Friday, May 7, 2010

The X-Ben 2x9 Experiment

What I am running this year and why

*pictures and weights to come
I have been getting a fair amount of interest in my current 2x9 setup whether it be online or passers by. Seems I am not the only one that has been left wanting more in terms of shifting performance, gear ratios, and weight savings. So I am here to set the record straight about my setup and how it came to be.
*disclaimer - yes I know that I am in no way being original and I got most of my ideas from other peoples setups.
It's really much less scientific than you might think. Pretty much the story goes........ I am used to running 11-34 cassettes with long cage derailleurs and triple rings up front (22-32-44). In the past, lets say, 5 years of riding and racing I have not come upon a situation that required me to use my 22 tooth or granny ring........ever. Sure there are situations that may exist, like Trans Rockies or maybe a super steep climb in Pisgah NC but I have learned to get by on a near 1:1 ratio from front to back. So in a conventional setup the easiest gear I would use was a 32 on the front and a 34 on the back (pretty well a 1:1 ratio). I would keep the small ring on for safety purposes. I could never really get a top swing front derailleur to completely block out the small ring using the lower limit screw. I found it would always start to impede the entire movement of the derailleur a few screwdriver turns from where I needed it to be to not have the chain fall down to the BB with no small ring. This problem is easily rectified by running the lower limit with cable tension alone but it is not a fool proof option, hence the reason for me leaving the granny on.
I was looking for a solution to shed grams and have tighter intervals between shifts. If you look at a race car you will find a close ratio transmission. This is to keep the rpms at an efficient rate and not have such big jumps between gears that will bog down the motor. My legs are no different. I found 1x9 had too large of intervals between shifts and I really couldn't be efficient to such large changes in gear ratio. I am somewhat sensitive to having the right cadence, it's just the way I train.
The 2x9 setup fixes every single problem I was having with conventional gearing except for one, I will talk about that later.


The Cassette
I am using a 9 speed 7700 DuraAce 11-27 cassette. Actually Shimano never made an 11-27, only a 12-27. I took the 11 tooth cog and cassette lockring off of a mountain bike cassette I had laying around to give me a little bit harder of a big gear. It shifts beautifully, it is very light, and it has shorter intervals between gears.

The Derailleur
I am using a 10 speed 7900 DuraAce short cage rear derailleur. Now this was a leap of faith for me. I had heard that Shimano had changed the pull ratio of this derailleur so that is was not compatible with older shifters. I guess this was not true. What dictates how many speeds a derailleur is, is the shifter. A 9 speed shifter makes a 10 speed derailleur a 9 speed derailleur, make sense? I am using a DuraAce rear derailleur because it tucks in close the the smaller diameter road cassette and guides the chain better along the cassette during shifts. Also it is a short cage so it keeps better tension on the chain which results in less slop overall. I did not require the longer tension leverage of a long cage rear derailleur because the difference from my largest cog to my smallest cog has narrowed significantly. The 7900 rear derailleur bolted on no problem and has worked perfectly ever since.

The Chain
I am using a KMC x10SL Gold 10 speed road chain. I heard from some folks that the narrower 10 speed allowed for better cross chaining and it also runs better through the 10 speed DA rear derailleur. It is extremely light as well.

Chainrings
I am using Specialites TA Chinook chainrings in 26/38 tooth counts. I have used these rings before in 26/40 combo and found I wanted to go a bit smaller on the big ring so that I could stay in the larger ring for slower singletrack. It also narrows the interval between shifting which increases smoothness up front which is a big factor for front chainrings. I am running these chainrings on the two inner mounting points, so where the middle and granny rings would be. This allows for much better cross chaining.

Front Derailleur and Cranks
I am now using the XTR 980 front derailleur designed for their 2 ring setup.  It is specifically profiled for 26/38 chainrings and it shifts my TA rings unbelievably well. I am also using stock XT cranks.

Out on the trail
This system performs amazingly well. The rear shifting is right on par, if not better, than any high end mountain bike system on the market. My easiest gear is now a 26 on the front and 27 on the back. That is very close to the ratio of a 32 on the front and 34 on the back which is the ration I have been using as my easiest gear for the past 5 years. There was zero adaptation curve with the new system for easiest gear and climbing. They are virtually identical gear ratios.
I have to shift 2 gears at a time sometimes where there are larger pitch changes. I think the 970 XTR triggers would work better because you can shift down 2 gears at a time with the release lever. Minor factor.
The front chainrings are decent. They are not spectacular but really do perform much better than their price. I have no major complaints about these. The only problem with the 2x9 system is you find yourself shifting a bit more with the front derailleur. Sometimes for the same section of singletrack the big ring is too much at times and the small ring is too small at other times. That would be my one and only complaint of the 2x9 system.
I have about 1500kms' on these components with almost no sight of wear. The chain is still well within its stretch limit, the cassette looks great, the chainrings are also in great shape.



Weight Specs of a conventional 3x9 setup vs my X-Ben 2x9
Rear Derailleur
XTR 970 11-34 - To come
DuraAce 7700 11-27 - To come

Chainrings
XT 870 22/32/44 - To come
Specialites TA 26/38 - To come

Chain
XTR/DuraAce 7700 - To come
KMC x10SL Gold - To come

Total Weight
Conventional 3x9 - To come
X-Ben 2x9 - To come

13 comments:

  1. This is all fine and dandy, but if you truly want crisp, clean shifting think out side the box. Think single speed, no shifting issues, ever, at all. Plus furter weight savings, just saying.

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  2. This comment has been removed by the author.

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  3. Not too sure what a furter is but it does sound more appealing than a single speed.

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  4. My previous post was removed as I accidentally copied and pasted instructions for building my working perpetual motion machine.

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  5. The mold of the XT triggers is identical to that of the 970 stuff. There is a little tab that shimano put in the XT shifter to prevent it from dumping 2 gears, and thus upselling the XTR.

    You can file it off with a dremel and then you have identical shifting to the 970 shifter, plus the system is lighter. Pop it open and you'll see what im talking about.

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  6. http://img.photobucket.com/albums/0903/Aaron/multishift1.jpg

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  7. Beauty! That is soo happening. Thanks for the link to the pic.

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  8. Did it today, works perfect. Thanks!

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  9. What chainring bolt did you use on the 38T? The original with a spacer or the ones for single speed..awesome blog by the way!

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  10. Thank-you. I just used original bolts/nuts with spacers. No reason in particular, that's just what I had around.

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  11. You state that you are running the XTR 980 FD designed for 2 rings, Isn't that FD 3x10, and not 2x10? The FD XTR 981 is specific for 2x10? Am I incorrect?

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  12. Yeah you are right. I just group everything together under the 980 designation. I am way too lazy to look up specific part numbers.

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  13. Update: I now have about 15,000km's on this setup and am still very happy with it. Just for kicks I may try to modify a shifter so that I can run a 10sp 11-28 cassette.

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