Building a compact crank
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Building a compact crank
I currently have an Alivio 48 38 28 crank paired with an 11-32 8 speed cog. The front and rear derailers are also Alivios shifted by Ultegra bar-ends. My normal shifting pattern starts off with the chain on the 38 ring and a middle cog, then upshift to the 48 then click up on the rear. I mostly cruise on th 48 ring. However I seem to stay at 3 out of the 8 cogs for the majority of my ride. I am thinking if I swap out the 38 and 48 rings to a 44 and a ring guard, I could spread the shifting to more cogs in the back. I rarely use the 28 on the commute, only when I took the bike (old 71 Super Sport frame modernized components) off road did I really felt the need to shift down that low. Can an Alivio front derailler handle a 44 to 28 shift or should I use a "road" derailler. I like the way I shift when riding my other roadbike with a 50 34 compact crank. The components are 8 speed era Alivios.
#2
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I currently have an Alivio 48 38 28 crank paired with an 11-32 8 speed cog. The front and rear derailers are also Alivios shifted by Ultegra bar-ends. My normal shifting pattern starts off with the chain on the 38 ring and a middle cog, then upshift to the 48 then click up on the rear. I mostly cruise on th 48 ring. However I seem to stay at 3 out of the 8 cogs for the majority of my ride. I am thinking if I swap out the 38 and 48 rings to a 44 and a ring guard, I could spread the shifting to more cogs in the back. I rarely use the 28 on the commute, only when I took the bike (old 71 Super Sport frame modernized components) off road did I really felt the need to shift down that low. Can an Alivio front derailler handle a 44 to 28 shift or should I use a "road" derailler. I like the way I shift when riding my other roadbike with a 50 34 compact crank. The components are 8 speed era Alivios.
You're running something like this
11-13-15-18-21-24-28-32
with big gaps in your cruising gears where you could have five choices like 15-16-17-18-19 on the big ring (instead of 3 of 15-18-21) and eight as 13-14-15-16-17-18-19-21 in the middle (not 4 of 13-15-18-21).
In the 8 speed era my favorite setup was 50-40-30 x 13-14-15-16-17-18-19-21, providing tight gearing for plains rides East of Boulder, CO and an ample low gear (like 42x28 or 39x26) enough to get me over anything in the Rockies West without changing cogs depending on which direction my lunch hour ride chose to go.
#3
Biking Viking.
I've used a 44 (with chain guard) and a 12-28 8-speed (or close to it) for commuting around DC no problem. I'd think the Alivio could shift a 44-28. Might have some trouble moving up to the 44 without pin or ramps.
#4
Constant tinkerer
The derailer should be able to handle the 28-44 shift. It may not be the smoothest but as you say you won't be shifting the front too often so I doubt it'll be a big deal.
+1 Consider different cassette options before switching up the crankset. SRAM still makes a 12-23 8-speed cassette. Not sure how many Shimano cassettes are still floating around in that range.
+1 Consider different cassette options before switching up the crankset. SRAM still makes a 12-23 8-speed cassette. Not sure how many Shimano cassettes are still floating around in that range.
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I prefer to have the low gears. The steps on the current cassette is fine and I like the low gear for cranking up on hills with a load. The current gearing actually feels fine other than the wear on the cogs is locallized to the 3 that's normally used on my daily commute. My goal with this swap is to spread the wear on the cogset as well as minimize the need for front shifting. Coming to a stop sign requires me to keep both hands moving to the shifters and brakes to ensure proper gearing on takeoff.
#6
Banned
The 44 as the middle, essentially of a triple , in order to find one
with the Index shifting details will be difficult . since they typically are either outers or singles..
Cyclocross uses 44t chainrings in single ring set-ups.
If you opt instead for a single speed chainring like the excellent ones
Surly offers in stainless steel will probably only work well with friction shifting.
but the chainring is long wearing..
with the Index shifting details will be difficult . since they typically are either outers or singles..
Cyclocross uses 44t chainrings in single ring set-ups.
If you opt instead for a single speed chainring like the excellent ones
Surly offers in stainless steel will probably only work well with friction shifting.
but the chainring is long wearing..
#7
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The key piece of data in your question is "Ultegra bar ends". It'll work fine.
#8
Mechanic/Tourist
Have you taken the time to make out a gear chart to see the impact of this change? You cannot distribute the wear to more cogs if you are using the same rear cassette, as they still have the same wide spacing between. You will shift which cogs, but all you will do is use one cog you did not before (the next smaller) and not use a larger one that you did previously, and worse - you will be forced to get used to different ratios than before. In addition the 44 will result in higher wear due to fewer teeth front and back for a given gear ratio.
You also do not say which 3 cogs you use - may make a difference in advising you about options that might work. But one option would be to build a custom cassette, something like 13-14-15-17-19-21-24-32. You lose the useless 118 gear inch high, still have the 32 for an ultra low, and group the rest much closer by adding a gear between the 13 and 15 and having only a 2 tooth jump, rather than 3 tooth, for the next two gears. The 28 also will of course have closer spacing, although you lose the 28/28.
You would have to buy 3 cogs at about $10 a piece. Your starting gear would probably be the 48-24, which in gear ratio is between the 4th and 5th cogs on the 38, or if on a rise the 48-32, which is just below the 3rd gear on the 38. In other words you would be using at least 5 cogs with the 48 instead of 3.
Below are the gear charts (in gear inches) for what is probably your current setup vs. what I propose. Percents are the jump from lower gear to the higher. To build your own charts: https://sheldonbrown.com/gears/
48
COG RATIO
11 117.8
18.2%
13 99.7
15.4%
15 86.4
20.0%
18 72.0
16.7%
21 61.7
14.3%
24 54.0
16.7%
28 46.3
14.3%
32 40.5
48
COG RATIO
13 99.7
7.7%
14 92.6
7.1%
15 86.4
13.3%
17 76.2
11.8%
19 68.2
10.5%
21 61.7
14.3%
24 54.0
33.3%
32 40.5
You also do not say which 3 cogs you use - may make a difference in advising you about options that might work. But one option would be to build a custom cassette, something like 13-14-15-17-19-21-24-32. You lose the useless 118 gear inch high, still have the 32 for an ultra low, and group the rest much closer by adding a gear between the 13 and 15 and having only a 2 tooth jump, rather than 3 tooth, for the next two gears. The 28 also will of course have closer spacing, although you lose the 28/28.
You would have to buy 3 cogs at about $10 a piece. Your starting gear would probably be the 48-24, which in gear ratio is between the 4th and 5th cogs on the 38, or if on a rise the 48-32, which is just below the 3rd gear on the 38. In other words you would be using at least 5 cogs with the 48 instead of 3.
Below are the gear charts (in gear inches) for what is probably your current setup vs. what I propose. Percents are the jump from lower gear to the higher. To build your own charts: https://sheldonbrown.com/gears/
48
COG RATIO
11 117.8
18.2%
13 99.7
15.4%
15 86.4
20.0%
18 72.0
16.7%
21 61.7
14.3%
24 54.0
16.7%
28 46.3
14.3%
32 40.5
48
COG RATIO
13 99.7
7.7%
14 92.6
7.1%
15 86.4
13.3%
17 76.2
11.8%
19 68.2
10.5%
21 61.7
14.3%
24 54.0
33.3%
32 40.5
Last edited by cny-bikeman; 01-08-12 at 12:45 PM.
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I also have the Alivio 48-36-26 crankset and am running an 11-24 8-speed cassette in back. I ride in the top two rings 98% of the time and use my 12-16 cogs way more than the 11 or 24. Unless I'm in the hills, I end up using just 3 or 4 middle cogs for the vast majority of the ride.
#10
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With the current drivetrain, 48 38 28 crank, 8 speed 11-32 SRAM cog, Alivio front/rear, Ultegra bar-ends and 622-35 Continental Contacts on a 35+ lb Schwinn Super Sport on Tiagra/CR18 wheels, my 225-230 lb self and 2 panniers and a lunch box. My shifting pattern that feels the best to me (I've tried other patterns), is to start with 38x16 (64.5), 48x16(81.5), 48x14(93.2) usually my cruising gear, maybe 48x12(108.7) on a nice straight aways with no stop signs. So the 16, 14, a little of 12 tooth cogs are bearing the brunt of the work for the majority of my rides. Sacramento is a fairly flat town but I intend to use this bike for loaded touring one of these days and like the low gears when going down dirt trails with rolling hills. With the 44 28 crank, assuming I use the same gear inches, I'll start of 44x18(66.4) then just click up to 44x12(99.6) or even 44x11(108.7) for a use of 4-5 cogs rather than 2-3. Coming to a stop from top gear would allow me to brake with the left hand, shift down back to proper gear on the right. I like this shifting pattern and experience this on my other road bike with a compact crankset. I also like the gear range. My issue is how to make this work, what issues hardware wise may arise. The current setup is not annoyingly bad, I can live with it but I prefer a more simple shift pattern and to spread out wear on more cogs.
#11
Mechanic/Tourist
As noted by the other poster, it will work but will not shift great from 28 to 44. If that's what you want then go for it, although in my opinion you are riding way too high a gear in general, unless you are "cruising" those 90+ gears at 20+ mph. By my calculations the 48x14 gear at only 70 rpm should get you almost 20 mph, and 70 rpm is typically near the bottom end of efficient pedaling. The 100+ inch gears should be out of the question on the flat when you are "cruising." I raced criteriums at up to 35 mph in bursts and never had over a 100 inch gear.
Last edited by cny-bikeman; 01-08-12 at 04:22 PM.
#12
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Maybe my cadence is not optimum. I just switch to a gear that feels comfortable for me. Anything slower tires me out, anything faster tires me out. The numbers I put out is based on the specs when I bought the cog, but without physically counting the teeth I am under the assumption that it is correct. Guess I just have to pony up the cash and be a guinea pig and see if it even works better than the previous setup.
#13
Senior Member
RT Metro, My guess is no matter how you re gear the drivetrain, you'll still use two or three of the cassette cogs in normal commuting for your GI preference, though they'll be different gears than what's used now.
A friend and I used to ride our mountain bikes after work on a MUP that spanned several intersections and although we were geared differently, we both upshifted both ends from a standstill.
I know a 32-44 shift using a mountain bike FD is smooth so I think the 28-44 is doable, it just may not be quite as smooth.
Brad
A friend and I used to ride our mountain bikes after work on a MUP that spanned several intersections and although we were geared differently, we both upshifted both ends from a standstill.
I know a 32-44 shift using a mountain bike FD is smooth so I think the 28-44 is doable, it just may not be quite as smooth.
Brad
Last edited by bradtx; 01-09-12 at 06:47 AM.
#14
Senior Member
+1 If the only reason to change is to spread the wear, you won't spread it as most of your riding is spent in 2 or 3 gears unless you come up with gearing that gives you lots of overlap in the GIs you normally run and intentionally shift just to spread the wear.
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After digesting what you guys said, I agree that wear spread will not be significant, due to flat terrain and fairly constant speed, one or two cogs will experience the most wear, same as right now, though on a different set of cogs. However shifting will essentially be mostly a one derailler issue, so that's good. Its essentially going to ride almost like a 1x8 drivetrain, with a granny.
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To actually answer the OP's question-
Triple front derailleurs are shaped to work best with a certain range of differences between the largest and the middle chainrings, and between the middle and inner chainrings. If you're planning on changing to a double chainring in the front, then the triple derailleur won't be optimal. Best would be a double derailleur with the straight cage. That being said:
1) Good luck finding a double derailleur with the "mountain" pull ratio. I'm not even sure they exist.
2) Using the triple derailleur will rattle and rub more in the extreme combinations, but otherwise should shift passably well. Give it a try and find out.
3) Be aware of the chainline change- the ideal spot for the chainline moves from the middle ring position to mid way between the inner and middle rings. This will require a 6-7 mm wider bottom bracket to maintain the same chainline. It will probably be OK, but the extreme combinations may be iffy- the chain will almost certainly rub against the larger ring when in the smaller ring and smaller cogs because of this and because of the larger difference between the rings.
Triple front derailleurs are shaped to work best with a certain range of differences between the largest and the middle chainrings, and between the middle and inner chainrings. If you're planning on changing to a double chainring in the front, then the triple derailleur won't be optimal. Best would be a double derailleur with the straight cage. That being said:
1) Good luck finding a double derailleur with the "mountain" pull ratio. I'm not even sure they exist.
2) Using the triple derailleur will rattle and rub more in the extreme combinations, but otherwise should shift passably well. Give it a try and find out.
3) Be aware of the chainline change- the ideal spot for the chainline moves from the middle ring position to mid way between the inner and middle rings. This will require a 6-7 mm wider bottom bracket to maintain the same chainline. It will probably be OK, but the extreme combinations may be iffy- the chain will almost certainly rub against the larger ring when in the smaller ring and smaller cogs because of this and because of the larger difference between the rings.
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