body­weight pres­sure points will bring dis­com­fort. So riders need space to shift from side-to-side and front to rear. Cruiser seats are tricky be­cause their rid­ing po­si­tion puts legs too far for­ward to sup­port body­weight. And thereõs no point mak­ing a sad­dle with space to move be­cause you canõt Ð your feet are out in front of you. Itõs a sit-in po­si­tion, what de­sign­ers call Ôsock­et­edõ. What you want is a wide, arse-shaped seat. Most ar­ses are broadly sim­i­lar; there­fore so are most cruiser seats.

This means the man­u­fac­turer has to rely on an­other seat de­sign fun­da­men­tal: ma­te­rial. In their Com­man­der and Hori­zon cruis­ers, Tri­umph used three so­lu­tions. The first was 95mm dual-layer seat foam. The top 15mm is made of lower den­sity foam that feels nice in the show­room. The bot­tom 80mm is a higher den­sity layer that sup­ports weight (foam den­sity is set by al­ter­ing the ra­tio of two liq­uids that, mixed to­gether, so­lid­ify into the foam). Tri­umph also add a sep­a­rate wedge of foam, us­ing a third den­sity Ð un­der the rid­erõs coc­cyx as a sub­lum­bar sup­port. They say it com­bats cruiser back-ache, re­sist­ing Ôs­lumpõ.

The seat vinylõs elas­tic­ity and grip has to be right. If itõs too rigid it wonõt yield and may mask the foam, and it also needs grip to stop the rider slid­ing about.

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