I’ve just bought a used Giant Trinity Advanced TT bike, however it has this strange center lock in the steering. When it passes the center position it locks and you need to apply some force to the steering to go out of the center position again. I assume that it is there for increased straight-line stability, but what a crap system. It is almost impossible to do sharp turns at speed.

Anyone know how to inactivate this system?

Maybe the headset bearings are just dead?

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Scott Foil Ultegra Di2
Scott Scale 35 26"
Scott Spark LTD 29" M8000

Someone has over tightened the headset. Or the cables are to short (unlikely). Or the headset isn't fitted properly.

My money is on a monkey with a long allen key.

Centre-locking headsets have long been a sign of over-tightening or shot bearings.

Try loosening the stem and refit.

You probably need a new headset. It is probable that the reason the previous owner sold it was to solve this problem. It could also be that if the previous owner ran the bike with poor tension on the headset that your frame is ovalized. more than likely you just need a new headset. No bike company would ever invent "center locking" as it could cause an accident and they would get sued.

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For certain parts stiffer is more important than lighter.