Archive for the ‘internal hub’ Category.

Seasons Speeding Tikit Porteur

April 17, 2009, 5:21 pm

I’ve finished my most recent round of hacking on my Bike Friday Tikit.

Side view with lots of visual clutter, making it hard to see the bike.

I callit the Seasons SpeedingTikit Porteur. Seasons because that is what Bike Friday calls the Tikit with an internal hub. Speeding because that is what they call it when you put on drop bars. Porteur because it has a (mini) porteur rack up front.

i9 hub, new dropouts

The new rear hub is a SRAM i-Motion 9 (or i9). The i9 conversion benefited from some brazing of the bike’s rear triangle. I switched the dropouts to the pivoting dropouts that Bike Friday makes. I also had to move the rear canti studs a bit. I made a photo essay of swapping out the dropouts. The i9 seems to work well and has a nice gear range. I had originally planned on building a custom bar-end shifter, but gave up on that project. The rear triangle will get fresh powdercoat soon.

The drop bars make the quick fold a bit wide, but remove the stem and it gets narrower than a stock tikit. I don’t need a compact quick fold very often, so this is a good compromise for me. I can ride on drop bars all day long, but flat bars hurt my hands after 20 miles or so. I really love the Tikit fold, it is very fast and all of the dirty bits on the bike get folded to the inside.

I made the mini-porteur rack a long time ago and it continues to function well. It looks really dressed up with the black powder coat.

The Tektro V-brake drop-bar levers are a lot more comfortable than the Diacompe 287-V option. They seem to work pretty well on the front, but the rear is a bit spongy from the long cable run. The levers work better if your V-brakes have shoes at the top of the slot than at the bottom.

I hacked up my favorite MKS Grip King pedals to have a quick release MKS EZ axle. This lets them pop off of the bike in an instant to make the fold smaller. Taking axles out of $60 pedals and putting them into $50 pedals is an expensive solution, I wish MKS just offered these with the quick release axle as stock.

I’m taking the bike on a train ride with me soon and looking forward to giving it a real test.

Category: Bike Friday, Brazing, bicycle, i9, internal hub, tikit  |  16 Comments

Accurately Measuring Cable Pull

October 9, 2008, 3:18 pm

I promissed some bike subjects again, and you can’t get too much geekier than this one.

I’m (slowly) working on converting my Bike Friday Tikit to use a SRAM i-Motion 9 internal hub. This bike will have drop bars and I want to convert a Shimano 9sp barend shifter to work with the hub. To do so I needed a way to measure cable pull very accurately.

I built two devices to do this, but I only took photos of the second and far more successful one:

Cable pull measuring device

And here is another shot of the back of it:

This was really easy to make. I used a digital scale that came off of the Digital Readout for my mill. These scales are just like digital calipers and can measure how far the slider in the center moves up and down along the ruler. I drilled and tapped a hole in a block of aluminum that fit a cable housing stop that I had lying around. The block is bolted onto one end of the scale. The center (sliding portion) of the scale has a cable clamp. The other side of the clamp connects a spring to the far end of the scale.

Twist the shifter (or move the lever of a barend shifter) and the scale moves and reports how far it went. These digital scales read out in millimeters or inches and let you reset them anywhere, so it is trivial to measure the motion per click.

I did that and generated this spreadsheet (yeah, it is lame to embed this as an image):

A Travel Agent is simply a cable pull amplifier using two concentric pulleys. It looks like this (image borrowed from Amazon):

The stock pulley amplifies cable pull with a 2:1 ratio. To make the i9 work with the Shimano shifter I need to make a new pulley with a 1:3.6 ratio. You can’t fit a much larger pulley on the Travel Agent, so that means a 32mm outer pulley to 8.9mm inner pulley. That isn’t a hard item to make on the lathe.

I hope to report back on how the whole system functions soon. I still need to build the wheel and install it into the bike.

Category: bicycle, internal hub, tikit  |  18 Comments