Dogtrousers
Kilometre nibbler
So "txirrindulariak" is Basque for cyclists. What an incredible language.
After some serious philological research (a couple of minutes messing around in Google translate) it seems that "txirrin" means "bell". And txirrindu means bicycle. So it would seem that the distinguishing feature of a bike in Basque is not its two-wheeled-ness, but the fact that it has a bell.
https://en.m.wiktionary.org/wiki/txirrindu#Basque