d2create

I'm not the most mechanically inclined person so this confuses me a little.
What would be involved in converting a typical road bike from a regular 8spd drivetrain to a 3 spd internal hub? Basicallly what Sheldon Brown is doing to this Bianchi...
https://sheldonbrown.com/harris/bianc...os8/index.html

Retro Grouch 

The two issues that you need to contend with are dropout spacing and chain tension.

A road bike with an 8-speed drivetrain will have a 130mm dropout spacing. A 3-speed internal hub will probably have 120mm spacing. If that's the case, you'll probably have to squeeze the chainstays together. Chainline is part of this too. Your front chainring and rear cog have to line up pretty perfectly or the chain will keep coming off.

The other issue is chain tension. If your chain is too tight, it'll bind and be hard to pedal. If it's too loose, it'll fall off of the sprockets. Most single speed bikes have horizontal dropouts so the rear wheel can be adjusted front-to-back an inch or so. Most modern derailleur bikes have vertical dropouts. There are three choices for solving this issue. 1. You can buy a singulator or similar product that acts like the spring loaded arm of a rear derailleur. You can even use a rear derailleur if you want to be frugal. 2. You can buy a "half link" or even a whole chain that's composed of half links. This will allow you to adjust your chain links in 1/2" increments rather than the 1" increments that are required by common bike chains. 3. If you're very lucky you might stumble into a chainring and cog size combination that'll work with your chainstays and a normal bike chain.

Good luck!

HillRider

The dropout width will not be a problem if you use a Shimano 8-speed or 7-speed Nexus hub. Shimano lists the OLD for all of their 8-speed Nexus hubs as 132 mm so they are obviously intended to be used on either road (130 mm) or MTB/Hybrid (135 mm) frames. Their 7-speed Nexus hubs have OLD's of 127 or 130 mm depending on model so they will be ok with a 130 mm road frame too. The 3-speed hubs are available in a variety of OLD dimensions from 120 to 127.4 mm so you have to pick the right one.

Chain tension will be an issue as RG noted unless your frame has horizontal dropouts. Note that the Bianchi in Sheldon's article does have them.

d2create

So I could get something like this? (borrowed from sheldon's website)

HillRider

Yes, that's definitely one way around the dropout problem for a single-speed or multispeed internal gear hub. Note that that particular item (by Tektro) isn't sold by Harris Cyclery.