Teaser 2749: Round the river

From The Sunday Times, 31st May 2015 [link] [link]

My school holds “Round the river” runs — a whole number of metres to a bridge on the river and then the same number of metres back. Some years ago I took part with my friends Roy, Al, David and Cy. We each did the outward half at our own steady speeds (each being a whole number of centimetres per minute). For the return half I continued at my steady speed, Roy increased his speed by 10%, Al increased his speed by 20%, David increased his by 30%, and Cy increased his by 40%. We all finished together in a whole number of minutes, a little less than half an hour.

What (in metres) is the total length of the race?