4 speed semi-automatic. Is it a stupid idea?
 

For some time I was planning to build a fast commuter, a simple yet elegant bike that I would use to get around the city, do shopping, go swimming etc. The city I live in is mostly flat but it is surrounded by hills on 3 sides (4th side is a lake) and quite often I need to get over some hill to get things done. I tried fixed gear for some time which was pretty fun but quite useless when I need to go vertical. So a FG/SS won't do the job for me.

I'm looking to build an easy on the eye (yet beautiful) bike so derraileurs are a no no. I was thinking of other options, like an Alfine 8 or Alfine 11 Di2 which are both expensive and not exactly what I need.

Last night I came up with the idea of building a two speed that is, one cog in the back, a chain tensioner and a double crank (thinking of 50/39)

Since aesthetics are a pretty important part of this project, I thought I could go with SRAM hoods, an s500 or s900 right lever and a Rival left shifter. They're almost identical and even someone with a trained eye wouldn't notice the difference without mentioning. A blade swap might be necessary but that's doable.

http://www.backcountry.com/images/it...0262/CBLEV.jpg
http://tenerife-training.net/Tenerif...9-shifters.jpg

Then I thought, why not combine this idea with this:

http://cdn.mccraw.co.uk/wp-content/u...-catalogue.jpg

This would give me 4 unique gear ratios and a semi-automatic drivetrain. With a 22t in the back you get the following ratios:

[table="width: 500, class: grid"]
[tr]
[td][/td]
[td]50 (1.0)[/td]
[td]39 (1.0)[/td]
[td]50 (1.3)[/td]
[td]39 (1.3)[/td]
[/tr]
[tr]
[td]Gear Inches[/td]
[td]60[/td]
[td]46.8[/td]
[td]82.1[/td]
[td]64.1[/td]
[/tr]
[tr]
[td]Gain Ratio[/td]
[td]4.4[/td]
[td]3.4[/td]
[td]6.0[/td]
[td]4.7[/td]
[/tr]
[tr]
[td]MPH @ 80 rpm[/td]
[td]14.3[/td]
[td]11.1[/td]
[td]19.5[/td]
[td]15.2[/td]
[/tr]
[tr]
[td]MPH @ 90 rpm[/td]
[td]16.1[/td]
[td]12.5[/td]
[td]22.0[/td]
[td]17.2[/td]
[/tr]
[tr]
[td]KPH @ 80 rpm[/td]
[td]23.0[/td]
[td]17.9[/td]
[td]31.5[/td]
[td]24.5[/td]
[/tr]
[tr]
[td]KPH @ 90 rpm[/td]
[td]25.8[/td]
[td]20.2[/td]
[td]35.4[/td]
[td]27.6[/td]
[/tr]
[/table]

The IGH shifts with centrifugal force so one concern I'm having is that not all 4 ratios would be usable. Some other post explains how the shifting speed can be adjusted by changing the spring tension of the hub.

Of course no one knows how it will ride until someone builds a bike like this but I want to hear your opinions.

Is this a stupid idea?

I'm assuming you're talking about a sprung loaded chain tensioner so you can shift chairings on the move in which case, you'd be better off using a real deraileur system with probably a single chainring at the front.

A better alternative might be the S3X 3 speed fixed gear hub from Sturmery Archer.

Failing that, try normal fg. I know you mentioned hills but you'd be amazed what you can climb once you get used to it. I actually live IN the hills that surround my city and it's only the extreme stuff that people with lots of gears suffer on that defeat me.

Just realised you're from Lake Como. Hmm, maybe you are talking about real hills (as in bloody steep)

Well, they're steep even with a 42/23 steel vintage bike.

As I mentioned, this is a project of obsession and perfection rather than functionality. IMO nothing looks better than a well built brakeless fixie but I first handedly experienced how dangerous it was. I really don't like the look of a derailleur. I like track ends but that would limit me to a single chainring on the front. This on the other hand looks clean and beautiful:

http://static.squarespace.com/static...p_2012%202.jpg

I read a lot about the Sturmery Archer 3 speed kick-shift and a major part of that was about how problematic it was.

Not the 3 speed kick-shift, the S3X which is 3 speed, fixed gear with a cable and lever shift. Not problematic at all if adjusted properly (I've got one).

Now, your tensioner. Will that give you the range you need to keep tension when you change between chainrings?

Just thinking aloud here: With your shifts at the front, if you use a shifter that's a friction shifter, you won't need to have that extra lever below the brake lever. I'm afraid I don't know of an integrated lever (brake and shifter) that does this, maybe modify one? Alternatively, a bar end shifter would give you clean brake levers and need not be too obtrusive. Maybe a single downtube shifter if you like the look of them (you can use a band on mount if you don't have brazed on mounts).

I doubt a single wheel chain tensioner would have anywhere near the chain wrap required to accommodate two chain rings.
Front shifting sucks. I would rather an IGH over any scheme that wants to shift chainrings.

The same could be said about the SRAM Automatix. I tried it, on its own. And even though it functioned well, especially after it was made into shift to overdrive a lot later, I could not get used to its constant tick in second gear.

So, I just went Nexus 8 -- same inner works as an Alfine 8 -- with an Alfine 8 rapidfire shifter. Which got me a completely silent bike. And for some reason silence is a lot more important than elegance to me -- especially on an all-year round commuter.

Early picture [with slack chain]:

https://lh5.googleusercontent.com/-Q...gazelletje.jpg

@europa

I didn't know about the S3X I'll look into it.

After some quick investigation, I realised that a single pulley wouldn't take the slack of a double chainring. I would need a two pulley chain tensioner or a locked RD. Not what I had in mind.

For now this project is just an idea, I think the earliest I can build it is in the next 18 to 24 months. About the friction shifter, I have strange obsessions. I wan't three road bikes with three brands. One with Shimano, one with Campy and one with SRAM. This would be the SRAM bike.

@Steev

Some times I think like I am the only person who likes front shifting in the forum. The Sora 3500 on my Trek just shifts fine, and it's a triple. I have never had problems with it, it never let me down. Not to mention the Campagnolo Nuovo Gran Sport on my vintage bike, it's almost 40 years old and shifts like a dream, I often need to look down to check if it really did change gears.

@ijsbrand

The Nexus/Alfine system does look indeed hassle free. Rapidfire shifter means flat bar to me, I wouldn't mount that thing on a drop bar. The third party Versa levers look ugly in my opinion. I didn't have previous experience with the Automatix but I'll take your word for it, silence is of course an issue. My ultimate dream is a bike with Alfine 11 Di2 and Carbon Belt drive but that combo is super expensive and pretty much limits the range of frames I can choose.

That's a nice looking bike you have there, and a pretty high frame!

I found this on a Japanese site:

http://ysroad-shibuya.com/assets_c/2...x337-11489.jpg

bigger pics:

http://ysroad-shibuya.com/assets_c/2...407-11489.html
http://ysroad-shinjuku-crossbikekan....s/P1040894.JPG

Shimano Alfine CT-S500 chain tensioner, Tiagra FD with a 48/36 crank. It's basically what I had in mind without the IGH. Still looks cleaner than a cassette and RD.

This is kind of off-topic, but I thought you'd like to see it. ( You'd need a new frame with teeth in the dropout! )

In the 1940s, the Campagnolo Corsa worked this way: With the first lever, unlatch the rear quick release while riding! Backpedal while using the second lever to move the chain to a new cog. Tighten the quick release.


http://bikeraceinfo.com/images-all/p...egnano-003.jpg


Gino Bartoli in the 1948 Tour de France:

http://bikeforums.net/attachment.php...hmentid=383224

Watch the shifting:

Why not a SA 5 spd rear hub with a bar end shifter since you're running drops? That way you can have a more modern version of an old school club racer.

@rm -rf

I'm familiar with the system, I've played with one in a local Colnago dealer the other day. For the "bling factor" they are unbeatable but the ratios are still very close, surely a big innovation of it's day but for real hills I have here I can't think of anything but a double crank.

@bikemig

Bar end shifters offer a nice solution but IMHO they look ugly. I would rather have down tube shifters instead of bar ends.

To illustrate in car terminology, what you (and most other guys) advice is this:

http://autonoleggiopercerimonia.com/...er-cloud-1.jpg

While I want something like this:

http://www.automotoportal.com/media/...60711010.6.jpg

My bad, I thought you wanted one of these ;),

http://bikeforums.net/attachment.php...hmentid=383051

The "ideal" garage/stable I have in mind would consist of these:



Racing - Maserati Grantourismo S: White / Full carbon Italian beast. Campagnolo all over the place. Bling bling bling.

Winter Trainer - Mazda Miata NC: White / Aluminium Japanese excellence. Shimano 105 or Ultegra. Fast & reliable.

Vintage - '67 Alfa Romeo Duetto: Blue / Classic Italian beauty. 70's Colnago frame with Campagnolo Nuovo Record.

Fixie/SS/Track - Nissan Skyline GT: Red / Street cred / Track day. Two sets of handlebars, one for street with brakes, one brakeless for track.

TT - Bugatti Veyron: Red / All about speed. Full carbon. 80mm rim in front, disc in the back. Not sure about the groupset.

City cruiser / Luxury - Rolls Royce Phantom: Green / Modern elegance. Full carbon. Everything silver, honey Brooks saddle and bar tape. What this thread is all about.


And this is thinking that I would never have an interest in MTB or CX. Which is highly unlikely.

Transmission crankset is an option. METROPOLIS components
http://www.metropoliscomponents.com/.../Patterson.png

IMO SS chain tensioners will always be uglier than a nice derailleur and cassette.

forever more elegant than even the nicest tensioner:

http://bikeforums.net/attachment.php...hmentid=383188http://bikeforums.net/attachment.php...hmentid=383189
even modern ones
http://bikeforums.net/attachment.php...hmentid=383190

Just get a Schlumpf two-speed crankset:

schlumpf innovations

You can get a Mountain Drive, with speed reduction, or High Speed Drive, with overdrive. Ratios up to 2.5:1 are offered. Much cleaner, and no tensioner or derailleur required.

a Nuvinci hub is another choice

I don't think a Nuvinci shifter will work on drop bars. The Schlumpf is shifted with the heel. No additional shifter. No cable. Very clean.

Dude... this looks almost just like a standard geared setup but less elegant and functional.

OP doesn't know what he wants is going down the road of weird for the sake of weird. If you want a simple gear system then how about a wide range 1x8 and a downtube shifter? Cheap, easy, effective. You will need a rear derailleur but you already mentioned using that Alfine chain tensioner.

http://bikeforums.net/attachment.php...hmentid=383293I have a twin speed SA rear hub. Tokyo is pretty flat so I have an easy gear / into the wind and a higher gear for down wind / workout situations. Once in a while I may go on a short tour which includes the Japanese alps. For these rides I put on a tiny front ring giving me a hill climbing gear and after a quick back pedal a gear suitable for flatter areas.

Wow, so many ways to make something as simple as 4 gears difficult.
Your bike has vertical drop-outs, so form of chain tensioner is needed, might as well use a short cage road derailleur.
To shift between only 4 (or maybe 3 or 5 ) ratios why have any more than 1 shift mechanism?
If you want sleek and clean, why have a front derailleur and a chain tension device at the rear?
Really, a small freewheel and rear derailleur is going to be simpler, cleaner and offer superior shifting to all this other stuff.

Edit. It's going to be way cheaper too.