We had to replace the chain, rear sprocket & front chainring at 15,000km on my bike, the chain was OK to carry on using, but the rear sprocket was getting very spikey to say the least and the front chainring was not that much better. With the eccentric bottom bracket, we had already removed 2 pairs of links from the chain due to chain stretch, so replaced the whole lot whilst we had the opportunity. It would probably have gone another couple of thousand km's but we were heading into Turkey and then onto Iran, Turkmenistan, and onto the northern silk road so decided to fit new at that point and carry new rather than end up putting the spares on before we had even left Turkey, but I really don't think we would have gotten much more than 17,000km out of it at all! Bear in mind that we did a lot of off-road on dusty & sandy tracks and all of it was fully laden. I would expect to get more in the UK staying on road with the bike less well laden.