differences between compact and standard cranks
- Thread starter Evilbofh
- Start date
Evilbofh said:
Well that difference, that you give, is in the chainring bolt circle. What's significant about it is that with a 110 mm bolt circle, aka compact, you can use smaller chainrings. Typical gearing on a compact crank is 50/36 or 50/34. Otherwise, there's no difference. both standard and compact weigh nearly the same.....or the same. Sometimes compact is even heavier.
One factor not often mentioned is the difference in relative size between the two chainrings for a 53-39 vs. a 50-34. The shift from small to large on the 53-39 is a 36 % increase. On the 50-34 the difference is 47%. More shifts on the cassette are required when shifting chainrings on the compact for this example. The 50/36 is pretty close to the 53-39 at 39%.Evilbofh said:
I wish I had understood this before I changed to compact. I would have gotten a 50-36 chainring combo instead of the 50-34 and a 11-25 cassette instead of an 11-23 (or just gone standard). I plan to make this change eventually.
compact comes handy if you are less fit. no use are bigger gear ratios (crank + cassette) if you cannot get a decent cadence on them.
some people like to use pro like gears no matter what, even if they are suffering on them, just saw some master riders doing that two weeks ago on a cat. 3 climb
on the other hand if you are in good shape you will not be riding to your liking on compact cranks
some people like to use pro like gears no matter what, even if they are suffering on them, just saw some master riders doing that two weeks ago on a cat. 3 climb
on the other hand if you are in good shape you will not be riding to your liking on compact cranks
I think thats why they came up with the compact crank idea. ("most of us should be riding on them")
But If you are doing a club ride on a rolling flat with compact cranks you can easily need a 50 x 14 for the 25 mph mark. Then you don't have much more gear options to tackle a downhill or sprint for example. (To ride at 25 mph means you are fit)
With today's cassette large options i think i'll stay with the 53/39 but remember in the past when you needed to change cogs beforehand according to the route-profile
But If you are doing a club ride on a rolling flat with compact cranks you can easily need a 50 x 14 for the 25 mph mark. Then you don't have much more gear options to tackle a downhill or sprint for example. (To ride at 25 mph means you are fit)
With today's cassette large options i think i'll stay with the 53/39 but remember in the past when you needed to change cogs beforehand according to the route-profile
You should spend some time with a gearing chart before you continue to dig yourself deeper.vspa said:
with my compact 50:34 chainrings and an 11:25 cassette I have a higher high gear than a 53:12 and a lower low gear than a 39:28 at the same time. I don't sacrifice anything in terms of high end or low end gearing I just spread the gear choices further apart which isn't a big deal with modern 9 and 10 speed cassettes.
Do the math, a 50:11 is 122.7 gear inches relative to the 119.2 gear inches provided by a 53:12. Even if you stick with a 50:12 you get 112.5 gear inches which still sends you down the road at over 30 mph when spinning 90 rpm and is more than big enough for sprinting.
Compact cranks offer plenty of high end gearing, even for very fit racers.
Most folks go to compact gearing for the low end advantages. Coupled with an 11 tooth cog you get higher high end as noted above, but the 34 tooth inner chainring drops the low gear substantially for steep climbing.vspa said:
Road derailleurs, especially short cage rear derailleurs limit both the maximum difference between chainring teeth and the largest rear cog you can use. The introduction of compact cranks along with 11 tooth cogs allows both a lower low gear without exceeding the 27 or 28 tooth cog size limit for most short cage road derailleurs as well as higher high end via the 11. So compact cranks provide wider gearing than standard road doubles but retain the crisp shifting provided by short cage derailleurs without introducing excessive chain slack to pick up or ultrawide spread between front chainring sizes which would also cause problems.
So basically compacts give you a lot more low end, a bit more high end at the cost of bigger steps between individual gears. If you don't live in the mountains or have a lot of steep hills then there's probably no reason to go to a compact crankset. But for those of us that ride and race in terrain like that it's awfully useful.
FWIW I've ridden several dozen road races and crits on compact gearing in the last few seasons quite successfully including contesting and even winning my share of the sprints. In those cases where I struggled, didn't make the selection or was outsprinted it definitely wasn't gearing holding me back, it was pure fitness, positioning or race tactics.
-Dave
you can go to Sheldonbrown.com/gears and calcuate gear inches for whatever chainring/cog combinations you can think of.
50-34 will give you 1.5-2 lower gears at the expense of losing a top gear compared to 53-39 using the same cassette.
It's possible to use a 52T chainring on a compact cassette; you'd end up with a 52-36 crankset, the delta between rings kept at 16.
Or you can go as low as a 46-34 and use a cassette with a 34T cog for some serious climbing duty.
Instead of worrying about compact versus traditional, figure out what gearing combinations work best for you. For most of us, the compact crank offers more useful options. The trick is to get the gearing set so you are in the big ring for most riding and use the small ring for climbing.
I regularly see riders using their 39 small ring with their smaller cogs on the flat to rolling terrain. If you try to do this with a compact, you'll be forever shifting between big and small rings up front. For people used to the tradtional cranks, switching to a compact can cause frustration. A cassette change may also be necessary. A change in shifting habits is also called for.
I've got a compact 50-34 with 12-27 on one road bike and I'm in the big ring 95% of the time. 50-12 down to 50-24 gives me enough range to handle a lot of rolling terrain without hitting the small ring. Sometimes I'll even use the 50-27 for short climbs. If I shift to the small ring, it means I've got a long climb or a short, very steep one. Easy enough with brifters to shift both derailleurs at once; the jump between rings is not hard to negotiate.
If I'm spinning out the 50-12, it means I'm going over 40 mph and the descent is usually going to get me going a lot faster all on its own.
I also ride a bike with 52-39 and 12-25. Since I don't normally ride it on long climbing rides I don't get a chance to see if I can spin out the 52-12. And it doesn't make me any faster on the flats.
50-34 will give you 1.5-2 lower gears at the expense of losing a top gear compared to 53-39 using the same cassette.
It's possible to use a 52T chainring on a compact cassette; you'd end up with a 52-36 crankset, the delta between rings kept at 16.
Or you can go as low as a 46-34 and use a cassette with a 34T cog for some serious climbing duty.
Instead of worrying about compact versus traditional, figure out what gearing combinations work best for you. For most of us, the compact crank offers more useful options. The trick is to get the gearing set so you are in the big ring for most riding and use the small ring for climbing.
I regularly see riders using their 39 small ring with their smaller cogs on the flat to rolling terrain. If you try to do this with a compact, you'll be forever shifting between big and small rings up front. For people used to the tradtional cranks, switching to a compact can cause frustration. A cassette change may also be necessary. A change in shifting habits is also called for.
I've got a compact 50-34 with 12-27 on one road bike and I'm in the big ring 95% of the time. 50-12 down to 50-24 gives me enough range to handle a lot of rolling terrain without hitting the small ring. Sometimes I'll even use the 50-27 for short climbs. If I shift to the small ring, it means I've got a long climb or a short, very steep one. Easy enough with brifters to shift both derailleurs at once; the jump between rings is not hard to negotiate.
If I'm spinning out the 50-12, it means I'm going over 40 mph and the descent is usually going to get me going a lot faster all on its own.
I also ride a bike with 52-39 and 12-25. Since I don't normally ride it on long climbing rides I don't get a chance to see if I can spin out the 52-12. And it doesn't make me any faster on the flats.
vspa said:
Poppycock. A 'compact' gives a higher high gear and a lower low gear than most standard doubles..53/39 and 12-25 compared to a 50/34 and 11/25. Compact has been around for decades, are used by more 'pros' that you will admit. It's a great idea that resurfaced about 4 years ago. It has nothing to do with how fit you are, everything to do with having applicable gearing for you and your ride, whether you are a 'pro' or not.
I'm sure you would rather see 'pros' struggle up 20 degree climbs with a 42 small ring and a 21t cog..but time marches on!
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