Compact double road

[Cugel]

Never had one before but my new road/gravel bike has one. I'm far from convinced.

I think I've only used the big ring about twice. The little ring is OK for road work but struggles at lower end off road on the steeper loose stuff. I'd imagine that it would also struggle on road fully loaded in the hills.

To my mind they've done it the wrong way around: rather than replicating a middle plus a big chain ring of a touring triple they should have done a middle plus a grannie. When I use my touring triple I rarely use the big ring, mostly in the middle but a bit in the grannie. I seem to spend all my time in little chain ring but on the smaller sprockets which is a recipe for wearing stuff out quicker.

But then I'm old and broken.....I remember when all I needed was a 52/42 and a big sprocket of 26....seemed to get me up the local Shropshire steep hills OK.

Might have to swap the chain rings for something smaller.

Modern MTB chainsets don't have the right chainline for a road bike. MTB is usually 50mm offset and a road bike likes 43.5mm. An MTB chainset on a road bike gives a very bent chainline on big ring to the larger sprockets. Small ring to big sprocket risks the chain unshipping then jamming agin the frame.

I like low gears too, even on the fast summer bike. I also like close ratio for the faster gears but have no need of 50X11 .. or 50X12. 50X13 is high enough for all except racing fellows. 50X14 is enough for me, even when sprinting for the village signs. (Look up the speeds you obtain for the various ratios, tyre sizes and cadences).

So, I have a 50-34 chainset and a 14-36 10-speed cassette. This gives a low ratio for the really steep heaves and a high enough top gear for sprinting or doing 30mph on the flat with the wind behind. The cassette is 14-15-16-17-19-21-24-28-32-36.... close ratio at the fast end with leg-easer gaps at the slow end. You have to disembowel and recombine two cassettes to get a 14-36 as no one sells a ready-made in those ratios.

You might need a compatible (same as STI road lever pull ratio) MTB rear derailleur, although the latest Shimano long-arm road mechs will probably take a 36 sprocket (they seem to be designed for a 34t maximum but usually have some extra capacity, in practice).

A bonus of these ratios is that I can stay in the big ring even at quite low speeds, as 50X32 is not too cross-chained. This is handy for the bumpy routes when the speed of a ride constantly goes from 10mph to 25mph and back again.

Cugel

[gxaustin]

I use a 46/34 with 11 to 32 cassette. I like the smaller gap in ratios between large and small chainwheels and less chain wrap is required so I get away with a medium long cage road derailer.

[slowster]

I am puzzled why a longer axle is recommended than for the triple (albeit only 2mm longer).

Because with fewer chainrings you tend/need to use a wider range of the cassette in each one. Normally you'd align the middle of the set of chainrings with the middle of the cassette, which would normally demand a 5mm longer BB spindle if you used the inner and middle of a triple, but I assume Spa felt that would spread the pedals a bit wide and that the extra 2mm is a compromise. In practice there's usually a bit of leeway to play with.

Agreed that keeping the chainline centred on the middle of the cassette would require a longer axle for a double than a triple (given that the triple TD2 cranks are identical to the double version: they are just drilled to accept an inner 74 BCD ring, at least that's my understanding), but that doesn't explain why a 110mm axle is recommended for the ordinary double vs. 115mm for the compact double.

Moreover the recommended BB axle lengths are given without reference to the rear hub OLN, e.g. 135mm or 130mm, or the seat tube size. The cage of the front derailleur versions for some large diameter seat tubes will of necessity be further out and may require a longer axle, e.g. Campag advised that a 111mm axle should be used for its Racing Triple chainset, but this increased to 115mm for larger diameter seat tubes.

As you say, there is some leeway to play with, but it does make it confusing when trying to determine what size axle is needed (or would be best) for a particular seat tube diameter/rear hub OLN.

[The utility cyclist]

It really depends on how you see using the big ring over the inner as to how much you use it because I quite like using the 50 to cruise along at low revs, I have a 50/36 and a 52/36 for my doubles. Also have a 33T ring that I can fit for rides that have more uphill and if there's a lot more climbing climbing+steep sections then I'll fit a 12-32 as opposed to my usual 11-28. It's gives about a 3% lower ratio than the 34T ring.

I still use my Stronglight 99 on the old Carlton which I use with a 48 or 50 plus I can fit a 32 or 28t so with a 28 sprocket for when it gets steeper, if you have a std thread BB it's certainly a cheap option to get the 'super compact' as they come up fairly frequently on ebay and rings are still available.

As for your present set-up, if you want a cruising ratio of 55-60" then that's 50 x 22/23/24/25 ish with say a 32mm tyre, the equivalent with a 34 is using the 15/16/17, if you get a 33T ring then you can get around the 28" range with a 32t sprocket, if you're really set on getting the 20" low then unless you want to use a 40T equipped cassette you deffo need an MTB compact double however wouldn't that throw up the problem of front mech shifting with road STIs?

[Bez]

but that doesn't explain why a 110mm axle is recommended for the ordinary double vs. 115mm for the compact double.

Because the ordinary double has rings in positions 2 and 3 (middle and outer), while the compact has them in 1 and 2 (inner and middle).

The centre of the chainring set is at "position 1.5" for the compact, position 2 for the triple and 2.5 for the double.

Also, road doubles of that vintage are normally for 130m hubs and triples for 135, which is a 2.5mm difference in chainline.

It's also possible (but not necessary, and I'm guessing unlikely—I've got both but haven't measured) that the ordinary double has a differently positioned taper, because it's a different crank, whereas the other two variants both use the triple crank.

[Greenbuilder]

Hi Si,
If you are really only using the little chainring on your compact double, why not give 1 x 10 a try on the gravel bike.
I have done just done it on my trail mtb.
Sunrace MX5 11-40 cassette, 32 tooth narrow wide chainring, 104 bcd, bolted to inside of Deore chainset, has good chainline.
The narrow wide stops the chain coming off. Deore long cage mech works fine. The whole thing is lighter and simpler.
34 tooth ring would probably work better for on road.
You can also get a 40 (or 42t) range extender cog to go behind your existing cassette; I fitted one to a friends bike, 10spd 11-36 cassette goes to 42t no problem, just wind in the B screw to stop jockey wheel hitting big cog.

[slowster]

Because the ordinary double has rings in positions 2 and 3 (middle and outer), while the compact has them in 1 and 2 (inner and middle).

The centre of the chainring set is at "position 1.5" for the compact, position 2 for the triple and 2.5 for the double.

Thank you for explaining that. I was struggling to think it through.

[scottg]

There is the old timey Simplex Tourist combos of 44/28 or 46/30.
Simplex rings go for extra silly money so.....

IRD make a 46/30, square taper, 94bcd, so you can find replacement rings, Middleburn, TA etc.
http://www.interlocracing.com/crank-arm ... -crank-set

Easton will soon have a 47/32 (really), and a 46/30, in carbon for gravel bikes.
https://www.eastoncycling.com/products/ ... ting-rings
Expensive, but interesting as mainstream taking up fringe interests.

Now if someone would make a 10s 13-30 cassette.

[Si]

If you are really only using the little chainring on your compact double, why not give 1 x 10 a try on the gravel bike.

I'm starting to wonder that. I avoided a 1x after discussion on here about them wearing out quick and the chain dropping when back peddling in the extremes...but at the moment I might as well have one!

[Brucey]

Now if someone would make a 10s 13-30 cassette.

not that difficult a recipe; start with

https://www.sjscycles.co.uk/cassettes/1125-shimano-105-cs5700-10-speed-cassette/

subtract 12T sprocket and lockring

add 13T lockring, spacer and dished 30T sprocket

simmer gently, enjoy at ambient temperature

cheers

[slowster]

There is the old timey Simplex Tourist combos of 44/28 or 46/30.
Simplex rings go for extra silly money so.....

IRD make a 46/30, square taper, 94bcd, so you can find replacement rings, Middleburn, TA etc.
http://www.interlocracing.com/crank-arm ... -crank-set

Easton will soon have a 47/32 (really), and a 46/30, in carbon for gravel bikes.
https://www.eastoncycling.com/products/ ... ting-rings
Expensive, but interesting as mainstream taking up fringe interests.

Now if someone would make a 10s 13-30 cassette.

Sugino similarly offer rather pricey 46/30 chainsets, e.g. OX601D. However, a Spa 42/26 double and standard Tiagra 12-28 cassette would give a similar (slightly better?) range of gears to 46/30 with a 13-30 custom cassette, e.g.

http://www.ritzelrechner.de/?GR=DERS&KB=30,46&RZ=13,14,15,16,17,19,21,23,26,30&UF=2220&TF=90&SL=2.6&UN=MPH&DV=gearInches&GR2=DERS&KB2=26,42&RZ2=12,13,14,15,17,19,21,23,25,28&UF2=2220

I would personally prefer 40/24, but I don't know if I will be able to get the front derailleur to work with such a small inner ring and not foul the chainstay or mudguard. I suspect I will just have to take a trial and error approach by starting with 40/24, and buy a 26 or 28 tooth replacement inner ring if that doesn't work.

With regard to a 1x10 set up, it's interesting to compare, say, a 11-40 cassette with 34t ring, with something like a 40/24 double and 12-28 cassette:

http://www.ritzelrechner.de/?GR=DERS&KB=34&RZ=11,13,15,18,21,24,28,32,36,40&UF=2220&TF=90&SL=2.6&UN=MPH&DV=gearInches&GR2=DERS&KB2=24,40&RZ2=12,13,14,15,17,19,21,23,25,28&UF2=2220

[Neilo]

I started with 50-34 with a 32-11 9s cassette when I had my CdF.
I then went to a 36-12 with a long cage M592 9s Deore rear derailleur, I probably didn't need the long cage, but better to be looking at it than for it. and it is compatible with my mountain, touring and commuting bike. It worked without a problem.
Recently I have changed to a Spa alpine double 46-30
https://www.spacycles.co.uk/m2b0s109p3383/SPA-CYCLES-Super-Compact-Chainset-with-Zicral-Rings

I thought I would have to change to a triple front mech, but I tried it with the original double mech first, It needed a slight adjustment to the lower stop for it to work fine.
It is a 135 OLD hub and the 115mm recommended bottom bracket length seems spot on.

Neil

[reohn2]

If you are really only using the little chainring on your compact double, why not give 1 x 10 a try on the gravel bike.

I'm starting to wonder that. I avoided a 1x after discussion on here about them wearing out quick and the chain dropping when back peddling in the extremes...but at the moment I might as well have one!

But that limits gear range or to achieve enough range can mean yawning gaps between ratios.

[Si]

If you are really only using the little chainring on your compact double, why not give 1 x 10 a try on the gravel bike.

I'm starting to wonder that. I avoided a 1x after discussion on here about them wearing out quick and the chain dropping when back peddling in the extremes...but at the moment I might as well have one!

But that limits gear range or to achieve enough range can mean yawning gaps between ratios.

Oh well, give it a year and it'll end up being a single speed like the rest of my 'good' bikes....problem solved

[horizon]

Spa Alpine double perhaps?
https://www.spacycles.co.uk/m2b0s109p33 ... cral-Rings

I have this on my Tern folder in 50/34 with the extra chain guard (obviously it's lower geared due to the smaller 24" wheels). It works well but as I've said before and as Si says, you're either in one or the other and I'd rather be in the middle.