Sjtaylor

Newly acquired Serotta Road bike (not sure of the year) has Ultegra group set. It’s fitted with 52-42-30 in front and 12-27 nine speed in back. The RD cage is 76mm c to c. I need touring gearing for the hills so I decided change the cassette to 12-36 and install a longer cage derailleur. I have an Ultegra RD with an 82mm cage and I picked up from the LBS a pretty used XTR RD with an 86mm cage. I don’t know how to figure which derailleur will cover the spread without just trying it. What’s the best place to learn about this?

I’d like to use the medium caged Ultegra RD to keep the group set intact but I’m guessing that it won’t cover the spread.

While I’m at this I also have an 11-36 cassette so what difference will I notice between the 11 and 12 tooth smallest sprockets? What’s the advantage to one over the other?

Is it unusual on a triple to have a derailleur that won’t reach the extremes and just know not to try to shift there?

Sorry for the newbie questions. Thanks.

rhenning

I suspect you will have trouble with the mountain bike rear derailleur as the shift pull is different than road bike shifters on your bike. Use a long cage Road bike derailleur not mountain. Roger

dsbrantjr

Plug the numbers into this calculator and see for yourself: https://www.kstoerz.com/gearcalc/compare/

Bill Kapaun

I believe as long as you stay <10 speed you are good on the REAR.
Personally, I'd get a smaller triple. My bikes do because the 48T+ are far too much for a decrepit old guy that NEEDS his close spaced gearing for various medical issues.

dedhed

His 6500 shifters will work fine with any MT RD up to & including 9 speed and road RD up to 10s

Front FD is a different story

3alarmer 

.
...with your current crank gearing, using an 11 tooth cog on the rear for hills makes no sense unless you plan on pedaling downhill a lot.

Barrettscv 

You will need a RD-M591 SGS long cage Deore rear derailleur to fit an 11-36. This rear derailleur is compatible with your drivetrain and the 11-36 cassette. https://www.jensonusa.com/Shimano-De...CABEgIstvD_BwE

The XTR derailleur you have may, or may not work, depending on if it's an older version or a newer model.

The 11 or 12 small cog shouldn't make much of a compatibility or performance difference.

Jeff Wills

Incorrect. When Shimano went 9-speed, all shifters were compatible with all rear derailleur. I have used various 9-speed shifters with a variety of rear derailleurs and they all worked in perfect harmony.

Before 9-speed, Dura-Ace would only play with Dura-Ace. After 9-speed, Dyna-Sys only worked with Dyna-Sys. 9-speed was the Kum ba yah of index shifting systems.

DiabloScott

9-speed (or newer) Shimano MTB rear derailleur (not dynasys) is what you need. MTB derailleurs don't have barrel adjusters though so if you have downtube shifters or otherwise don't have one somewhere, you'll need an in-line adjuster.

I should have a better photo of this.

zacster

I don't know what my MTBs have for the lowest gearing, but they are so low that I find them impractical to use anywhere I ride. In fact, I don't think I've ever used the small ring for anything other than testing, or when I accidentally go onto it. The lowest practical gear I've had on a road bike was a 34/34, and in San Francisco with the hills it was enough. I suppose if you want to climb trees on your bike you need lower. By the same token, my highest gear on my current bike is a 50/13, not high by anyone's standards, but I've never felt I needed more. When I rode up Mt Haleakala I did wish I had more than the 34/27 that the rental had. Even a 30 in the rear would have been great. I struggled.

That said, 9sp is pretty compatible across all. Dyna-sys is a different beast altogether.

davidad

Swap out the 30 for a 24 and put a 39 in the middle. On the back you can put a 30 to give you a 23 inch low gear or leave the 27 for a 25 inch gear. Harris cyclery has a cassette that is good for your use. https://www.harriscyclery.net/produc...ssette-702.htm
If your cassette is still good you can replace the 12 with a first position 13 and add a 30 to the back. They can be 9 speed cogs and will work fine.

MoreLowGears

With regards to gearing: the 9sp 12-36 has much better ratios than the 11-36. The 11-36 has a 20% jump near the end (15-18) whereas the 12-36’s has a much more reasonable 16-18 jump there. Given your big ring is a 52 you probably won’t need an 11 anyways.

Using a 12-36 with a 30-42-52 will require a lot of capacity (46t), which most RDs won’t have. Shimano’s new M2000/M3000/M4000 RDs are your best option: 45t listed capacity and they officially support the 36t cassette.

frankenmike 

The OP, the way to figure out the spread is to calculate the total wrap capacity you need.(front spread +rear spread) which in your case happens to be 46. (52-30)+(36-12)=46. The wrap capacity should be stamped on the rear derailer or listed in the specs. Voila!

MoreLowGears

Your equation is correct, but the answer is 46 not 36 (22 + 24)!

Bill Kapaun

What's the smallest cog you expect to need with a 52T ring.
For "touring" gearing, maybe a 13 or 14T might be more appropriate to give you closer steps.
I'd buy either a 13 or 14-25 cassette and mix with a "mountain" cassette with the largest cog you want.
You can make your own.

frankenmike 

Oops! Noted and corrected, thanks.

ctak

+1 on the m591