Cheap Bike Chain Stretch Tools - Just how accurate are they?

In this video I test a few cheap bike chain stretch tools, comparing them to digital vernier calipers (the bench mark in accuracy) and a cheap pressed metal chain stretch guide indicating 0.75% and 1% stretch (the bare minimum). I also show you how I change a chain, showing how to check fit and tension for any geared bike, including use of a chain break tool to press links out to get the correct length.
Chapters:
- The bikes: 0:00
- The chain stretch tools used: 1:51
- Example of how to use all tools on one bike: 3:47
- Checking a brand new chain 6:17
- Changing a chain from scratch: 7:09
- The results: 14:15
The Campagnolo chain stretch guide referred to is here:
www.campagnolo.com/
Search for '11 and 12 speed chains Technical Manual' - page 17