Can you tell a difference between a 12-25 and a 12-27?
- Thread starter trek301
- Start date
trek301 said:
That depends on your needs, strengths, and terrain. If you're on steep terrain or tired while climbing, the extra two teeth in back could be the difference between finishing or getting off and walking.
If on your climbs you find yourself spinning slowly in the 25, you would likely benefit from a 27.
If you can't keep 70rpm+ on many of your hills, go the 12-27.
If you tihnk you need it, you probably do.
To go even further my gf was running a 12-27, after using a 12-25. She was very happy with the change. On the latest bike we went even further and put on a compact with 12-27. Its not so good for my ego as she is now staying on my tail FAR better as she is not having to torque it out as much when she doesn't have the stength. With a better spin she is able to develope more power, consistantly, and remain fresher til the end of the ride.
Today she did the final lead out for the last 5km+ at the end of a 100km ride after us boys had worn our selves out a bit more on some long up hill stretches. I was very impressed with her!
If you tihnk you need it, you probably do.
To go even further my gf was running a 12-27, after using a 12-25. She was very happy with the change. On the latest bike we went even further and put on a compact with 12-27. Its not so good for my ego as she is now staying on my tail FAR better as she is not having to torque it out as much when she doesn't have the stength. With a better spin she is able to develope more power, consistantly, and remain fresher til the end of the ride.
Today she did the final lead out for the last 5km+ at the end of a 100km ride after us boys had worn our selves out a bit more on some long up hill stretches. I was very impressed with her!
trek301 said:
Get one and try it. Get a low end one, which should be the rule for cogsets and chains anyway..least expensive compatible cogset and chain, since they are consumables.
a 9s 12-25 is 12-13-14-15-17-19-21-23-25, a 12-27 is 12-13-14-15-17-19-21-24-27, very useful.
trek301 said:
It worked for me. I switched from 12x25 to 12x27 (with compact 50/34) but I actually just installed a SRAM 11x28 (I could not find a 12x28 for Shimano) now I'm glad I did. The 12x27 did not have enough of an appreciable change (IMHO) from 24T to 27T.
Now the 11T gives me a great lift on the flats and the 25T to 28T change is noticeable on steep hills (Atlanta area)
I have moved the 12x27 to my triple set-up (another bike) for mountain road trips and commuting.
The question should be: "Can YOU notice the difference?"
I ride steep hills and usually I don't notice much difference between a 23 and a 25. I generally 'prefer' the 23 if I can output the power to keep the leg speed up. But when I'm tired, down on power or have hit the wall, those extra two teeth for a bail-out or recovery gear are mighty nice to have around to drop on to.
As others have suggested, gear choice is dependent on your terrain, your strength/power output and climbing preferences. I prefer to run a bit higher gear than some climbers, lower than some others and all achieve the same result.
I ride steep hills and usually I don't notice much difference between a 23 and a 25. I generally 'prefer' the 23 if I can output the power to keep the leg speed up. But when I'm tired, down on power or have hit the wall, those extra two teeth for a bail-out or recovery gear are mighty nice to have around to drop on to.
As others have suggested, gear choice is dependent on your terrain, your strength/power output and climbing preferences. I prefer to run a bit higher gear than some climbers, lower than some others and all achieve the same result.
I guess you could ask 'what's the detriment?'. It's hard to see any real downside to the 12-27.trek301 said:
I'm middle aged and have had a few surgeries. My back doesn't like grinding high gears. I got a compact crank and a 12-27. If I run out of gears going downhill I coast. I can pedal up to 60kph so it's a rarity. If you run out of gears going uphill, you walk. Your choice.
jjiam1234 said:
It depends on the gears. Compact cranks typically have smaller chainrings. using a 27t cog with a standard small chainring, i.e. 39t, you get a gear ratio of 1.44, whereas with a 34t chainring on a compact crank and that same 27t cog, you get a 1.26 gear ratio. Lower is easier to pedal. Going from that 39t to the 34t produces a 14% reduction in gear ratio with the 27t cog. That's pretty darned large.
A triple typically offers even easier pedaling since triples most often have a small chainring that can be smaller than a compact's small chainring.
The argument about which is better, triples or compacts, is nearly religious and completely stupid. Use what you need. Determining what you need isn't terribly difficult. As I showed, gear ratio is just (# of teeth on chainring being used)/(# of teeth on cog being used). If that number doesn't tell you much, you can multiply it by the circumference of a tire to get how far your bike will move thru one pedal cycle. In both cases, smaller numbers are easier to pedal and require less force applied to go up a given grade. Larger numbers mean you can attain higher speeds before spinning out and also that pedaling will require the application of more force for a given road grade.
Triples weigh a bit more, but that weight has no real performance cost. To some, triples don't look very cool. If you're doing loaded touring, triples are your friends.
Compacts are the new thing. They're lighter than triples, but as I said, that means diddly in terms or performance. They look like standard cranksets so for people that need to blend into the collective, they're the ticket. Ultimately, triples can offer a wider gearing range than compacts, though. A compact can use standard crankset gearing.
Standard cranksets are what used to, at least, be standard on most bikes...at least recently. Standards, now, are 53/39 cranksets. They used to be 53/42 or summat. Some folks say you don't need anything less than a standard, but those folks are idiots.
You gotta remember, though, that it is cheaper to change a cassette than it is a crankset. Still, a cassette change isn't always the right thing to do. There are, as they say, many ways to skin a cat (or as they also say, there are more than one way to crush a Palin under a Peterbilt tire.).
I faced this same question last week to prepare for a long group ride. Switching to the 27 definitely made a difference. My front is 53/39, and I used the 39/27 combo often to spin up steep parts of the climbs. I think it was what helped me stay with the fast climbers who were pushing heavier gears. As pointed out, it is simple to calculate gearing ratios and quantify the difference. And for me, I definitely felt the difference, especially in the latter climbs.trek301 said:
jjiam1234 said:
I have both, but ride the compact (50/34) with a new 11x28 cassette (had a 12x27 before). Now the 11x28 gives me a better "mix" than the triple with 12x25 cassette (OME). I only ride the triple (now with the 12x27 cassette i removed from the other bike) on the North Georgia mountains or for commuting. My compact double shifts much "better" (read quieter, smoother) than my triple ever did, BUT I'm also comparing 105 (triple) to Ultegra (double)
Overall, I "like" the compact set-up better than the triple for the typical riding I do: short very steep climbs and long flats with gentle rolling hills.
For people looking for lower gearing, a compact double with the SRAM 11-28 cassette seems like a reasonable choice, and what I went with on my recent upgrade. A 27 toth low may be enough, but I went for the SRAM to get all I could on the bottom end with a road group.
Based on LBS recommendations, with Shimano 105 I needed a medium or long cage RD (I believe for chain wrap, but it may be for cog clearance) to go with my 50-34 chain rings. I went with long, in case I decide to move to a triple at some point.
I am very large (over 300 pounds) so I don't do any serious climbing, but on the little climbs I do, I can virtually crawl up the hill on the 34x28 gear. This isn't as low as going with a road triple, or a touring triple, but frankly, if I was to go slower, I would probably get off and walk anyway since it would be difficult for me to maintain my balance at speeds lower than that.
And while many people have pointed out the numbers, and the gear ratios of the various gear combinations... I have never been able to figure out whether I needed a 3% lower gear to climb a hill. This is good in theory, but in practice I think the truth is really, "If you feel the need for a lower gear it may work for you, try it and see."
Order of difficulty for getting lower gearing:
1) Cassette with larger cog or smaller inner chainring if your crank and front derailleur can handle it.
2) Compact double
3) Triple crank
Based on LBS recommendations, with Shimano 105 I needed a medium or long cage RD (I believe for chain wrap, but it may be for cog clearance) to go with my 50-34 chain rings. I went with long, in case I decide to move to a triple at some point.
I am very large (over 300 pounds) so I don't do any serious climbing, but on the little climbs I do, I can virtually crawl up the hill on the 34x28 gear. This isn't as low as going with a road triple, or a touring triple, but frankly, if I was to go slower, I would probably get off and walk anyway since it would be difficult for me to maintain my balance at speeds lower than that.
And while many people have pointed out the numbers, and the gear ratios of the various gear combinations... I have never been able to figure out whether I needed a 3% lower gear to climb a hill. This is good in theory, but in practice I think the truth is really, "If you feel the need for a lower gear it may work for you, try it and see."
Order of difficulty for getting lower gearing:
1) Cassette with larger cog or smaller inner chainring if your crank and front derailleur can handle it.
2) Compact double
3) Triple crank
On my "Climb any mountain" road bike (well, I only have roadbikes!) I have a 12 - 27 with a 38 up front.
That gives me 38.1 inches (per rev of the pedal).
That seems just that little bit better for steep bits than 42.1 inches with 39/25.
On my race bike I have 39/23 which seems fine in the heat of racing and also because our race courses are never as steep as my training roads(at times) .
That gives me 38.1 inches (per rev of the pedal).
That seems just that little bit better for steep bits than 42.1 inches with 39/25.
On my race bike I have 39/23 which seems fine in the heat of racing and also because our race courses are never as steep as my training roads(at times)
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