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It's a CDX drive, here's some of the email I sent to the shop explaining the problems with the bike:
"There were two problems with the bike build:
The two drive pulleys were not aligned, as supplied there was a 3.5mm offset between the front and rear pulleys (measured with both pulleys parallel). According to Gates the pulleys MUST be exactly in line with each other. I fixed this by reversing the offset rear pulley which then set the pulleys in line with each other
The front pulley was not centred on the crank arm spider with meant the belt tension varied by more than 40Hz leading to slack and tight spots in the belt. I centred the pulley by progressively loosening and re-tightening the pulley bolts whilst testing the tension at multiple points on the belt
There was a third issue that I could not overcome, with the belt tensioned to the recommended tension the wheel axle is pulled downwards in the dropout (or the frame upwards off the wheel). It is not possible to tighten the axle sufficiently in the frame using a QR to prevent the axle 'walking' under maximum torque on steep climbs. On one occasion this led to me going over the handlebars and landing on my face on the tarmac after the rear wheel came out of the dropout and the belt came off. The belt has come off due to the axle 'walking' on more than six occasions. A nutted or through axle might overcome the problem. Alternatively a revised dropout slot which keeps the belt tension constant at all positions might help."
It was built with 39 x 21 pulleys which resulted in a short belt length and reduced contact area on the pulleys. We'll, it's getting converted to chain drive and at least I'll only need to carry a spare link in future...
