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Silk - the new belt drive 20" models
10-19-2012, 08:18 AM (This post was last modified: 10-20-2012 03:27 AM by joewein.)
Post: #1
Silk - the new belt drive 20" models
The new range of belt drive 20" (Pocket) models looks interesting. The redesigned rear triangle makes it possible to install/remove the belt around the rear fork. The old triangle was designed for a chain with a breakable link.

I also like the disk brakes on the new models. On steep descents (10%+) I sometimes worried how hot the rims got and if that might affect the tires. I think disk brakes are the way of the future, even if they're a little heavier than conventional brakes.

The Shimano 11 speed hub offers as wide a gear range as a triple crank derailleur setup but there's no derailleur to be damaged from any impact, no derailleur adjustments and less vulnerability to dirt, sand, etc.

The Shimano Alfine 11 speed model looks nice, but why is it so much more expensive than the 3 or 8 speed model? Is this the Di2 version?

Quote:As our Pre-Launch Introduction, we are making Belt Drive versions of Silk available to Bike Friday Owners first, allowing pre-orders for February delivery at significant savings. These Specials are available for orders paid by November 16.

You can choose from three basic versions of Silk, with all available on 406 or 451 wheels:

Silk 8.0:/ Gates CDC Carbon Belt System with Shimano Alfine 8-speed internal hub, Origin 8 disc brakes, sealed bottom bracket, threadless headset and flat bars. Launch Price will be $1998. INTRODUCTORY BIKE FRIDAY OWNER PRICE: $1698

Silk Infinity:/ Gates CenterTrack Belt System with NuVinci N360 internal hub, Avid disc brakes, sealed bottom bracket, threadless headset and flat bars. Launch Price will be $2198. INTRODUCTORY BIKE FRIDAY OWNER PRICE: $1858

Silk 11.0:/ Gates CenterTrack Belt System with Shimano Alfine 11-speed internal hub, Avid disc brakes, Chris King headset, Thomson Elite seat post, FSA Gossamer cranks and drop bars. Launch price will be $3595. INTRODUCTORY BIKE FRIDAY OWNER PRICE: $3195

The Bike Friday Silk can fold and fit into a Samsonite Suitcase for Airline Travel. Its frame is guaranteed for life, and each Silk will be hand-built to fit an individual's body.

In addition, the new design makes for a smoother, easier fold for our 20-inch Bike Fridays with no chance of the Belt Drive falling off during the fold!
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10-19-2012, 09:52 AM
Post: #2
RE: Silk - the new belt drive 20" models
The typical price difference between Alfine 8 and Alfine 11 on other bikes has been $500. Hopefully the price will eventually come down on the 11's.

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10-19-2012, 10:01 AM
Post: #3
RE: Silk - the new belt drive 20" models
Smile Intriguing! Hoping to see a few photos or comments on fitting finders and rack.

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Stuball
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10-19-2012, 10:06 AM
Post: #4
RE: Silk - the new belt drive 20" models
Intriguing! Hoping to see a few Silk photos/comments of Silk with fenders and racks.

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10-19-2012, 11:02 AM
Post: #5
RE: Silk - the new belt drive 20" models
Any thoughts on using fenders and racks with the new models?

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10-25-2012, 01:34 AM (This post was last modified: 10-25-2012 03:37 AM by joewein.)
Post: #6
RE: Silk - the new belt drive 20" models
A friend of mine who had rebuilt the front wheel of my Pocket Rocket 105 using a Shimano DH-3N80 dynamo hub commented on my Facebook posting about the new models. According to him the NuVinci hub has too much drag.

So I looked around to get some figures on how much power is lost through friction. This is what I found:

Traditional derailleur gears are highly efficient, in the region of 96-98% (2-4% power loss) if they are clean and lubricated. If they lack lubrication or get grit in them they not only lose efficiency, but also wear out more quickly. This is one significant advantage of belt drive systems.

So how do the various internally geared hubs on the market compare?

The Rohloff Speedhub 500/14, the premium brand of IGHs, is also 96-98% efficient, i.e. 2-4% losses.

I have not seen any efficiency figures for the Shimano Alfine 8 or 11. My friend reckons the 11, while it offers a wider spread of transmission ratios, is actually less efficient than the 8 in terms of losses.

According to the Wikipedia article on the NuVinci CVT, Fallbrook Technologies has not published any efficiency data for it:
Quote:Fallbrook Technology refuse to publish any efficiency data for the NuVinci CVT. However, The NuVinci is a variant on the "Tilting-ball drive" type of continuously variable transmission (CVT), and the efficiency of "Tilting-ball drive" type CVTs is typically in the range of 70% to 89%.

If the NuVinci N360 was 15% less efficient than a derailleur gear setup, it would slow you down anywhere between 15% (low speed climbing) and 5% (high speed cruising on flat roads).

It would be interesting to get the real data for all these IGHs.

Here are two published articles discussion efficiencies of derailleur gears and IGHs:

Chester Kyle and Frank Berto (page 3, 2001):
http://www.ihpva.org/HParchive/PDF/hp52-2001.pdf

Bernhard Rohloff and Peter Greb (2003):
http://www.hupi.org/HParchive/PDF/hp55/hp55p11-15.pdf
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01-07-2013, 06:01 PM
Post: #7
RE: Silk - the new belt drive 20" models
I am eagerly awaiting the delivery of my BF Silk in about a month. Thanks to Walter who has been both helpful and patient during the ordering process.

Does anyone have any info on the production ramp up on this new model? I'm also interested in a better understanding of how the Ratcheting Adjustable Dropout (RAD) works. For example how do you adjust the belt tension evenly on both sides? Is there some type of marking or indents that allow you to keep both sides synchronized? -- Tim
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02-12-2013, 02:02 PM (This post was last modified: 02-12-2013 02:13 PM by Titerban.)
Post: #8
RE: Silk - the new belt drive 20" models
I feel to jump in, for I too am eagerly awaiting delivery. Good Walter seems to have made a slight error and put an anticipated ship date that was one month pre-mature. On the redesigned rear triangle: there is no triangle. Seems a radical design, but feel confident as it would appear that Rob English has been racing on such a frame, and a new blog on Beta testing the bike reports that it has held up to slamming. I would suspect, and this will be a boon, that it will afford a smoother ride: the fork rather than triangle will absorb shock, while still allowing good power transfer. Excited about the Alfine 11. Crazy thing is that I am trying to sell my PRP and belt drive Tikit, because in 2011 when I decided to get the bike of my life, I asked Walter for a belt-drive Pocket Rocket. But sorry, they do not work that way. So the 10 cassette has satisfied my riding appetite for a fine road bike - like the younger days of racing. Then I just had to get a Nexus 8/belt drive Tikit. But now the Silk has it all in one. I do not mind going a bit slower, I have done it already, and if I am riding alone, it can seem fast enough. The Silk I can load for touring, and probably put on larger tires for revisiting the dirt. Think the ratcheting may have to do with adjusting the dropouts for the right amount of belt tension. To tension the chain on a track bike, the right side is tightened first with the wheel twisted to the right and pushed back to tension the chain. Then after tightening the right hub nut, by pushing against the rim from the right chainstay, the wheel was aligned and tension leveraged on the chain thereby while the left hub nut is then tightened. This may be how the dropouts are set. With my Tikit, I removed and replaced the wheel without having to tension the belt because the dropouts were set. Reports are that the lower gears of the Alfine 11 feel soft and mushy. Having been early trained on pedaling technique, I tend to smoothly spin low gears. When tromping lower gears, the internal hub does not give that solid kick-back that a chain and sprocket does, and that may be the perceived difference. We will see. Have enjoyed the Nexus 8 and the belt drive on the Tikit. My legs can tell the difference. Not better so much as regal. I am ready for regal - with two R's upon the hood (or my forehead).
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02-20-2013, 05:17 PM
Post: #9
RE: Silk - the new belt drive 20" models
Per the BF Inside Scoop, the Silk entered full production the week of 2/7/2013. I received an automated email that mine was picked up by FedEx on 2/19 and is on its way to me. Yeah!
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02-26-2013, 12:02 AM
Post: #10
RE: Silk - the new belt drive 20" models
Congratulations, tjdwyer! Tell us how you like it!
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