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Old 07-24-17, 05:36 PM   #1
NYCDahon
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Want to change crankset for harder gears on Dahon Vitesse I7 (Nexus hub)

I want to change crankset for harder gears on Dahon Vitesse I7 (Nexus hub) - It has a stock 39T or 40T on it right now - would a 52T with 170 cranks be a wise choice? Or would you go 54T or 56T -- or are all these too much of an increase? I would like to get 2 harder gears - my top "7" gear feels like nothing when the wind is to my back - it is nice and flat here in NYC.

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Old 07-24-17, 05:58 PM   #2
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When I changed out my crank ring, I used this calculator to play around with and see the gear inches and ratio. Was really helpful... BikeCalc.com - Bicycle Gear Inches Chart You will be able to see the incremental changes, what you gain and what you lose.
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Old 07-24-17, 06:16 PM   #3
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Thanks for the quick response. It has a nexus seven hub and I think it has 18T on the rear and the Crank is 39T on the front - I don't need any low gears really - it is flat here - I would like to add 2 harder gears - so bump everything up a few gears. I have the tools (and have done it in the past on other bikes) - I can't figure what to do with that chart since it is an internal hub. I am just trying to make gear 5 what my current gear 7 is - and thus make 6 and 7 both harder than what I now have. I have a 20" wheel with 1.75 tire...

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Old 07-24-17, 06:20 PM   #4
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just go up like 4 tooth in the front 53 will be a bear to get going
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Old 07-24-17, 06:21 PM   #5
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internal hub gear calculator: https://www.sheldonbrown.com/gear-calc.html
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Old 07-24-17, 06:34 PM   #6
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just go up like 4 tooth in the front 53 will be a bear to get going
Can't I just shift to 4th gear to get going then ride mostly in 6 - keeping 7 for downhill or wind at my back times? Am I missing something? Also can I change the back gear on these Nexus 7 hubs? I think it has 18T on the rear and the Crank is 39T on the front but will have to count again...
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Old 07-24-17, 06:37 PM   #7
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internal hub gear calculator:
Thanks again - I hope ny head can handle all this math..
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Old 07-24-17, 07:00 PM   #8
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OK -- math and me are oil and water...

I have a Nexus 7 HUB
a rear gear cog of 18T (Back) & 39T crank gear (Front)
according to dear late Sheldon I think I have this (could have screwed up the calc)

----low 1.9 2.2 2.6 3.0 3.5 4.0 4.7 High
Gears 1 2 3 4 5 6 7

I only ever use 4th gear to go up bridges etc -- I ride all the time in 7 and really feel like I am peddling too fast and not enough resistance. Would like to make my current gear 7 into my current gear 5 and add 2 harder gears.
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Old 07-24-17, 07:01 PM   #9
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Cheapest is togo down to 16 t sprocket and then decide if you want more.
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Old 07-24-17, 07:01 PM   #10
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OK -- Thanks to you both for the help.

Math and me are oil and water...

I have a Nexus 7 HUB
a rear gear cog of 18T (Back) & 39T crank gear (Front)
according to dear late Sheldon I think I have this (could have screwed up the calc)

----low 1.9 2.2 2.6 3.0 3.5 4.0 4.7 High
Gears 1 2 3 4 5 6 7

I only ever use 4th gear to go up bridges etc -- I ride all the time in 7 and really feel like I am peddling too fast and not enough resistance. Would like to make my current gear 7 into my current gear 5 and add 2 harder gears.
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Old 07-24-17, 07:02 PM   #11
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Cheapest is to go down to 16 t sprocket and then decide if you want more.
I was wondering that - just how low can I go on a Nexus 7 hub? I can't post links yet but a youtube ( titled "Nexus hub sprocket replacement.m4v" ) says I can get a 14T on there if I remove the dust cap - that might be the cheap easy ticket! ...and I can keep the 70's retro brown smokey plastic chain guard... woohoo

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Old 07-24-17, 07:30 PM   #12
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According to Sheldon's page:
https://www.sheldonbrown.com/nexus7.shtml
The ratios for the nexus 7 are....... .632/.741/.845/.989/1.145/1.335/1.545. which according to my understanding, you are not even 1 to 1 ratio until you hit 4th gear.

To calculate your gearing, divide 39T in front by 18 in rear which gives 4.24 ratio times the diameter of your wheel @ 19 giving a one to one ratio of 41.16. In other words, given a single speed fixed gear, your gearing would be that.
I used 19 inches because I measured my 1.5 406 and they are exactly 19 inches in diameter. Maybe a hair more for the 1.75 tires, but definitely not 20". Anyways that's splitting hairs compared to general calculation for your gearing.

So using the one to one ratio of 41.16 and using Sheldon's gearing ratios given above for the nexus 7, I came up with these gear inches for your current setup:
26"/30.4"/34.7"/40.7"/47.12" /54.9"/63.5"
(Better count your teeth again because this seems extremely low geared!)

So if you go up to a 52 T chainring, 52 divided by 18 x 19" gives a gear ratio of one to one of 54.8
this gives you
34.6" low to 84.6" high gear inches.

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Old 07-24-17, 07:46 PM   #13
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ok let me chime in
if you change front or rear
either way you change every gear

smaller in rear is cheaper and you dont need a new chain
bigger in front might need a complete crankset and new longer chain
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Old 07-24-17, 07:55 PM   #14
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I'd try a 14 in the back first. You'll probably need to shorten the chain a bit. Cheap and easy fix. And next time you need a new rear tire you could try a 2.00 Big Apple. Great for NYC potholes.

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Old 07-24-17, 07:59 PM   #15
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Maybe, but going with a smaller cog will not change his ratios as much as a larger chainring.
If he does have a 39T chainring, a 16 tooth cog will only only give a top gear of 71.5 inches.

39/16x19"=46.3" fixed gear times 1.545 top gear equals 71.5"
If a 14 would fit, that would give a high gear of 81.7 inches (close to changing the front chain ring to 52)

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Old 07-24-17, 08:04 PM   #16
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I'd try a 14 in the back first. You'll probably need to shorten the chain a bit. Cheap and easy fix. And next time you need a new rear tire you could try a 2.00 Big Apple. Great for NYC potholes.
Thanks - I will try this. Do you know if the Nexus 7 hub would use a FLAT -- 3 pin -- Sturmey-Archer 1/8 14t coaster brake cog?
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Old 07-24-17, 08:11 PM   #17
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Maybe, but going with a smaller cog will not change his ratios as much as a larger chainring.
If he does have a 39T chainring, a 16 tooth cog will only only give a top gear of 71.5 inches.

39/16x19"=46.3" fixed gear times 1.545 top gear equals 71.5"
I do have a 39T chainring and a 18T rear cog -- So even worse than that... I will start with a 14T in rear -- then if still not great I can think about changing the chainring. I have done that and it is easy enough. I got this Vitesse i7 slightly used -- but is this stock? anyone know? Dahon's site hides away these type of specs.
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Old 07-24-17, 08:13 PM   #18
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I'd try a 14 in the back first. You'll probably need to shorten the chain a bit. Cheap and easy fix. And next time you need a new rear tire you could try a 2.00 Big Apple. Great for NYC potholes.
I think you are right about the cog -- but I like the Marathon tires on here - I think they are stock.
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Old 07-24-17, 08:14 PM   #19
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ok let me chime in
if you change front or rear
either way you change every gear

smaller in rear is cheaper and you dont need a new chain
bigger in front might need a complete crankset and new longer chain
Do you know what stock gears/cogs come on this bike?
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Old 07-24-17, 08:16 PM   #20
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According to Sheldon's page:
https://www.sheldonbrown.com/nexus7.shtml
The ratios for the nexus 7 are....... .632/.741/.845/.989/1.145/1.335/1.545. which according to my understanding, you are not even 1 to 1 ratio until you hit 4th gear.

To calculate your gearing, divide 39T in front by 18 in rear which gives 4.24 ratio times the diameter of your wheel @ 19 giving a one to one ratio of 41.16. In other words, given a single speed fixed gear, your gearing would be that.
I used 19 inches because I measured my 1.5 406 and they are exactly 19 inches in diameter. Maybe a hair more for the 1.75 tires, but definitely not 20". Anyways that's splitting hairs compared to general calculation for your gearing.

So using the one to one ratio of 41.16 and using Sheldon's gearing ratios given above for the nexus 7, I came up with these gear inches for your current setup:
26"/30.4"/34.7"/40.7"/47.12" /54.9"/63.5"
(Better count your teeth again because this seems extremely low geared!)

So if you go up to a 52 T chainring, 52 divided by 18 x 19" gives a gear ratio of one to one of 54.8
this gives you
34.6" low to 84.6" high gear inches.
Thanks really to all of you! ...and nice figuring HVRanch- now if I knew how to get my gears all moved up a few notches - I hope trying a replacement of my rear 18T and putting in a 14T will do a move up of 2 gears across all the 7 gears - I will get the part and report back.

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Old 07-24-17, 08:40 PM   #21
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hope trying a replacement of my rear 18T and putting in a 14T will do a move up of 2 gears across all the 7 gears - I will get the part and report back.
You would get 60.6" in 5th gear compared to your current 7th gear of 63.5" so pretty close to two gears higher on all gears.
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Old 07-24-17, 08:51 PM   #22
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You would get 60.6" in 5th gear compared to your current 7th gear of 63.5" so pretty close to two gears higher on all gears.
Smart! Thanks!

Now I just hope this video is right for my little 20" folder and the Nexus 7 hub can take a flat Sturmey-Archer 1/8" 14t coaster brake cog, I found this video which is a Nexus 8.

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Old 07-25-17, 03:12 AM   #23
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39T Chainring
Nexus 7 HUB &
these 2 rear cogs

Gear----14T-vs-18T
-----------new---old
1---.632---33---26
2---.741---39---31
3---.843---44---35
4---.989---52---41
5---1.145--60---48
6---1.335--70---56
7---1.545--81---64

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Old 07-25-17, 03:38 AM   #24
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Thanks - I will try this. Do you know if the Nexus 7 hub would use a FLAT -- 3 pin -- Sturmey-Archer 1/8 14t coaster brake cog?
I mix and match all the time. If they look the same they usually are the same. As small as 14 is not dished I think I remember. Not sure why. You sort the chainline out by putting the spacer on the right place (side).
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Old 07-25-17, 06:05 AM   #25
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I mix and match all the time. If they look the same they usually are the same. As small as 14 is not dished I think I remember. Not sure why. You sort the chainline out by putting the spacer on the right place (side).

Great stuff - Thanks!
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