I have gone 1x8 on my Diamondback Overdrive. With my preferred type of riding (technical obstacles and such), even "fast" stuff was only rarely requiring anything past the 3rd largest cog (32, 26, and 21) on the middle (32t) ring. Given the wasted cogs from so rarely using the bottom 4, I seriously looked into lower gearing options. Plus, after barely making some longer, rough climbs, I decided I'd rather have the option of slightly-reduced effort so I can go for longer rides without as much fatigue. I finally settled on the Shimano HG61 (9speed) cassette, and removing the 14t cog to work with my 8speed shifter after swapping out the spacers. In addition, I went ahead and got the Anderson 30T SS Chainring, which was $82.50 shipped (it is $15 cheaper to get the non-ramped Single-Speed version, which also has taller and beefier teeth).
I included an image showing the new ratios compared to the old, but I basically ended up with the factory 1st-4th gears spread out into 3rd-7th, with two lower gears. My 8th gear is about halfway between factory 6th and 7th, and I’ve still never had the desire or need to go as fast as this allows. Effectively, my 30/36 combo gives about the same torque as using the factory granny
gear on the 2nd-largest cog (22/26), and is definitely a big change from the previous 32/32 combo. It is a hair more than a 20% increase in torque.
I have taken this setup on a few rides now, and in the lowest gears I can now clean aggressive climbs on which I’d previously always run out of steam, and after exhausting myself I can still take on those long, arduous hills without as much fatigue. I find myself using roughly the bottom 5 gears as often as I previously used the bottom 3, riding in 3-5 where I normally used 2nd and 3rd, and using the largest cog for the big obstacles that momentum alone can’t beat.
Also, I am only using an outer bash ring, but otherwise no guide. My crank had no provision to install an inner ring, as it turned out the factory inner ring was just riveted to the middle ring. However, after looking at some pictures I realized that an inner bash ring is not nearly close enough to actively keep the chain on like a derailleur would, so I decided to just pull the front derailleur and see if it worked. So far, I haven’t dropped the chain, and I love the quietness without the derailleur.
The only problem I’ve had so far is sometimes in the 2nd-largest cog, the chain wants to start creeping up onto the large cog. I haven’t fiddled with it very much, but I am going to see if I can’t get it to work any better. I might actually take out the 2nd cog completely and just space the large cog more toward the outside. This is partially because I don't really need that intermediate gear (I usually double-click between 1st and 3rd now for clearing obstacles), and partially to get a slightly better chain line in the lowest gears. But, I will play with it some and see what I can figure out. I do like to tinker, though
But, otherwise I am extremely pleased with the modifications! It is quieter, I have a more usable range of gears for my style of riding, and I can now climb up things like this (coming toward the camera) from a stand-still with ease! (This is not my bike btw, just a shot I found of a local trail).
If anyone wants pics of the setup I can post some tomorrow.