Alpine double - what's that then?

[Tigerbiten]

............
Or better still the 26/40 mentioned or even a bigger outer? Is the difference too big? I custom built my last triple and thought that you could only have an 11 or 12 tooth difference between the rings?

I've run a 48-36-22 triple in the past with no problem.
I run a 54-38 double for a 16t difference now.
So a 14t difference between rings should be ok.

You'll really need to find a MTB front derailleur that will work with whatever shift levers you use and is designed for small chainrings.
A triple with a blank outer ring (a chainring with all the teeth filed off) will help stop outward overshifts and a "dog fang" will stop inward.
Both the above points will help shifting over a large tooth difference.

[gloomyandy]

If you are thinking of using SRAM 10 speed road shifters then I happily run an 11 speed YAW front mech with a SRAM 42/26 X5 (MTB) crankset with SRAM 10 speed Apex shifters. I suspect that the front mech would work fine on a road chainset with a similar set of rings if you can find one. I swould guess that 11 speed would also be fine, but I've not tried that. I actually run a very wide range (11-36) cassette on this bike using a SRAM X5 (MTB) rear mech and can happily use all 20 gears with no rubbing or other problems.

[pwa]

If you are thinking of using SRAM 10 speed road shifters then I happily run an 11 speed YAW front mech with a SRAM 42/26 X5 (MTB) crankset with SRAM 10 speed Apex shifters. I suspect that the front mech would work fine on a road chainset with a similar set of rings if you can find one. I swould guess that 11 speed would also be fine, but I've not tried that. I actually run a very wide range (11-36) cassette on this bike using a SRAM X5 (MTB) rear mech and can happily use all 20 gears with no rubbing or other problems.

I've never used anything from SRAM, except their chains, but I do like the way they allow their road and MTB stuff to work together, like Shimano used to do.

[mnichols]

If you are thinking of using SRAM 10 speed road shifters then I happily run an 11 speed YAW front mech with a SRAM 42/26 X5 (MTB) crankset with SRAM 10 speed Apex shifters. I suspect that the front mech would work fine on a road chainset with a similar set of rings if you can find one. I swould guess that 11 speed would also be fine, but I've not tried that. I actually run a very wide range (11-36) cassette on this bike using a SRAM X5 (MTB) rear mech and can happily use all 20 gears with no rubbing or other problems.

I've never used anything from SRAM, except their chains, but I do like the way they allow their road and MTB stuff to work together, like Shimano used to do.

I've got a SRAM Rival 1 and it's great. It seems more robust that my Shimano setups

[mnichols]

Lots to think about there. My only reservation is that when I've mixed and matched before it's never quite as slick as an off the shelf setup, but maybe that's just triples, as most of my problems have been at the front end......which is why the Alpine double appeals.

[tatanab]

most of my problems have been at the front end.

My experience over the last 5 years - it is a long way down from 40 to 24, and under less than ideal conditions the chain can go down quickly which may cause it to overshoot. I use a n-gear jump stop (dog fang sort of thing) to prevent this. As I understand it, with Shimano indexed front changers you hit the lever and the change is made with no further control, so a chain catcher could be greatly advantageous. I use Campag Ergo levers which are not indexed, just a multistage ratchet, so I can "ease" the chain down. I still use the chain catcher for the odd occasion where things don't quite go right.

[gloomyandy]

One of the nice things about the SRAM YAW front mech is that it has an integral chain catcher that will guide the chain down onto the small ring...

[mnichols]

One of the nice things about the SRAM YAW front mech is that it has an integral chain catcher that will guide the chain down onto the small ring...

Having had success with SRAM Rival 1, I'm tempted by the Rival 22

[mattsccm]

I have used all sorts of mismatches over the years but for the past 5 both my road and rough stuff bikes run a modern alpine double. A standard MTB double is 28\42. One bike runs an 11-32 cassette, the other 11-25. Both on SRAM Rival mechs. 10 speed early fronts and a medium cage for the 32 and short for the 25. One has 10 speed shifters the other 11. It all swaps as I need.
Works well. 42\11 does spin out on long gentle descents when trying to keep up with my mates but that's rare.
Recommend.

[Brucey]

Lots to think about there. My only reservation is that when I've mixed and matched before it's never quite as slick as an off the shelf setup, but maybe that's just triples, as most of my problems have been at the front end......which is why the Alpine double appeals.

It is worth mentioning (again) that triples with STIs are an entirely different kettle of fish vs triples with some other kind of shifter, IME.

Also that the Q-factor and chainline of MTB doubles is (in a road bike context), pretty hopeless.

cheers

[gloomyandy]

Also that the Q-factor and chainline of MTB doubles is (in a road bike context), pretty hopeless.

cheers

As someone who switches regularly between a road bike with a road bike chainset and one with a MTB one I notice pretty much nothing at all. So for me the difference in Q factor is not an issue. Of course your experience may differ, but lots of people seem to happily ride MTB chainsets on MTBs and hybrid bikes.

As to the chainline I'm not convinced it is that bad (especially with 135 OLN rear wheels). On a SRAM road setup the large chainring is at 48.1mm from the centre line, on a MTB chainset it is at 52.5. So the chainline is 4.4mm further out. The spacing on a 10 speed cassette is 3.95mm so in effect the ideal chainline is one sprocket further out when using an MTB chainset. With something like a 42/26 set of chainrings in my experience you spend most of your time in the big ring and smaller cogs on the cassette. The chainline for this combination is actually pretty good. Even when using the small chainring, I'd say you spend most of your time in the middle part of the cassette (I only use the very low gears of an 11-36 setup when climbing very steep hills), which again has a reasonably good line. I typically get 3,000 miles plus out of a chain and don't seem to get through any more cassettes/chains than I do on my other bike that uses a standard road bike setup.

Do you regularly ride a bike with this sort of setup?

[Brucey]

I did mean to mention that not everyone will notice or care about Q or chainline; after all a chainline that is 'wrong' might be right for some folk who happen to use some gear ratios and not others; that might be the case with your 42 big ring, as you say.

I wouldn't be overly worried about 4.4mm difference in chainline, except that it might already be a bit out.

The chainline to the centre of a 10s cassette is (given a few givens) about 22mm from the inside face of the dropout, That makes the centre chainline ~43mm on a 10s 130mm hub and 45.5mm on a 10s 135mm hub. The chainring spacing on a double is about 8mm. This would mean that the chainline is OK using a standard road double chainset but it could be up to 5.5mm out if you use an MTB double chainset on frame with a 130mm back end. [It is worse yet if you use an MTB triple big ring of course].

Given a choice, I'd usually argue for a narrower chainline being preferable, since one is likely to spend least amount of time/load in top gear and perhaps the most amount of time/load in bottom gear, on a hilly tour.

Put it this way, if it is OK even to use bottom gear with the chainline 5.5mm outwards, then maybe a 2x14 setup will be OK too; the chainlines would be about the same.

cheers

[gloomyandy]

Looking at this another way, the big ring of a SRAM MTB double chainset is at 52.5, the small ring is at 44.5 the chainline of a Shimano road triple is 45mm which given the 8mm spacing mentioned above puts the big ring at 53mm. So the chainline for a SRAM MTB double is very similar to that for the outer and middle rings of a Shimano road triple. I'd certainly not be losing any sleep over the chainline.

I'm not sure what sort of frame the OP will be using, but given that these days many frames use 135 OLN (rather than 130) to use disc brakes, then there is a good chance that the cassette will be an extra 2.5mm further out, improving the chainline a little when using an MTB crankset.

It is interesting that SRAM now produce a "wide" version of their road doubles for use with bikes with 135 OLN which moves the big ring chainline out by 2.5mm to 50.6mm (v 52.5 for an MTB CS) and the inner ring to 42.9mm (v 44.5). Which means for a 135 OLN setup the difference road to MTB is 1.9mm for the big ring and 1.6mm for the small, considerably less than one sprocket.

[Brucey]

normally on a double, I'd suggest that it would be a bad idea to use (say) the big-big combination,(or the middle-big combination on a triple) because the chainline is so bad. It doesn't stop folk from using it though...

If the chainline is worse than normal on a double then maybe it is as simple as not using two of the larger sprockets with the big ring. However bottom gear might as you say be as bad a chainline as middle-big on a triple, but that is a gear that I wouldn't normally choose to use either, even if the chainline is 'good'.

I'd also note that the chain angle varies with the length of the chainstays. Short chainstays vs long chainstays (for 700C rims) make about the same difference in angle as one extra sprocket; what is tolerable on a touring bike with long chainstays might not be on a road racing frameset.

cheers

[mnichols]

I'm not sure what sort of frame the OP will be using

An old Enigma Etape, rim brakes not disc, 56cm size