Originally Posted by
kamtsa
I think need to pay attention more to the gear range (min/max GI, see http://sheldonbrown.com/gears/ ) rather than the number of gears. A 2x10 gear bike that does not get low enough will not help you with steep hills.
The low gearing 6sp Brompton has a hi/low ratio of 300% that with 44T chainring gives 30-90 GI. You can compute what is the GI for each combination of your current bike and determine what gear range you need. The Tern verge X20 spec is 28 - 93 GI which is about the same as a low gearing 6sp Brompton.
Some products that have large high/low ratio are SRAM Dual Drive and Rohloff but they add to the weight.
And, if you will find the perfect folder, I will also get one ;-)
Yes, Kamsta. The way I think, there are three factors to consider: 1) Amount of gears, 2) Low and top gear inches, and 3) Evenness of spacing between each gear. In general I prefer bikes with lower gears than the average bike comes with and so I'm prepared to customize the chainrings if necessary to achieve my goals.
My Brompton is a pre-wide-range 6sp. It didn't have quite low enough gear for me. At first I changed the front ring to the 44T, but felt the need for even lower gear and didn't love lowering of highest gear, so then I went back to the original chainring and added a second "granny" front chainring which I switched to manually. I got the range I wanted, but it was a bit of hassle to have change manually (used foot to move from large ring to small, but had to stop and use stick to move it back at top of hills), so that led me to try the Schlumpf. I don't think I would have liked the newer wide-range 6sp version because I find the spacing between gears to be perfect and wouldn't want them to be much wider.
I'm assuming that the lighter the bike, the less low the low gear needs to be. Going to test-ride the Tern 10x. Light weight and may be able to customize to have acceptable range.