Three principles to remeber.KISS
Simplify and add lightness
Cheap / light / strong - pick 2
That's what it says in the books, but looming over all of this is customer/client expectations and following the market (wherever that leads and however fickle it is). Maybe I should email this to some of my clients!!! 
Three principles to remeber.KISS
Simplify and add lightness
Cheap / light / strong - pick 2
For me 'fit and forget' is a far better principle. KISS, yeah fine but I don't (but have) ridden a no brake fixie. That's the most KISS bike there is. Cheap / Strong / Light, well MTB isn't cheap as per the prices in my last post so I'd go with saving up a bit and getting something which will last so 'Strong' and 'Light Enough'. Honestly if it weighed 100g - 200g more I couldn't care less as long as it was reliable.
solution in need of a problem, how much and how complicated would it be to get indexing thrown into the mix. Then you have the issue of small hydraulic cylinders coated in crap, seals leaking, maybe twice as much hose. etc.
Everything has been tried on bikes more than once already. Why is no one seriously looking at hydraulic systems? maybe because they are worse than the alternatives, and when you think about L shapped cranks, biopace etc. They have to be really crap to not be reintroduced.
As for disc brakes, They need bleeding once in a while but there is no indexing, no exact postion to worry about. As long as when you pull the lever the pad hits the disc they work.
in that case it would lock up as the ambient temp changes surely. The TESI bimota motorcycle had hydro steering in one incarnation in exactly the manner described and they found this to be an issue.
Unless the volume in the hoses and the volume of the fluid expanded and contracted by the same amount as ambient temp changes you would get volume changes which would create pressure differentials which cause the seals to distort and lock teh system
Really ?
I dunno much about hydraulic fluid but I'm assuming the thermal expansion over a range of, what, max 50 celcius or less would be pretty minimal and shouldn't interfere with what's only needing a low pressure system anyway. Definitely wouldn't expect to have to make running adjustments during a day - maybe once for winter/summer ?
As for disc brakes, They need bleeding once in a while but there is no indexing, no exact postion to worry about. As long as when you pull the lever the pad hits the disc they work.
I think that's the key part.
Everything has been tried on bikes more than once already. Why is no one seriously looking at hydraulic systems?
Indeed, but sometimes an idea has to wait for technologies to catch up. I'm sure somebody tried a hydro disc brake on a bike ages ago and decided that, on balance, it was lumpen pain-in-the-ar$e. Fast forward to a time of CNC machines, market demand, ecomonies of scale and better/more available material (amoungst a, probably, long list) and Bob's-your-mothers-brother.
Doesn't mean I think it's a good/bad idea just that its time isn't now (for all of the reasons discussed above, and Di2 in particular).... as it may, or may never, be in the future.
scardypants - it won't be a lot but the only system I know of that was similar was the tesi steering and they had to put in a mechanism to allow for this. sure it wouldn't need to be done loads of times a day and could be made automatic - expansion chamber with ports that are closed as the lever moves - its just an area where there is more complexity thus more parts thus more weight.
Basic cables witha teflon coated outer works fine for me using one of these to keep the cables oiled and clean
Seems to be some confusion here between open and closed systems, and their respective behaviour under temperature.
First up brakes get hot because they convert kinetic energy into heat. Gears won't do this. Environmental temperature fluctuations will cause negligible volumetric expansion in hydraulic fluid.
In any case, in a closed system thermal expansion would increase system pressure. In an open system thermal expansion would cause the hydraulic fluid level in the reservoir to increase i.e. if it was an indexed system everything would remain the same.
And you don't need dual action slave cylinders. Cables only work under tension so only pull in one direction. Why can't a hydraulic system have a spring return?
I think they'd be a great idea and I'd love a set. It was Scott Allen Fife Enerprises (S.A.F.E) who tried in around '96 I think.
As for open vs closed, although a closed system wouldn't be an issue, an open one would be easier to service. When not have a ststem that opens to reservior each time you shift to the smallest sprocket (ie, zero presuure when the mech springs pulls down). I really liked the was the SAFE shifters worked with conventional mechs and a couple of inches of cable. If I had access to the kit I'd have made myself one long ago.
waderider - the tesi steering system was a closed two way system like that being proposed here for gears and ambient temperature changes affected it to the point it was abandoned. basically it locked up as ambient temp rose as due to the incompressibility of the hose and fluid as the fluid expanded as ambient temp rose then pressure in the system rose enough that it deformed the seals and caused the whole system to lock up.
Maybe this effect would not be significant in a hydro gear change system but adding in a mechanism to allow for fluid expansion under ambient temp rise would add complexity and thus weight
TJ, I thought that one of the significant problems with the Tesi was engine-generated heat rather than ambient?
I thought it was a bad idea to lube cables??
I use SP41 cable outer (5 metres is 30 quid or something) and stainless steel inners. Fit dry with no lube and they last 1-2 years before needing replacement.
I prefer no-lube myself.
Some cables that have the teflon liners don't need lube and if you do lube them it must be a compatible lube. I prefer basic cables and lube 'em( I wrongly put teflon outer that don't need lubing above rather than teflon coated inners)
Again, a moot point - I'm sure it at comparable weight at a cost, but that cost would be mental. Speaking of mental costs, the Rot5 setup appears to be using reltively thin plastic hose. I have no idea what the comparable weight per m of two runs of that full of fluid is compared to a steel reinforced brake cable outer with a steel cable in it.
That is why Nokon on do carbon cables. others do polyamide cables etc
A lot of people here have enough trouble bleeding brakes, imagine the fun they'd have bleeding gears.
Makes no sense at all! Hydraulic systems are good for high force but not for precision movements. Look at what they're normally used in - brakes and rams! If you use them with tiny gearboxes you'll need electronic systems to keep them calibrated in which case you might as well use electrics to deliver the shifting force.
you might as well use electrics to deliver the shifting force
Fine on a road bike maybe. Cover in mud and neglect = bad. I'm not too sure that I would agree with the fact that hydraulics aren't suitable for gears. If they weren't then why would they appear on the most precision sensitive user actuated moving part on the bike? The brakes.
TandemJeremy - Member
Some cables that have the teflon liners don't need lube and if you do lube them it must be a compatible lube. I prefer basic cables and lube 'em( I wrongly put teflon outer that don't need lubing above rather than teflon coated inners)
If they weren't then why would they appear on the most precision sensitive user actuated moving part on the bike? The brakes
But you don't use indexed brakes. The derailleurs have to move large distances but stop precisely at predetermined intervals without the help of a human to 'modulate' them.
I'll tell you the main reaon it'll never happen - Price.
Look how much you can by a REALLY cheap mech for these days - Well under £10. They are simple, built from hunks of cheap metal and can be made for bobbins. Even an XTR mech is only refined version of a cheap SIS mech when it comes down to it. Easy to make. Cheap to make. Big profit margin.
Now look how much a basic hydraulic disc brake is, and how many components there are in it. And, remember, the lever needs to work with the caliper, so they are supplied as a set. As hydraulic gears would have to be.....
So what you'll never get is volume production due to the cost, so there'll never be as much profit as a simple, tried and tested, cable set up.
And remember, hydraulic discs were a big lep foreward in performance for every rider. And when they were new they stood out, so everyone wanted them on their bikes to keep up with the Jonses. So people were happy to spend the money for the gains they gave.
Hydraulc gears will look pretty much the same, and work exactly the same as cables, so they'll be harder to sell to the riding public.
Electronic shifting has been out for years but never really got anywhere. I doubt hydraulics will ever get that far, if at all.
cynic al - nope - I do know the difference. I suggest yo check it. Basic outer cable is not teflon lined.
But you don't use indexed brakes. The derailleurs have to move large distances but stop precisely at predetermined intervals without the help of a human to 'modulate' them.
Sure, maybe for starters they could make a hydraulic 'lever' resemble something along the lines of a thumb shifter. Linear, no ratchet rubbish etc. The lever moves with full freedom until a plate is forced against it giving some resistance in the part that it needs to be.
TJ - oh well I guess I define "decent quality" as teflon lined - I've only seen unlined cables on the cheapest of bikes, and even then not for many years.
Electronic shifting has been out for years but never really got anywhere. I doubt hydraulics will ever get that far, if at all.
Good points and more than likely the reason. There are profits to be made though. I would personally love a set.
You're wrong to consider them to be the same and dismiss them because of this. Imagine the difference in cable discs to hydraulic ones. Immense. There would be minimal friction, minimum maintenance, hardly any cost after the initial outlay (which cannot be said for cables - if you kept the hydraulic shifter and derailleur for 4 years that could be a saving of £80).
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