Trust me, theres no way you'd be splittin H2O in your tires. )) (Drawing some vague knowledge from uni chem) H2O just wont spontaneously split in 2 on its own without some sort of chemical or metallic catalyst or current.
To put this into perspective, to get N2O (Nawwss) to split into nitrogen and oxygen spontaneously, it needs to be exposed in combustion chamber (1000C) for it to give you the O2 to give you the 'go'. Unfortunately even so, this aint the same with H2O. Tyres at 1000C anyone? Haha
Boiling water just means the water has changed from a liquid to a gaseous state. It doesnt mean the water is splitting up, or it wouldnt be water anymore would it? (Ie water vapour)