If I take my Whippet shopping I will need to use my big lock. There’s no way I could put it in my backpack so thinking of carrying it on a rack like this. Are carbon seatstays hollow or solid? I would be happy to use the qr support if solid.
It would only be on the bike in rare shopping trips.
https://www.ebay.co.uk/itm/313991217852?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=ybu0gl2mtjq&sssrc=2349624&ssuid=SyLfpeirQlG&var=&widget_ver=artemis&media=COPY

Are carbon seatstays hollow or solid?

Normally hollow.

I’m sure they can take some weight on them…

It doesn’t look as though you’d need a lot of force applied to the quick release. I’d probably use some old tube or something as a shim to provide a bit more grip and less hard contact with the frame, and then close the quick release with light pressure.

Aluminium seat post? A seat post only mount would be a safer bet
For carrying the lock only? Can you rig something on a bottle cage mount?
Shopping in the back pack…YMMV

Would it not fit in a big saddle bag?

My friend crushed his seat tube on a planet x dirty disco frame over tightening his front mech. I wouldn’t use that rack on a carbon frame.

As above, seatpost only clamp and don’t put too much weight on it.

Topeak do an excellent rack that clamps on the seatpost without the extra struts. I have one and it accommodates the slide on bag system. Doesn’t move, carries decent load, easy to fit. Worth whatever it cost me some years ago!
Hope this helps.

I have that exact rack and haven’t got on with it I’m not sure I’d want to clamp those arm to a carbon seat stay. However had a rack like the toppeak one then when in place didn’t move a mm for years, not QR though

I’d mount at the QR axle and the rear brake bridge. Tubus make attachments to both for their racks. Both mounting points are used to taking a load. I wouldn’t be using p clips on carbon seatstays.

Or go topeak beam rack on an alloy seat post. I have one and it’s great. Takes a lock easily. I prefer the one with side pockets rather than drop down pannier sides. I replaced the QR with a bolt so nobody else takes it with them. I’d use that on a carbon frame with a decent insert into the frame. It’s well made and doesn’t move.

£31 with free postage.

By the time you’re done faffing to make sure it works I’d have thought something like this would be cheaper, plus it’ll keep your bum dry when it’s wet…

https://www.ebay.co.uk/itm/354108618612

If your lock won’t fit in your backpack, how are you planning on carrying any shopping?

IMHO, get a more compact/stashable lock or a practical shopping bike. A whippet isn’t entirely versatile.

I’ve got too many bikes and not enough space. My current shopper has not been used this year, I keep it just in case. It’s not worth much so I use small locks that fit in my backpack.
If I could use a suitable rack on my whippet that would carry a wheel to the bike shop and a rack to carry my big lock I could lose a bike .
Maybe I will investigate a rack for my fatbike instead.

If I could use a suitable rack on my whippet that would carry a wheel to the bike shop…

https://www.ebay.co.uk/itm/185213266510

…and a rack to carry my big lock

As the replies above

Several +1 is better though 🙂

I’ve got too many bikes…

but have you got space for a fold up trailer?…

Y-Frame

I got one of these.
https://www.ebay.co.uk/itm/154998060747?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=9kapSP5XRGK&sssrc=2349624&ssuid=SyLfpeirQlG&var=&widget_ver=artemis&media=COPY
I can use it on my shopper.
Would it be ok with my suspension seatpost on t’whippet?

I was wondering if there are any racks out there like the tailfin system which clamps on both the seatpost and onto the rear axle so no reliance on seatstay strength. i.e. the load being taken through the axle rather than the seatpost.

but not at £159 or more for the tailfin system…

Tubus will clamp to a seat post, you just need an adaptor. I use Cateye seat post light mounts on my recumbent trike – two of them to mount a rack. Tubus have adaptors to fit racks to the QR axle. they also do a 35mm long extended stay which I also have on another folder to rotate the rack back (short chain stays mean I bang my shoes on the pannier).

clamp https://www.sjscycles.co.uk/lighting-spares/272-supernova-seat-post-clamp-for-e3-tail-light-black/

QR kit https://www.sjscycles.co.uk/carriers-racks/tubus-adapter-set-for-quick-release-axle-mounting/

Long stay (I use 360mm) https://www.sjscycles.co.uk/carriers-racks/190mm-black-tubus-roundstay-l/

Nice rack (tubus are out of stock at sjs) https://www.spacycles.co.uk/m5b38s79p1772/TUBUS-Airy-Titanium

(OK a very nice rack but others are available 😀 )

A QR for the seat post could make for very fast removal – take out the axle and replace, then unclip at the seat post.

Would it be ok with my suspension seatpost on t’whippet?

As long as you aren’t cranking it down really tight. I’ve put one on a dropper with no ill effects.
The ex did a week of light weight touring with one of them, a bar bag and a couple of dry bags.
(I have the proper rack version of that, as i have in the past done shopping with it.)

I’ve got too many bikes

No you don’t.

and not enough space.

Just a prioritisation issue… 😉