Road changer for 46t double

[CPeachey]

46t is a bit small for most road changers so has anyone found one suitable for Shimano Sti levers? (Double or triple)
(Chainstay/seatstay angle is Road not MB)
Also can a SRAM double changer work with a 105 triple LH lever?

[Norman H]

I don't think you will have a problem with a normal road front mech. I've run 48T and 46T chainrings on a 5600 front changer.

Shimano also do a CX specific front mech. CX70

http://www.chainreactioncycles.com/shimano-ultegra-cx70-double-10sp-front-mech/rp-prod70123

I don't know about Sram, suck it and see!

[Tonyf33]

Older shimano triple derailleurs (read 400LX) work perfectly fine with a 46T big ring, they also happen to work with STI's as well..
Suntour derailleurs are more than likely to work with a 46 and the one I have had fitted was fine with a double STI lever.

[Brucey]

Also can a SRAM double changer work with a 105 triple LH lever?

IIRC sram use the same pull ratio for road and MTN but shimano don't, so probably not.

If you are handy, you can change the pull ratio of front mechs by altering the cable attachment point slightly.

Double STIs with no (or no need for) trim position on the inner ring often use a cable pull that is much larger than it needs to be ( the mech position is defined by the stop screw, not the STI) so some combinations will work even though the pull ratio of the mech is probably 'wrong' for the lever.

Note also that the shift ratio of front mechs is nowhere near constant; it changes through the stroke. Normally this isn't a huge problem but changes in chainline can catch you out and even something simple (like using a road triple STI with a road double mech) might not work perfectly as a consequence.

cheers

[CJ]

Quite a few of Shimano's road double mechs are also good for a 46T outer. Accordign to the catalogue, some do 50-53T and others do 46-52T. You need to be more specific: what groupset quality level? how many rear speeds? if you want a specific recommendation. For example there's no 105 that does 46, but the non-series FD-CX70 is a 105 quality 10-speed cyclo-cross mech that should be particularly good for that size.

[CPeachey]

Hi Chris. I read your article and thought of converting the tandem, (Middleburn cranks), from 24-38-49 to something like 22-42 or 24-44/46 using our 105Sti 10sp shifters. Back end has 10sp 11-36 with an XTR 9sp changer. (works perfectly). Just ordered a SunTour XC microshift front changer from e-bay. Not sure yet what it's capable of so will experiment. The problem with the current triple setup is that the spider is a MB type and the chainline is 50mm so road changers would not reach out to the big ring,(which we never use anyway!!!)
...so a 110/58 double road spider would seem the right way to go providing I find a suitable front changer.

[iainb]

Don't know about the more modern stuff but the bike I ride to work has a 42 x 28 chainset and a 105 7 speed mech works OK on that.

Regards

Iain

[Anthony FX]

Don't know about the more modern stuff but the bike I ride to work has a 42 x 28 chainset and a 105 7 speed mech works OK on that..............Regards Iain

hi...can i butt in..?
i have an older bike with 52/42 and a 5speed 14-28 freewheel
Simplex SX410 rear and Shimano [model ?] front derailleur

quite hilly where i live now so
could i fit a 42/28 with no modifications.? [newbie question.].
i assume the FD would have to be repositioned lower on the seat tube
and some links removed from the chain

thanks

[Brucey]

a front mech that copes with a 10T gap isn't necessarlily going to cope with a 14T gap, but it might. You will need to get a different chainset of course, you can't very easily get a 42-28 chainset these days, so choice is limited.

cheers

[CJ]

a front mech that copes with a 10T gap isn't necessarlily going to cope with a 14T gap...

I wouldn't worry about that. Barring ancient stuff, I've never known a mech so short that it wasn't rated for AT LEAST a 14T 'gap', and have generally found that mechs will shift much bigger differences than they're rated for.

All of Shimano's current road doubles are rated for 16T, so no worries. I can't tell you how much more that that they'll do but it looks like quite a bit more - unless you have an unusually wide chainstay angle (this may be the case if your bike has smaller than 700C wheels but does not re-position the mech further aft).

The rated capacity of a front mech contains an allowance for unusual frame geometry such as smaller wheels and steeper seat angles, both of which cause the cahin to run lower in the cage. Provided your bike is of normal geometry, you can use that allowance to run a much bigger chainring difference than that rated capacity.

I haven't tried this with a road double mech, but the SLX mech that's happily shifting a 40,20 double chainset on my touring bike (and prior to that was shifting 42,22) is rated only 14T. It undoubtedly helps that my touring bike will have a smaller chainstay angle than the mountain-bikes this mech is designed for, so the chain runs higher in the cage. However I am also getting six more teeth performance, without any help from a smaller-than-expected chainstay angle, out of the Shimano-105 triple mech on my audax bike, that's rated 20T but happily shifting 24,39,50.

P.S. Don't try that SLX mech with a 46T outer. It's designed for a 36T outer and isn't really safe with more than 40T, or usable with more than 42T, since the cage curves down more sharply than the bigger ring, which is then in danger of catching the back of the cage in its teeth, which if they did catch would probably demolish the cage!

[Brucey]

you are right of course, provided the frame isn't weird or something.

Perhaps I am being unusually cautious at present; I recently refurbed a front mech mount on an unusual frame, only to discover (after quite a lot of welding work) that it was at a daft angle anyway, and I had critically reduced the normal capacity of the front mech so that it wouldn't even do what it said on the tin any more. D'oh!

cheers

[Tonyf33]

Suntour Cyclone MKII & a Shimano 600EX double are quite a rangy front derailleur's, certainly the latter will run a half step triple with small inner.
I just sold my 600 and had used it with a Stronglight 99 (48/34), before buying a shiny new DA 8 speed which also seemed to work fine. Dunno if the DA would run to a 28 mind.

[CPeachey]

Found what I need in my box of bits! Shimano XT FDM-773 triple front changer. This is a mountain bike changer with the cage set at road bike angles (63-66degrees). Bought it from ROSE a few years ago and forgot about it. They do seem to have some current equivalents. Cage angle is perfect for 42t and am currently using it with 24/40 and 105 triple STi shifter. (have ordered 22/42rings) Being a triple changer and shifter there is plenty of adjustment when using it as a double. Mech looks quite capable of handling 20/42 or 24/44-46.
22/42 gives me a range of 17"-107" with an XTR rear changer and 11-36 10sp cassette.