jonwvara 

As a C&V bike tourist, I'm always on the lookout for ever-more stylish, expensive, and complicated methods of mounting bags on my bikes. That has inevitably led me to consider one of those tall handlebar bags that are supported by a small rack below and a decaleur above. There's no arguing with their general French coolness (Randonneur! Constructeur! Decaleur! Look at all those -eur words!), but I'm kind of confused as to how they actually work.

Two questions (I think I know the answer to the first one, but I think I know the answers to a lot of things that I turn out not to):

First, when it comes to the effect of a load on a bike's handling, does it matter where the load is attached, or just the position of the load itself? In other words, a 6-lb load in one of those 1970s handlebar bags that mounts up high, on a metal-rod frame that fits over the stem and handlebars, is going to have a pretty pronounced effect on handling. If you mount that same bag and 6-pound load on a platform front rack right over the wheel, it's going to have a much smaller effect. I know that much from experience.

But if you were to position the same load on a front rack but partially supported by a decaleur, will it behave identically to the same load supported completely by the rack? Or does the fact that part of the load is supported by the decaleur raise the effective center of gravity, even though the bag itself is in the same position as the entirely-rack-supported bag? Does that question even make sense?

My hypothesis is that it's only the position that matters. But maybe there's more to it.

Secondly, how does one go about distributing the weight of a load between rack and decaleur? Depending on how high or low one drills the decaleur-mount holes in the bag, it seem to me that it would be quite possible to create a situation is which the bottom of the bag just barely grazes the front rack, with almost all of the load carried by the decaleur. Alternatively, it would seem possible to mount it in such a way that virtually all of the weight is borne by the rack, with the decaluer doing nothing more than preventing the upper part of the bag from flopping around.

Is that the case? Or through some sort of mystic Frenchness, does the load always somehow get divided 50-50 between bag and decaleur? And if not, does it matter?

Sorry to be so long-winded. This is quite possibly the kind of thing that becomes immediately obvious once you lay hands on it. Not sure when I'll do that, though.

mpetry912 

This is a really good question.i

Bikes that were built with a handlebar bag in mind seem to have pretty neutral response to loading. Having said that, I'd suggest that lightweight stuff (jacket, power bar, phone) go in the handlebar bag and heavier stuff go into panniers on the rear wheel.

Bearing the above in mind, you should not have to worry about distribution of weight between the decaleur and the rack. The decaleur is there to stabilize the load, and the rack takes the weight.

Again, heavier stuff goes in the back.

Mark Petry
Bainbridge Island, WA USA

TenGrainBread 

The position of the weight is the only thing that matters regarding handling. Where the attachment points are does not affect handling. The bag is fixed in position regardless of how it is mounted. The proximity of the bag to the steering axis and center of gravity affect the handling.

As far as ideal weight distribution between rack and decaleur, the rack should take most of the weight. The purpose of the decaleur is to stop the bag from moving and falling off the rack (aka stabilize). Whenever I build a decaleur I try to position it so that the bag has some sag over the rack so that the decaleur isn't holding the back off the rack.

gugie 

As Mark noted, the decaleur is there to stabilize the load - it stops the bag from wagging left and right. Properly designed it won't take any vertical weight.

I'll be the contrarian on weight distribution. The rear wheel already has more than half the weight on a bike on it just from the rider. Try standing on the pedals uphill with a full rear panniers - there's the "tail wagging the dog" syndrome; it's hard to keep a straight line like that. To counteract the twisting forces on a frame, many bike designers design heavier gauge or larger diameter tubing, which deadens the ride. The Surly Long Haul Trucker is the best example of this genre. It's been said it rides the same loaded or unloaded - dead.

I like riding a light, lively frame, even when touring. If I'm credit card touring, my kit won't fit into just a handlebar bag, about 5-6 pounds goes into a saddle bag, about 8-10 goes into my handlebar bag. If I'm camping with tent, sleeping bag and cooking kit I forego the saddle bag and use low riders, and all the extra weight goes up front. The enabler is low trail.

Here's a pic of 10 bikes on the way to un-meeting 2016. All of us were going to be camping. Eight of the ten have most or all of the kit loaded in the front. Riding uphill on the zero-shoulder Columbia River Highway I could stand and pedal without wobbling from side to side.



Heavier stuff goes in the front when I ride on my low trail bikes. If you have a high trail bike, yep, keep the heavy stuff out of the front. It'll mess with your handling.

gugie 

Ditto!

More thoughts: traditional racks designed for handlebar bags have a "tombstone" or "backstop" built in. Handlebar bags designed for this have a strap in the back that the tombstone slides up into. The angle of the tombstone matches the head tube (~73 degrees).




A traditional decaleur has a set of pins and receivers and are angled perpendicular to the road. This mismatch helps keep the bag from flying off on bumpy roads. If you hit a bump, the bag moves up along the tombstone angle, but the decaleur constrains the bag to only a "straight up" trajectory, with the result that the bag "tightens" up on the system. You notice this when you take the bag on and off the bike - you have to bend the bag a bit to get it on or off.


pic courtesy of Eric Langley

mpetry912 

Alright, so I agree on the low rider thing - esp. positioning the load so it is neutral to the fork axis of rotation.

is there a rule or formula for the ideal trail measurement when a front bag / decaleur combo is part of the design ?

Here is why I ask the question. I've owned several Alex Singer touring bikes and twice - twice - I have managed to steer myself out of a "for sure" wipeout when the front tire slid on wet or oily pavement. One of those times I was leaned over where I knew I was going down ! and was able to recover it. BOTH of those bikes were front bag / decaleur equipped "by design".

What do they know that we don't ?

Mark Petry
Coronado Island, CA

jonwvara 

I know almost nothing about trail, frame angles, and all that stuff. But this thread is connected with my plan to go on a lightly-loaded four or five day tour with my PX-10, which I understand has a reputation for having lots of trail. It's not the bike I'd ordinarily tour on, but I'm bound for Eroica so the PX-10 seems like a logical fit for the event.

I'm going to go really light for a camping tour--basically just the clothes I'll be wearing, a super-light down jacket, light down quilt, foam pad, and bivy sack. So no panniers, front or rear (I ordinarily use only front panniers--I don't even own a set of rears). I'm figuring that most of the stuff will go in my Carradice Camper saddlebag. No doubt there will be a little overflow, which I guess will go into a Jannd handlebar bag (originally designed for stem mounting) that I plan to reconfigure so it mounts on one of the old Blackburn platform front racks to keep the weight low. Hoping to keep the total load to 15 lbs or less, with no more than 5 in the front bag. Based on what people have said here, that seems like a better option than a larger handlebar bag.

EDIT: I should have mentioned that I'll only be riding from San Francisco to Cambria, not all the way across from Vermont, more's the pity. I would need panniers in that case.

gugie 

"Several" Alex Singer touring bikes?

repechage

Some are twice blessed.

repechage

My thought on thefront bag system, is that bikes with a handlebar bag in mind often have lower trail. The rack imaged by @gugie does show a solution I like as well as it helps the bag from shifting around.
Still needs some restraint up top.

gugie 

Indeed. Even with this designed-in way of keeping a bag from self-ejecting, it can still happen. To make it truly eject-proof, there are several solutions.

Compass Rene Herse decaleur with locking device:



RaClips from Waxwing bags



"Ortlieb hack" decaleur, an idea I stole from Ocean Air Cycles


I've also seen velcro used to attach the bag to the rack.

repechage

Waxwing bags look decent. I forgot about those.

palincss

The decaleur stabilizes the top of the bag. It doesn't support the load.

natterberry 

I have a Waxwing bag, and ordered the raclips and Dock-It decaleur. I can take pictures of that setup Thursday.

jdawginsc 

Just going from an article I read in Bicycling magazine YEARS ago... I think I remember the formula for weight distribution was something like 50/20/30 (front pannier/handlebar bag/rear panniers+rack sackage). I think the article also said that handlebar bags were actually handling killers, except when panniers were also in the front.

gugie 

I'm pretty sure that Bicycling magazine actually invented the "horizontally stiff, vertically compliant" mantra.

TenGrainBread 

Not sure how there could be a "formula" that exact without taking into account variation in design and geometry between bikes.

Most things written in Bicycling should be taken with a spoonful of salt...

rhm

The lightweight racing bike is a certain aesthetic ideal. Clean lines, skinny tires, nothing attached to the bike except a frame pump and maybe a tiny little tool bag under the seat, and maybe a tubular tire. If that's your ideal, then an accessory like a decaleur is going to seem bizarre, if not downright perverse.

The thing is, a decaleur may look like an accessory you attach to a bike, but it makes sense only as a part of an integrated system. Obviously that system includes a bag and a rack, but it doesn't stop there-- or should I say, it didn't start there. The weight on the front wheel, turning with the rest of the front end, throws off the handing of the bike unless the frame was designed for it.

Hence gugifacazione.

palincss

True for certain front end geometries, most definitely not true for others. Of course, even though this was known as far back as the 1930s we forgot it by the time the Bike Boom rolled around, and didn't rediscover it until the turn of the new century.