Hello. I am building a hillclimb bike and would like a pointer towards an appropriate rear derailler.
Requirements/conditions of use as follows:
Will take 34T cog
Only needs to accomodate a 11 tooth difference (I am using a single front ring and the 4 top cogs of an 11-34 cassette)
Friction shift, so no particular indexing required.
Price is an issue- I like to be on the sweet spot of the grams/$ scale, not the AX Lightness end of things

Anything come to mind that would work

Also, I'm also looking for a single superlight caliper- barely has to work since max speed is 6 mph and it is only used once.

SRAM XX or Shimano XTR + tuning

or SRAM Red 2012+ Mid-cage (+ tuning), but I believe it only goes up to 32t.

Maybe cheapest solution: buy a used (pre-2012) SRAM Red RD ($100), tune, have fibrelyte or other provider create a longer cage so you can go up to 34t.

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Exp001

I snagged an old 9spd XTR RD for about $60 that fully accomodates an 11-34 cassette, though I use it for CX. It works with 9 & 10spd Shimano just fine.

Something like this.

Exact Model is SHIMANO XTR 952 which weighs in at about 210g.

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Who, what, huh?

looking at SRAM XX it lists at 190 grams which seems pretty good. How much could I expect to take off by "tuning" it?

XX derailluers are already fairly "tuned", iirc all of the limit bolts are alloy, and the cable clamp bolt is ti. You might be able to shave a few grams off the body of the der, but not without some heavy dremeling.

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My drawings:
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My bike:
http://weightweenies.starbike.com/forum/viewtopic.php?f=10&t=107451