Yes it's true, and after a quick look on Google it appears I'm not the only one to suffer this.
Heading down the A-67 Autovia form Torrelavaga to Palencia in northern Spain I looked down to my left to see a yawning gap where my pannier used to be

Of course on that particular stretch of motorway I happened to be 20 miles from the next turn off, so I had to do 40 miles just to get back to where I noticed it missing. I then ended up going a further 75 miles back to a petrol station where I last filled up. Now I was pretty sure it was still there when I filled up - or was it? I was focused on the ride ahead (280 miles into Portugal) so maybe I didn't notice it was gone. Well, anyway it was only another 20 minutes to the previous overnight hotel so I went right back to the beginning.
Nothing.
I was left with no option but to set off again. I asked at the petrol station, they had nothing. After another one and a half hours riding while scouring the verges for a stray pannier, debris littered across the road, clothes and some camping gear blowing in the wind, anything; no not a thing.
I can't believe the pannier just came off because it's such a pig to get on or off normally. Same as if it was stolen at the petrol station. I literally filled up, paid and left. I could never have got it off in that time even with a key, and why would anyone want too anyway? That's why the inner bags are such a good idea; fit the panniers once and just offload the inner bags when you get to your hotel. Except you cant easily get to the bungee hooks with the panniers fitted.
Like I said I have heard of other instances of panniers dropping off, even on this forum I think. But how could that happen without me noticing in my rear view mirror, something come loose and bouncing down the road. I must say with just one heavy pannier on one side the handling of the bike did not change at all as far as I could tell. It's all a complete mystery

I keep expecting to go "oh, there it is, it was there all the time". But that's not going to happen.
Of course thinking back there are little things that cross your mind. Mainly that I noticed the pannier did rattle a bit when locked in position compared to the other side which was solid. But I only noticed that the morining I set of from England and it still felt ok. I've had the panniers for 5 years or so and done around 15,000 miles with them fitted. Do the locks wear out? It's a bit rubbish if they do.
So after riding around 8 hours 400 miles I finally arrived in Breganza, Portugal with only the clothes I was stood in and no way of cooking if I decided to camp. The stretch of road from the A-52 motorway into Bregaza was an amazing switchback for 25 miles over the mountains but I really didn't appreciate it; I was knackered and somewhat pissed off. I went and bought some new gear but I had to limit what I bought as I couldn't carry it anyway. Eventually everything became a big struggle I wasn't enjoying, so I bailed out and got an early ferry home

The upshot is, if anyone happens to find a left side Ducati pannier (white top) by the side of a motorway in Spain, there's a good chance it's mine! And if anyone has a spare left hand pannier (maybe you lost the right hand pannier

) get in touch we can do a deal
