2_i 

Aluminum stays in Brompton rear rack/carrier had been a problem for me and other people. Some aftermarket racks look good, but you cannot find out whether they are an improvement over the original rack without a significant investment. The top of the original rack is fine, so the natural question to ask whether simply the stays could be changed into other non-corroding. I first looked into stainless steel stays, but some on-line engineering calculators indicated that for the same physical dimensions stainless steel would bring marginal strength gains and quite a lot of weight penalty. On the other hand titanium would increase the strength quite a bit with a modest weight gain, 8g/stay.

Surprisingly the price per Ti tube, 8mm OD 6mm ID 25cm length, was not that dramatically higher than per stainless or alu tube, $10 including S/H, vs $5. Presumably one could lower the price buying all at once, but I was trying out first with 2 tubes, looking whether this would work at all. To make strong tube ends I even made a jig out of an alu piece, but I am not sure this was really necessary. Now I have a pretty sturdy rear rack on the Brompton. It is the first time since a long time that the folded bike rolls on all 4 roller wheels simultaneously. How the rack will fare in travel remains to be seen. The photos illustrate the progress.

The work was my first serious experience working with Ti as material. It is quite easy in machining and its one funny feature is that it is a bit gooey. It feels at moments like working with a candy bar. When you even edges on the grinder, the sparks are beautiful, like from a Christmas sparkler. It seems that in the future projects, that require modest amounts of material, I will be looking into Ti as option.



New Stays On


New Stays On


Crimping Tube End


Crimped End and Jig


Old and New Stay


Set of Old Alu Stays

torbenp

Did your Solution work over the years? I have the same problem with a bending Rack and looking into doing the same modification.

2_i 

Oh, yes. Tons of travel and everyday use and the problem of buckling stays is gone for good.

mingo

Where did you find the right diameter tubing?

2_i 

I bought them both on Amazon and Ebay, balancing the cost and anticipated reception time. E.g., you find them here on Amazon and over here on Ebay. AliExpress may have them for less but you may need to wait longer. I first got 2 and went with mounting them to see how I was doing.

torbenp

Great, that sound promising. I will try making them by myself.

Schwinnsta

I seldom use the rack to carry stuff. I have not yet had the rack stays buckle. I primarily carry loads on the front block. I have carried up to 30 pounds, not recommending it. Steering gets dicey over 25 pounds.

Yet I too worry about over stressing the rack, primarily when using the bike in shopping cart mode. In order to facilitate shopping I added an outrigger wheel such that the center of mass stays inside the wheels when in shopping cart mode. It makes for a big improvement. Most of the time in shopping mode the rack carries half the load of the bike and the half is on the rollers not attached to the rack. However to steer the "cart" I have to lean it back so that the front rollers are in the air and the back rollers then take the load of the bike and the contents in shopping back which is way over the rack allowable of 10kg. I can feel feel the flex. So far my set up works but I would like to give it extra support at the cantilever roller. A strut would be ideal. I bought an 8mm AL strut but I would need to to do a very tricky bend to keep it from hitting the front wheel in the folded position if it were to go from the roller down to where the struts attach to the frame. It would also compromise the capacity of the strut as bent columns are not as strong. Here are some pics.



I plan now to provide support by adding a cantilevered beam, a 1/4" x 1/2" beam cantilevering off the rack at 45 degrees and attaching at the cantilevered wheel. I will also run a tube between the rear wheels to tie it together. Note the cantilevered wheel does not extend out beyond the distance of the fixed pedal

2_i 

I went only half as far on the rack side and only a bit from the ear. The ears have been strengthened by a local frame builder already a while ago. Sorry for the poor angles.