Spinning bike speed vs outdoor ride speed I have been riding indoor on spin bike and I average 40 km/h, would someone help me translate these speed to outdoor cycling?
Based (very roughly) on this calculator here, I'll guess 28 km/h or less.

Using a 0 weight rider and bike with no wind and 200 watt output you get roughly the speed you are getting on the trainer (the weights are used for rolling resistance).  Leaving the power the same and changing to 80kgs, a 9kg bike and 15 km/h wind it gives 28 km/h which is a significant drop.  I am not sure about all the formulas the calculator is using, but introducing rolling resistance and wind resistance will surely take big chunks out of that speed.

I am not sure what kind of spin cycle you are using, but depending, it may be introducing some sort of resistance that it equates to rolling/wind/mechanical resistances.  However, it's likely much less than what you would encounter out on the road.