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advice on cassette sought.

Original Post
Rokjox Teleski · · Boise, Idaho · Joined Sep 2015 · Points: 0

I have been learning about working on my bike.  The lesson hasn't gone too far.

I have a 2007 Spec. FSR stumpy with a XTR derailleur and an 11x34 gearset.  I found a good deal on a 12x36 and as I spend a lot more time pushing uphill than blastin downhill pedaling hard, I thought I might replace the heavily worn old set with the bigger gears.  

Unfortunately, I didn't like the angle and way that the jockey wheels on the cage sit on the top gear.  No clearance, it bumps along the chain slightly.  It would work, but its not elegant.  If the springs of the XTR would allow (force) the cage to sit rotated an inch further back, it would provide all the clearance and lift needed. (Wanted...)  I look on the web and I notice that many derailleurs have a higher tension setting that is usually left unused in factory sets, but can be changed by placing the associated spring into a second, anchor hole, leaving you with a stronger resistance to forward pull, I assume.

But the XTR doesn't have an obvious second hole for the anchor, that I could notice... so I took the whole thing to a local shop to see what they thought.  Am I clueless on how this is done?  ((well, yes I am, but...))

The local shop isn't the premier shop locally here, I guess... the mechanic seems to have not understood a thing I said... he put it together like I had tried, and with the same results, a crammed chain path.  He seemed to have no idea that the tension of a derailer might be changed or why, and he didn't seem to find the setup he had created had anything bad wrong.  MAybe it IS ok??   ((nawwww...))

I am changing the set back to the old gears, and will replace the cassette with an exact replacement part again later.

But am I missing something?  Is it possible;e to run the old XTR with the extra size gearing?   It kinda is too far for the chain tensioner, bottom gears are almost loose chain when used and top gears are ALMOST too tight; but a change in tensioner tension would allow the gizmo to take up the slack better also.

Do I just need a stronger spring, maybe available from a better source?  Or am I trying to reinvent the wheel?  Or trying to make an XTR derailler do something it can't?

I am just creating a lot of trouble for myself I guess.   Walking isn't the worst thing that can happen on a steep climb.

Brock Warner · · Beaverton, OR · Joined Nov 2014 · Points: 1,176

You can likely find a spec sheet for your derailleur by googling its model number, something like RD-M###.  This model number can usually be found on the back plate of the parallelogram of the derailleur.  If you're lucky and find the right spec sheet, it will tell you the Maximum Sprocket Size.  This is the largest tooth count your derailleur is designed to handle on the low gear of your cassette.  If your derailleur can't handle a 36T cassette you can try creative solutions (some people have tried using a longer B-tension screw) but remember your equipment has limitations.  As a 6 year professional mechanic, I can tell you these days I tend to just play it by the book.  Getting creative usually nets you halfway or temporary successes (in my experience).

The spring you are describing sounds most like the lower knuckle spring.  Yes, it can be moved to the secondary position but my understanding of this procedure is that it breathes new life into old derailleurs whose springs are worn out in the factory position and the cage can't properly tension a chain anymore.  It would not affect Max Sprocket Size; that has more to do with the inherit geometry of the derailleur.

If your XTR can't do the 36T and you really want it (I'm all with you on wanting lower gears) then my advice is to first see if you can get a new derailleur to accommodate the cassette, but that may be less-than-desirable depending on your current drivetrain.  Second, check out this:  It's designed for road bikes but I don't see why it wouldn't work in your situation.  Consult with your local shop first though ;)

Rokjox Teleski · · Boise, Idaho · Joined Sep 2015 · Points: 0

I'm one of them guys with insominia...

That is a GREAT answer to my post, thank you so much.  

Guideline #1: Don't be a jerk.

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