Compact cranks

[Chris]

I have just bought an new bike, what a nice feeling. However with this new bike I have moved back to standard cranks from a compact. This was not necessarily by choice. The bike came with standard cranks, it would have cost me a bit to change them over and I would have had to wait a little while to get them. So the long and the short of it is I am currently back to standard cranks with a bigger cassette at the back.

This may change, I will see how it goes.

For a little background a typical compact setup is a 50/34 with a 11/25 will give you the equivalent in the standard world of a 11.66/28.7 at the back. As you can see you get a much greater range with a compact. The other thing you get is a much tighter spacing when shifting at the back than you do with a 11 or 12 - 27. The downside is you have to shift two gears at the back when you change chain rings.

I liked my compact and I know a couple of pros have ridden with them. However I also know the bike shop assistants label you as a Fred immediately and the traditionalists hate you as well.

So what is the herd view on compacts?

PS
For the record my old bike came with a 50/36 which falls somewhere in between a standard and a true compact.

[SueP]

I really can't see the disadvantage in them unless you spin out in a 50/11!

Smaller front chainrings, presumably a little lighter and a little stiffer?
Tighter and smaller cogs at the rear - again a little lighter perhaps, smaller jumps between gears.
My old bike had a compact and I never had any issues with changing the front cog - with the STI levels these days you can pretty much shift up front and 2-3 shifts at the rear simultaneously.

Some say that they and the chain may wear out a little quicker as its running on less teeth?? But other than that - why wouldn't you (run a compact)?

[Driver]

Chris, you run em if you like em.

They are definitely better if you struggle on the climbs, the larger disadvantage being bigger 'gaps' between gears.

A 50/11 is a bigger gear than a 53/12 and not many people need a 53/11... ever.

Ideally I would love one bike with a compact and a 11-25 and a std with a 12-27.

Shim do a 105 cassette in 11-25 - very handy - and unless you run new 7900 or 6700 or Sram the 11 - 27 is not an option.

This is handy;
http://home.earthlink.net/~mike.sherman/shift.html

[MatthewL]

There was a similar question on the old forum, and I think Michael Hanslip weighed in with the view that compacts are better for most people (with, if I remember correctly, Robbie McEwen being a possible exception) because they give better ratios for climbing and very few people spin out with 53/12.

[gsavage]

I have a 34/50 and a 12/27 on the rear (both Shimano 105). Seems to work ok, I really appreciated the 12/27 going up the hills on the Fitz's weekend and I don't think I lose too much top end speed :)

[Chris]

I have the new Ultegra so I can go the wider spread if I wanted but I think I will pick up some cheap Ultegra 6750 cranks of the net and sell my 53/39. If I sell them for $70 I will still be better off. Who would say no to a new set of cranks for $70. I will then most probably move my new 12/27 to my old bike and move my old 11/25 to my new bike. I have been good with the chain so it is still in good condition.

[Driver]

I'll take em

[Jez]

I would be lost without my Compact,..I run ton a 50 / 34 , and 12/27,.. for me the feel of a compact is a bit more speed for less effort,... and for me spinning just that little bit quicker feels better, and works for me,....at the end of the day,..the bike is yours,...do what feels right for you,.... :)

[Ross]

I haven't found a hill yet that I can't ride up on my Cervelo (inc Fitz's and TOB - think I've only done TG on the Felt though) with 39 front and 25 on rear, but saying that I have compact on the Felt but very rarely go into the large cog on the back. I'm more of a masher than a spinner so this suits me. The Cervelo is a fair bit lighter than the Felt so that helps with hill climbing too.

I too noticed that the ratios of the standard FSA crankset on the Felt was in between a (Shimano) standard and compact.

The closer spacing of gears is good on the Cervelo but so too is the easier gearing of the Felt for when I am tired or feeling lazy.

Run whatever gears you want, it's your bike. What sort of bike did you get?

[anla]

what did you buy chris?

[Chris]

TCR Advanced 1 - the TCR with Ultegra 6700

[Bean]

Nooice!

[Chris]

OK I was doing a little research if you want to go compact you should either get one of the new shiny Ultegra or Dura-ace derailleurs or a long cage derailleur of your choosing from the old series. The new derailleurs can hand a 50/34 and a 11-28 if one existed.

However it appears that old Ultegra and Dura-ace derailleur does not officially support 50/34 tooth chain rings. While it will work you would not be able to run a 12-27 or an 11-25 on the back you would be limited to a maximum range cassette range of 12-25 or 11-23.

Here is how it works:
From the spec sheet Ultegra 6600 and Dura-ace 7600 standard cage rear derailleurs have the following figures:
* Total max tooth difference 29 (the total number of teeth a derailleur can shift between on the front and the back added together).
* Min cassette tooth 11
* Max cassette tooth 27
* Max front tooth difference 14 (this I think is calculated on the max Ultegra and Dura-ace cassette tooth difference)

From these number we see that an old standard cage derailleurs can not officially handle a front tooth difference of a 50/34 compact. A 50/34 has a front tooth difference of 16 teeth where there derailleurs have a 14 tooth max. This figure is derived by subtracting the maximum cassette spacing of 15 (12-27) from the maximum tooth difference these derailleurs support 29 teeth. This implies a max front tooth difference of 14. However if you limit you rear cassette selection to no more than a 12-25 (a 13 tooth difference) you would be able to handle a 50/34 on the front. Alternatively you could do a 11-23.

So how would this stack up in practice.
* A 50/34 and a 12-25 would give you a range equivalent to a 53 with a 12.72-26.5 on the back and a 39 with a 13.76-28.68
* A 50/34 with a 11-23 would give you a range equivalent to a 53 with a 11.66-24.38 and a 39 with a 12.62-26.38

[SueP]

Just go the new DA (OK slight cost involved). Thats one of the main reasons I wanted to upgrade - can get a 165mm cranklength in a compact crankset AND the grips and levers are smaller and reach adjustable therefore better for small hands. Add to that the flexibility of a whole range of compatable rear clusters and its an attractive option.

[milto]

I run old Dura-Ace with a compact and 12-27. Never knew it didn't work according to the spec sheet.

Interesting that it is not supposed to be run. Maybe I need a new bike now or at least a new groupset.

[Ross]

Gee Chris, my brain hurts after reading that post! http://www.clicksmilies.com/s1106/fragend/confused-smiley-015.gif

I have a 105 compact on the Felt and have had 12-27 with no problems. I normally use a 12-25, no probs either.

[Chris]

Gee Chris, my brain hurts after reading that post! http://www.clicksmilies.com/s1106/fragend/confused-smiley-015.gif

I have a 105 compact on the Felt and have had 12-27 with no problems. I normally use a 12-25, no probs either.


If your Felts is like my old felt it comes with a 50/36, rather than a 50/34, which gives you the extra 2 tooth capacity needed to safely use a 12-27.

[gsavage]

If your Felts is like my old felt it comes with a 50/36, rather than a 50/34, which gives you the extra 2 tooth capacity needed to safely use a 12-27.

My Cannondale definately has a 50/34 and came originally with an 12/25, I changed it to a 12/27 at the bike shop. Could this be why my chain keeps wearing out after a few thousand km's?:confused: Do I need to go back to the 12/25?

[milto]

A couple of thousand K's is pretty normal for a 10sp chain. I am doing well to get that.

[gsavage]

A couple of thousand K's is pretty normal for a 10sp chain. I am doing well to get that.

Thanks Milto, sounds like I can stick with the current setup, having the 27 is good for me at the moment with some hills. :)

[Chris]

A Pro wrench could possibly shed more light on the subject, but without seeing your bikes, Milto and Mr Savage, I suspect there are two possibilities.

Firstly you may have a long cage rear derailleur (these are typically used on bikes with triples). If the Cannondale came with a compact it is possible that they may have put one on the bike to allow for the compact. The longer cage allows the derailleur to take up more slack - a bigger tooth difference 37 max and a 22 tooth difference at the back.

Most road/race bikes use the short (standard) cage derailleurs. This is the situation I was talking about when I raised the technical issue ie converting a standard bike to a compact. It is worth remember that Shimano has only just come the the compact party. They have had a set of compact cranks at around the Ultegra level for only a couple of years and it certainly wasn't branded as being part of any groupset. It is only with the latest upgrade to Ultegra and Dura-ace that they have started actively supporting compacts at this level.

Secondly you can actually use a compact 50/34 with a standard cage derailleur you will just run into problems with either the biggest or the smallest gear combinations. A 12-27 will most probably work provided you avoided using the 27 with the big chain ring. If you do the derailleur will have a hard time providing enough slack. If you looked at the drivetrain when you are doing this you will see the bottom chain run (not sure what the technical term) will be stretched tight and the derailleur will be pulled hard forward. This will put a lot of stress on the derailleur and I suspect changing in and out of this gear will be difficult.

The alternative adjustment would have the derailleur provide enough lack for the 50-27 combination by allowing the chain to droop down when you are in the 34-12. I am not sure which is better. I suspect it is better to have a tight chain in a combination that you won't use much as opposed to a loose chain in another.

Any one else have a view?

[milto]

I have the old non group crankset. I would never ride little to little but there is no slack there, My mtb triple has some slack in it little to little. I will occasionally ride big to big when trying to power over a small hill. It has no problems with this. There have been quite a few mechanics look at the setup and nobody has said anything. Maybe one of those cases where they have a rule but it is not that bad to bend it a little.

[Ross]

If your Felts is like my old felt it comes with a 50/36, rather than a 50/34, which gives you the extra 2 tooth capacity needed to safely use a 12-27.

I changed from the standard FSA compact cranks to Shimano 105 compact cranks when one of the FSA cranks broke. The 105 is 50/34.

[Hoops]

My TCR came straight from the shop with a 50/34 12-27. Runs fine and I often ran the 50-27 combo as i don't like changing to the small chainring unless absolutely necessary. Since i bought a 11-23 cassette i don't use the 12-27 unless i know i need lazy gears.

[Bean]

I'm looking at upgrading from 9 spd 105 to 10 spd Ultegra with the possibility of going compact, so this is useful info Chris. I've got the added confusion of whether or not my AC 420CR's need a special spacer for a 10 spd cassette and/or whether or not I can make the change-over gradual (e.g. start with a 9spd compatible 10 spd Ultegra rear derailleur but keep other components) or if I have to go the whole hog. This discussion certainly helps a little. Going the whole hog with a compact might certainly be an option for me atm.

[tor.lattimore]

I'm looking at upgrading from 9 spd 105 to 10 spd Ultegra with the possibility of going compact, so this is useful info Chris. I've got the added confusion of whether or not my AC 420CR's need a special spacer for a 10 spd cassette and/or whether or not I can make the change-over gradual (e.g. start with a 9spd compatible 10 spd Ultegra rear derailleur but keep other components) or if I have to go the whole hog. This discussion certainly helps a little. Going the whole hog with a compact might certainly be an option for me atm.

10 speed cassettes usually come with the spacer required. I have lots of spare ones hanging around if you need. I'd be surprised if it wasn't much cheaper in the long run to switch everything at once.

[Bean]

Indeed my thoughts Tor... it's just the matter of handing over all that dough at once is all!

[SSSimon]

Hi All.
My 2c worth - if you're running a triple on your road bike then you'd probably benefit by converting to a compact crankset - i.e. changing your BB and cranks to to a compact set will qive you a better Q factor (which is good) with only a slight loss in the longest gear department. In this case your current front and rear derailiers will be able to pick up the slack with no problems. You will have to adjust your front derailier to suit your new compact double.

If you're changing for the standard road set up (which can be 39/52, 39/53, 42/52 or 42/53) then you will also need to change your front derailier to a compact compatible one - this will have inner plate with a profile to hit your new smaller (30/34 tooth) chainring. This is in addition to doing the calc mentioned above regarding the slack capacity of your rear derailier (essentially the difference between your front CRs + the difference between the biggest and smallest cog on the back - this is the maximum amount of chain slack that you will be asking your rear derailier to pick up if you shift to the small CR and the smallest rear cog).

If you are going convert to compact cranks also take the opportunity to optimize your crank length - for most people contemplating compact cranks, investigate picking up 165mm length cranks - the shorter crank length is better for spinning fast and reducing knee strain.

With the new style outboard BB's, changing cranksets has become very easy. On the same bike you could run the compact double 165mm set up for road races and crits, then swap to traditional cranks for TTs.

Regards,
SimonC.

[dadcram]

Ben if your nine speed is functioning then leave it and look out for the magic end of model deals. Either for a new bike or a groupset. Ultegra SL at Wiggle (http://www.wiggle.co.uk/p/cycle/7/Shimano_Ultegra_SL_10_Speed_Groupset_%28OE%29/5360031980/)

[MatthewL]

A 12-27 will most probably work provided you avoided using the 27 with the big chain ring. If you do the derailleur will have a hard time providing enough slack. If you looked at the drivetrain when you are doing this you will see the bottom chain run (not sure what the technical term) will be stretched tight and the derailleur will be pulled hard forward. This will put a lot of stress on the derailleur and I suspect changing in and out of this gear will be difficult.

Chris, someone was reporting exactly this situation happening to a friend on Fitz's challenge (Tharwa edition). The general opinion then was that they must have stuffed around and taken a few links out of their chain - but this sounds like the source of the problem.

Hoops, isn't your groupset 105? The discussion above has mostly focussed on Ultegra and Durace which maybe have shorter (hence smaller and lighter) cages??

[Bean]

I'm doing that too Daz! New bikes are still on the possible list

[gsavage]

Chris, someone was reporting exactly this situation happening to a friend on Fitz's challenge (Tharwa edition). The general opinion then was that they must have stuffed around and taken a few links out of their chain - but this sounds like the source of the problem.

Hoops, isn't your groupset 105? The discussion above has mostly focussed on Ultegra and Durace which maybe have shorter (hence smaller and lighter) cages??

Matthew, I have a 105 groupset on my bike except for the derailleur which is a ST-6600 Ultegra. According to the doco that came with the bike the max sprocket it can handle is a 27 and the min is an 11. So I think my setup is fine for the 12/27, maybe it only applies to older Durace and Ultegra gear...

[bosworth*]

TCR Advanced 1 - the TCR with Ultegra 6700

Very similar to mine and Leigh's, we have the TCR Alliance 09 with 105's.

[Chris]

Matthew, I have a 105 groupset on my bike except for the derailleur which is a ST-6600 Ultegra. According to the doco that came with the bike the max sprocket it can handle is a 27 and the min is an 11. So I think my setup is fine for the 12/27, maybe it only applies to older Durace and Ultegra gear...

The minimum and maximum gear sizes for last generation Dura-ace, Ultegra and current 105 are 11 and 27 respectively. The other figure you need to consider is the total tooth difference that the derailleur can maintain correct chain tension over. For all of these derailleurs the max tooth difference it listed as 29 or less. A 12-27 cassette gives a tooth difference of 15, therefore you can have a 14 tooth difference (29 - 15) between the front chain rings. This equates to a 50/36 or a 53/39.

A 11-25 give a tooth difference of 14, there for you can operate a 15 tooth difference at the front with would allow a mythical 50/35 or a 53/38.

By the sounds of it the derailleurs can operate outside this specified range by a little. So the moral from anecdotal evidence you can run a 50/34 and a 12/27 if you are a little careful.

For anyone that is interested I am getting these numbers from the Shimano technical site. The links are 5501 (old 105) (http://techdocs.shimano.com/media/techdocs/content/cycle/SI/105/RD-5500-5501/SI-5TK0D-En_v1_m56577569830603908.pdf)
5600 (current 105) (http://techdocs.shimano.com/media/techdocs/content/cycle/SI/105/SI_5VN0B_001/SI-5VN0B-001-ENG_v1_m56577569830683908.pdf),6600 (old Ultegra) (http://techdocs.shimano.com/media/techdocs/content/cycle/SI/SI_5VG0C_001/SI_5VG0C_001_En_v1_m56577569830616226.pdf), 6700 (new Ultegra) (http://techdocs.shimano.com/media/techdocs/content/cycle/SI/SI_5X90A_002/SI-5X90A-002-ENG_v1_m56577569830675227.pdf)

PS You can check whether you have a standard or long cage derailleur by the serial number. The long cage has GS after the number ie a 5501 GS is an old 105 long cage derailleur.

[RobF]

Ben - the Am Classic wheels do need a spacer, and it should have come with them. You also need some plastic pins or clips for the 10 speed cassette, which also came with my wheels. The instructions are on their website.