Guru (can I address you by your first name?),
Thank you for the question!
The 48T chainring is the proper choice for riding fast on the flat or downhill at pretty high assistance. It also encourages the rider to use middle gears, and the cassette cogs last longer that way. The Praxis ring is easy to install and it allows the use of the chainguard.
The choice of the 38T steel chainring is the choice for riding the Vado in true mountains (with many steep hills). In case you can have a 11-46T cassette combined with the long cage derailleur, you are getting close to the MTB gearing of 20 gear-inches. Combined with the TURBO mode, it allows easy climbing of 19% grade inclines (I haven't tried even more steep climbs). It is even possible to get the 11-51T cassette for the 11-speed drivetrain (it requires a dedicated derailleur), and that puts the Vado in the MTB league (I did not need to do that!) When you are riding in the mountains, it is either a climb or a descent. You simply do not pedal your e-bike downhill, as getting at speed of, say, 40+ mph is dangerously easy there without any pedalling!
The 42T chainring feels the sweet point for me. It gives me a good climbing capability in the area I live, and I can also ride easier in the rough terrain such as the forests we have here. The top speed is somewhat limited (the cadence limits you at some 25 mph) but I could ride at 29.2 mph by mad spinning the cranks just yesterday. The drawback is the 4 smallest cogs are the ones mostly used, which leads to their premature wear. Fortunately, these cogs can be bought and replaced by a mechanic, making it possible to make an inexpensive repair instead of replacing the entire cassette. Note: I feel a 44T chainring could be even better for me here!
The Garbaruk company is a fascinating phenomenon. Mr. Garbaruk, a Ukrainian, has got an extremely good know-how in metallurgy. He has also understood the drivetrain mechanics to the expert level. He set up his factory in Nowa Huta, Poland (a steelworks city) to benefit of manufacturing inside the European Union country. Garbaruk drivetrain components are of top quality, are lightweight, and expensive
I had a look at how Garbaruk designed his chainring: it has exceptionally long teeth, preventing the chain drop. I'm a fan of Garbaruk products now!
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A display of Garbaruk cassettes at the biggest bike store in Poland. Very expensive products! The prices start from US$240 there.