Relativity was devised to explain some things about electromagnetic radiation. It explains nothing about things that aren’t photons or photon related. Cerenkov radiation is an example of something of possible interest.
Hm. I guess you learned a different theory of relativity than the rest of us did.
Length and time are also affected. The latter, at least, has been experimentally demonstrated. For example, muons are created when cosmic rays interact with the atmosphere. The decay rate of muons is known, and from that we can predict how many muons should be detectable at the Earth's surface. The number of muons actually detected is consistent with the time dilation effects predicted by special relativity.
Sorry....
Now you've gone and reminded me of Dr. No!
(The gloved hand slipping down into the water with the reactor with the Cerenkov radiation giving the nice eerie blue glow...)
Cheers!
Full Disclosure: Pop a cold beverage to help me celebrate--we just found a house we like in Minnesota, after living in exile for years in Phoenix. :-)