Rack Rail Size
 

When the size of the rail of a rack is given, for example, 8 mm, 11 mm, etc, what exactly is that measurement? Is it the circumference of the rail, side to side distance?

Btw, does the Ortlieb backroller classic waterproof bag's hooks fit onto Topeak (Explorer) racks without adaptors? Thanks.

It's the diameter of the tube. My Topeak rack is 8mm, and Ortliebs come with little inserts that more or less permanently fit into the hooks for the smaller diameter tube.

As an aside, Backrollers are huge, so unless you really need all that capacity, you may want to get Front Rollers and use them on the back.

Thanks Alan.
Yes there is a gap between the rail and the inside of the hooks. However, with the third point of attatchment to the lower part of my rack, the bags seem pretty secure. Would you still think it necessary to use the inserts? I am hesistant, because if I decide to use another rack with wider rails someday, the inserts might be tough to remove.

I just looked at mine and I'm sure I could pop the inserts out without much trouble using my staple remover (handy tool in my desk). I didn't actually remove them because the insert may break but I don't really think it would. I would use them, and if I go for Tubus or such racks on my new bike I'll pop the inserts out. And save them for when I ride my old bike again.

I do have the front bags and use them on the back, mostly because if I had the back rollers I would fill them up. I'll still get a set one day for touring.

Thanks Enigma.
I commuted today with the Ortliebs, and they stayed nicely in position despite many bumps, and I didn't have to use the inserts.
The lower lever keeps the bag from moving forward, and the back bar of the rack prevents it from sliding back. Nice!

Depends on how much you mind the rattling over bumps and such. Some folks ignore it completely, others it will drive nuts.

The inserts aren't easily removable, but they are removable. I've used a small thin-bladed screwdriver, something like an eyeglass screwdriver. There's probably a better tool, but I don't own a better tool.

Alternatively, you could try the build-up method. My Tubus rack is 11mm. The no-name rack on my other bike is 8mm. I marked where I mount the Ortleibs on the second bike, and wrapped electrical tape around the rail until I built up 3mm. Works great.

Thanks for the idea TSI!
I hadn't noticed any rattlin' but if it becomes noticeable, I'll try the tap method.

FWIW, I got a New set , and ordered a spare hook set, old type , and put those on ,
+ transferred from my older set, a second set, they are 10mm only,
I use them on my Ortlieb racks, and the fit is perfect.

swapped the newer hooks off one pair onto the set i hang on my Bike Friday
they use a tube slightly smaller than 8mm to make their pack flat racks.

a little tape and rubber on the lower portion, for that hook..

I contacted Ortliebusa, and the rep recommended using the inserts to reduce vibrations and to prevent deformation of the top hooks over time. So I put'em in.