Weel nuts loosen themselves?

I have a set of Hairpins on my 25 for about 2 or 3 years and never got a problem. However for the last two months i notice the nuts were loosen.



The first time, happened two days after the car cames from the car repair shop. The car started to vibrate and making weird noises. There was 3 or 4 loosen nuts.



Today, it started to do the same, and when i went to check, it doesn´t even have one of the nuts and 2 or 3 more were loosen too. It always happen on the front wheels.



On the tire shop they told me it could be the nuts aren´t the correct ones to these wheels and maybe they need conical nuts. It´s this true? What kind of nuts do you use on your Hairpins? They replaced 4 nuts (two in each wheel) for conical ones to test.



I have never had any problem with them but on the last two months it has happen twice.. I hope this isn´t a bad taste prank..



Forgot to mention and maybe it isn´t related at all, but this only happened after the brake discs were rectified.

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