The whole footpath (nature strip) is covered in them. I feel like going back with a weeding fork and digging them all out. Found the thorns stuck in the bottom of my thongs.
Emex has shovel shaped leaves and a woody burr with three spines, and was last reported in Canberra in 1982. Tribulus terrestris has leaves with many leaflets. The seedcase is relatively flat and breaks up into five sections, each with two spines. There are two other sightings on CNM.
About bike tyres. My daughter was at Roseworthy College in rural SA where the main burr was Three Cornered Jacks. The only way she could use a bike at all was one with solid tyres. Inner tubes on ordinary tyres got shredded in no time.