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PostPosted: Mon Jul 01, 2013 8:23 pm 
Gold Trader / PoTM Winner / RB Rider
Gold Trader / PoTM Winner / RB Rider
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Joined: Tue Feb 26, 2013 6:26 pm
Posts: 16905
Location: 54 Festive Road Winchcombe GLOUCS Yarp...
Thanks. Ipad here. :cry:


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PostPosted: Tue Jul 02, 2013 1:18 pm 
Retro Guru
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Joined: Mon Mar 02, 2009 4:22 pm
Posts: 1481
I don't think you'll really notice. With the range of a 12-28 on the back I don't think you'll see it.


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PostPosted: Tue Jul 02, 2013 1:29 pm 
Gold Trader / PoTM Winner / RB Rider
Gold Trader / PoTM Winner / RB Rider
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Joined: Tue Feb 26, 2013 6:26 pm
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Location: 54 Festive Road Winchcombe GLOUCS Yarp...
Thanks. Looking for a period stronglight double now and mech and changer!


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PostPosted: Wed Jul 03, 2013 8:28 am 
Dirt Disciple

Joined: Tue Nov 13, 2012 1:39 pm
Posts: 35
Location: argyll
One tooth at the front is worth 3 off the back. As a crude rule of thumb.


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PostPosted: Wed Jul 03, 2013 10:02 am 
Retro Guru

Joined: Wed Dec 10, 2008 9:19 am
Posts: 2093
Location: Sheffield, top city
g eisler wrote:
One tooth at the front is worth 3 off the back. As a crude rule of thumb.

and that is quite crude. It depends where at the back.

Its about %ages

one tooth on a 50T chainring is 1/50 or 2% difference
one tooth on a 25T rear cog is 1/25 or 4% difference
one tooth on a 12T cog is 1/12 or 8% difference

that is why when you buy a cassette, it will be something like 12,13,14,16,18,21,24. It keeps the % differences fairly constant all the way through, even though the small cogs are close together in absolute terms.

So for you alternating between 48/49T up front will make half as much difference as putting a 25T instead of a 24T at the back (roughly).
hope this helps


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PostPosted: Wed Jul 03, 2013 10:02 am 
Retro Guru

Joined: Wed Dec 10, 2008 9:19 am
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Location: Sheffield, top city
double post, pc hanging


Last edited by pigman on Wed Jul 03, 2013 10:04 am, edited 1 time in total.

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PostPosted: Wed Jul 03, 2013 10:03 am 
Retro Guru

Joined: Wed Dec 10, 2008 9:19 am
Posts: 2093
Location: Sheffield, top city
triplle post, pc hanging, i got trigger happy


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PostPosted: Wed Jul 03, 2013 10:38 am 
Gold Trader / PoTM Winner / RB Rider
Gold Trader / PoTM Winner / RB Rider
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Joined: Tue Feb 26, 2013 6:26 pm
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Location: 54 Festive Road Winchcombe GLOUCS Yarp...
Thanks. Was surprised to find two cogs with just a tooth difference.


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PostPosted: Wed Jul 03, 2013 11:36 am 
Retro Guru

Joined: Mon Feb 11, 2008 9:42 am
Posts: 2363
The History Man wrote:
Thanks. Was surprised to find two cogs with just a tooth difference.
Its not uncommon, most trackies will have a selection of chainrings and sprockets in their tool kit, something like 47 ish up to 50 or 51, then sprockets from (maybe) 14 thro 17. They can then fine tune gear ratios (almost by the inch!) dependent on the track/event. Hill climbers do the same.
Road testers also used to do the same before you could get cassettes with a decent spread, take a 51/52/53 with them depending on wind direction, course profile and length.
My father had his sequence of old sprockets and chain rings on a couple of nails in the garage wall (used to TT on a fixed back in the late 50s/early 60s). All long since sent to the skip.


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PostPosted: Wed Jul 03, 2013 1:03 pm 
Gold Trader / PoTM Winner / RB Rider
Gold Trader / PoTM Winner / RB Rider
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Joined: Tue Feb 26, 2013 6:26 pm
Posts: 16905
Location: 54 Festive Road Winchcombe GLOUCS Yarp...
Amazing that you can get that specific. Was thinking of finding an early front mech and double crank but maybe i'll just leave it as is and original. It's on the armstrong in case you haven't guessed.


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