JSMaxwell

I have a stock 2010 Specialized Tricross Comp:

https://www.specialized.com/us/en/bik...rosscomp#specs

I'm making plans to take on some silly steep terrain including some dirt road. Some of this includes some very long rides and hill climbs. The stock bike has a 110 BCD Truvativ Elite crank & chain rings (48x34T).

The cassette is a 12-27t Shimano 105. I have no idea if its a long or short cage derailleur (also 105); I couldn't find anything stamped into the derialleur itself and I don't know what I did with any docs that I used to have.

Anyway, 34x27 = 1.26 & I would love to get a gear around 1.0.

Any suggestions on the best way to accomplish this? Do I need a whole new drivetrain? Can I lift one off a mountain bike? Is it possible to put a very long mountain bike derailleur on the back and a mountain bike 11x36t cassette with the existing front setup?

Thanks for any advice. I have no idea what I am doing.

fietsbob

Many of those things are possible .. A 11-36t cassette, or 34t
drop the 50 for a 46, and the 34/46 will shift back and forth easier. less difference jump.


Probably a new crankset made with a triple chainring set, including BB .
and a new FD of the triple type..

probably time for a new chain anyhow,
maybe the wear on the Cassette says It should go too.

FBinNY 

if it's a 110BCD crank it's likely to have a 74BCD granny position, which will accept a ring as small as 24, but you might have FD issues if there's not a triple on there now.

Adding that may create total tooth spread than your RDs capacity. (capacity = sum of big/big - sum of small/small) If so you have 2 choices. You can live with things as they are, understanding that the granny can only be used with the larger sprockets of the cassette, or you can buy a longer cage RD.

Or you might increase cassette size, but that can create a too short chain situation which is totally unacceptable, so it's most likely that you'll need a new chain, and the RD capacity issues would be the same.

If the crank doesn't have a granny position, then you need to decide if you can live with only a larger cassette (and new chain).

I'm a big believer of triples for hilly touring where you want ultra wide gearing. This allows you o set up the 2 chainrings and cassette for optimal riding in flat to rolling terrain where you do 90% of your riding, and have the granny as a bailout for those steep or very long hills where you want it.

fietsbob

Picture shows a compact double , external bearing I'd guess
2Pc tube spindle fixed to right crankarm won't take repositioning outward,
to make room for #3.

3 PC square taper types need a longer BB,
though I bought a Campag Race Triple years ago
the double Rt arm is made different, entirely, than the Rt triple arm.
to share the same 111long BB

hamster

The cheapest move is to buy a 11-32 cassette, put it on, adjust the length of the chain (or get a new one) to make sure that you can go big-big without jamming, reverse the B-screw on the rear derailleur, and to see if it works. Chances are good that it will work with only a mild rubbing when the RD is on the biggest ring. A new SRAM PG1070 11-32 cassette will cost you about $70 shipped.

If you don't want to take risks or you want to go lower than 34/32, you can get a 11-36 cassette and a low-end mountain RD such as Shimano Deore, for about $50 extra.

Going triple in front is an option too, but now we're talking new FD, new BB, new shifters, new shifter cables, we're talking $300 or more in parts (less whatever you can get selling your existing parts on craigslist/ebay).

Hendo252 

Me too! Unfortunately, some manufacturers (like Specialized) are dropping the triples from many of their bikes (like the Roubaix). And retro-fitting gets expensive since most of the drivetrain needs to be replaced.

Oh well...

-Tom in SoCal

fietsbob

Any how in Cyclocross, you don't need a granny gear, when it gets steep,
you shoulder the bike , and run up the hill .

fun2none

In order of expense from lowest to highest

1) Find an older triple crankset with 110/74 BCD and select the big/small rings to create 2x10 double crank to your desired gearing. Installing chain catcher is a good idea.
2) Swap the 48/34 original crank for for 2x10 mountain bike crank in 39/26 or 42/29.
3) Swap 12-27 cassette for a pie plate (11-34 cassette) and install long cage derailleur. You might need a longer chain.
4) Swap 2x10 drive train for trekking/touring triple drive train using touring crankset (48/36/26). You'll need a new left shifter (rear), new crank, and front and rear derailleurs.

JSMaxwell

Thank you all for these great suggestions!

Agree that a triple would be a great setup for what I have in mind, but I'm hoping to get away with a bit less expense.

This is the crank https://www.sram.com/truvativ/product...set#fragment-1
It uses "GXP external BB system". I have no idea what that means.
The big ring is actually a 48T in this case. I don't know why they chose this instead of the usual 50T, but there it is.
I really have no idea, but am skeptical that I can get smaller rings on this crank. The online documentation is not helping me. I'll have to take a look at it tonight.

If I could get away with an 11-36T new rear cassette, new chain and a new mtn bike long deraileur, I would be as happy as a clam. If I can't pedal up something with a 34/36 ratio, I might as well walk/run.

Will the mtn bike deraileur fit on the frame? I suppose the cassette hubs are the same.

Any reason to choose the SRAM PG1070 over a Shimano Deore or similar Cassette? The crank is SRAM/Truvativ, but the rest of the rig is Shimano. I'm just thinking that like branded components often work a little more smoothly together, but again, I don't know.

If I can do new cassette, rear deraileur, and chain for $200 parts and not have to touch the front end, I think I'm in business. I think I can even install that, but maybe I should put a dork disk on just in case. Will that work?

hamster

Yes, the mountain bike derailleur will fit on the frame. No, no good reason to use SRAM PG1070 over Shimano. SRAM seems to be more popular on Amazon, 14 reviews (average 4.6 stars) vs. 1 review for Shimano XT CS-M771. Most Shimano MTB cassettes on Amazon are 9-speed.

JSMaxwell

I love Amazon. You are right, many of the Shimano parts don't have review for whatever reason. Maybe SRAM has been availlable longer on Amazon or Shimano keeps changing their part numbers/skus.

I can get
Shimano RD-M593 Rear Derailleur
Shimano CS-HG62-10 Cassette
Shimano CN-HG54 Chain
Thank you again to everyone on this forum. The Internet is awsome.

desertdork

Nope, M593 is Dyna-Sis. Not compatible with your road shifters. Pick a previous generation "9sp" RD instead.

fietsbob

Hold the bike up to the monitor and it might self assemble itself.

ThermionicScott 

They used a 48T big ring since most people are unlikely to "need" a gear bigger than 48/11, thus they can use a slightly tighter gearing in front. Compact cranks almost always use a 110BCD for both rings, limiting you to a 33T inner. I guess that's better than the days where you couldn't have anything smaller than a 42T...

fietsbob

In short, Best solution for a granny gear?

N+1, buy a second bike with the triple crank already on it.

load that new one up with a rear rack to make it more practical.
See touring/commuting threads ..

the prior rig kept stripped down to save weight.

JSMaxwell

Desert, thanks for commenting. I'm confused, why did you write "9sp"? The bike has a 10sp cassette now and I'm looking at a 10sp mountain bike cassette. What is a previous generation called? Are you saying I hav eto go 9sp to use a Shimano derailleur that will work with my shifters? thx.

Someone else suggested the SRAM X.7 2011 10sp long cage RDR.

Yes, much better than my old 42. In this case the biggest gear is a 48x12. I thought I might spin it out from time to time in heavy tailwinds or going down hill, but its pretty hard to go that fast on this bike.

JSMaxwell

This is a great idea! I should have the parts by this weekend, so if you could wait in front of your monitor on Saturday at noon...

hamster

The derailleur might say that it's "9sp", but it will work fine with 10sp cassette and shifters.

SRAM X.7 won't work with your shifters.

I don't think so. M593 and M662 are traditional, M663 and M780 are Dyna-Sys.

fietsbob

I'll be the old guy wrenching at the LBS, Saturday, drop by,
or use the transporter room..

be sure to get the coordinates right, there is a lot of Old stuff
piled up in the Basement.

You would hate to re materialize in the middle
of some of that stuff..

JSMaxwell

Desert,

I tihnk you are recommending the Shimano M662 SLX w/o dyna-sis that is a 9 sp. That appears to be the only non-dyna-sis RD shimano has on offer. Is that why you wrote " previous generation 9sp"?

Maybe I should just use the SRAM X7 o X9 instead. Assuming that will work with my Shimano 105 shifters.

redlude97

There are alot of 9 speed mtn RD that would work, Deore https://www.amazon.com/Shimano-Deore-.../dp/B002PTQFXA, XT https://www.amazon.com/Shimano-RD-M77...ef=pd_sbs_sg_4

JSMaxwell

This Shimano page implies the M593 is Dyna-sys. The service instructions pair it with the SL-M591 shifter and that is Dyna-sys.

(WTF is Dyna-sys? nevermind, just frustrated with Shimano documentation.)

The M663 is clearly Dyna-sys on the Shimano website.

The M662 appears not to be Dyna-sys, but is "9sp" and while it has 45T capacity, it says available sprocket combination up to 11-34. (Maybe it can do 36, but there was no such thing when this product was released for 9sp?)

The M592 says 9sp, but has 45T capacity, is not dyna-sys, and says can accomodate an 11T small sprocket and a 36T large sprocket.

For the record, a "9sp" derailleur will shift all the way through a 10sp cassette?

Thanks again for all your help.

redlude97

yes a 9-speed RD will shift all the way through a 10 speed cassette, the width on a 9-10 speed cassette is essentially the same

JSMaxwell

Okay. Its looks like I'm going with the
RD-M592 Rear Derailleur (Deore - only one of this gen that specifically says it can accomodate a 36T rear sprocket. The 662/772/972 all say up to 34T. I think I'd rather have a bit higher level, but want to be sure I can access the 34-36 combo.
CS-M771 Cassette in 11-36T (XT line)
CN-M980 Chain. (XTR line)

Thank you forum.

Simonius

Your 105 RD is a short cage model, about 55mm between the pulley centres.
The secondhand value of the RD is less than a new set of pulleys. If yours are not wobbly then selling it without the pulleys may be wise.