How fast (average mph) do I have to go to be competitive in the bike part of a sprint triathlon?

Results from virtually every triathlon over the last decade are posted online. Check previous results for the race you're considering to figure out how you might have done in your AG (...or overall if you think you're hot $hit).

If you're up in the masters age groups, low 20's might be enough if you're a decent runner. Younger or overall, you'll need to be 25mph+.

Of course it all depends on who shows up for that race on that day. I've come home with hardware for $hitty performances, and other days have nothing to show for a PR.

It depends on you age group, competition level and the course. A sprint is short so you have to consider that the startup, turn (?) and slow down will impact your average speed.

If the course you're running was done on previous years look up the split times to figure a benchmark for you group.

If you have any cycling experience and a good bike 21mph would be a target. 25mph would be outstanding.

Reported average speed for the last Tour De Paris (competition) was 48km/h (30mph), along undulating route

That means you got do cycle much faster since sprint usually not along route as undulating

If the course is flat, about 25 mph

35 mph

The best thing to do is check the results of the previous races. Every course will be different so that is only way to find out.

25+mph when in peak training i can cruz 35+ mph

Average looking with a great personality.

Jimmy Johns fast.

Average is roughly 18MPH, decent would be 21-25MPH.