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SRAM PG-1070 Cassette Fitment Question

Old 10-04-11, 01:36 PM
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SRAM PG-1070 Cassette Fitment Question

Hello all,

I have a 2007 Giant TCR A1 with Shimano 105 equipment. Originally it came with a 12-25 rear cassette. Last year I swapped it out for an Ultegra 12-28 cassette for hills. I have now purchased a SRAM PG-1070 12-36 cassette and according to the SRAM website it should fit without any issues. Before I take to to the LBS and waste both our time, does anyone here know if it will fit without any other new components?

Here's the specs from my bike (except for the rear cassette swap noted above)

https://www.bikepedia.com/quickbike/B...R+A1&Type=bike

Hopefully someone can provide guidance.

Lamar
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Old 10-04-11, 01:51 PM
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I don't think you're going to get that cassette to work with your 105 RD. If you really want that gearing, get yourself a Shimano Mountain 9spd RD (such as a Deore, SLX, XT etc.), and a longer chain. The Shimano 10spd mountain RDs won't work with your shifter or the cassette.
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Old 10-04-11, 05:14 PM
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Rule of thumb, more than 28 teeth, you need to go long cage in the rear derailleur. It's generally easier and cheaper to leave the 28 tooth cassette in and go to a compact crankset with a 34 tooth inner ring.
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Old 10-04-11, 06:40 PM
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Originally Posted by sideshow_bob
Rule of thumb, more than 28 teeth, you need to go long cage in the rear derailleur. It's generally easier and cheaper to leave the 28 tooth cassette in and go to a compact crankset with a 34 tooth inner ring.
That's not correct advice. A long cage ROAD rear derailleur won't handle any larger a big cog than its short cage version. It will "wrap up" more chain and handle wider range gearing but it won't clear a larger cog.

As MNron noted, the OP needs an MTB rear derailleur to allow the use of a cog that large and, as further noted, he's got to use a 9-speed era Shimano rd since their current 10-speed MTB derailleurs aren't compatible with road brifters.
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Old 10-04-11, 07:24 PM
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https://sheldonbrown.com/deakins/lowgears.html

Sheldon says I'm right and I tend to believe in Sheldon.

To quote:

"If you find that the derailer must be rotated so far back that the screw head doesn't rest on the frame stop, NOW it's time to get a long-cage derailer

These are available in every price range. These have a longer parallelogram, so will accomodate 34 Tooth cogs without having to screw in their B screw completely."

Might not be at exactly 28 teeth, but give or take that's about the point you may start to find you've run out of room on a short cage.
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Old 10-04-11, 10:17 PM
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According to the specs for my bike, I already have a compact with 34/50 teeth.

Originally Posted by sideshow_bob
Rule of thumb, more than 28 teeth, you need to go long cage in the rear derailleur. It's generally easier and cheaper to leave the 28 tooth cassette in and go to a compact crankset with a 34 tooth inner ring.

Last edited by kidcymucks; 10-05-11 at 02:49 AM.
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Old 10-05-11, 08:08 PM
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Yikes, if you're running 34 on the front and want to go 36 on the back - you'd probably be able to grind up Mt Everest
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Old 10-06-11, 06:26 PM
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As Hillrider said, a long cage ROAD rd, meant for a triple road crank, will not likely work. You need a long cage mountain bike rd as in deore, LX, XT, etc. At any rate, the 105 you have will not work with a 36t cog.
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Old 10-06-11, 06:59 PM
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HillRider is correct. A rear derailleur's cage length controls how much chain can be wrapped to avoid chain sag when using a small chainring. A long cage road derailleur has the same cog size limitation as a short cage road derailleur. For a 34 tooth or larger cassette cog a mountain bike derailleur is needed.
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Old 10-09-11, 11:58 AM
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I've done the Savageman Triathlon 2 years in a row and I was looking to have some extra gears when needed for the 2 major ascends.

Originally Posted by sideshow_bob
Yikes, if you're running 34 on the front and want to go 36 on the back - you'd probably be able to grind up Mt Everest
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Old 10-09-11, 12:28 PM
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Ok guys, thanks for the assistance so far.

It seems as though I have 2 options.

1. keep new 12-36 cassette, buy deore mt RD, new chain

2. return 12-36 cassette, buy shimano triple crank

3. Lose weight, get in better shape, so the hills don't kill me. (until then, refer to above 2 options)

I've seen Shimano has a few different triple cranks; there's price differences as I'm sure there are quality/weight differences also. Which one's will work with my bike?

A. Tiagra 4603
B. 105 5603
C. 105 5703
D. Ultegra 6703
E. Dura-Ace 7803
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Old 10-09-11, 12:35 PM
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I don't think that the shomano 9 speed der will shift to a 36. The 10 speed mountain der. doesn't have a fine adjustment screw on it, so it won't be easy to set up on a road bike.
I would go for the triple and change out the 30t small ring for a 24.
The Tiagra will be fine unless you have the urge to spend the money for the higher priced ones.
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Old 10-09-11, 11:01 PM
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Thanks davidad. So the individual rings on the triple can be swapped out? This upgrade thing is getting more complicated with each post...LOL

Originally Posted by davidad
I don't think that the shomano 9 speed der will shift to a 36. The 10 speed mountain der. doesn't have a fine adjustment screw on it, so it won't be easy to set up on a road bike.
I would go for the triple and change out the 30t small ring for a 24.
The Tiagra will be fine unless you have the urge to spend the money for the higher priced ones.
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Old 10-10-11, 01:14 AM
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Changing the front to a triple is going to cost a lot! New cranks, fd, brifters, and chain, maybe bb. Best option, more moutain training, 2nd best option new RD.
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Old 10-10-11, 12:56 PM
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Ok, now I'm confused. It APPEARS as though I'm getting conflicting information. If I change to a triple crank, would it work with my current setup or not? Can someone answer that question definitively?

Originally Posted by velorider562
Changing the front to a triple is going to cost a lot! New cranks, fd, brifters, and chain, maybe bb. Best option, more moutain training, 2nd best option new RD.
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Old 10-10-11, 06:19 PM
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I recommend just swapping the cassette, RD and chain - It is much, much cheaper and easier than a crank and front derailleur swap (which could also involve getting new front triple shifter... $$$)

I recently did a new cassette + RD with my wife's road bike (Shimano 9 speed drive train - replaced cassette w/ 34t 9 speed MTB cassette and put on a very inexpensive MTB 9 speed RD and chain.) It was very easy and pretty cheap (~$75-100 including cassette?) It shifts perfectly with her road shifters, she loves it. Although I've replaced a few RD's now, I distinctly remember the first one I did and there were no "gotchas" at all. Many online guides to adjusting limit screws and indexing, it's very easy.

Your shifters are 10 speed so you have a new Sram 10 speed MTB cassette. It will fit your wheel no problem.

But, now getting to the MTB rear derailleur you'll need: I've heard that the 10 speed MTB RD will not work with 10 speed road shifters, but I've heard that you can make it work with a 9 speed MTB RD (with 10 speed shifters and 10 speed cassette). I've never done it, so take that for what it's worth.


Now back to what became a confusing misinformed subtopic:
https://sheldonbrown.com/deakins/lowgears.html

Sheldon says I'm right and I tend to believe in Sheldon.

To quote:

"If you find that the derailer must be rotated so far back that the screw head doesn't rest on the frame stop, NOW it's time to get a long-cage derailer

These are available in every price range. These have a longer parallelogram, so will accomodate 34 Tooth cogs without having to screw in their B screw completely."

Might not be at exactly 28 teeth, but give or take that's about the point you may start to find you've run out of room on a short cage.
I didn't go to the sheldon brown website to read the full context of the above quote, but the following are facts regardless of the words quoted:

On a road derailleur, the "long cage" vs. "short cage" versions of the same derailleur (in this case 105) only pertains to the capacity for taking up chain. It does not apply to the size of the largest rear sprocket it will clear. For both, the capacity will be 28 teeth give or take. The long cage derailleur will be able to handle the large difference in front chain ring size you'd find in a triple crankset. The short cage would not be able to accomidate that large difference in chain ring size, but would only handle a normal or compact double chainset.

In other words, there are two distinct specifications, chain capacity and rear sprocket capacity. Large chain capacity does not translate into large rear sprocket capacity.

The mountain bike derailleur, on the other hand, even if the cage/chain capacity is the same as the long cage road derailleur, will have a larger rear sprocket capacity - in other words, it has clearance for a larger rear sprocket, usually at least 34 or maybe even as much as 36 teeth.

Last edited by Camilo; 10-10-11 at 06:59 PM.
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