I've got two mountain bikes and a road bike and I have almost identical road and mountain bike shoes (Specialized BG Comp). When I ride the road bike, I seem to claw my toes up inside the shoe, so that my foot is canted outwards. I do it subconsciously and, when I realise I've done it, flatten my feet on the insoles. But it takes a few minutes and they're clawed up again. This never happens on the mountain bikes, even when I rode long, flat miles on the Canal du Midi in September.
As mountain bike chainlines are 50mm and the road bike's is 43.5mm, I'm thinking the whole crankset is probably 10 to 15mm narrower and thus my feet are too close together, which makes me compensate by clawing my toes in the shoe. I heard that Lance Armstrong runs spacers on his pedals and I'm wondering if anyone's tried this. Are there special spacers you can buy or is just a pack of big washers OK?