Best way to change gear ratio

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Tom_Pinchenzo
Posts: 6
Joined: 26 Aug 2019, 4:40pm

Best way to change gear ratio

Postby Tom_Pinchenzo » 26 Aug 2019, 5:00pm

Hi All,

New to this forum so - hi! I'm a fairly experienced cyclist but not so confident with mechanics/technical bits.

I recently had a child (now 15mnths) and so I'm touring with the increased weight of a fairly heavy trailer... my Dawes Galaxy currently has a 7-speed cassette at 12-32 and chain rings of 26-36-46.

I'm finding this is way too high and I'm almost never out of the lowest chain ring and usually in the bottom 3 of the cassette, but feeling like l could do with a few more gears to drop into on

My question is this: Is the best way change this a) new cassette with a super low, mtb style cassette (I can't really find any 7-speeds that are much lower than 32) b) change my 26 chain ring for a smaller one c) overhaul the whole system and have an 11 speed or something....

Many thanks for your help!
Tom

whoof
Posts: 2330
Joined: 29 Apr 2014, 2:13pm

Re: Best way to change gear ratio

Postby whoof » 26 Aug 2019, 8:13pm

Are you sure that you have a 7 speed cassette or freewheel?

https://www.parktool.com/blog/repair-he ... wheel-type

whoof
Posts: 2330
Joined: 29 Apr 2014, 2:13pm

Re: Best way to change gear ratio

Postby whoof » 26 Aug 2019, 8:25pm

If you are sure it's a cassette you could get one with a 34
https://www.sjscycles.co.uk/cassettes/1 ... -cassette/
And a 24 inner chainring check the bolt centre diameter bcd

https://www.spacycles.co.uk/m2b0s149p24 ... eel-24-36T
This would reduce your lowest gear from 22" to 19" which is a drop of a little under 14%.

Brucey
Posts: 39498
Joined: 4 Jan 2012, 6:25pm

Re: Best way to change gear ratio

Postby Brucey » 26 Aug 2019, 8:40pm

https://www.sjscycles.co.uk/cassettes/ztto-8-speed-cassette-shimano-compatible-1140t/

is an 11-40T cassette. Fit this without the 11T sprocket and with added shims (eg cut from coke can) to bring the spacing up to 5.0mm. You may need a different cassette lockring. A hanger extender or a new rear mech will be required to get onto the 40T sprocket. The sprockets remaining will be 13. 16, 20, 24, 28, 34, 40T.

In combination with a 24T chainring this will give you a couple of gears that are lower than the present ones. Ratios compared here

http://ritzelrechner.de/?GR=DERS&KB=24,36,46&RZ=13,16,20,24,28,34,40&UF=2185&TF=90&SL=2.6&UN=MPH&DV=gearInches&GR2=DERS&KB2=26,36,46&RZ2=12,17,20,24,28,32,14&UF2=2185

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Tom_Pinchenzo
Posts: 6
Joined: 26 Aug 2019, 4:40pm

Re: Best way to change gear ratio

Postby Tom_Pinchenzo » 27 Aug 2019, 3:10pm

whoof wrote:If you are sure it's a cassette you could get one with a 34
https://www.sjscycles.co.uk/cassettes/1 ... -cassette/
And a 24 inner chainring check the bolt centre diameter bcd

https://www.spacycles.co.uk/m2b0s149p24 ... eel-24-36T
This would reduce your lowest gear from 22" to 19" which is a drop of a little under 14%.


Hi Whoof,

I’ve watched that video and I think you might be right that I have a freewheel. I don’t know there was a difference. So thanks for that! I guess your answer is still valid but I would have to swap out the whole freewheel to one with a 34 and then swap the chain ring to a 24.

Would you say 14% is a significant difference? What’s the lowest hearing on a mountain bike setup?

NetworkMan
Posts: 715
Joined: 25 Aug 2014, 11:13am
Location: South Devon

Re: Best way to change gear ratio

Postby NetworkMan » 27 Aug 2019, 3:44pm

Your 12-32 7 speed has an average between gears of 17.8%. If you change 32 to 34 at back and 26 to 24 at front you'll get a change of 15.1 %, so a little bit less than one of your gears. Perhaps only you can decide if it's worth it.

Brucey
Posts: 39498
Joined: 4 Jan 2012, 6:25pm

Re: Best way to change gear ratio

Postby Brucey » 27 Aug 2019, 3:47pm

IIRC 7s freewheels in 12-32 are like rocking horse poop. On that basis alone I thought it was most likely a cassette, but if in doubt some photos will show what it is for sure.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Valbrona
Posts: 2293
Joined: 7 Feb 2011, 4:49pm

Re: Best way to change gear ratio

Postby Valbrona » 27 Aug 2019, 4:15pm

Buy a fairly cheap mountain bike without any suspension. Fit smooth tyres.

Comes with low gearing 'built-in'. More suitable for pulling a trailer.

If your galaxy is 7 speed it is dated, and apart from that, drop bar bikes are not very suitable for pulling trailers.

Or if you like faffing around with bikes and pieces of tin can ...
I should coco.

RobinS
Posts: 160
Joined: 9 Apr 2015, 10:01am

Re: Best way to change gear ratio

Postby RobinS » 27 Aug 2019, 5:36pm

On my tourer I took the inner chainring right down to 22 tooth, this combined with a 12-34 cassette gives me the lowest possible gear that I can remain vertical with - it is designed for crossing the Alps or Pyrenees with a heavy "3 month camping" load.

LittleGreyCat
Posts: 766
Joined: 7 Aug 2013, 8:31pm

Re: Best way to change gear ratio

Postby LittleGreyCat » 27 Aug 2019, 7:48pm

Tom_Pinchenzo wrote:Hi All,

New to this forum so - hi! I'm a fairly experienced cyclist but not so confident with mechanics/technical bits.

I recently had a child (now 15mnths) and so I'm touring with the increased weight of a fairly heavy trailer... my Dawes Galaxy currently has a 7-speed cassette at 12-32 and chain rings of 26-36-46.

I'm finding this is way too high and I'm almost never out of the lowest chain ring and usually in the bottom 3 of the cassette, but feeling like l could do with a few more gears to drop into on

My question is this: Is the best way change this a) new cassette with a super low, mtb style cassette (I can't really find any 7-speeds that are much lower than 32) b) change my 26 chain ring for a smaller one c) overhaul the whole system and have an 11 speed or something....

Many thanks for your help!
Tom


How old is your Galaxy?

IIRC Brucey helped me to identify my 7 speed as a freewheel but my Galaxy is pretty old.

However my rear cluster seems to be 12-28 if I counted correctly in the dusk.

Jamesh
Posts: 1278
Joined: 2 Jan 2017, 5:56pm

Re: Best way to change gear ratio

Postby Jamesh » 27 Aug 2019, 10:39pm

Getting a 36 tooth 7 speed cassette would reduce the gears somewhat with only a tenner or so cost + new chain £20

Cheers James

rmurphy195
Posts: 1754
Joined: 20 May 2011, 11:23am
Location: South Birmingham

Re: Best way to change gear ratio

Postby rmurphy195 » 27 Aug 2019, 10:45pm

This sounds like the setup on my late 80' Galaxy, "hard as nails" paint, probably british racing green. It had 3 x 7 speed indexed, downtube shifters, 7-speed rear cassette, Shimano STX I think. Band-on front changer.

Be careful of fitting smaller chainrings

If you just change the smallest chainring you may find the front changer - or the front+rear changers - can't cope with the difference between the largest and smallest chanirings (not enough capacity for the difference)

Ditto if you fit a rear cassette with a bigger sprocket or sprockets.

If you reduce the size of the chainrings overall, then you'll probably have to drop the front changer down a bit, and may find the tail of the changer fouling the chainstay!

You may have to change the chain length as well, for example
Every 2 teeth reduction in the largest chain ring size needs a reduction of 1 (pair of) links in the chain length
Every 2 teeth increase in the largest rear sprocket size needs an increase of 1 (pair of) links in the chain length
Brompton, Condor Heritage, creaky joints and thinning white (formerly grey) hair
""You know you're getting old when it's easier to ride a bike than to get on and off it" - quote from observant jogger !

whoof
Posts: 2330
Joined: 29 Apr 2014, 2:13pm

Re: Best way to change gear ratio

Postby whoof » 28 Aug 2019, 12:32pm

Tom_Pinchenzo wrote:
whoof wrote:If you are sure it's a cassette you could get one with a 34
https://www.sjscycles.co.uk/cassettes/1 ... -cassette/
And a 24 inner chainring check the bolt centre diameter bcd

https://www.spacycles.co.uk/m2b0s149p24 ... eel-24-36T
This would reduce your lowest gear from 22" to 19" which is a drop of a little under 14%.


Hi Whoof,

I’ve watched that video and I think you might be right that I have a freewheel. I don’t know there was a difference. So thanks for that! I guess your answer is still valid but I would have to swap out the whole freewheel to one with a 34 and then swap the chain ring to a 24.

Would you say 14% is a significant difference? What’s the lowest hearing on a mountain bike setup?


It's probably going to feel like one gear lower if that makes sense. Whether that will do you only you can say.
Mountain bike chainsets tend to do down to 22 t inners. This is £20 from Decathlon and would give an 18" gear with your current 32 cassette. But you would need to check about bottom bracket length and if it would work with you front mech.
https://www.decathlon.co.uk/7-to-9-spee ... gLOg_D_BwE
As to how low a gear you can have and still keep your balance it's a personal thing. Mrs Whoof runs 22/36 on her tourer and has no stability issues at low speed whilst carrying luggage.
If you can put up some pictures and or make/ model(inc numbers*) of your rear hub/freewheel(cassette?)/ gear mechs and gear changers it would be helpful.

i.e not just Shimano 105 as they have been making this for 30 years and there's loads of different models. So 1050 or 5800are both Shimano 105 but are a world apart.

https://en.wikipedia.org/wiki/Shimano

User avatar
horizon
Posts: 10173
Joined: 9 Jan 2007, 11:24am
Location: Cornwall

Re: Best way to change gear ratio

Postby horizon » 28 Aug 2019, 12:50pm

Although you can lower your gears and get a lot of benefit (if there is a way) I'm wondering whether you are just struggling with a heavy weight up a hill (even a moderate one).

If you are indeed touring you might be pulling more than just the child. How heavy is the combined weight of luggage, trailer and child and what kind of hills are you coping with? The bike itself isn't light either. Lower gears will help but they might not be the end of your tribulations.
When the pestilence strikes from the East, go far and breathe the cold air deeply. Ignore the sage, stay not indoors. Ho Ri Zon 12th Century Chinese philosopher

Tom_Pinchenzo
Posts: 6
Joined: 26 Aug 2019, 4:40pm

Re: Best way to change gear ratio

Postby Tom_Pinchenzo » 28 Aug 2019, 1:31pm

whoof wrote:
Tom_Pinchenzo wrote:
whoof wrote:If you can put up some pictures and or make/ model(inc numbers*) of your rear hub/freewheel(cassette?)/ gear mechs and gear changers it would be helpful.

i.e not just Shimano 105 as they have been making this for 30 years and there's loads of different models. So 1050 or 5800are both Shimano 105 but are a world apart.
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