Gear ratio too low?
02-12-21, 12:39 PM
#1
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Thread Starter
Gear ratio too low?
Hi, I just recently bought a Giant Transcend EX bike. Second hand, of course, as this model was discontinued a long time ago. The bike is equipped with Nexus 8 gear internal hub. I love this bike as it is super convenient for committing. There is one thing though that is bothering me: I find myself riding mostly in the 7th or 8th gear and even this feels a little too easy sometimes and I wish I could bike faster. With my previous bike which was also an internal hub bike I rode mostly in the 4th or 5th gear and hardly ever advanced to the 8th - unless I was riding down the hill. I thought of replacing the chainring with a larger one - to raise the gear ratio. Alternatively, I could go inside the hub (which I could, but would rather not do) and fiddle with gears there. Has anybody else had this kind of problem? What do you think would be the best course of action?
02-12-21, 12:45 PM
#2
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Just put a smaller cog on the hub.
02-12-21, 12:52 PM
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I agree with Bill. But IMO the best way to handle this is to pedal faster
. Andy
. Andy
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02-12-21, 01:03 PM
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smaller cog or larger chainring. have you seen the inside of an IGH? I don't think any part of it is designed with modification in mind. maybe if you're an engineer with a powerful working knowledge of how they work and access to a machine shop. otherwise, I wouldn't touch it other than the occasional dip in IGH oil.
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02-12-21, 03:32 PM
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Internal modifications are not possible. There are different IGHs with different ratios if you really wanted to go that route, but it is very easy to swap to a smaller cog or (possibly) a larger chainring. Or both.
Here is a link to a gear calculator:
https://www.sheldonbrown.com/gear-calc.html
My suggestion is to first enter the equipment you have (number of teeth on chainring, on cog, and your model of internal hub), and set the 'gear units' to 'km/h at 100 rpm' or similar, and see what your current value is.
Then do another one with a range of possible chainring sizes and cog sizes and the same IGH, and try to find a 'km/h at 100rpm' value similar to your existing value, but in a lower gear. I believe 5th gear is 'direct drive' in your hub so theoretically will be the most efficient, so try to find a cog/chainring combination that in 5th gear has the same value of your current setup in 7th gear. Then you will have three 'overdrive' gears for downhill or tailwinds or drafting off greyhound busses, and 4 'reduction' gears, for climbing or when you want to spin your legs a little faster.
NB. entering multiple chainrings and cogs with an IGH will give you a large chart of numbers, so don't be intimidated if that's not your cup of tea - just look for the calculated value close to your existing setup.
Here is a link to a gear calculator:
https://www.sheldonbrown.com/gear-calc.html
My suggestion is to first enter the equipment you have (number of teeth on chainring, on cog, and your model of internal hub), and set the 'gear units' to 'km/h at 100 rpm' or similar, and see what your current value is.
Then do another one with a range of possible chainring sizes and cog sizes and the same IGH, and try to find a 'km/h at 100rpm' value similar to your existing value, but in a lower gear. I believe 5th gear is 'direct drive' in your hub so theoretically will be the most efficient, so try to find a cog/chainring combination that in 5th gear has the same value of your current setup in 7th gear. Then you will have three 'overdrive' gears for downhill or tailwinds or drafting off greyhound busses, and 4 'reduction' gears, for climbing or when you want to spin your legs a little faster.
NB. entering multiple chainrings and cogs with an IGH will give you a large chart of numbers, so don't be intimidated if that's not your cup of tea - just look for the calculated value close to your existing setup.
02-12-21, 03:47 PM
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Internal modifications are not possible. There are different IGHs with different ratios if you really wanted to go that route, but it is very easy to swap to a smaller cog or (possibly) a larger chainring. Or both.
Here is a link to a gear calculator:
https://www.sheldonbrown.com/gear-calc.html
My suggestion is to first enter the equipment you have (number of teeth on chainring, on cog, and your model of internal hub), and set the 'gear units' to 'km/h at 100 rpm' or similar, and see what your current value is.
Then do another one with a range of possible chainring sizes and cog sizes and the same IGH, and try to find a 'km/h at 100rpm' value similar to your existing value, but in a lower gear. I believe 5th gear is 'direct drive' in your hub so theoretically will be the most efficient, so try to find a cog/chainring combination that in 5th gear has the same value of your current setup in 7th gear. Then you will have three 'overdrive' gears for downhill or tailwinds or drafting off greyhound busses, and 4 'reduction' gears, for climbing or when you want to spin your legs a little faster.
NB. entering multiple chainrings and cogs with an IGH will give you a large chart of numbers, so don't be intimidated if that's not your cup of tea - just look for the calculated value close to your existing setup.
Here is a link to a gear calculator:
https://www.sheldonbrown.com/gear-calc.html
My suggestion is to first enter the equipment you have (number of teeth on chainring, on cog, and your model of internal hub), and set the 'gear units' to 'km/h at 100 rpm' or similar, and see what your current value is.
Then do another one with a range of possible chainring sizes and cog sizes and the same IGH, and try to find a 'km/h at 100rpm' value similar to your existing value, but in a lower gear. I believe 5th gear is 'direct drive' in your hub so theoretically will be the most efficient, so try to find a cog/chainring combination that in 5th gear has the same value of your current setup in 7th gear. Then you will have three 'overdrive' gears for downhill or tailwinds or drafting off greyhound busses, and 4 'reduction' gears, for climbing or when you want to spin your legs a little faster.
NB. entering multiple chainrings and cogs with an IGH will give you a large chart of numbers, so don't be intimidated if that's not your cup of tea - just look for the calculated value close to your existing setup.
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02-12-21, 03:48 PM
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I did a couple for you because my life is so full and exciting. I have no idea what size the gears are on your bike so I guessed just to make an example.
Also, cogs for Shimano IGHs are not available in every size, nor are chainrings, so it's best to figure out what you can actually get before you are married to any one particular setup.
As you can see in the first chart, if you have a 44-22, 7th gear gives you approx. 36.7km/h
In the second chart, there are values similar to that in 5th gear. I circled 50-18 as an example.
If the chainring on your crank is not replaceable (common) and you stuck with the original chainring (in my example, 44 teeth), you would lose a bit of speed in 5th gear, but in 6th gear you have options a bit higher and a bit lower than the original setup.
Hope this helps!
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02-13-21, 09:19 PM
#8
Junior Member
Thread Starter
Thanks to all who responded. I'll start with a slightly larger chainring and see where this would take me.
02-13-21, 09:32 PM
#9
Really Old Senior Member
How much cheaper is a larger ring vs this $6 cog? No new chain needed.
See post #2
https://www.universalcycles.com/shop...ls.php?id=4171
Last edited by Bill Kapaun; 02-13-21 at 09:37 PM.
02-14-21, 04:48 AM
#10
Senior Member
Im betting it needs to be more than "slightly" larger ig you can pedal 7th and 8th all the time. I own a bike with the same hub, 42/19 cogs and and 700x35 tyres. Seems reasonable.
