I have never watched the Tour de France go by, but we did once go and watch the Tour of Britain when it passed through North Yorkshire. We positioned ourselves halfway up Blakey Chimney Bank - Gradient 33% (or 1 in 3 in old money). The riders came by quite slowly, in fact after the first few - those in serious contention had gone by - many of the later riders were off their bikes and walking so there was a fair bit of banter between the riders and the spectators.

Later that evening we watched the stage on TV and found out that a rider had been penalised several seconds for taking assistance - helpful spectator had given him a shove to get started again after he had stalled on his bike.

Definitely worth doing once, even in Britain where cycle racing is not so popular as in France.