Originally Posted by aliasfox

I cruise between 18-20mph, or about 29-33kph. I do this with a 50T ring up front, and between 13-16T out back, depending on terrain. That leaves me gear ratios between 3.33-3.85, driving a 28mm rear tire.

With a 40T ring up front, similar gearing would be between 10-12T. If your cassette starts at 11T, you'll likely be spinning up quite a bit on long gentle downhill grades - I can get around 22-24mph (36-39kph) on a -0.5-1.5% stretch, and I use 50x12 for that, sometimes stretching into 50x11 if I'm feeling good.

I think a 40x11 top gear would be a bit limiting, but not so much that it wouldn't work, especially if you're running slightly bigger tires to compensate. I'd personally want something with a slightly bigger ring in front, or a 2x setup, if I were planning on a fair amount of road @30kph or better.