In part 1 I wrote about how suspension can be an advantage on a fast bike. And in the end I mentioned the added comfort. Now especially American riders often seem mighty concerned about rear suspension. They (excuse me for the generalization, but this is the impressions I get from following the forums )say it soaks up energy when they climb. And they are worried about the extra kilogram it ads to a bike. Don't they know that extra kilo makes your bike more comfortable and faster? And keeping your wheels on the ground also is a mayor safety feature.
Anyway, the climbing thing. If you want a bike with rear suspension and rear wheeldrive, you need the right chain line. The 'right' chain line is more than just a line trough the pivot point of the rear swing arm. That's what many people think. I can't do the calculations, but this website is a good tool for those who are not an experienced ' bent designer.
You can control the chain with an idler. When that idler is placed at the right place, all the power you put in at the front, is transferred to your rear wheel. If you do it wrong, energy is wasted in making your bike bounce. Now some say that the solution is a stiffer spring. Wrong! Very, very wrong. A stiffer spring only makes the problem less noticeable. There's less movement, but just as much loss.
Especially when climbing that is a big problem. When you climb, you often pedal less ' round' and you put in more power. Now let's look at a Nazca Gaucho Highracer. That has comfy, safe and fast rear suspension, but also allows you to climb like a mountain goat. I haven't done any serious climbing, apart from my Spezi adventure, but others have. I have ridden it, and now matter how hard and I stamp on the pedals, I can't sense any movement in the rear swing arm.
Now if you're a racer, you're looking for what is absolutely the fastest. Than you might worry about a tiny little bit of loss. But for the 98% of the riders, the advantages of proper rear suspension can not be ignored.
My old Cruiser did not have a chain idler when it left the factory. Cruisers didn't get an idler until 2009 or so. I added on with help of the website I mentioned earlier. On my way to the Easter meeting earlier this year I got to climb a bit. And even when I really tried to get the suspension to pogo, it didn't.
Conclusion. Not having suspension only is an advantage for a small group of people. They race on super smooth roads. Everyone else who commutes, travels or tours will be happier with good suspension.