Originally Posted by
Frog Man
It is common for front derailleurs to have 16t to 22t capacity.
Why not more?
Suppose I wanted a 34-70t double chainring?
Could a front derailleur with a long cage be used to get more than 22t capacity?
An extra chain tensioner to increase capacity.
Where would I find someone that knows the answer?
You use'ta could. It was called a triple. That middle chain ring either gave another set of ratios (often near duplicates) or acted as a chain guide. Kontact described it quite nicely. Just too much gap to reliably make the jump, but the chainring in the middle made it work.
My last triple was a mountain bike and I bought a steel ring for the largest ring and used it as a bash guard since the big ring kept loosing teeth.