Changing gear ratio on 3 speed internal gear hub bike
 

Ok, i'm very new to all this, but i will try to explain my problem. Perhaps someone could help me and make useful suggestions or tips.

I own a mango bike (google to see pictures). They usually make fixies (44/16) but have recently started selling geared 3-speed versions. Now my problem is that i live in an area with many short steep hills making my riding quite difficult in the lowest gear.

I do prefer riding on larger gears uphill, but not having an option to downshift gear is making things really difficult.

My question is, can i change the gear ratio on the 3-speed internal nexus hub so that gear 1 becomes the middle gear or in a worse case scenario the 3rd gear. Can i change the 'cogs' on the bike to achieve my goal without messing around with the 3 speed hub?

Your advice is much appreciated

Here are some pics of the nexus hub

Most all IGHs can have the cog swapped out for one of a different size. The new cog must match the mounting spec to fit onto the hub. You can check on the Shimano web site for their options or go to your LBS and ask their help in fitting a different cog. There is some interchangeability between brand and models of IGHs, i just don't remember the details of your hub's options.

BITD it was advised that 3rd gear be set up (ratio wise) to be the standard/flat road ratio. My 3-spd follows this suggestion and it works well for all but the long and steep hills. Andy.

Thanks for your input. Just to clarify, because i am quite a novice - i would put a larger cog on the back to achieve easier riding uphills on the lowest gear.

what sort of size cog would i be looking at?

my local bike shop can do all the fitting work, i would just need to tell the, what size cog to change.

Apart from the cog changing size and probably adding a few links to the chain, would i need to adjust anything else?

You can change the cog to raise or lower all of the gears. A larger cog will make all 3 gears easier, a smaller cog will make all 3 gears harder.

According to this: Shimano Internally Geared Hub Part - Harris Cyclery bicycle shop - West Newton, Massachusetts , Shimano 3-speed cogs are available in 16 through 22 teeth. You may need to experiment to find what works best for you.

This is a good reference: Shimano 3-speed Hubs

I am not certain about your hub but some IGHs have limitations on the gear ratio between the chainwheel and cog to avoid overtorquing the hub, which could limit how low you can go. Best to obtain and check the documentation.

IF the hub in question had been a SA AW (knowing it's not but as an example)- 2nd gear is direct drive. 3rd gear is 4/3 of direct drive. So if the OEM cog was a 16T you will need a 21T to ge almost the same ratio in 3rd as you had in 2nd.

The gear cable will likely need some adjustment as the wheel's position in the drop out slot will change. Also the rear brake pad/rim contact might have to be changed due to the same wheel movement. Andy.

a smaller drive cog on the crank , and a larger driven cog on the wheel , both are ways to create a lower Gear Ratio.

comes as (44/16), try a 42/18.. -/+ 2t so same chain will stay .

I changed the cog on an old Schwinn Speedster with the Sturmey AW 3-speed from the 16t all the way up to a 22t, and mounted a new chain.

On a super heavy bike like that, the lower gear ranges make it a lot easier to pedal up hills. Although I lowered the top gear, the bike is heavy enough to accelerate itself on downhills, so I'm not losing much. And the brakes are lousy enough to discourage me from going faster anyway.

On your bike, which is probably way lighter, maybe try a 19t or 20t cog. That and a new chain should be pretty cheap.

On my old Raleigh Sports, I've replaced the 18t cog with 24t cog from SRAM / Sturmey Archer / Shimano sprocket / chainwheel for hub gears And I can use the 3rd speed for flat with 1st and 2nd for hill.

The spacing between gears is set inside the hub and can't be easily changed, however you can change the ratio between the chainring and sprocket to move the whole range up or down. As an example, I currently have 44/21 on my 3-speed. I think it's best to set it up so that 3rd gear is your flat-ground ratio, with 2nd and 1st used for acceleration and climbing. Going down hills, you can always coast. This way I find that all three gears are useful and I can get up most hills.

wow nice ride! the new generation ...

you may find this interesting ...

i'd love to see some more pics of the new generation of bikes and their components

http://www.bikeforums.net/commuting/...term-test.html

you're in the UK I presume (or the EU)

here is where to look in the UK:

16T through 23T

The rear sprocket is the standard 3-prong style, held in by a circlip. It is tricky thing to replace but you don't need any special tools.
Shimano sprockets are made for std 5/6/7/8-speed style chains (3/32" chain pitch). Sturmey Archer sprockets are usually made thicker for singlespeed chains (1/8"). Both use the same 3-prong fitting but the SA sprocket is too thick for the hub.
Usually you change the chain at the same time due to wear patterns.
Many new bike shops have no experience with hub gears so check that they know what they are doing.