how to decrease or control the Tumbling in tumblers

[trinity]

I have been rearing tumblers from past 15 years and use them for races once in a year.
All these years what has been a problem is many birds in when they are young tend to tumble too much and by the next year racing season will not be in a position to fly at all.
anyhow we will have other young birds which would have by then turned into adult bird and would also have reached upto 8-12 hours or more flying time, i just wanted to know is there any method to control the tumbling so that they can atleast fly for some time.