Mountain Bike Reviews Forum banner

Anyone installed a 36-38 rear cog?

6K views 38 replies 18 participants last post by  20.100 FR 
#1 · (Edited)
I have an actiontec Ti 38T cog I'm trying to put on a 11-34 XT (m760) cassette and have run into a problem. Was wondering if anyone else had done this (or on an SRAM cassette).

Please no comments on if its needed or not. I have weak legs. Its either this or a 20T front ring w/ shaved bolts to fit a four bolt XT M760 crank.

I'll also try to explain this so maybe someone else who hasn't actually tried it could still help. Things I know:
1) From Sheldon Brown: 9sp spacing is 4.34mm (each cog+spacer must equal this)
2) Actiontec cog comes w/ spacer so the whole thing is the proper width.
3) The M760 XT has a 11, 13, 15 separate. The 17-34 is on one carrier.
4) The spacer between the 17 & 15 is built into the 17-34 cluster.
5) The 15T is just the cog
6) The 13T has the spacer built into it (for between the 13-15)
7) The 11 has the lockring teeth and a spacer built in.
8) An SRAM PG980 is built almost identically (well, at least the 11 & 13 cogs).

The PROBLEM is that the 11T has a ~1mm wider spacer because it nests ~1mm inside the 13T cog. This makes removing a gear tricky.

Let me "draw" a picture. "s" stands for spacer. Its beside a number if its built in. Its separated by a "-' if its loose. "LR" = lockring

M760 XT:
34s30s26s23s20s17s - 15 - s13 - s11 - LR = works perfectly
Remember the spacer on the 11 is 1mm too wide, and there is a matching 1mm recess in the 13 to compensate.

W/ the Actiontec solution #1 (no 11):
38 - s - 34s30s26s23s20s17s - 15 - s13 - LR = problem
The lockring is too small to reliably grab the 13 since it has a recess machined in it.

W/ the Actiontec solution #2 (no 13):
38 - s - 34s30s26s23s20s17s - 15 - s11 - LR = problem
The gap from the 15 to 11 is ~1mm too large. I could machine off ~1mm of the 11T spacer but I fear it will BARELY (if at all) grab the ends of the splines on the hub. The spline recess on the 11T are already very shallow since all 9th gears sort-of 'hang off' the end of the hub.

W/ the Actiontec solution #3 (no 15):
38 - s - 34s30s26s23s20s17s - s13 - s11 - LR = problem
There are now two non removeable spacers between 17 and 13. I could machine off a few mm of the 34...17s effectively making it a 13/17 (no "s")?? You can't machine the spacer off the 13. Its splines are only on the spacer side due to the recess cut into it

Anyone done this? It seems machining the 34...17 might be the only way to go. I could "reverse" the operation if I ever wanted to go back by making an aluminum spacer ring.

Custom M760 "restored" back to 34...11:
34s30s26s23s20s17 - s - 15 - s13 - s11 - LR = works perfectly

Thoughts????

Edit: I've called the helpful folks at Actiontec and hes never seen this problem. He said he knew people were using it, but wasn't sure with which cassettes.
 
See less See more
#2 ·
I'll PM you my paypal account info so you can send the money for my solution, it's really simple, but since I had to tell you it'll cost. :skep:

Get hold of a 9spd road cassette, use the 13t cog off of say a 23-11 where the last cogs go 11,12,13,14. The 13t on that cassette won't have the recess and all you'll need is a 13t lockring.

You're welcome.
 
#3 ·
You can just buy a first position 13t cog. And buy the corresponding larger lockring. They got 'em on Sheldon's own site, Harris Cyclery. Any shop can order them, too. QBP or direct from Shimano (QBP part #FW4700 for the cog). Easy as pie. Run ya less than $15, depending on shipping, etc.
 
#4 ·
Lynx,
Im new to this mixing/matching so let me double check what your saying.

1) Get the 13 out of a road cassette. It'll have no recess if its the 3rd or higher gear. Straight forward enough.
2) Get a 13T lockring?? Im guessing thats from a XX-13 type cassette? Makes sense that it could be a larger diameter than the XT 11T lockring. Never even occurred to me these would be different sizes. Duh!

Then I can run:
38 - s - 34s30s26s23s20s17s - 15 - s - 13 - LR(from larger 13T cassette)

The 13 won't have the little teeth to keep the lockring as tight, but thats MUCH easier to get around. I can either punch the teeth and/or use a little loctite on the ring. It gets rid of the 11 cog too, which is what I was after.

This is going to get expensive. Whats your paypal addr? ;)

SMD
 
#6 ·
I've been trying to do this mod for a while now, using a SRAM 11-34 cassette.

I was going to just drop the 15 tooth cog out and add the 38 behind the 34.

My main problem is that the Ti Actiontec cog, being so thin, is going to eat into the softer CK alloy hub.

I have no solution to this so far.

I sure would love to get that 38 tooth Ti cog on there though. It would make a really nice steep climbing gear.


R.
 
#7 ·
LOL, thanks Sparrow have a "few" cassettes laying around so experimenting on stuff like this isn't hard - built myself a 27-12 last year out of a few different cassettes as I find with the 29er I don't need as low gearing. Switched to a SRAM PG990 this year and 24/34/46 rings to do the trick instead.
 
#9 ·
Rainman,
It involves fabrication but get someone (actiontec?) to make you a Ti splined center spacer. Same OD as the inner part of the 38T (=~48mm). I don't know about the SRAM (mines at the office), but the back of the XT cassette is 'hollow'. You can actually machine off >8mm from under the 34T w/o affecting anything. If you made the new Ti splined spacer 8mm+2.5mm(orig spacer)=10.5mm and tack welded weld it to the 38T in a couple spots between the arms you'd have huge >12mm wide splines to bear on the hub. W/ a spacer that wide you might just be able to rivet or pin it instead of welding.

Im going to have to face the backside of my XT and make a custom spacer anyway. The back of the hub (under the 34) is very thin and rounded. The supplied actiontec spacer is hard plastic. Im pretty sure the lockring pressure will cause the XT cassette to press into the spacer causing the plastic to creep. I fear I'll never be able to keep the cassette tight. I think the spacer is designed primarily for all Ti cogs which don't have this problem side to side. I'll just turn a little stainless spacer on the lathe...

There was some comment from the guy @ actiontec that the 38 wouldn't work w/ SRAM derailleur, but a 36 would. He had just tried. He said 38 worked fine w/ shimano derailleurs though. I wasn't thinking clearly at the time that or I would have asked for more explanation since Im running X-9 on the 29er. I still don't see why I just cant adjust the b-screw farther out.

SMD
 
#11 ·
smdubovsky said:
Rainman,

There was some comment from the guy @ actiontec that the 38 wouldn't work w/ SRAM derailleur, but a 36 would. He had just tried. He said 38 worked fine w/ shimano derailleurs though. I wasn't thinking clearly at the time that or I would have asked for more explanation since Im running X-9 on the 29er. I still don't see why I just cant adjust the b-screw farther out.

SMD
I almost ordered a 38t from actiontec a few months back but didn't because they said the 38t wouldn't work with SRAM. The 36t was backordered for something like 6 months at the time. If/when you get it working, post up pics. There's a number of people on here who like these oddball gearing choices.

I've gone with a mountain tamer in the meantime (my spider was replaceable so it was a cheap solution). Works well enough for me that I don't think I'll go with the actiontec hugemama cogs.
 
#12 ·
SMD:


I can't understand why the 38 tooth wouldn't work with the SRAM X9 derailleur in a 1 x 9 setup.

If you do the math.. the SRAM short cage derailleur can handle 30 teeth. . . 38 minus 11 = 27... still within the range of the derailleur.

I couldn't understand why he says that, unless there is something i'm not taking into account here...?

As far as the Schlumph drive goes, I looked at those, but would definitely prefer a cheap rear cassette cog option, if possible.

I'm running a SRAM 9 spd cassette on the CK hub right now, and the back of the cassette is hollow. It's the red PG-990...a very nice cassette.

I don't quite understand what you mean about the machining bit... but when I look at some of my Boone Ti cogs, they have spacers pinned to the sides of the cog to make it wider. That is the sort of thing I was thinking of doing to the Actiontec cog to prevent it cutting into the CK hub.



R.
 
#13 ·
Ok, I've completed this and it works. I haven't had it on the trail yet, bit it rides around the yard/road just fine. Here's what I had to do. (hopefully the pics attach correctly - and in the correct order)

1) I ordered a 13T road 1st position gear from a 9sp. Here is a pic of a 12T road gear (left) vs a XT 11T gear(right). You can see the extra width of the 11T spacer that normally nests inside of the 2nd position gear. You need the corresponding larger lockring too.

2) Even when you put it together - all is not good. The 38T Ti gear is too close to the 34T. The chain rubs on the 38 when in 34. Because.... the rear of the 34T cog and the rear of the cassette are NOT aligned. You can see the gap under the straightedge. Its a little less than 1mm. The supplied spacer is therefore not wide enough. Also notice that the center lip is rounded. This concentrates alot of pressure on the plastic spacer too. It was designed to go between flat Ti gears. The XT (and possibly SRAM) cassettes throw it for a little loop.

3) I machined the arch off the back of the center (about 0.5mm) just to give a nice flat edge to work with.

4) I machined a spacer that was the width of the included plastic spacer PLUS the gap from the back of the 34T cog to the center.

Im happy to report a X9 long cage derailleur works fine in a 2x9 configuration.
 

Attachments

#14 · (Edited)
R,
A spacer simply pinned to a gear will NOT help the splines digging into an aluminum CK hub. Your spacer needs to have inside splines too to help distribute the pressure over a larger area. Imagine grinding all the outside teeth off something like a 12T gear (leaving the inside splines intact) and pinning that to the 38T. The gears are ~1.85mm thick, but the spacer you need is ~2.5mm thick. You'd still be ~0.65mm too narrow. You'd still need a thin spacer -OR- what I suggested originally, get a custom width splined spacer made. Distribute the load over as wide an area as possible on the hub. Make sense?

Im starting to think a 20T front crank ring and its associated bolt head troubles would have been less hassle;)

SMD
 
#15 ·
...or a stainless steel cassette carrier.

Not sure I agree on the splined vs. unsplined spacer though. Unless the splines are a physical extension of the larger cog I don't see how they could make a difference.

Qualifier: I have been drinking a lot of red wine at this point...

smdubovsky said:
Im starting to think a 20T front crank ring and its associated bolt head troubles would have been less hassle;)
 
#16 ·
Hmmm...quite complicated, isn't it.. :madman:

I'm about to try a 3rd approach though, dunno if it will work, but i'm hoping it will... :thumbsup:

As a matter of interest, does CK make a steel hub body for the cassette, or only alloy?

I'll have to look into that, too.


R.
 
#18 ·
Rainman said:
I can't understand why the 38 tooth wouldn't work with the SRAM X9 derailleur in a 1 x 9 setup.

If you do the math.. the SRAM short cage derailleur can handle 30 teeth. . . 38 minus 11 = 27... still within the range of the derailleur.

I couldn't understand why he says that, unless there is something i'm not taking into account here...?
The maximum cog size that a rear derailleur can accomodate is not related to its "capacity".

If your reasoning was correct, road derailleurs would work with 11-34 cassettes if you combined them with the right chainrings. They don't, even if the range is within the specified capacity, because a typical road derailleurs geometry does not allow it to clear more than 28T (or up to 30T according to Sheldon Brown).
 
#19 ·
Rainman said:
Hmmm...quite complicated, isn't it.. :madman:

I'm about to try a 3rd approach though, dunno if it will work, but i'm hoping it will... :thumbsup:

As a matter of interest, does CK make a steel hub body for the cassette, or only alloy?

I'll have to look into that, too.

R.
When I was looking into this I was told my Donkey that I would need to replace the alloy cassette body of my King with the optional steel body available from King. So yes they do make it and it is the route you want to go apparently. I never got around to installing the 36 or 38 tooth cog. Maybe one day though.
 
#20 ·
You guys for doing this. I;ve been wanting to see such a setup for years. It's THE way to overcome any gearing isseus caused by larger wheels over the 26" people may have been used to.
It would be great to also get customized longer derailer hangers to makes things even better fitting.

How does the 34-38 gear shift feel, in terms of step size?
If you want to switch between 30-34-38 a lot, I suppose that's the way to go. For myself, I'd first try a 38- 32-28-24-21-18-16-14-12 and ditch the 11, swat the 12t for a 1st position cog. The 38 would really be a bail gear, for instance when wanting to stay on the middle ring. The step is barely larger for 32-38 than for 24-28.

Another thing to try would be from seperate cogs: 38-30-24-19-15-12 for a fast 6spd with good range, and manageable steps. All between 25% and 26.7%. Geared and singlespeed meet, making multi-speed. Shift only if there's a reason to.
 
#21 ·
PeanutButterBreath said:
The maximum cog size that a rear derailleur can accomodate is not related to its "capacity".

If your reasoning was correct, road derailleurs would work with 11-34 cassettes if you combined them with the right chainrings. They don't, even if the range is within the specified capacity, because a typical road derailleurs geometry does not allow it to clear more than 28T (or up to 30T according to Sheldon Brown).
Agreed with regards to capacity.....but I rode a 9speed ultegra RD with an XT 11-34 cassette for years with no ill effects.

So it can be done:)

B
 
#23 ·
Wow! what a project. Thanks for trying all this; can't wait to hear how it works.

FWIW, I've set up two 4-bolt 64mm bcd shimano cranks with the Actontec 20, and filing the castings is a minor craft project. --Especially compared to chucking and milling stuff on your lathe! :D :D :D

Takes about 15 minutes with a round hand file, less with a grinder. Chainring comes from A-tec with easy tips: just screw in the steel 12mm chainring bolts and remove enough aluminum to make the outside of the casting the same diameter. You just need patience to get it all the way done, and to not cut any sharp edges that might make stress risers.

Race face cranks usually don't even need any filing.

Now for 7 hour rides at Tahoe, I think a 20front-38rear would be just the ticket! Has anyone tried one with the SRAM x-9 r der?

I'm running 20/32 in front.
That's would be a 15inch low gear from my current 17inch :thumbsup: but a 72inch high from my current 85inch if I lose the 11 and have to use a 13:skep: hmmm. might be worth it, but...
Shimano, I'll be needing that ramped 18-28-38 XT triple crank, in a 175, please. No problem if you have to invent a new bcd standard. Black or silver will be fine. Thanks.



:D
 
#24 ·
PeanutButterBreath said:
The maximum cog size that a rear derailleur can accomodate is not related to its "capacity".

If your reasoning was correct, road derailleurs would work with 11-34 cassettes if you combined them with the right chainrings. They don't, even if the range is within the specified capacity, because a typical road derailleurs geometry does not allow it to clear more than 28T (or up to 30T according to Sheldon Brown).
You are correct about what max cog capacity is, but just as some mtb derailleurs can work on that 38t cog, some road models work just fine on a 34t. I am using a short cage Tiagra with no issues on a 34/24x11-34 setup.

The main reason SRAM derailleurs are not as forgiving as Shimano in this regard is the way the jockey (top) pulley is positioned.
 
#25 ·
shiggy said:
You are correct about what max cog capacity is, but just as some mtb derailleurs can work on that 38t cog, some road models work just fine on a 34t. I am using a short cage Tiagra with no issues on a 34/24x11-34 setup.

The main reason SRAM derailleurs are not as forgiving as Shimano in this regard is the way the jockey (top) pulley is positioned.
The funky cogset set up probs I encountered with a SRAM seemed to be due to the lack of a B-tension screw. Moving the wheel aft in the horizontal dropouts ended up solving the problem. The SRAMs have a fixed pulley path. The Shimano adjusts to the cassette in fact better. At least for me.
 
#26 ·
mtnfiend said:
When I was looking into this I was told my Donkey that I would need to replace the alloy cassette body of my King with the optional steel body available from King. So yes they do make it and it is the route you want to go apparently. I never got around to installing the 36 or 38 tooth cog. Maybe one day though.
Well then, that solves the problem, imo..

You could use the stainless CK hub with a custom Actiontec set of cogs to make up the cassette... 38, 34, 30, 26, etc..

The Ti cogs wouldn't cut into the stainless hub, and because the ActionTec cogs are all customisable as regards number of teeth, it should be possible to get your "ideal" gearing setup.

It would cost a bit, though... :eekster:

I could run 1X9 using a 30 tooth Extralite chainring and the Actiontec custom cassette with the 38 cog as my super-climbing gear... :thumbsup:

Sounds good..

R.
 
You have insufficient privileges to reply here.
Top