There are two aspects to this question, IMO, so I'll attempt to tackle them separately.
Passenger Ergonomics:
The reason I bought a C 400 GT in the first place is:
1) My sole bike at the time (June 2022) was a 2008 Burgman 650 Exec. It was long in the tooth, and if something major happened to it, e.g., a drive-train problem, I wasn't going to fix it. So I had been looking for a new bike. The AK 550 was tops on my list for a year or so, and I probably would've bought one, had I been able to sit on one.
(Aside: I think the AK looks sharp, too, and the absolute latest version to hit these shores -- or is just about to -- has factory cruise. The lack of that on the C 400s sticks in my craw, and don't even get me started on the jackass Schrader-valve positioning on the Beemer.)
2) In May 2022, my wife (passenger) and I had done two Edelweiss tour weeks on a C 400 X (in Tuscany,
www.billanddot.com/2022-05-Tuscany/, and then around Vienna,
www.billanddot.com/2022-05-Vienna/). At the end of those weeks, my wife said to me, "This is really comfortable. Why don't you get one?"
So that was that, and the day after we got home I called the local dealership, put down a deposit, and ordered one. End of looking for a new bike.
She liked the size and comfort of the rear seat, its position, the position of her feet, and the flatness and position of the pad on the OEM top case.
By contrast, she had never liked any of this on my Execs. The seat is too wide (although this may have changed slightly on the second generation of those 650s) and in conjunction with the floorboard positions means that a typical passenger has to be both bow-legged and pigeon-toed.
BTW, my 2012 Victory Cross Country Tour came stock with three-height-positioning passenger floorboards. And well before that, on my 2000 Valkyrie Interstate, for instance, I replaced the passenger pegs with these super-adjustable mini-boards (along with some other changes for her):
View attachment 4481
Also, the sorryass excuse that Givi calls a backrest pad is too hard, poorly shaped, and badly positioned. In fact, a couple of years after buying my first Exec in 2007, I got some HD-clone forms and had a local upholsterer go to work, and wound up with this:
View attachment 4477
So when my wife said that she was comfortable, it wasn't some idle comment. That is, making bikes comfortable for her wasn't our first rodeo.
By the way, I don't think I'd ever seen a C 400 GT (the only version sold in the USA) in person. When I went to take delivery, I was shocked to see that it had built-in passenger floorboards, like the Big Burgers. I had assumed that it would have passenger pegs, like the C 400 X. Well, luckily, the built-in boards fit my wife just fine, better than even the X pegs, so that was a happy ending. Phew!
Bottom line in the ergo dept.: if you have an average size passenger, one who won't ride back there on
any bike, rented or owned, without some kind of backstop, then the C 400 GT handles two riders picture perfectly.
Power For Two?:
Now, if your question was instead, or in addition, about the ability of the C 400 to get out of its own way with two aboard, I'd say the short answer is "mostly yes."
Indicative of those bike modifications, my wife and I have done a fair amount of two-up touring over the years. Locally, of course, but also down and back from Albany, NY, to Houston, for example. And western North Carolina. And Gaspe, in Canada. And in addition to those two Edelweiss scooter tours, another European tour, for a week and a half, on an R 850 R (at the same time that I owned one of those myself).
But now that both of us are in our 70s, we don't do long two-up trips. (I'm planning on a C 400 GT jaunt to Asheville, NC, next month, for instance, but it will be solo.) And anyway, long interstate-highway slogs are pretty boring, and no one does Iron Butt or Saddle Sore 1000 runs two-up, right?
Locally, the C 400 is peachy, IMO, just as it was for those out-and-back day trips around Florence and Vienna.
I have a couple of short videos from October 2022, from a day of two-up leaf-peeping in the Catskill Mountains on the scoot:
1)
www.billanddot.com/C400GT/#S-70 in my C 400 GT gallery, or
www.youtube.com/watch?v=Ye4ZEyzhDg0 directly on YouTube (six minutes).
2)
www.billanddot.com/C400GT/#S-71 in my C 400 GT gallery, or
www.youtube.com/watch?v=FAyQGkypYT4 directly on YouTube (17 minutes).
I'd say that we kept up a reasonable back-road pace for that activity. And I just checked my telemetry for the day, and it turns out that we had a top speed of 72.3 mph. Fast enough, I think, and remember that I wasn't even attempting to push it -- my wife's not overly fond of hooliganism -- but there's simply about a dozen-mile stretch of 65-mph interstate that I take to get out of town (cross over the Hudson River) going south, is all.
If you want to see more videos, for just a few minutes, with a
little more emphasis on two-up handling, here are two from our Vienna-area trip. We're two-up on a C 400 X, following a solo rider on a C 400 X, who's following the guide on a 300 Vespa (and note that speeds are in km/h, so we're not going all that fast):
3)
www.billanddot.com/2022-05-Vienna/#S-17 (start at about the nine-minute mark)
4)
www.billanddot.com/2022-05-Vienna/#S-18 (start at about 6:30, and note that at 7:38, despite my best efforts to show him what we can do, a rider on a GS, I think, flies by).
So, really, how fast or how far do you want to go ... two-up ... on a scooter?
Interestingly, a few weeks ago on BurgmanUSA there was a discussion of some maxi-(or at least biggish)scooters that were referenced in a recent e-mag article. Someone looked up a bunch of alleged weights and power figures, and did some comparisons of power-to-weight figures. I added to that discussion by asserting that bike power-to-weight figures without adding a rider into the mix are silly, which alters things a bit.
Here's the chart that I came up with, mostly using the figures already bandied about in that thread, but adding a rider:
View attachment 4479
(BTW, I think that figure for the Kymco is BS, i.e., really a dry weight, not a wet one. Some of this info is really difficult to find.)
Well, that's my story, regarding, um,
two-up-ness on the C 400.
Personally, I think that even my 20-HP Meteor 350 is up to the task of fun local two-up back-road riding (even if it maxes out -- one-up! -- at 72 mph). I've had that bike since last July, and so far my wife refuses to even sit on it in the garage (and I have an added backrest). She claims the passenger seat is too narrow, but my position is that looks can be decieving. I hope to convince her to give it a shot, at least for one day, when the weather warms up a bit around here.
