2 Jul 2012

Minimalist, ultra-lightweight trike rack for a saddlebag.

3rd July 2012.

The Carradice Camper saddlebag needs a firm mounting but I had no desire to add the usual trike rack. I didn't have the usual, brazed-on fixing points on the seat stays. Nor the funds to buy a new rack. Though I could have silver soldered my own screwed bosses in place it seemed like a lot of unnecessary effort. I would need a trike rack to be able to position the screw bosses accurately.

It occurred to me that most saddlebags do not enjoy a rack to support them underneath. They merely hang loosely from the saddle loops. I decided I could do even better. By providing a more gentle strap support and something for the bag to lean against.

The problem was finding suitable clips to fit the Higgins tapered chainstays. Then I discovered brake clips. These come in a range of sizes at quite modest cost at most cycle shops. About 12-15kr or £1.20-£1.50 (equiv) each locally.

It should be mentioned to those who still have some paint on their seat stays that these clips are easily opened wide to place over the stays. They can then be closed by finger pressure alone. With care, this will completely avoid paint damage. One could slip a length of tape inside each clip. Sticky side out. To avoid paint damage when the clip is tightened and then finally adjusted while still fairly tight. 

At first I fitted an alloy tubular crossbar to support the bag straps and thought I was finished. Unfortunately the bag curled its "toes" around the trike's seat stays. Which was great for bag stability. However, with the already minimal heel clearance for my size 11s I found these protrusions got in the way while I was pedalling. So I added another crossbar lower down to push the bag away from the trike's seat stays. This also keeps the bag more evenly supported at the bottom.

One Carradice bag owner even added his own, matching, internal dowel at the bottom, inside the bag, for extra stiffness. I did not want to screw through the bag fabric. Since it was probably unnecessary with my minimalist rack in place.

Now I needed some screw heads which would not slowly bore their way through the bag's cotton duck material. I found dome-headed screws in 6mm x 25mm long. With a square shank under the large head for locking against rotation. Much like a coach bolt but fully threaded. The screws were also lightly galvanised. I already had plain and Nyloc nuts and washers.

The clips did not want to lie flat against each other so I added a plain nut and spring washer between each pair. This avoided the clips trying to bend the alloy crossbar around the seat stays as they are tightened. A Nyloc nut safely avoids it ever coming loose.

The 12mm clips fit the alloy crossbars. The latter were made from scraps of old aerial tubing. I gave the tubes a rub with wire wool to remove the worst of the oxidation. I suppose I could have polished them in the lathe but decided to see how they fared in use first.

The top crossbar was drilled for the 6mm screws to simplify matters. Otherwise I would have had to use two more clips. The screws alone look much neater, I think. They are placed between the seat stays to give the straps a clear run without distortion. Nor are there any sharp edges to fret at the edges of the traps. Only time will tell whether the tube has been weakened by the drilled holes.

The whole arrangement is very simple, cheap and incredibly lightweight. The clips are quite substantial and springy enough to allow some leeway in sizing.

I used 15mm clips for supporting the bottom crossbar fixing. Here the seat stays are larger than at the top. There are no real loads on this crossbar. Though I added a cord to stop the bag lifting or bouncing over severe bumps. Using the same riveted, strap fixing tab as is normally used to strap the bag to the saddle pillar on a bike. (see bottom picture)

Note: In retrospect the bottom stay clips should have been placed between the seat stays too. This would avoid all chance of heel contact with protruding screws or nuts. One can easily saw off an over-long screw but risk ugly rust on the bare metal. Stainless steel screws would be better, if available.

Hopefully, the pictures show all the details required. The spacing of the clips is critical on the top crossbar only if the tube is drilled. If two pairs of 12mm clips are used then the clips can be tightened at whatever height they need to be on the trike's seat stays. The only requirement is that the hanging straps have a clear run around the alloy crossbar just outboard of the trike's seat stays. This sets the minimum height for the crossbar due to the angle between the stays. Trying to bring the hanging straps inboard of the seat stays is likely to place the bag far too low.

In retrospect, avoiding drilling the tube may actually be a good thing. It probably does weaken the tube. Though this shouldn't really be a problem in use. Since the leverage is very low and very close to the hole and the supporting clip.

Update: I moved the clips between the seat stays on the lower crossbar. I also added a second nut instead of the spring washer to each side between the clips. This pushes the bag slightly further away from the seat stays. Perhaps avoiding rubbing the seat stay paint away at all.

One could add adhesive protective strips to the rear of the seat stays. Such as those which are commonly attached to the chainstays of posh racing bikes. To protect the paintwork from the chain when the wheel is dropped out in a hurry.

One could also stretch some cords or webbing between the top and bottom crossbar to keep the bag further away from the paintwork. Or, perhaps the easiest solution: Just use longer screws and then increase the packing between each pair of clips. This should help to move the bag even further away from the paintwork on the stays. The image shows the latest set-up. The bag only contacts the crossbars now instead of the trike seat stays.

Alas, it is much too late for my Higgins.  Assorted, dangling sports bags have already rubbed away much of the paint from the rear of the seat stays. I promise to make good some time soon. 

Later I cut some over-long, plain, red, garden hose to slide over the lower crossbar. This helps to stop the bag from being marked or rubbed away by the bare, alloy crossbar across the bottom. The top crossbar does not contact the bag. So it can be safely left as naked alloy. There is always some vibration of the trike from road surface roughness. So anything which isolates the bag from rubbing and sharp contact points is a good thing for a very long life. 

A perfectionist might use clear tubing instead of garden hose if appearance is a very high priority. Stainless steel tube might also be used. Though with some weight penalty over light alloy. 10 and 12mm diameter stainless steel tube is readily available from DIY outlets and builder's merchants. Even in a smart "brushed" finish. Weight could be saved by making the top crossbar much shorter. Mine is much longer than necessary. I think I may try to find a pair of 10mm clips. Then use a shorter length of the brushed stainless steel tube I have lying about.

This very simple rack is a vast improvement on all my experiments with sports bags and cut-down, rucksack frames. The one factor which made it at all possible is the natural stiffness, and internal dowel stiffening, of the Carradice saddle bag. The downside is the limited capacity of even this largest Carradice model: The Camper Longflap. As stated elsewhere the Achilles heel of all sports bags is always the zips. Convenient, but very short lived. The thin cloth used on many of them is prone to rapid wear too.

Another update: I found two more 12mm clips in another bike shop. I  also bought some longer M6 x 30mm A4 stainless steel screws with quite large, domed cross heads. So now I could push the rack well away from the seat stays at the top as well as the bottom. The effect is that the rack is now parallel with the stays.

The image shows how I used a short length of smaller alloy aerial tubing to space the clips well apart. The bag now clears the seat stays nicely and no paint frettage wear is likely.

I haven't found any 10mm clips yet. So the stainless steel top crossbar is on hold. I have now made a shorter, top crossbar from a new piece of tubing without any holes to weaken it. It was squared off and polished in the lathe this time. A fine file and steel wool would do just as well. I may update and compress this post when the latest mod is fully assessed on the road.

This is the latest iteration.

I hope you agree that the appearance of the trike is not diminished by using these "brake clips" and simple crossbars. Since the clips, at least,  are standard bicycle spares. I think they look the part. The bag sits absolutely rock steady in use. A luxury and feeling of total bag security, on bumpy corners, I have not enjoyed until now. Interestingly, the bag settles into a central position where the straps do not contact the clips or stays. So any wear is due to the polished tube from which the bag straps hang. The straps should last for decades!

I'm getting more dexterous with the Carradice buckles now. The main trick is to allow the buckle locking pin to drop out of the way when undoing the straps. Or to deliberately push the pin down first. The Longflap device is valuable to make much more room for carrying goods. Though I still miss the capacity and large open top of even my smallest sports bag.

Had the Camper bag been the size claimed by the manufacturer it would hold considerably more. Doing so, without ever resorting to the Longflap option. I see this as a lost opportunity of tragic proportions. The manufacturer's may save a 3" wide strip of canvas, for the missing bag sides and bottom, but they cripple the bag's potential carrying capacity. 

Click on any image for an enlargement.

No comments:

Post a Comment