Trek Domane Review
remarkably simple in operation. The moulded carbon-fibre seat tube flares into the bottom bracket as per standard Madone practice. Unlike the design of the Madone – and every other diamond frame – it is not rigidly connected – in the case of the Madone via a moulded joint – to the junction of seat stays and top tube and is, instead, free-standing in the gap between the stays.
Until, that is, the IsoSpeed bearing is installed. This comprises two regular cartridge bearings, one located in each seat stay as it crosses the seat tube. There’s a bulge in the front of the seat tube through which passes a hole, co-axial with the two bearing housings. A through-bolt connects the bearings to the seat tube; there’s a plastic cover that clips into place over the bearings and a rubber bumper that sits in the gap between the stays and seat tube to prevent grit penetration.
Cut through the seat tube below the IsoSpeed mechanism and the tube can be rotated around the bearing axis. The rubber bumper limits the extremes of travel but not movement a few degrees either side of what amounts to “normal” positioning; it cannot, therefore, contribute a dampening function.
Of course, the seat tube is attached, and rigidly, to the bottom bracket. Any rotation around the bearings of the seat tube – constructed as a mast extending above the junction, as with the Madone – will require the section below to “bow” in the middle.
A load applied downward to the saddle rotates the mast backwards and bows the tube forwards. This can be seen merely by leaning on the Trek Domane saddle and observing the bottle on the front of the tube move towards its fellow on the down tube.
The effect of introducing a pivot at the site of the IsoSpeed axis is to give the Trek Domane rider, according to Trek, double the vertical compliance experienced on the machine’s nearest competitor. In real terms this means 32.9mm of movement somewhere between road and rider’s posterior with IsoSpeed where the competitor’s rider gets a mere 16.5mm.
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