Wanting to know what derailleur I need
 

I have a 2011 jamis xc mountain bike and I have a ztto 8 speed 11-40 that is supposed to be compatible with shimano. I need to know what derailleur I need to get, so my chain will go on the biggest gear, the 40 tooth gear. The 8 speed gears are a cassette
Thanks for any info that you can tell me.

There are no Shimano 8 or 9 speed derailleurs compatible w/ a 40 tooth big cog.
And...again...this thread should be in 'bicycle mechanics' not GD.

Bummer. Can you return the cassette?

You can use a derailleur which is designed for a higher number of speeds.

Interesting. Maybe post an example?

No you can't.

Dakar XC? Looks like the Comp was 10sp Sram and the Sport was 9sp Shimano.

Are you trying to go 1x? I'd probably get a full setup. 11-sp SLX is fairly cheap, might be tough to find a rear shifter at the moment. 11-46 cassette, 7000 Rear Derailleur, 7000 shifter (make sure you get the bar clamp model), 11sp chain.

Let us know what you have and what you want to do with it for better info.

Can this be made to work?


https://cimg2.ibsrv.net/gimg/bikefor...1434bcaa0a.png

The Shimano RD-M772 Shadow LONG CAGE is listed as:
9-speed
Chain Wrap: 45T (rear cog difference + front ring difference)
Largest Cog: 36T

A few of the M-772 derailleurs are up on E-Bay, but I think that is part of a whole class of derailleurs which I'd have to look up later.

The ALTUS RD M2000 SGS Long Cage Shadow is newer, with similar specs, but probably not quite as good of quality.

So that gets you to 36T.

So... 36T to 40T = 4T or 2" difference in circumference.
Circumference = πD = 2πR = 2".

So, the radius of the 40T is about 1/3" larger than 36T.

It will probably be close, but it may work as-is. If not, there are:
Wolftooth Road Link or
Wolftooth Goat Link
Wolftooth Goat Link 11

Ahh, the Goat Link looks like it is designed to work with the Direct Mount derailleurs (above), and give a little extra clearance.

Not directly.

https://en.wikibooks.org/wiki/Bicycl...ing_Dimensions

The "Shift Ratio" for most Shimano up to 9-speed is 1.7
Then for MTB, it goes to 1.15 for 10/11s, and 1.4 for Road 11s.

There is a JTEK Shiftmate that can be used to convert between different pull ratios.
Jtek ShiftMate Gear Shifting Adapter for Shimano Campagnolo and SRAM components

I think I'd try either the M-772 (or similar derailleurs), or the Altus M-2000 first. Possibly with the Goatlink or Goatlink-11.

Thank you all very much for your info. I have three gears on the front. I am going to be going cross country with this bike and will have a pretty heavy load on it. I will have paniers on the front and on the back rack I will have saddle bags and will also be pulling a bob trailer. I usually haul a little over over 300 lbs
Thanks again. You all have given me alot to think about and to work with.

So not a Dakar I reckon. It would be tough to do full panniers on a Dakar XC.

At 90 RPM, with 2" 26er tires
24x34 is 4.91 mph.
24x40 is 4.18 mph.

Changing the small chainring to a 22 (if possible on your crankset)...
22x34 is 4.51 mph

A lot of derailleurs that will work with that cassette and a single chain ring, wont be able to select all gears with that cassette and a triple chain ring.

It may not be possible to get a derailleur which can select all gears with that cassette and a triple chain ring.

You can:

Look into which derailleur will work with the widest gear range.

Use just one of the front chain rings. You can leave the others there, but not use them. Adjust the front derailleur so it can't change gears.

Not use all of the sprockets on the cassette, and leave it a triple up front.

Use a different cassette, and leave it a triple up front.

Set it up so you can use all sprockets on the cassette, and leave it a triple, knowing you can't select all rear sprockets with all front sprockets. If you select the wrong gear, you could damage something. So it is probably not a good idea.

I am running an old style 7 speed freewheel on my bike. I like it because the sprockets are thicker, and should last longer. It is triple up front. Of course you would need a new wheel, to change to a freewheel, so maybe not a good idea. Just that I prefer thicker sprockets, than more sprockets, so they last longer.

I suggest you share the sizes of the smallest and largest chain ring, and the smallest and largest sprocket on the cassette, and people may be able to let you know if it is possible to get a derailleur which can select all gears.

Yes, it is an important number. See "Chain Wrap" above. So, for the M772 (and I think the M2000 is similar), one gets 45T (give or take a couple of teeth).

Here is an example project I was working on a while ago. I was playing around with my Jamis Coda a while ago, trying to convert it to a touring/cargo bike.

https://www.bikeforums.net/attachmen...hmentid=606547

Rear: 11spd 11/37/42
Front: Dura Ace 7703, 30/39/53
Rear Derailleur: RD-M8000 Shadow (capacity 47T, recommended max sprocket 40T triple, 42T double, 46T single).
Shifters: Bar End: Left: Suntour, Left: ? Shimano.

Above setup capacity: 31T rear (26T to second sprocket) (23T front (30/53), 9T (30/39))
Total capacity: 54T (49T for 53/37, or 40T (39/42))

The M8000 just didn't have enough capacity. I had a choice of the chain going slack on the small/small (11/30), and working on the big/big (42/53), or the opposite, tight on small/small, and not fitting on the larger combo (42/53).

I chose to cut the chain to be tight on small/small (11/30).
I believe that the chain barely stretched to the 53/37 but was to short for the 53/42.

Inevitably I made a couple of bad shift attempts, either shifting up on the rear from 53/37 to 53/42, or shifting in the front from 42/39 to 42/53. In both cases, the chain simply refused to jump up to the larger sprocket. And, within one or two crank revolutions I realized my error and chose different gearing.

So far the derailleur was not harmed (I did do the mis-shifts, but I also try to be gentle).

I was able to do reasonably well friction shifting 11 speeds. However, the derailleur cable pull was too great for the right Suntour bar end shifter's capacity. The ? Shimano shifter was able to be adjusted to pull the full 11 speeds, but was really over-shifting on both ends, and was hard to hold in those sprockets. There is a Microshift Mega 11s bar end shifter that I will try someday which should fix the problem. Or I may try to modify the right Suntour shifter for greater capacity.

I think I did drop the chain a few times on the front, and would like to eventually try a front chain catcher.

With this type of setup, I would be asking if you only use the middle and large chain ring, how do the numbers measure up. If it works, good luck.

If not, I wound make the chain length to suit big-big. If you need to not use small-small, even two or three small gears, so be it. Some Tour de France riders are climbing with big-big. It is supposed to have less resistance. Big sprockets should also wear slower, and last longer. It would be nice to come up with some way to prevent it from being put in a gear you can't use unintentionally, but that might be challenging. At least, if you do go too small with small, it is less likely to cause damage.

You will have to ditch the 40t cassette but the Deore 9 speed RD will work with your 8 speed triple. I would not venture further down the food chain for loaded touring. You will be limited to a 34t cassette. If you think you need easier gearing, investigate a smaller inner chainring.

https://cimg4.ibsrv.net/gimg/bikefor...eb59a81e70.png

Ahh.. yes... so the M592 is the shadow version of that, taking a 36T cassette and 45T chain wrap (similar to the M772, and M2000 above).