Yesterday was in Little India. Passed by this tyre shop (the one along Serangoon Rd, next to one of the "higher" end Mustafa outlet.
Saw the men used a special tool to cut grove on a worn out tyre. Dont know he was asked by his customer to do that or he just do that and sell the "newly cut" tyre as 2nd hand tyre.
Dont know this practice is common. Just want to warn everyone here beware of such thing.