Chris, you may already know this.
Yamaha did not agree with the FJR having both panniers and top box at the same time. Dunno why - either weight or aerodynamic considerations I assume.
If you are planning a trip with your mate on the back perhaps you should check it out before loading the bike up.
Well done on the deal and taking your mate out.
Cheers Steve, I had heard that about panniers and also don't know why.. The answer ought to be in the manual.
An FJR forum member found this in Yamaha literature, applicable to all Yamaha bikes
I have come across literature promoting yamaha luggage and it specifed that Yamaha "does not advise using topbox as well as panniers BECAUSE OF THE RISK OF OVERLOADING" for all the yamaha range of motorbikes/luggage combos.
Apparently Gen1 bikes could develop a crack right out at the back of the rear subframe near the rear lights, but mine is a Gen 2 and won't be as badly affected. There is a strengthening bracket available on the aftermarket
I watched a Youtube review by an Aussie bloke who had side and top panniers attached and his wife on the back, and he reported it felt a bit light at the front at times.
The best practice that is being adopted is to use the top box for light stuff only, and tank bag for particularly heavy things. The top box is mounted a long way behind the rear axle, and most of the side panniers are behind the rear axle, which to my mind would naturally cause the front to seem light if they had too much weight in them, especially when accelerating out of a corner on the side of the tyres
The solution seems simple. I should eat more cake to keep more weight on the front !