Archive for March, 2010

Front Rack Design- Randonneur Sportif

Above is a conceptual sketch for a low-rider attachment for rando racks on bikes without low rider bosses.

I had been looking at different ideas for front racks for my Circle A which is really designed as a Sportif, because I couldn’t resist providing for the option of carrying a small front load in addition to the frontbag/handlebar bag that will go on the rando rack.

There have been a good number of variations over the years on the “low rider” attachments to french style rando racks. Look at this beautiful Boxer rack, which attaches to the dropout at the bottom and the small rando rack at the top:

or the Grand Bois, which is a little more contemporary as it bolts to separate low rider bosses in addition to the rando rack and the dropout:

These racks were traditionally designed for Sologne/Berthoud style panniers which differ from Ortlieb style bags in that the French bags have their attachment points at the top edge of the bag, whereas the Ortliebs mounting rail is about 3-4 inches lower. On the same rack, the Ortliebs will sit 3-4 inches higher.

Additionally, since most of the French bikes did not have low rider bosses, the bags were generally centered over the axle, rather than further back close to the steering axis as you see on modern low riders.

I like my Ortliebs and wanted to see if I could find a way to mount them lower and further back, without providing low rider bosses, partially because I think a lot of people might find the design useful, but mostly because I didn’t want to look at the empty low rider bosses for the 95% of the time that I would not have the low rack attached. Additionally, I thought there was a certain elegance to the lines of the rack that was lost when I drew it with a low rider boss.

The rack as drawn will result in the center of the Ortliebs being at the height of the axle, but pushed back so the steering axis passes through the center of the bag projected onto it (as the axis passes between the two bags, not through them).

I hope this will result in minimal wheel flop and good handling on a low trail bike.

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Velocity Dyad says oooowww!

I guess I learned that there is no such thing as a “bombproof” wheel today. Whereas everywhere else in the Northeast seemed to get either a ton of snow the week before last, or a ton of snow and a ton of rain, Providence got basically four days of torrential rain, which combined with the normal freeze/thaw cycles of late winter washed out every crack of sand supporting fractured pavement in the entire city.

Worse than just the resulting giant potholes are the pavement seams that can be just as deep but almost invisible until you’re right on them. In this case, I was going downhill at about 25 mph and changing lanes, so I was looking back over my shoulder leaning back with all my weight on the rear wheel. I turned around just in time to see my front wheel drop into a three inch wide and four inch deep seam between the lanes. My unloaded front wheel skipped lightly but violently (if that makes any sense) off the front edge of the hole. With my entire weight, the rear hit the front edge of the seam like a sack of potatoes, the 35mm Paselas more getting out of the way than anything else. Worse still, the rim didn’t hit squarely but rather it only hit on the left side, perhaps as I was crossing towards that side.

Amazingly, I did not crash or even flat, and the rim stayed perfectly true within the pads, if you excuse the fold in the braking surface. It was about 1/2″ closer to the hub, however. The force was great enough to partially pull spokes two spokes away through the wall of the rim as the rim tried to expand over there to make up for its collapsing at the point of impact.

Perhaps on a lighter rim I would have crashed.


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