compact chainset ?

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landsurfer
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compact chainset ?

Postby landsurfer » 20 Sep 2015, 3:49pm

My bike is currently fitted with a Microshift triple chainset and levers. Managing chain runs to prevent rubbing the front changer is becoming tedious. LBS says fit a compact double chainset. Square tapered axle. LBS says the triple changer lever will be fine. Any thoughts ? Or recommendations for a compact square axle chainset,( 50 - 36 rings).
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Valbrona
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Re: compact chainset ?

Postby Valbrona » 20 Sep 2015, 4:37pm

I don't know if your Microshift controller is triple or both double/triple compatible, but the general thinking is that a triple shift lever can be set up to work with a double crankset. If your LH shift lever gives simple indexed clicks and allows trim, like a Campag lever, then it should work with a double crankset no problem. If it is more to a Shimano pattern where a click typically shifts the chain entirely onto a different chainring, then using it as a double might be a little awkward - you might just have to ignore a click.

Your existing FD should work with a double compact chainset no problem. You can usually limit travel sufficiently enough by adjusting the limit screws.

Check out Stronglight Impact chainsets available in both triple and double compact formats. These fit onto a JIS axle, but it is just as well to buy a new BB with one because they are only cheap. It is important to get correct chainline - a new double crankset might stick out too far if you put it onto your existing triple-length axle.
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cycleruk
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Re: compact chainset ?

Postby cycleruk » 20 Sep 2015, 4:50pm

I don't know about a 50-36 (as opposed to 50/34) but it may have the chain rubbing the inside of the big ring when on small to small gearing.
Not that you should use small to small but one does now and again. :oops:
The major problem with compact chainsets is the big change in gearing (cadence) when changing chainrings.

If you have never tried a compact then make sure you do before spending the £££££s.
I think you will still have the need to "trim" it as I do on mine. (50/34
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JohnW
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Re: compact chainset ?

Postby JohnW » 20 Sep 2015, 5:48pm

Personally, I'd stick with a triple. I used 52/42 for over 30 years; I did try a 50/36 set up on one occasion early on, but I found the 42/52 a better relationship. A lot depends upon the range on the cassette/freewheel, but you'll know the range of gears that you require.

When I became Granpa age (65ish) I needed lower gears and opted for a granny ring - first time I'd had a triple. I've had no problems with a triple - you can get a bit of chain-rub where you don't want it, but it's soon adjusted away. Of those of my contemporaries who went for the 'compact' chainsets, nearly all have either reverted to a triple or returned to a double, but using granny ring (about 28 or 30 teeth) and 'middle' ring where the big ring used to be. They all said that the jump from little ring to big ring on a compact was too great and thy found themselves having to change front and rear when some changes were necessary.

Each to their own though.

robc02
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Re: compact chainset ?

Postby robc02 » 20 Sep 2015, 6:30pm

I think the points about the large jump between chainrings on a "compact" are very valid. I have a 50/34 on one bike and a 50/36 on another and find I generally get on better with the 50/36 - 50/38 might be better still. The larger jump of the 50/34 works best with a wider ratio cassette (12-25 10 speed in my case compared to 13-23 on the bike with 50/36), as the jumps between cogs are slightly larger than with a close ratio cassette so fewer cogs need to be changed across when making the double shift often necessary when front changing. Also, the wider ratio means there is less need to drop onto the small ring.

You always have the option of other combinations, such as 50/38, 48,36, 48/34 depending on your needs for top and bottom gears.

JohnW
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Re: compact chainset ?

Postby JohnW » 20 Sep 2015, 9:14pm

On a 12-25T cassette/block, with 42-32 chainset you'd get a high of 94" and a bottom gear of 35" and for general cycling, would you need higher or lower than that?

landsurfer
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Re: compact chainset ?

Postby landsurfer » 21 Sep 2015, 4:48am

Good point JOHN, BUT WHO SELLS A 42 / 32 CHAINSET ?
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stewartpratt
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Re: compact chainset ?

Postby stewartpratt » 21 Sep 2015, 9:36am

It should be easy enough to get a 4-arm MTB chainset in 22/32/42, just take the inner ring off. Possibly also fit a ~5mm shorter than designed BB axle. Failing that the XD-2 cranks with Stronglight rings from Spa is the obvious custom compact choice. Any colour you want as long as it's silver. (If you want black, I'm about to remove an unused FSA Vero 50/34 from a new bike, if that's any use…)

It should be possible to get a triple running without trouble in most cases, though. Have you checked everything? Getting the cage parallel to the rings is critical, for a start.

JohnW
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Re: compact chainset ?

Postby JohnW » 21 Sep 2015, 9:40am

landsurfer wrote:Good point JOHN, BUT WHO SELLS A 42 / 32 CHAINSET ?


Good question.........you can do it using TA cranks or you can remove the 52 ring from a 52/42/32 chainset - works for me, but the 52 ring was worn anyway - those of us who've been around a long time and have spares buckets the size of a bike shed can probably cobble something together buying rings from Spa, but yes - it's a good question.

As I say, you can do it with TA cranks, but the total ensemble would be very expensive. A bargain price 52/42/30 (or 30) would be a cheaper option.

pwa
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Re: compact chainset ?

Postby pwa » 21 Sep 2015, 9:54am

JohnW wrote:
landsurfer wrote:Good point JOHN, BUT WHO SELLS A 42 / 32 CHAINSET ?


Good question.........you can do it using TA cranks or you can remove the 52 ring from a 52/42/32 chainset - works for me, but the 52 ring was worn anyway - those of us who've been around a long time and have spares buckets the size of a bike shed can probably cobble something together buying rings from Spa, but yes - it's a good question.

As I say, you can do it with TA cranks, but the total ensemble would be very expensive. A bargain price 52/42/30 (or 30) would be a cheaper option.


I bought Spa's XD2 cranks, designed for triple, and made a 40/28 double for my wife's bike. I chose the two rings to suit her requirements and put a black chainguard ring where the outer would normally go. Combined with a Shimano square taper bottom bracket. Looks nice and gives you freedom of ring choice. And less distance left/right between pedal arms than MTB chainsets I have.

JohnW
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Re: compact chainset ?

Postby JohnW » 21 Sep 2015, 10:37am

What WOULD we do without Spa.................?

Valbrona
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Re: compact chainset ?

Postby Valbrona » 21 Sep 2015, 2:35pm

Small chainrings:

- might no be able to get FD low enough down seat tube.

- use an MTB crankset and you might get chainline problems.
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JohnW
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Re: compact chainset ?

Postby JohnW » 21 Sep 2015, 6:22pm

Valbrona wrote:Small chainrings:

- might not be able to get FD low enough down seat tube.

- use an MTB crankset and you might get chainline problems.


I can't think of a frame which would not allow the front changer to come far enough down the seat-tube for the smallest of available chainrings - but there could problem if the cable for the rear changer runs on the top of the chainstay. I've had to have a couple of frames from the 1970s and 80s altered to run the cable under the chainstay, but it is something we can do ourselves, if you can find a bike-shop that sells the appropriate cable guides.

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cycleruk
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Re: compact chainset ?

Postby cycleruk » 22 Sep 2015, 8:25pm

JohnW wrote:
Valbrona wrote:Small chainrings:

- might not be able to get FD low enough down seat tube.

- use an MTB crankset and you might get chainline problems.


I can't think of a frame which would not allow the front changer to come far enough down the seat-tube for the smallest of available chainrings - but there could problem if the cable for the rear changer runs on the top of the chainstay. I've had to have a couple of frames from the 1970s and 80s altered to run the cable under the chainstay, but it is something we can do ourselves, if you can find a bike-shop that sells the appropriate cable guides.


There can be problem with the bottom of the derailleur cage catching the chainstay when changing to a chainset with smaller rings.
That is if using a "road" FD of course. Yes the FD can be lowered but may need to left a bit higher than ideal to give chainstay clearance.
IMG_2160 (Large).JPG

As can be seen - this is with a 50/40/24 triple. If going down to a smaller chainset the FD can't go lower as it would bottom on the chainstay.
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Brucey
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Re: compact chainset ?

Postby Brucey » 22 Sep 2015, 8:43pm

Back in the day the TA cyclotouriste chainset (or the stronglight equivalent) had it all taped up, and if you didn't need smaller than 28T the Stronglight 99 etc (plus SR versions of the same BCD) would see you right. These days one is a bit stuffed for choice really....

As per previous threads if you want a 'road' alpine double then there is

- velo orange 86mm BCD ( stronglight 99-a-like)
- compass touring chainset
- middleburn chainset
- converted triple chainsets (with empty outer positions)
- single chainsets with bolt-on inner chainrings
- secondhand stuff

and that is about it, isn't it?

Re front mechs; on touring bikes the combination of large wheels, low BB height, small chainrings and slack seat angle will push a lot of front mechs into the chainstay. It is a common problem. Often a chainset/mech combination that works fine on a 26" wheeled MTB will cause problems on a 700C wheeled touring bike or hybrid.

cheers
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