Decaleur purpose and design

[Jimmy Livengood]

I'm mulling over an idea I have for a decaleur of sorts and wanted to get all y'alls' input. For my day job I recently did a bunch of looking around for quick-release hardware, and after solving the problem I was tasked with, I started thinking about how the hardware I found could be used as a decaleur of sorts. 

I see four major functions of a decaleur:

1. Keeps the bag away from the handlebars, leaving room for hands.

2. Keeps bag in place while a rack supports the weight (i.e. no attachment to rack, just gravity).

3. Keeps upper part of bag from flopping around (some soft bags, even when attached at their bottom to a rack, the upper portion can be floppy).

4. Allows for varying levels of quick-release function to remove a bag from the bike and take it with you (and quick re-attach function).

Am I missing anything? I'm curious how bqrr readers use their decaleurs, and which features they wish theirs did better. 

I'm also curious about peoples' opinions on various mounting points or buying decisions. In my mind any decaleur should be able to work with most racks and most bags. That is, people probably already own a bag and or rack, then purchase the decaleur. I would expect a successful design would have to be able to be easily bolted/screwed/attached to existing bags, racks and/or handlebars and headset areas of most bikes (at home with simple tools that most of us have). 

It's a fun problem to think about because I feel that designing a rack with special brazed-on hardware that fits into special parts that are sewn onto a specific bag is easy-ish to do, but making a more universal kit is a fair bit trickier to get right. 

My initial instinct is to abandon all headset and handlebar-attached hardware. It seems too much at the mercy of  too many variables like head tube length, handlebar height, stem length, rack height over tire, rack distance from head tube, bag size, stem type, bar diameter, etc. I feel like a rack-mounted decaleur is a better solution to pursue, but have my hesitations is regarding points 1 and 3. 

PS not trying to be intentionally vague, but want some input before talking specifics. It's really just sketches at this point. 

Things like this Yipsan bag/rack seem so perfect. 

http://www.flickr.com/photos/renold_y/5457987668/in/set-72157625959776283

All it would take is creating a hook kit for the underside of the bag, and this idea could be used on any GB or nitto rack. Friends I know have done very similar using Ortlieb hardware. Are there advantages a decaleur has over this rack-based sort of QR and retention system?

Jimmy

Seattle

[Steve Palincsar]

On 11/15/2013 12:15 AM, Jimmy Livengood wrote:
>
> I'm also curious about peoples' opinions on various mounting points or
> buying decisions. In my mind any decaleur should be able to work with
> most racks and most bags. That is, people probably already own a bag
> and or rack, then purchase the decaleur. I would expect a successful
> design would have to be able to be easily bolted/screwed/attached to
> existing bags, racks and/or handlebars and headset areas of most bikes
> (at home with simple tools that most of us have).
>

Neither of the decaleurs I use (Berthoud & Velo Orange) have anything to
do with the rack itself. The decaleur attaches either to the stem, in
the case of the Berthoud, (and Berthoud makes several models for the
various stem designs) or to a spacer in the threadless spacer stack, in
the case of the VO. In the case of decaleurs that attach to stems I do
not believe it possible to create one design that will work with all stems.

Also, your purchasing sequence is off. Since decaleurs either have no,
or at best only a small adjustment range, you need to purchase a bag of
the appropriate height to fit the space between the bottom of the rack
and the decaleur attachment point. For low handlebars and small head
tubes, this means you need a small bag; for high handlebars and tall
head tubes this means you need a large size bag.

[Jan Heine]

There are two important requirements that many designs overlook:

5. Bag must remain securely attached even when going over rough ground.
6. Decaleur must be maintenance-free and reliable for many years and
tens of thousands of miles.

I have had too many bags fly off during rides on test bikes, and I've
seen too many broken decaleurs.

>I feel like a rack-mounted decaleur is a better solution to pursue,
>but have my hesitations is regarding points 1 and 3.

The biggest problem is that a rack-mounted decaleur must be
cantilevered upward, which leads to flex and (often) premature
failure.

I think a better solution is to work off the handlebar or stem - they
are ideally located and provide a strong mounting point - and just
make decaleurs with different drops to accomodate different bag sizes
and frame sizes. After all, most of use buy stems in a single length,
too, rather than try to come up with a one-size-fits-all adjustable
stem.

Jan Heine
Editor
Bicycle Quarterly
http://www.bikequarterly.com

Follow our blog at http://janheine.wordpress.com/

At 9:15 PM -0800 11/14/13, Jimmy Livengood wrote:

>I see four major functions of a decaleur:
>1. Keeps the bag away from the handlebars, leaving room for hands.
>2. Keeps bag in place while a rack supports the weight (i.e. no
>attachment to rack, just gravity).
>3. Keeps upper part of bag from flopping around (some soft bags,
>even when attached at their bottom to a rack, the upper portion can
>be floppy).
>4. Allows for varying levels of quick-release function to remove a
>bag from the bike and take it with you (and quick re-attach
>function).

--

[Jimmy Livengood]

Thanks for your comments, both here and those who commented off-list.

[Ken Freeman]

A little late to the party, I guess!

I think the decaleur exists to hold the top of the bag steady.  

• No sliding forward while braking
• No sliding sideways while turning, leaning, or negotiating bumps
• Minimize vibration so you can keep reading the map
• Help to limit the vertical motion of the bag
• Help to keep the bag upright so the pockets and their flaps remain accessible, and any provisions for rain management remain functional, such as drip paths on bag lids.
• And reliability, durability, beauty, et cetera.

The rest of the picture is for the rack:

• Support the weight of the bag and load
• Prevent the lower portion of the bag from moving up, forward, or sideways.
• Prevent a flexible bag bottom from sagging over the rack platform and stressing the decaleur.
• Plus reliability, durability, beauty, et cetera.

So holding the bag in place is partly the rack xand partly the decaleur.  The decaleur stresses should be primarily in the horizontal plane and the rack stresses both in horizontal plane and in the vertical direction.  The horizontal functions of the rack could be provided by a strap around the tombstone, but the vertical functions are less-well satisfied.  Both functions can be nailed well with a bottom attachment.