Wind - How much does it hurt times

[Toolish]

I know this is a bit of a how long is a piece of string question, but is there a rule of thumb for how much wind affects TT Times.

I have a rectangle loop about 1 km on the short side 4km on the long side for 10km overall. Wind was 30kmh gusting to 5okm pretty much straight into/striaght with on the long side.

Into it I was luck to crack 27kmh, downwind I was averaging more like 45kmh.

Overall I know a wind like this hurts time, but just wondering how much.

[RonK]

On a course such as the one you describe, with the wind at fairly constant speed and direction, I'm not sure it would make any difference at all? What you loose on the upwind leg you make up on the downwind leg...