Bicycle Mechanics - Nexus hub and Shimano trigger shifters.

Hello All.

I'm carrying from where 'someone' left off trying to use standard Shimano trigger shifters with a Nexus (7) roller hub via a TravelAgent. I've been using an icky Nexus7 combined gripshifter and brake lever and although it sort-of works, it isn't very precise in the feel and I'm always expecting it to break.

I want to use a pair of Shimano STX-RC trigger shifters (I use a double 48/42 chainset up front), and asked the question of the excellent Harris Cyclery if there was any further information over and above what I had gleaned. They replied below...

....Yes, you can put a shifter together with a ratio-changer.
You need 5.5mm of cable pull for each gear change on the Shimano 7s and 8s.
If you wanted to use a Shimano 7 speed derailer shifter, it pulls 2.9mm of cable for each shift. So you need to find a ratio changer that converts 2.9mm in to 5.5mm output.
That's a 53% change.
You'll need to do some research to find the right ratio adaptor. Sorry, I don't have that info here.

.... So yes, it's possible. I'll be buying a Travel Agent soon and will double-check that the pull amendment is circa +50%,then proceed with the build. If anyone has done any further work on this, I would apprciate their input.

Thanks...

If the cable pull is the same between gears for both the Shimano 7 and 8 speed hubs as per Harris Cyclery's information then you might as well go with the 8 speed Nexus/Alfine dual trigger shifter and forget trying to use a derailleur indexed shifter and travel mate. Just do not try to make the shift into 8th gear.

Here is a Shimano 7 speed trigger shifter for the Nexus listed on Amazon too.

http://www.amazon.com/Shimano-ST-7S20-RapidFire-Shifter-Optical/dp/B000A6DEAC/ref=sr_1_10?ie=UTF8&s=sporting-goods&qid=1243036127&sr=1-10

One problem with trying to use derailleur indexed shifters is that the steps do NOT all pull the same amount of cable. In that respect the Harris Cyclery information is NOT correct. The center steps pull less cable than the end steps due to the cable to parallelogram geometry of Shimano derailleurs. Measurement of derailleur indexed shifter cable pull for a 9 speed Shimano shifter is listed in the Files area on the Geared Hub Bikes Yahoo group linked to below in my signature block. Only accessable to group members.

Here is a Shimano 7 speed trigger shifter for the Nexus listed on Amazon too.


I have that shifter on two of my Nexus-7 bikes. It feels much better than the gripshifter thing. It is not the most elegant piece of equipment I have ever seen. But it feels solid and has been utterly reliable for me. I can't imagine going through the trouble of a travel agent when this straightforward solution is readily available.

And, if you are careful, you can stretch out the clamp to fit on drop bars!

jim

I would also add that the non-linearity of indexed derailleur shifters is also well illustrated graphically in Frank Berto's 1988 book on upgrading your bicycle. These were early 6 and 7 speed indexed shifting systems but the basic derailleur geometry has not changed.

The book is usually available used on Amazon at reasonable prices, like under $10.

Jtek is now offering their bar end shifter for the Shimano 7 speed hubs too. I have the 8 speed version on an Alfine hub equipped bike and it is working well. No cable adjuster included so you need to install an inline cable adjuster too.

http://jtekengineering.com/jtek_bar-end_shifter.htm