Estimating FTP from Strava analysis
You own a power meter - just fit it and go for a hard ride.



For others who don't own a power meter (and lets face it, they're not cheap)

Its a poor data point, but a chap at work has a power meter and he can compare this number with strava's estimated power.  We've compared ~three races and strava's number was high or low by up to 30% 

So your 230W could be as low as 160W or as high as 300W.  Repeated tests will help narrow the range.

Another analogue solution is to ride hard for ~20 minutes to the point you can say words but not a whole sentence.  Then use Strava's estimator on that segment.  Repeat.

If you have a Heart Rate Monitor, try and hold your heart rate at around ~90-95% of your rated maximum, which is about 220-(your age in years)