1. •  
     CommentAuthorPeter-DG
   • CommentTimeMar 23rd 2008

    
   I've been helping a new biker spec out a bike and the shop is trying to get her to select a compact crank. I don't think compact cranks make any sense (with one possible exception after all sorts of other options are exhausted). Anybody care to discuss/defend their use?
2. • CommentAuthorKelletcycles
   • CommentTimeMar 26th 2008

    
   Having riden 52/42 chainrings for many years and, perhaps 10 years ago, switched to 52/39 all my bikes are set up with Campag Ergos/front changers for 2 chainrings. Now in my 60s the change to compact was the next obvious choice. 50/34 on my winter bike and, the rather better spaced, 50/36 on my summer bike. I rode the Etape du Dales (UK) and the Col du Telegraphe, Col d'Allos, Col des Champs (Fr) on 50/36 x 26. Unless you are touring with panniers a compact should get you up most things and a compact just looks so much better than the alternative.
3. •  
     CommentAuthorPeter-DG
   • CommentTimeMar 26th 2008

    
   Kelletcycles: "50/36 x 26"
   Is the 26 the big cog on the cassette? I guess that makes some sense. You'd gain more with a larger cog on the cassette rather than dropping to a compact chainring. Is the 26 the biggest you can get/use for your shifting system?
4. • CommentAuthorKelletcycles
   • CommentTimeMar 27th 2008

    
   Even with a 'short' Campag rear mech you can run a 28 cog with a 39 chainring. I use a 26 with my 50/34 or 50/36 but could use a 28 or 29 as I've a med rear mech. With older club cyclists in the UK there is a resistance to 'dinner plate' sized sprockets.
5. •  
     CommentAuthorPeter-DG
   • CommentTimeMar 27th 2008

    
   With 34 compact chain rings vs 39 standard you gain 13% climbing force.
   With 29 cog vs. 26 cog you gain 11.5%. Why not go with the 29 cog on the cassette, rather than the compact with which you lose some high speed cruising ability (but only 4%). Or else for more climbing power would you not want to use the 29 cog even with the compact chain rings?
6. • CommentAuthorKelletcycles
   • CommentTimeMar 28th 2008

    
   I'm what Machinehead http://www.machinehead-software.co.uk/gear_inch_ratio_table26.html
   calls a 'die hard traditionalist and masochist.' ie I still think in terms of measuring gears in inches. I still calculate my gears based on a 27in wheel where 52 x 14 gives a gear of 100 and anything below 40in is low.
   Yes 39 x 29 would give a gear suitable for most climbs but my 34 gives me the option of a new cassette and even lower gears if I need them. The compact is lighter ie smaller rings, smaller cogs and less chain and still looks like a sports/racer not a touring bike. It is a case of choosing a suitable bike for your friend and I think a compact is a good balance between the other options. If she MAY race then 53/39; if she MAY tour or if she is used to using very low gears ie on a MTB then a tripple. I, however am pleased with my change to compacts.
7. • CommentAuthorRobS
   • CommentTimeMar 28th 2008 edited

    
   I started cycling 3 years ago at 41yo and I've kept mental notes of things like speeds and gear ratios. When I started my legs were reasonably strong but my cardiovascular fitness was poor and I was about 8 kg heavier than I am now. I use to do 10km walks at 6 to 7km/hr without any trouble and could sprint (run) at about 30km/hr (but it would take several minutes for my heart to recover after a sprint).
   
   I ride on roads in Sydney Australia which are fairly hilly but I don't do long climbs which last several km's.
   
   * Year 1:
   
   Bike 26" MTB, 15 speed, solid forks, knobby tires, 16.5kg, F 48/38/28, R 14/.../24/28,
   
   I trained on a 20km circuit which had some steep hills.
   Started at 40km/wk but quickly went upto 80km/wk and with occasional 40km rides.
   I tended to munch a bit uphills and crank the living hell out of it down hills.
   Never used the 28 at the front.
   On hills I tended to use 38/24 munching a fair bit and 38/28 with "better" cadence.
   
   F/R teeth Gear Ratio Gear Inches
   38/24 1.58 41.1
   38/28 1.36 35.4
   
   * Year 2:
   
   Bike above and later
   26" MTB, 24 speed, hard tail + fron shocks, smoother tires, 14.5kg, F 42/32/22, R 11/12/...21/24/28
   Some other MTB's as well with 48/38/28 and one with 42/36 chainrings.
   
   Increased training circuit to 25km, did 25km commutes, occasional 40-50km rides.
   Typically 80km/wk.
   Tried to do less munching and more free spinning to improve endurance.
   Never used the 22 on the front.
   Rarely used the 28 on the rear.
   On hills I tended to use 32/24 and 32/21.
   
   F/R teeth Gear Ratio Gear Inches
   32/21 1.52 39.6
   32/24 1.33 34.7
   
   * Year 3:
   
   This year I've been doing about 90km/wk avg with 26km regular commutes, and regular ~48km rides.
   I've been focussing on increasing speed, and pedalling more relentlessly to do longer rides.
   
   Over the year I started to think I should get a road bike. I set up the 24spd MTB with thinner smoother tires and I used the 42 on the front more often in order to get used to roadies gear ratio.
   Just after Christmas I decided to buy a lighter flatbar road bike with a Shimano 105 set-up, 700x28 road tires. I considered the gearing very carefully.
   
   Using the above as a guide I'm looking at 40 gear inches for common hills and 35 gear inches for occasional evil hills. The larger rear sprocket on a roadie tends to be around 25 teeth (more teeth are available in the higher end stuff). So based on a 27" nominal outer diameter this means the front chainring needs to be 32 (occasional) and 37 (most).
   
   From this I concluded that I would be better off getting a triple on the front.
   I preferred that I only use the lower front gear on evil hills. That way for most riding I can just change the rear gears. So I decided to go 39 on the front. The 39/25 combination gives 42 gear inches. With a 42 front chain-ring I would have to drop down the triple a little too often. So based on that I need to go for the hollow-tech 2 cranks. The triples come in 30/39/50 which is more than enough to cope with evil hills and get a good top speed.
   
   
   As far as the hills go this choice to go with the triple has worked out great. For evils hills I tend to use 30/21 (39 gear inches), if I'm really stuff I might use 30/23 (35 gear inches) but it's pretty rare.
   I could also probably use the 39/25 (42 gear inches) for a lot of hills but I find it easier just to knock the front back to the evil hill gear. For the majority I generally use 39/21 (50 gear inches) and might drop back to 39/23 (46 gear inches). With the lighter bike and the fact I'm pushing harder and getting stronger I'm using the lower gearing less. In retrospect I'm still happy I went for 39 instead of 42 on the front and that I went for a triple.
   
   If you are starting out cycling I think you need to go down to 35 gear inches. For a 26" with a 39 chain ring that means you want a 29 teeth sprocket on the rear. If you can only get a 27 toothed sprocket then I can see the value in going to the compact crank for hills. The thing that would concern me is the limited speed of the 36 and the big jump when changing to the 50, from this point of view at 39 with a granny gear set-up is probably better. (For kick about riding the 36 works OK, as I had an MTB with this) Your needs depend on the terrain too.
8. • CommentAuthorRobS
   • CommentTimeMar 29th 2008 edited

    
   This guy has some comments on compact cranks and uses the same ball-park gearing as I do,
   http://www.epinions.com/content_180701597316
   
   Another thread on beginner gear ratios:
   http://www.bikeradar.com/forum/viewtopic.php?t=12563352&postdays=0&postorder=asc&start=0
9. • CommentAuthoralanm
   • CommentTimeApr 2nd 2008

    
   As a mechanic, I've done lots of conversions of road bikes to mountain bike back ends for the same results.
   
   The traditional "road" setup is good for young bucks and wanna-be-pro warriors, but pushing a 12-23 on the back and 53/39 on the front likely dissuades more than encourages getting out more often, especially on hilly terrain.
   
   If shopping for a new bike, I recommend people look for either a "road triple" (30/39/53) or a compact (34/50) setup with an 11-27 on the back. This allows most people to spin up most hills, keeping cycling fun and encouraging more rides.
   
   The conundrum is what to do with an existing road bike with traditional gearing? Converting to a triple is outrageously expensive (BB, shifters, crankset, front & rear derailleurs, cassette), and coverting to a compact is expensive (BB, crankset, front & rear derailleurs, cassette).
   
   A less expensive option is to leave the shifters, 39/53 crankset, front derailleur and bottom bracket alone. Swap out the cassette for a mountain cassette (11-32 or 11-34) and put on a long cage mountain derailleur (e.g Shimano XT SGS). This provides the same overall gearing range as a road triple or compact at much less cost. The only downside to this approach is the larger jump between gears. For most, this is an acceptable trade-off against the cost of a triple of compact conversion, or the cost of a new bike.
   ...alan
   Winterborne Bicycle Institute
10. •  
      CommentAuthorPeter-DG
    • CommentTimeApr 2nd 2008

     
    Exactly! I replaced my original Shimano ultegra 12-27 cassette with a Shram 11-34 cassette and a long cage. It's fun to spin up short steep gullies that everybody else is walking. The front is the original 30/39/53 so I'm not giving up anything at the high speed end. Hence my original comment "why use a compact crank"? The valid answers I've seen are: compact looks more classy, my cassette looks more like a pie plate, my chain is long and sloppy, and the compact is lighter (maybe 50 grams?). OK.
11. • CommentAuthorKelletcycles
    • CommentTimeApr 2nd 2008

     
    Campag?
12. • CommentAuthormrwr382
    • CommentTimeApr 3rd 2008

     
    IRC also makes a good 10 speed 11-34 cassette (from Sheldon Brown); If you want to keep using your 10 speed shifters.
    It seems to me that most road bikes have an option for 50-34 cranks (at least here in Colorado.)
13. •  
      CommentAuthorPeter-DG
    • CommentTimeApr 3rd 2008

     
    Kelletcycles - "Campag?" - maybe "Campy" or Campagnolo.
    mrwr382 - "IRC" - thanks, I'll look into that.
14. • CommentAuthorKelletcycles
    • CommentTimeApr 4th 2008

     
    Campag UK; Campy US; Campagnolo It (or the rest to save confusion)
15. • CommentAuthorRobS
    • CommentTimeApr 6th 2008

     
    "why use a compact crank"?
    
    I think real answer is that it gives you lower gear ratios on a double. As far as I know that's the reason why the compact was "invented". The other aspects are more incidental.
16. • CommentAuthorKelletcycles
    • CommentTimeApr 8th 2008

     
    110 BCD 'touring' chainsets have been available from Stronglight for over 25 years. Many early MTBs also used 110 chainsets, with a lower inside ring bolted on. The upsurge of sportives in Europe has led racing cyclists to look for a lower gear, or two, without much change to their 'racing bikes'; 110 BCD chainsets give those used to racing gears a lower option with little change from their existing machines. Although the name 'compact' maybe a recent invention the chainsets have been available for a considerable time.
    http://en.wikipedia.org/wiki/Chainring#Compact_crankset

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