Shimano Nexus 8 IGH : recommendation or changes in bike setup for high altitude ride

My answer will be based on the assumption that "ride faster" means heavier gear ratios!

I understand that you have changed your rear cog from a 19teeth to 22teeth. I believe that makes your gear ratio actually smaller, therefore "riding slower".

Assuming that the IGH internals won't be altered, you can vary the gearings you want by changing the cogs and the chainring!

To get a higher speed / harder gear, you would want a smaller cog at the back and a bigger chainring at the front.
To get a lower speed / lower gear, you would want a larger cog at the back and a smaller chainring at the front.

Since you already changed your cog to a 22teeth, it might be wise to change your chainring to a larger one, in consideration that the 22teeth cog is new. To change to a larger chainring, compatibility concerns include:

1. Chain pitch - Single-speed 1/8″ chain or Derailleur 3/32″ chain
2. Chainring pitch - similar to chain pitch
3. Existence of front derailleur? - If no, choose a one-by specific chainring. (I'm guessing a no, since you are looking for heavier gear ratios)

Hope this helps!

It sounds like your hub needs basic service and you'll likely be fine. It may just need bearing adjustment, but on a used bike it's a good idea to go a little further to make sure all is well.

Take it to a shop that's proficient with modern IGHs and ask for a dunk. The Shimano hubs are intended to have their core pulled, externally cleaned, dunked in an oil bath, certain parts greased, and the core reinstalled and the main bearings adjusted. While you're in, you can get a visual that the pawls and gears are looking good (every once in a great while you see a broken one, and they can typically be replaced.) The bearing races can also be inspected, but it takes a lot to mess them up on Nexus hubs. I've only really seen it much in maritime poor storage/maintenance type cases. The whole thing takes maybe 30-45 minutes, a lot of which is spent getting things clean. If there are problems that really warrant replacement, the shop will typically not charge you for the time spent to figure that out if you do them the courtesy of having them do the replacing. But that's not usually how it goes.

Shimano has lowest allowable gear numbers for all their hubs. This is their way of keeping you from breaking something by putting too much torque through the parts. Ask the shop to get you that gearing setup. They may do it by changing either or both the gears, depending on the bike, clearance considerations, what you have now, etc.

Assuming you stick with the Nexus 8 and simply get the mechanical issue sorted, your total gear range is pretty well constrained. The lower gear ratio provided by that 22 tooth cog may be helpful to get up hills with a loaded touring bike, but it does take your chain gearing below the 2-2.2 range Shimano recommends for those 8 speed hubs. There's probably some engineering safety factor in that recommendation, but it's worth considering whether you might be getting up to that limit, considering your intended use of touring in the alps.

If you can mount a sprung chain tensioner (like the Shimano CT-S500, or a 'dummy' rear derailleur) to take up the chain slack, it may be possible to use a front derailleur for more top-end gear range, although it doesn't look like your frame has a derailleur hanger. an older, claw-style rear derailleur, or an emergency hanger like this might be a workable solution, but the non-turn washer presents an obstacle. If you go that route, you'll need a narrower, multi-speed chain to match the crankset and FD, and a narrower cog like the CS-S500 (2mm, available in 18 or 20 teeth). Mounting a front derailleur and multiple chainrings on a frame that wasn't designed for it, is its own messy can of worms, and a conversation you may want to have with a trusted bike shop. Other than the 2:1 minimum recommended gear ratio, issues there include BB shell width (yours appears to have a 68mm threaded bottom bracket, so that's not a limiting factor in this case), chainring size/chainstay clearance, and FD cable routing.

Edit: I based these gearing/speed estimates on what appears to be the current model year of that bike, with 700c wheels, not 26,” so my gear estimates are wrong and speeds are overstated. On the gearing front, there's also the possibility of changing to a different internally geared hub altogether, but that's a lot of expense if you don't really need a wider gear range. Even with those 38/22 tooth cogs, and assuming the Schwalbe 47mm tires specced on that bike actually measure closer to 44, the top gear on that bike is a little over 37 km/h or 23 MPH at a comfortable 100 RPM cadence. That's faster than most people ride on level ground, outside of a paceline, and pretty fast for a touring rider with panniers. when riding down a hill, you're not losing much by not having a high enough gear to keep pedaling, but you can always work on raising your cadence if you feel you're missing out just a little too much.

Most of the time spent on a bike, the limiting factor isn't gear range. Aerodynamics and comfort are key.

You may want to lower your handlebars, so that you present a smaller profile to the wind, if you can do so comfortably. Your saddle should be suitable for the angle of your back. as you lean forward, a wide saddle can hinder your leg motion and not give you the right support in the right places. a very upright riding position can also prevent you from using your more powerful leg muscles. I like my saddles to have very minimal padding, or even none at all, but it all depends on your riding style and flexibility.

In a similar vein, clip-on triathlon/time trial bars, and/or the many touring handlebars with additional hand positions, can allow you to get lower and smaller to the wind, and the movement and additional positions are especially nice on longer rides.

Form-fitting cycling clothes are great for both comfort and aerodynamics. Social comfort is a separate issue. It doesn't have to be all or nothing- there are steps between baggy and skin-tight.

I find it very helpful to ride with a cadence sensor. If I get bogged down on a hill without shifting to a low enough gear, it's much harder to recover after that hard and slow pedaling, and my speed on flat ground is more sluggish afterwards.

What can I change or upgrade in the bike so that I can even ride faster in the high altitude with Nexus 8 IGH?

With your current hub, there's not much you can do to alter your speed. Just ensure your riding position is a good compromise between aerodynamic advantage and comfort (drop handlebars would help here but I doubt the IGH shifter is compatible with drop handlebars), and that your tires are high performance tires inflated to high pressure. The problem is, most gearing systems of bicycles have already so wide spread of gears that the highest gear you have is almost always too high, and the lowest gear you have is almost always too low. And the gear spacing is typically ridiculously dense. For example, I have 2x10 gears in a bike I just rode 20 km, and during the ride I only actually used 1x4 gears out of these. In an Alpine ride I would probably have used more gears but 8 is plenty.

However, there are a couple of things to note about internal gear hubs:

• The efficiency is always a couple of percent below that of derailleur gear systems. Thus, you constantly lose some speed. The difference isn't too big however, as losing 2% efficiency loses actually only about 1% of speed due to the non-linear nature of the primary resisting force, air resistance. In any case, the difference in speed a swap from a bad tire to a good tire makes is about 8%.
• Fixing a rear flat is a major pain. You should prepare yourself for that. The more times a flat fix takes, the lower your average speed is.