Bottom Gear

[Chris S]

I'm learning to ride on a 3-speed Raleigh with a Sturmey Archer gear hub. Going up steep hills is heavy going.

Bottom gear works out at about 1.704:1, 46/18 - (46/18 x 0.3r)

Is this particularly high compared to most other bikes?

If it is I'll get a bigger rear cog, if not I'll just keep practicing.

 

[RedBike]

I'm learning to ride on a 3-speed Raleigh with a Sturmey Archer gear hub. Going up steep hills is heavy going.Bottom gear works out at about 1.704:1, 46/18 - (46/18 x 0.3r)Is this particularly high compared to most other bikes?

Because the wheels on the shopper are only small (20"?) then the gears are low relative to a larger wheeled bike. When comparing gear ratios you might find it easier to use gear inchesFrom Sheldon Brown...

One of the three comprehensive systems for numbering the gear values for bicycle gears. It is the equivalent diameter of the drive wheel on a high-wheel bicycle. When chain-drive "safety" bikes came in, the same system was used, multiplying the drive wheel diameter by the sprocket ratio. It is very easy to calculate: the diameter of the drive wheel, times the size of the front sprocket divided by the size of the rear sprocket. This gives a convenient two- or three-digit number. The lowest gear on most mountain bikes is around 22-26 inches. The highest gear on road racing bikes is usually around 108-110 inches. Unfortunately, the handwriting is on the wall for all inch-based measurement systems.

Or just use the online calculator here.
http://www.sheldonbrown.com/gears

For a comparison your lowest gear (For 20 X 1 1/4 / 28-451 tire with 170 mm cranks) has a gain ratio of 3.4
A MTB (26 X 1.9 / 47-559 / MTB tire with 170 mm cranks) 22x32 would have a gain ratio of 1.3
A standard double on a road bike 39x25 would have a gain ratio of 3.1
My fixed wheel road bike 5.2

 

[jimboalee]

Low gear on you Sturmey if its an AW3, is:-

( Ring (48 ) / Sprocket ( 18 ) ) x wheel diameter x 0.75.


Sturmey loaded bikes are ALWAYS overgeared unless its a Dawes. Raleighs are notorious, including my BSA 20 built by Raleigh.

Luckily, its possible to get a larger sprocket on the Sturmey.


Ideally, No. 2 ( middle ) gear on the bike should be close to the Penny Farthing wheel size YOU would have been riding.


I also have a Halfords own Gents city bike which came with rediculously high gearing.


To get this arrangement on the 20", it has the std 44 ring and a 22 sprocket, making No. 2 gear 52".
On the 26" wheel gents city bike, it has the std 46 ring with a 24 sprocket ( SRAM from Wiggle ), making No. 2 gear 50" ( cus 23 wasn't available ).

Increase the number of teeth on the sprocket by 4. This enables 1 whole chain link to be added and the rear axle stays in the same position in the dropouts.

Hope this helps.

PS That BSA 20 has been round an Audax DIY 100km BP.

 

[jimboalee]

On a 26 x 1 3/8" wheel bike ( or a 700C with thin tyres ), an ideal set up would be a 42 ring to 22 sprocket, making No. 2 gear 52" or the same ratio J.K.Starley set up on his Rover Safety bike. That's where the 42 tooth inner ring came from.

Low would be 39". If you think this is a bit high for a 25lb bike, it wasn't 100 years ago when cyclists WERE cyclists.

High would be 69", a nice cruising gear.