Dre wrote:

(...)
Yep, a chain guide for downhill bikes. They have a single ring up front, no
front derailluer and a chain tensioner/guide.

I have one on my DH bike and the hardtail I'm building up atm. I run a 9
speed 11-32 cassette and have plenty of range for what I do...

MRP, Blackspire, E-13 are a few brands that can get you started...

Cheers Dre

Thank you Dre!

--Winston