New chain tension: aim for half an inch of play.

Set it so you have about 12-15mm of vertical movement at the midpoint of the bottom run. That’s roughly half an inch.

Most people overtighten because it feels more secure. It’s not. Too tight puts heat into the bearings and the chain itself, and can even snap a derailleur or bend a hanger. Too loose and you’re asking for chain slap or a derail when you hit a bump.

The trick: check tension with the cranks in the position where the chain is tautest (usually when the crank arm points forward). If it’s tight there, it’ll be too tight elsewhere. Give it that half-inch of slack at that spot and you’re golden.

A slightly loose chain is safer than a perfectly tight one.