i have a rear rack but often I would like to carry a duffle bag on my bike and it doesnt fit on my rear rack.

I have seen people use 2 kitty litter panniers to carry large things but are there other alternatives without going to a special long wheel base etc bike?

Can panniers be used to widen the rear rack, or are they to skinny/floppy?

How about 2 smaller bags/ panniers on each side of the rack?

Depending on the size and weight of your duffle bag, two low cost solutions that I've either tried or currently contemplating:

-Find you some old election campaign signs and put them in the bottom of your bag. Then use a cargo net to hold it down to your rack. Jandd and Ortleib both have rack duffles, but I think they use foam, and they incorporate velcro straps to anchor to the rack.

-Do what I did.

yeah LEEBO thats one of the things i was wondering, has anyone used 2 normal, fabricy panniers to widen a rear rack to hold something like a duffleback/suitcase?

How about a large wald basket fastened to the rear rack?

There are some rear 'luggage' systems out there that have 2 saddlebag panniers that hang off the side of the rack and another bag that mounts on top of those. Different interpretations of the concept at varying price points and execution. Here's one for illustrative purposes- https://www.amazon.com/M-Wave-122310-...8360876&sr=8-5

How about , Plywood,say 3/8", 10mm thick , ?
and P clamps, plastic should do , with enough of them used.
and some screws into the wood, or bolts thru it.

I widened a narrow front rack , in this manner.

Depending on the mass of the OP's duffel bag, the same could be done using coroplast without adding too much weight...

one can always cut out holes.. ,
OTOH/FWIW, There is Polycarbonate Coroplast..
extra strong , in comparison to the regular stuff ..
but won't be free, on the day after election season no longer needing lawn signs.

I complimented a fellow commuter on a similar sounding setup yesterday on my way home. He had a wide/long platform of what looked to be 1/4" plywood on his rear rack, with a rubbermaid tub attached to it. Didn't see if it was bungee corded or what, because he was passing in the opposite direction.

I use 4gal bucket panniers that I made such that when they hang on the rack, the top of the buckets are even with the rack platform. That gives me about 24" of extra width on the rack.

I use a wired on 1/4" plywood rack extender for big, heavy loads such as bags of cement.
For a lighter school bag, a few layers of coroplast glued, bolted, rivetted, ziptied together will be fine. Punch some holes, add some reinforcement and ziptie to the rack. This should last a couple of years.

The materials are zero cost, you can pick up coroplast and zipties for free.

Skateboard deck. You can get them up to 12" wide. Definitely able to hold a sm-med duffel. Clip, zip, or bolt it to your existing rack. if it's too long, you can easily cut it to fit. They're usually ply and polyester resin. Makes it weatherproof and easy to reseal if you need to do any cutting or drilling.

i like the idea of being able to remove the rack-widening feature but some of those ideas (like plywood/skateboard deck) seem pretty cool although prevent me from using panniers if i wanted to (not that i do now).
Does anyone think something like this could be used or is using the fabric style panneirs not conducive to rack widening?

I cant use my panniers with my deck expander.
I'm pretty sure that you could design a deck expander that is pannier compatible, with suitable cutouts. You would need the right kind of pannier mounts ie Ortleib?Rixen and Kaul style locking QR.

No I mean use the panniers as a deck expander, like tieing a wide load to the top of the panniers like in post#6, but not a premade system.
And yes bolting on something like plywood would make attaching panniers difficult.

I think a Topeak basket will work with panniers. You'll have to get their rack, as well.

https://www.topeak.com/products/baskets/MTXBasketRear

Only hard-shell panniers would work as deck expanders but even then, not very well. You cant lash items to the edge of the pannier platform, only to the rack and you cant open the panniers when carrying a load on top.
The 3-part panniers that drape over the rack are no good for carrying big loads, the top compartment usually does not have stiffening over the top of the side compartments (else it would obstruct their opening).

When my 2 cloth panniers are fully loaded, they do offer some support for big, lightweight items such as 6-packs of kitchen paper roll.

I have a pair of backrollers and, when I'm going to play a concert, I stuff my usual clothes-stuff into my panniers, strap my saxophone to my back (backpack style case), and use the shoulder straps of the panniers to strap my collapsible music stand to the top of my rack such that it is partially supported by both panniers and the rack.

Is that close enough? It seems to work reasonably well for me.

(I picked up a used Yak for $100 this week so I won't be doing the stand on the panniers bit again, though.)

I've seen this done a few times.

Also when I used to run cargo as a courier, I strapped a board to the top of my rack to just give it a few more inches of length (it was the same width), to make loads like bankers boxes of documents more stable. Just bungee-ing a board to the rack sufficed, and I was able to quickly remove it when I wanted.

If I was the OP I'd be tempted to take a sturdy board and cut out some holes in it to lash it to the rack, and maybe cut some tie-slots for the duffel near the out edge. Surplus military leather buckle straps can often be found online and could secure it to the rack and also be quick to remove the whole set-up if/when needed. Although I usually use bungees, or a bungee net, I also use these leather straps regularly for different loads.

Hi! First post.
What I did was take a milk crate, and using a table saw, cut the sides down to about 3". Then I cut one of the sides off, leaving me with a little pickup bed, open at the back. I ziptied it to the top of the rack, and it's rock solid. With a couple bungee cords, it's way more useful than a skinny rack, or a full size milk carton.

Rear rack brands should offer an wide platform option that fits securely onto their racks like their trunk bags that slide into their racks.