John Lewis wrote: My trike runs 13 to 120 GI via a SRAM dual drive and I have had occasion to use them all.
Wow - just re-read that. 13 GI sounds like the specs of a winch not a drivetrain. On a bike you'd probably just wheelie and flip, but I guess on a trike or velo with low centre of gravity it would be ok.
The hills on my commute are steep in parts (15-20%) but not all that long (max 60m vertical altitude) and of course not that steep all the way. When I first started riding them I struggled a bit with 39-25 lowest (41 GI) but soon got some strength and fitness and no problems now. The hills are at the end of my 18km commute home which never helps when you're mentally tired from work too.
Did the guys from ROAM have a front cog lower than 30 on their triples? I know Harry Lieben ran a 11-32 cassette on his mango but may have also swapped out the final drive cog from 26 to 22 on those days were they did a lot of climbing. I assume that would mean shortening the rear chain etc too.
I am hoping I will be able to get by on an 11-28 cassette which actually still has fairly close ratios until the 28 tooth cog (jumps up from 24). The drop from 39 to 30 on the front cog is a reduction of 23%. The mango will take my gross mass from around 85 to 105 kgs so an increase of 24%. Going from a max of 25 to 28 on the rear is a further reduction of 11%. I'm hoping this will more than compensate for the increase in mass. Nitramluap has a lowest gear of 30-25 so I'm going to arrange a few more rides with him before I decide. I'll get him to ride my commute hills as I want to confirm the 90mm drums are up to it too.
If only Sinnerbikes were easier to communicate with hey