Now I have reversed the pulley mounting clamp so that the pulley adopts a much higher, but protected, position. The downtube cable run is no longer exposed.
I have an identical but larger pulley which could improve the cable run even further towards the norm. It would push the downtube cable forwards and downwards without the cable hitting the bottom bracket shell on the exit. Drilling a series of "lightening" holes around the pulley might make it look quite "techy." The image shows the smaller pulley still in place.
The pulley clamp is now skewed slightly to point the cable towards the upper arm clamp. This is because of the offset forced by the lower clamp bolt pressing against the chainstay.
The radius arm is now hanging behind the seat tube and bottom bracket. I re-adjusted the bends to match the new position.
While the arm pivot clamp is now above the front changer. Which looks a bit untidy.
Since I have now settled on the rearward arm position I can re-adjust the cable clamp spacing to match the new needs. While carefully maintaining the correct clamp bolt hole spacing ratio from the pivot.
Or, I could move the pivot clamp back below the front changer and adjust the clamp spacing holes to suit. While ensuring that the holes and clamping bolts do not coincide with the chainstay.
This is the advantage of making a rough mock-up without wasting time on finish and appearance in the earliest stages of the trials. There is no inertia working against modification in case it spoils the looks. Or takes a long time to repair cosmetic damage to the parts. Treating the parts as disposable frees up the creative thought processes.
I had to saw and file the pulley clamp to make it sit as low as possible while still clearing the bottom bracket, seat and down tubes.
I have removed the rear bottle cage to allow a better view but should have removed the wireless cadence sensor as well for the photography.
A short ride to check how well the gear-change behaves under real loads. Seven miles with a few hills was enough to test out the indexing.
Either I am remarkably lucky or the XT11 MTB rear changer is very tolerant of indexing faults. Without so much as looking at the downtube cable tension adjuster I had perfect indexing from scratch! This was simply from tensioning the cable with the changer on the 3rd sprocket but the lever in top gear. The slight difference in changer position allows all the cable slack to be taken up without losing top gear due to the cable being made too short. It is important to strip all the cable from the handlebar lever to put it in top gear. Failing to do so will result in a number of "dead" clicks as the slack cable is taken up.
I shall now have to calculate the correct clamp spacing if I move the radius pivot clamp below the front changer clamp. A more "stealthy" ratio changing arm should confuse anybody interested enough to notice an MTB rear changer with Campag Ergo 'road' levers.
The arm is probably complete overkill in its present dimensions for a humble pull ratio converter. Until I had some experience of the loads applied by the cable I couldn't be certain what I could get away with in width of the strip material. Moving the arm back behind the seat tube and lowering the pivot will shrink the overall dimensions.
Raising or lowering the cable attachment angle from the pulley to the arm will alter how the rear changer sees the lever. I could compensate for over-shifting by raising or lowering the pulley. Moving the clamping holes away from the pivot would have a similar effect. So the swinging arm design is remarkably flexible in application.
I believe I read somewhere that 10 speed Campagnolo levers increase the pull towards the end of their gear range. This difference in pull could be easily managed by reducing the pull conversion ratio by reducing the gap between the arm's cable clamps. Once the arm was zeroed in top gear the arm would move progressively less per lever click as it crossed the block.
BTW: I am using forced flash and macro settings on my camera in the weak winter daylight. The flash seems to produce a very pleasing effect without the usual deep shadows and burnt out highlights. Using flash in darker conditions is not nearly so beneficial.
These images make the radius arm look very bulky and downright fuggly. If I could find a narrower length of stainless steel strip it might look a lot better without loss of strength or stiffness. I have sheets of the stuff but it is very hard stuff to cut. I'd rather find something existing which can be easily turned to my purpose with a couple of drilled holes. If I can shrink the arm small enough an old stainless steel butter knife or spatula might provide suitable donor material.
At the end of a rather long day working on the trike I have now mounted the larger pulley as low as the clamp will go. This greatly improves the cable run on the downtube.
Then I used the previous top cable clamp hole in the arm as a [ratio] guide to the site the new upper clamp bolt. [94/1.38 = 68mm] The previous top clamp has now become the lower one. By sheer coincidence this coincided perfectly with the cable clamp bolts clearing the chainstay. With the lever pivot clamp raised tightly under the front changer one clamp is above and the other below the chainstay without obstruction.
It is too late to do much more now but the trike is ready for another test run tomorrow. My apologies for talking this project to death but writing about it helps me to see further possibilities.
I hope I have proved that you are not at the mercy of the monopolistic manufacture's dictatorial marketing ploys. With only a couple of hinged, front changer clamps and some readily available, scrap materials, I have MTB gearing on my trike. I am using only a double chainring and a standard 11 speed MTB cassette with really useful sprocket sizes. All the components are by different makers and provide realistic gearing for touring and cyclo-cross without the need for a triple.
The new and lower gears are all under under the control of a pair of completely unmodified "road" [racing] levers from yet another manufacturer. Using all 11 speed components I have a Shimano MTB rear changer, Sram MTB cassette and Campagnolo Chorus Road Racing "brifters."
My downtube cable pulley is rather over the top and could easily be changed for a classical "tunnel" type cable guide. Finding one in your own frame tube size might be a problem. eBay seems to be flooded with "rare" Campag cable guides but from an era when frame tubes were still skinny. It only requires that the downtube cable reaches the ratio-changing lever as close as possible to a right angle. How it does that is up to you. Planet-X in the UK sells cyclo-cross cable direction changing pulleys for absolute peanuts. No doubt other dealers do too. Problem solvers are the specialist US source of pulleys on smart tube clamps. You do need hinged clamps though. A rear radius arm could hang over the clamping screw itself if there is enough room.
The dimensions of the ratio-changing lever/arm can be easily calculated using the available material under an online search for "Shimergo." Named after Shim for Shimano and ergo from Campagnolo's Ergo range of [excellent and repairable] dual purpose gear/brake, road racing, handlebar levers. I have provided links to these sites in earlier posts on this subject. The use of the term Shimshramergo is technically incorrect but a lot more fun.
You really can use any gear lever, with any rear changer and any cassette intended for the same number of gears without serious compromise. You are not a slave to the endless hype, forced compound price inflation and built in annual obsolescence planned in distant board rooms. Shimergo has really taken off over the last couple of years. It must be judging from the forest of hits compared with the few trailblazers of only a short while ago. Shimergo is becoming establishment.
I am still waiting for a Chinese manufacturer of bicycle components to completely trash the established monopolies with new ideas and universal cross-compatibility. I saw a price tag of nearly £3.5 thousand pounds for Campagnolo's latest electronic "groupset." This is completely crackers! Insane! Obscenely expensive!
Now there is talk of wireless connections between electronic components. No doubt at an even more ridiculous price premium. Are the monopolistic manufacturers using open source and freedom to rewrite the software to use alternative components? Are they hell! It's a monopoly and monopolies are like communism. Choice? Huh? Does not compute!
Sram uses very different cable pull ratios to the other "big two" manufacturers. Yet some of their components are directly cross-compatible with Shimano. Using a simple ratio-changing lever or pulleys you can mix Sram components from road and MTB for your own purposes. And, mix them freely with components from other manufacturers.
I cannot personally recommend the clever Jtek Shiftmate because the very small pulleys severely stress the cables into rapid fraying. One can easily understand the desire to make a tiny, stealth system to a high cosmetic standard. Which is why I chose to use larger cable pulleys for my own system. Which I then severely undermined by bending my gear cable around two clamping bolts! Using pulleys would have been much better. Perhaps with a single cable clamp on a straight run. Or, the cable could be repeatedly wrapped around the pulleys to increase friction enough to stop slippage.
Now there's an idea! The pulleys need not rotate so could act as friction clamps without any cable damage as it follows an s-shape. It probably needs a calculator to work out exactly where the entry and exit radii will lie relative to the pivot and different pulley sizes. Watch this space. ;-)
BTW: DO NOT use any of my foolish ideas for altering brake systems unless you really know what you are doing! A missed gear change is an inconvenience. A lost brake system is almost certain death or serious injury! Let's starve the parasitic ambulance chasers of more victims if we can. Nothing you read here should be seen as encouragement to copy my experiments. I cannot control the skills you bring to your own inventive idiocy. I offer my ideas only for your amusement and reflection. There must be much better ways to revolt against the tyranny of the cycling component monopolies and their "compulsory" annual "upgrades." Hopefully without "investing" in ridiculously overpriced vintage kit to hang on an old frame which was never really that much better than any other.