The present invention relates to a wheel air gap for a motor vehicle of which according to the invention at least one section of the wheel air gap open air comprises a sound-absorbing material.

Aspects described herein generally relate to a sol-gel that is the reaction product of a hydroxy organosilane, a metal alkoxide, an acid stabilizer, and a corrosion inhibitor. The hydroxy organosilane is represented by Formula (I): ##STR00001##
wherein R is selected from alkyl, cycloalkyl, ether, and aryl. The acid stabilizer is at a molar ratio of acid stabilizer to metal alkoxide of 1:1 or greater and the sol-gel has a pH from about 3 to about 4.