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Shimano 39-55?

Old 06-24-23, 05:36 AM
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Shimano 39-55?

I recently hit my outer Shimano 9100 Dura Acre 39-53 chainring. The damage is only cosmetical, but I am thinking that I might want to replace it with a 55 tooth chainring. Will this combination work? Shimano recommends either 39-53 or 41-55. What about 39-55?
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Old 06-24-23, 07:14 AM
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You should be OK with the 55 tooth chainring. It's possible that you may need to reposition and/or adjust the FD, and you may need to lengthen the chain. Depends how you are currently set up.
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Old 06-24-23, 03:18 PM
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Originally Posted by Keefusb
You should be OK with the 55 tooth chainring. It's possible that you may need to reposition and/or adjust the FD, and you may need to lengthen the chain. Depends how you are currently set up.
Depends on how you define OK. That exceeds the recommended tooth jump for the front derailleur. How well it will work will only become clear once you do it. And then there is the question of why the OP needs a 55t ring. That's what world class sprinters use with a lead-out train. Of the other 99.99% of riders, it's much more effective to learn how to spin a higher cadence.
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Old 06-24-23, 03:26 PM
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Originally Posted by smallet
I recently hit my outer Shimano 9100 Dura Acre 39-53 chainring. The damage is only cosmetical, but I am thinking that I might want to replace it with a 55 tooth chainring. Will this combination work? Shimano recommends either 39-53 or 41-55. What about 39-55?
Another, Very Important thing to consider.. what is the "Total Chain Wrap" your REAR derailleur will handle.. add the 16 tooth difference at the front to whatever the total difference is on your CASSETTE, add the two figures together, then look up your Rear derailleur's Max WRAP specification... 28-11 =17.. 55-39=16.. 17+16=33... example... that is the "max wrap", or "overall capacity" of an Ultegra short cage rear 6700 Derailleur......... a mid or long cage der. should be fine for your plans.....

typical Shimano Cage Code.. SS is Short, GS is mid(some road ders. call this "long"), SGS is Long cage.

Diameter change is less onceyou get to bigger tooth counts, but you want to watch for "Tail drag" or chain rubbing on the front der too....

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Old 06-24-23, 03:37 PM
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Originally Posted by KerryIrons
How well it will work will only become clear once you do it.
I would say that a very large number of bicycle modifications would fall into this category.
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Old 06-25-23, 03:13 PM
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Originally Posted by KerryIrons
And then there is the question of why the OP needs a 55t ring. That's what world class sprinters use with a lead-out train. Of the other 99.99% of riders, it's much more effective to learn how to spin a higher cadence.
This is the second poster in the last week or two asking about a 55 tooth ring. And I thought the jump from 52 to 53 was significant!
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Old 06-25-23, 07:58 PM
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Originally Posted by smd4
This is the second poster in the last week or two asking about a 55 tooth ring. And I thought the jump from 52 to 53 was significant!
i just had a customer request a 24 tooth rear sprocket be put on his nexus 7 sp. hub, in place of the 18T they usually come with..... he wanted "lower gears" I told him that was a mighty big jump, and will make the bike nearly unrideable, but he insisted... so, being a tricky old fart, i swapped on a twenty tooth gear... he came back the next day and test rode the bike..."WOW! It's PERFECT! I told you it was what i wanted! " I just nodded, and billed him for the 20T sprocket, new retainer ring, and a new, slightly longer chain... off he rode off in ignorant bliss... i wonder how long it will be before he counts those cog teeth....

some folks will buy a new Ferarri, and never exceed 100mph...

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Old 06-25-23, 08:01 PM
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HA! Love it.
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Old 06-25-23, 08:06 PM
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I run a 56-39 and 11-32 but with SRAM eTap Mid RD. Works fine. I've also run it with Ultegra mechanical FD fine. Dura ace?? No idea
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Old 06-25-23, 08:07 PM
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Velomobile riders run 61-33 chain rings. Try shifting that!
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Old 06-26-23, 07:44 AM
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Originally Posted by KerryIrons
Depends on how you define OK. That exceeds the recommended tooth jump for the front derailleur. How well it will work will only become clear once you do it. And then there is the question of why the OP needs a 55t ring. That's what world class sprinters use with a lead-out train. Of the other 99.99% of riders, it's much more effective to learn how to spin a higher cadence.
I live in a hilly place. When I go downhill at 70 km/h, I need to pedal at 110+ rpm with 53-11. It's not a sprint, I cannot spin at 120 rpm for a few minutes. Going from 53 to 55 is less than 4% improvement, but if I can get it, why not?
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Old 06-26-23, 08:03 AM
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Originally Posted by smallet
I live in a hilly place. When I go downhill at 70 km/h, I need to pedal at 110+ rpm with 53-11. It's not a sprint, I cannot spin at 120 rpm for a few minutes. Going from 53 to 55 is less than 4% improvement, but if I can get it, why not?
Because it will cause your drivetrain to work poorly.
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Old 06-26-23, 10:26 AM
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"Because it will cause your drivetrain to work poorly."

Only if the mechanic doesn't work well.

50-34 is 16T

55-39 is 16T
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Old 06-26-23, 12:27 PM
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Originally Posted by smallet
I live in a hilly place. When I go downhill at 70 km/h, I need to pedal at 110+ rpm with 53-11. It's not a sprint, I cannot spin at 120 rpm for a few minutes. Going from 53 to 55 is less than 4% improvement, but if I can get it, why not?
Actually, at that speed you will be faster if you coast in a tight tuck. Anything over about 55 km/hr and you are faster in a tuck. Pedaling at those speeds is just a waste of energy.
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