Originally Posted by Duragrouch

That's 63. I'm guessing 3 front x 9 rear x 3 IHG = 81 = no reason for it on that bike.

Reasons for an IHG with cogs:
- No front derailleur so can use a chainguard.
- Needs a tall overdrive because of tiny wheels, like a Brompton.
- Needs an ultra-low granny because pedaling a recumbent towing a heavy trailer up hills.