Sunderland in the FA Cup in 1973 was another enormous away following although I think that their numbers were swelled
by Rags due to their match having been called off. The attendance of 54,000+ that day was never officially beaten again at
Maine Road (who knows how many were there against Charlton in 1985?).
Before my time but in the '50s they used to reckon derby matches at both Maine Road & Old Trafford were typically
split 60/40 in favour of the home team. Since some of these matches were 70,000+ I'm guessing United are the biggest
ever away following at City and vice versa.