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How short is short? The Shimano Zee RD

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How short is short? The Shimano Zee RD

Old 09-07-22, 07:22 PM
  #26  
Ron Damon
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Originally Posted by tomtomtom123 View Post
I have a 20" wheel with the Shimano RD-4700-GS which has a 41T capacity. I use a 12-34T cassette with custom cogs and 24/44 double chainrings. Total chain length is 42T. So small-small will drag on the pulleys, so I never use 9th and 10th on the small chainring. This gives me a 519.4% range, around 14.0-72.6". The lower pulley goes slightly past the edge of the rim, but I have 2.00-2.15" tires, so it still has some clearance to the ground, but the chain gets really dirty.
Do you like that range?
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Old 09-08-22, 03:24 AM
  #27  
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Originally Posted by Ron Damon View Post
Do you like that range?
The highest gear 72.6" is only used a few minutes per ride, so it's not really a problem.

The 14" is also used only a few minutes when going up ramps. I haven't used it in hilly places but I would imagine 14" to be useful there.

My cogs are 12,13,14,15,17,19,21,24,28,34

So the second lowest is 17" with a 21.4% jump.
it's followed by 16.6% and 14.3%. The others are much smaller jumps except for going from 15 to 17 is 13.3%.

If I had 11 speed, I would try maybe adding 1 gear in between 15,16,18 to reduce the step a little because it's in the area where I spend my most time in while on the big chainring. But 11 speed cassettes I've never seen without a spider, so the last 3 i could find are 27,30,34, which may actually work.

I only use 12,13,14 while on the big chainring because the chain would start rubbing on the big chainring while in the small chainring, and in 12,13 the derailleur pulley is dragging from the max capacity.

Because I have 44/24 chainrings, I can only shift chainrings to 44 while pushing together on the right shifter to downshift to get the chain to rise at a higher angle to catch on the ramps of the big chainring. Maybe once every 15 times it will fail to catch so I just have to repeat it a second time.

Once I reach cog 28 on the big chainring, next I move to the small chainring and shift the rear 4 to 5 cogs to 15 or 17. I think the rapid fire trigger can move 5 cogs in one push
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Old 09-08-22, 04:29 AM
  #28  
Ron Damon
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Originally Posted by tomtomtom123 View Post
The highest gear 72.6" is only used a few minutes per ride, so it's not really a problem.

The 14" is also used only a few minutes when going up ramps. I haven't used it in hilly places but I would imagine 14" to be useful there.

My cogs are 12,13,14,15,17,19,21,24,28,34

So the second lowest is 17" with a 21.4% jump.
it's followed by 16.6% and 14.3%. The others are much smaller jumps except for going from 15 to 17 is 13.3%.

If I had 11 speed, I would try maybe adding 1 gear in between 15,16,18 to reduce the step a little because it's in the area where I spend my most time in while on the big chainring. But 11 speed cassettes I've never seen without a spider, so the last 3 i could find are 27,30,34, which may actually work.

I only use 12,13,14 while on the big chainring because the chain would start rubbing on the big chainring while in the small chainring, and in 12,13 the derailleur pulley is dragging from the max capacity.

Because I have 44/24 chainrings, I can only shift chainrings to 44 while pushing together on the right shifter to downshift to get the chain to rise at a higher angle to catch on the ramps of the big chainring. Maybe once every 15 times it will fail to catch so I just have to repeat it a second time.

Once I reach cog 28 on the big chainring, next I move to the small chainring and shift the rear 4 to 5 cogs to 15 or 17. I think the rapid fire trigger can move 5 cogs in one push
Ok, ok...I believe you.
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Old 09-10-22, 05:43 AM
  #29  
CEBEP
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With my setup on my 18í Birdy is 11-32 10s rear and 53/39t which gives me 1.75 to 6.94m development. I can climb 12 degrees hills sitting on the saddle and do about 32km/h of speed which is plenty for me.
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Old 09-11-22, 05:12 AM
  #30  
tomtomtom123
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Originally Posted by CEBEP View Post
With my setup on my 18í Birdy is 11-32 10s rear and 53/39t which gives me 1.75 to 6.94m development. I can climb 12 degrees hills sitting on the saddle and do about 32km/h of speed which is plenty for me.
Some people are stronger than others and need lower gear ranges.

I see that you have used 18" as your nominal diameter, but if you actually sit on the bike and measure the distance traveled per revolution, you will probably find the real meter development smaller.

Your 1.75-6.94m is 21.9-86.8".

My 55-406 tire when sitting on the bike and rolling it travels around 1580mm per revolution, or 503mm 19.8" effective diameter. I can't remember the 47-406 but I think it's 495mm 19.5".

So assuming that you have 47-355, your effective diameter is probably 444mm 17.5", 97.2% of 18. Your gear range is closer to 1.70-6.75m or 21.3-84.5".

I am typically in 58-62" 4.63-4.95m when pedaling on flat ground at 76rpm. Average 21.8kph.

If I'm going downhill, my top gear of 72.6" 5.79m at 86rpm is 29.9kph.

I can't remember exactly but I measured a test with my maximum climb approximately 14 degree incline at 14" 1.12m and 80rpm.

I have a 165mm crank arm so it has slightly less leverage and requires higher rpm. But a little more comfortable on the knees.
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Old 09-11-22, 05:22 AM
  #31  
CEBEP
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My tires are actually 50-355. I am not using the bike all that much and not all that fit which is why Iíve added double chainring to my Birdy exactly to be able to climb short but steep 12 degree hills where I live.
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