Seat of the pants stuff

by Simon Hargreaves

The science of sitting comfortably is harder than it looks

For a manufacturer, technical challenges aren't all cutting-edge electronics and active suspension. And it's easy to dismiss cruisers like Triumph's new Thunderbird Commander and Horizon LT as low-tech and simple to design. But they have their own challenges like, for example, making a comfy seat. It sounds easy: make it comfy. But there's 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 to find traction. On sportier bikes the rider's weight focuses through two bones called the ischial tuberosities (the bones you feel sitting on your fingers), so the seat is wide at the back to support, tapering at the front to get feet down; a classic saddle shape. Yet despite using arms and legs to support bodyweight, eventually, pressure points bring discomfort. So riders need space to shift from side-to-side and front to rear – designers call this ‘roominess’.

Cruiser seats are tricky because their riding position puts legs too forward to support bodyweight. And there's no point making a saddle with space to move because you can't – your feet are out in front of you. It's a sit-in position, what designers call ‘socketed’. What you want is a wide, arse-shaped seat. Most arses are broadly similar; therefore so are most cruiser seat shapes.

Which means the manufacturer relies on another seat design fundamental: material. Which brings us to the Commander and Horizon.

Triumph have three solutions to get more comfort from their cruiser seats. The first is to use 95mm dual-layer seat foam. The top 15mm layer is made of lower density foam that feels nice in the showroom. It also takes the edge off the bum’s pressure profile and blurs the edges of support on the road. Meanwhile the bottom 80mm of foam is a higher density layer that does the job of supporting weight (foam density is set by altering the ratio of two liquids that, mixed together, solidify into the foam). It's a bit like a memory foam mattress.

Triumph also add a separate wedge of material – again, dual foam, but using a third density – under the rider's coccyx as a sub-lumbar support. They say it combats cruiser back-ache, resisting ‘slump’ and reduces the effort of keeping a straight back.

The seat vinyl's elasticity and grip has to be right. If it's too rigid it won't yield and may mask the foam, and it also needs grip to stop the rider sliding about, in leathers or textiles.

The trial and error of finding the optimum depth and density for the Commander and Horizon seats took Triumph over nine months and tens of thousands of miles; longer and further than any of their other bikes. It's some claim considering they also build the Trophy 1200, Sprint GT and Explorer 1200, none of which are uncomfortable.

But it proves there's no such thing as an easy bike to design; just different challenges.