Two Cranky Topics

November 29, 2012

Cranky Topic #1: Cranks

It's a signature of the Grampies touring style that they go slow. A speed of 10 kph is average, what with ups and downs, and on the flat it is rare to see the Grampies exceeding 18 kph.

Cruising along in Europe last summer, I noted that I seldom seemed to be using the largest ring on the front crank. In fact,for what seemed an inordinate portion of the time I was using the smallest, or "granny" ring. The rings we are talking about were already quite small, the crankset being 52-42-30. Even with 30 as the largest ring on the cassette in the back, I sometimes also seemed to wish for a lower low gear.

Now that we are heading out on a much hillier course than the basically flat river valleys of Europe, I decided to go beserk with some ultra low gearing. So Amazon brought us each a 42-32-22 crankset, and rear cassette ending in 32. Combined with the fact of the 20 inch wheels, you would expect our little legs to be spinning wildly and the bikes going nowhere. This may yet be the case, since the bikes are resting by the fire and have yet to venture outdoors with their new gears.

Our friend Art Birkmeyer reported that he also regeared for his trip this summer , over the southern part of our route, and then the Sierra Cascade. However all he did was to go from 29 to 32 on the cassette, and to change the largest front ring from 52 to 50. I would expect Art's lowest gear for the tour was 32 to 32 on 27 inch wheels, for 27 gear inches. Our lowest gear is now 22 to 32 on 20 inch wheels, for an insane 14 gear inches. I am sure Art will choke on his latte when he reads this!

New third ring no bigger than old second ring

Derailleur not so sure about this either: We have reduced the size of the smallest front ring and increased the size of the largest rear, which creates a challenge for the derailleur to handle the vast range of chain length needed to handle the gear possibilities. Normally, the demand put on the rear derailleur is measured by "chain wrap", which is the difference between the number of chain ring teeth plus the difference between the cog teeth. For example a 53/39 with a 12-25 cassette requires 14 + 13 = 27 teeth of wrap capacity from the rear derailleur. So in our case, the wrap requirement is 41, which should be ok for a medium cage derailleur.

The derailleur is really stretched forward, doing 32->32

The derailleur is really folded backward, doing 22->11

On the other hand, going from 22 teeth front to 11 teeth rear really asks the derailleur to take up a lot of chain slack. A longer cage can handle this, but the darn thing is, with the small wheels of the folding bikes, the medium length derailleur cage already almost strikes the tire. Right now, with careful adjustment, the derailleur is standing behind our crazy gearing scheme, but it doesn't look happy about it. One might say it is a bit cranky!

Bike Friday rests by the fire. Wind and rain on the coast seems very far off.

Cranky Topic #2: Opinion of another expensive Bike Friday part shattered

Typical full fenders sell for $30 for a set. Bike Friday fenders sell for $60. So they will be great quality, right? Well for one thing they have no stays, just one attachment point. Maybe that is a feature. But have a look at what Dodie's fender did yesterday. It is made from a normally fairly flexible plastic. To shatter like that suggests UV damage. Is this another case of the bike is fine as long as it does not go outdoors? (Something we heard while complaining about rusting problems).

Oh well, as least we expect no dangerous sun on the Coast right now!

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