Larger IGH cog question
06-30-17 | 07:40 PM
#1
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From: Prince Albert, SK - Canada
Bikes: 1993 Trek 520 Touring, 2009 Globe SF 2, 2011 Giant Dash 3, 2011 GT Traffic 3.0, 2011 GT Traffic 5.0, 2012 GT Aggressor 3.0, 2014 Surface 604 Element
Larger IGH cog question
I'm looking to lower gear ratios on my Nexus Inter3 by switching to a larger rear cog.
Currently running 42/16 with the rear axle about halfway in the drop outs. Can I go up to 19T without needing a longer chain?
Would also consider smaller chain ring - crank is 104 BCD.
Currently running 42/16 with the rear axle about halfway in the drop outs. Can I go up to 19T without needing a longer chain?
Would also consider smaller chain ring - crank is 104 BCD.
06-30-17 | 08:04 PM
#2
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From: Sacramento, CA
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...not enough information. Whether you can get by with the same chain depends on the length of your rear dropouts, and where the axle sits right now with respect to any further adjustment. It's certainly possible. Anyway, new chains are pretty cheap.
Treat yourself if you have to.
...not enough information. Whether you can get by with the same chain depends on the length of your rear dropouts, and where the axle sits right now with respect to any further adjustment. It's certainly possible. Anyway, new chains are pretty cheap.
Treat yourself if you have to.
06-30-17 | 08:42 PM
#3
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From: Prince Albert, SK - Canada
Bikes: 1993 Trek 520 Touring, 2009 Globe SF 2, 2011 Giant Dash 3, 2011 GT Traffic 3.0, 2011 GT Traffic 5.0, 2012 GT Aggressor 3.0, 2014 Surface 604 Element
Forgot to mention, bike has disc brakes - not sure if enough adjustment available on the calipers.
I will be ordering parts as LBS only has 16T cog in stock and short 1/8" chains for BMX.
I will be ordering parts as LBS only has 16T cog in stock and short 1/8" chains for BMX.
06-30-17 | 09:49 PM
#4
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From: New Rochelle, NY
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Simple math.
The hub moves forward roughly 1/8" per added tooth, likewise it moves back by the same amount with smaller sprockets.
Here's the reasoning.
Each tooth adds 1/2" to the circumference of the sprocket. The chain wraps half way so you need 1/4" more chain. That's divided between the upper and lower loops, so the hub has to move 1/8" to make up the difference.
So, measure the amount of usable room and make a decision. If you have the dough, you can reduce the chainring and increase the rear by the same # of teeth, and the hub will barely move. (you still get a bit of movement because the upper and lower loops aren't parallel, which screws up my simple calculation slightly)
The hub moves forward roughly 1/8" per added tooth, likewise it moves back by the same amount with smaller sprockets.
Here's the reasoning.
Each tooth adds 1/2" to the circumference of the sprocket. The chain wraps half way so you need 1/4" more chain. That's divided between the upper and lower loops, so the hub has to move 1/8" to make up the difference.
So, measure the amount of usable room and make a decision. If you have the dough, you can reduce the chainring and increase the rear by the same # of teeth, and the hub will barely move. (you still get a bit of movement because the upper and lower loops aren't parallel, which screws up my simple calculation slightly)
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An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
06-30-17 | 10:19 PM
#5
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From: Elevation 666m Edmonton Canada
Bikes: 2013 Custom SA5w / Rohloff Tourster
You could just get a half-link. My bike has about the same GIs.
But anyway. 42/19T is a really poor choice at about 44. 60, 82 GI. 1st will wizout at 8 or 9 mph and 2nd at 16 or 17. An 18T would be far better with the gear change at 10 mph, so you would be using 2nd most of the time. I go at 13 mph into the wind a lot.
I am too often in less efficient 1st gear myself, up to 14 mph. My cranks are also too short on this bike, which makes a tougher upshift. My SA 5w started at 46.5 GI also, not bad at all.
But anyway. 42/19T is a really poor choice at about 44. 60, 82 GI. 1st will wizout at 8 or 9 mph and 2nd at 16 or 17. An 18T would be far better with the gear change at 10 mph, so you would be using 2nd most of the time. I go at 13 mph into the wind a lot.
I am too often in less efficient 1st gear myself, up to 14 mph. My cranks are also too short on this bike, which makes a tougher upshift. My SA 5w started at 46.5 GI also, not bad at all.
Last edited by GamblerGORD53; 06-30-17 at 10:28 PM.
06-30-17 | 10:56 PM
#6
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From: Prince Albert, SK - Canada
Bikes: 1993 Trek 520 Touring, 2009 Globe SF 2, 2011 Giant Dash 3, 2011 GT Traffic 3.0, 2011 GT Traffic 5.0, 2012 GT Aggressor 3.0, 2014 Surface 604 Element
You could just get a half-link. My bike has about the same GIs.
But anyway. 42/19T is a really poor choice at about 44. 60, 82 GI. 1st will wizout at 8 or 9 mph and 2nd at 16 or 17. An 18T might be OK with the gear change at 10 mph, so would be using 2nd most of the time. I go at 13 mph into the wind a lot.
I am too often in less efficient 1st gear myself, up to 14 mph. My cranks are also too short on this bike, which makes a tougher upshift.
But anyway. 42/19T is a really poor choice at about 44. 60, 82 GI. 1st will wizout at 8 or 9 mph and 2nd at 16 or 17. An 18T might be OK with the gear change at 10 mph, so would be using 2nd most of the time. I go at 13 mph into the wind a lot.
I am too often in less efficient 1st gear myself, up to 14 mph. My cranks are also too short on this bike, which makes a tougher upshift.
I've also made several test rides with my 26" hardtail (heavier bike with suspension fork) using only the 42T chainring and moving through the 14/34 freewheel and am confident the 19T cog will be the best good compromise for my purpose.
06-30-17 | 11:02 PM
#7
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From: Prince Albert, SK - Canada
Bikes: 1993 Trek 520 Touring, 2009 Globe SF 2, 2011 Giant Dash 3, 2011 GT Traffic 3.0, 2011 GT Traffic 5.0, 2012 GT Aggressor 3.0, 2014 Surface 604 Element
Simple math.
The hub moves forward roughly 1/8" per added tooth, likewise it moves back by the same amount with smaller sprockets.
Here's the reasoning.
Each tooth adds 1/2" to the circumference of the sprocket. The chain wraps half way so you need 1/4" more chain. That's divided between the upper and lower loops, so the hub has to move 1/8" to make up the difference.
So, measure the amount of usable room and make a decision. If you have the dough, you can reduce the chainring and increase the rear by the same # of teeth, and the hub will barely move. (you still get a bit of movement because the upper and lower loops aren't parallel, which screws up my simple calculation slightly)
The hub moves forward roughly 1/8" per added tooth, likewise it moves back by the same amount with smaller sprockets.
Here's the reasoning.
Each tooth adds 1/2" to the circumference of the sprocket. The chain wraps half way so you need 1/4" more chain. That's divided between the upper and lower loops, so the hub has to move 1/8" to make up the difference.
So, measure the amount of usable room and make a decision. If you have the dough, you can reduce the chainring and increase the rear by the same # of teeth, and the hub will barely move. (you still get a bit of movement because the upper and lower loops aren't parallel, which screws up my simple calculation slightly)
I hadn't really thought about the "circle math" and my 9th grade students just finished that unit -LOL.
Most of my calculations were on the ratios and GI I'm trying to acheive.
06-30-17 | 11:17 PM
#8
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From: New Rochelle, NY
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
BTW- I didn't mention it earlier because I believe you;re still well within the limits, but anyone reading this needs to be aware that IGH hubs may have low gear ratio limits.
As you lower the primary gearing you increase your leverage, and therefore the maximum input torque. These are just guideline numbers because obviously rider strength varies. But heavier or stronger riders, and those riding steep hills need to be mindful of these limits, and even apply them more conservatively based on your conditions.
As you lower the primary gearing you increase your leverage, and therefore the maximum input torque. These are just guideline numbers because obviously rider strength varies. But heavier or stronger riders, and those riding steep hills need to be mindful of these limits, and even apply them more conservatively based on your conditions.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
06-30-17 | 11:26 PM
#9
Thread Starter
Senior Member
Joined: Apr 2013
Posts: 300
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From: Prince Albert, SK - Canada
Bikes: 1993 Trek 520 Touring, 2009 Globe SF 2, 2011 Giant Dash 3, 2011 GT Traffic 3.0, 2011 GT Traffic 5.0, 2012 GT Aggressor 3.0, 2014 Surface 604 Element
BTW- I didn't mention it earlier because I believe you;re still well within the limits, but anyone reading this needs to be aware that IGH hubs may have low gear ratio limits.
As you lower the primary gearing you increase your leverage, and therefore the maximum input torque. These are just guideline numbers because obviously rider strength varies. But heavier or stronger riders, and those riding steep hills need to be mindful of these limits, and even apply them more conservatively based on your conditions.
As you lower the primary gearing you increase your leverage, and therefore the maximum input torque. These are just guideline numbers because obviously rider strength varies. But heavier or stronger riders, and those riding steep hills need to be mindful of these limits, and even apply them more conservatively based on your conditions.
