Gear inches

Re: Gear inches

Postby CW83 » Mon Sep 02, 2013 10:30 am

In my 20s I used 22" to c.95" touring bike gearing. In my mid-50s I got back into touring and at first found the 22" too high for long, loaded climbs. A bit fitter now, I reckon 22" would be ok; but to be prepared for those long mountain climbs at the end of the day, or when really tired, I'd want 19". And I like the smaller gearing gaps offered by a triple crankset.

On a loaded tandem with my not very strong partner we use 19"-c.110". She's too scared to go very fast, and I'm too cautious to try to go faster than she wants ("The stoker is never wrong—they may not be right, but they're never wrong."). I reckon we could do with another gear drop below that, tho' once you reach 4km/hr it may be better to walk!

I also think ordinary road bikes are over-geared, esp. if you ride a lot on your own, as I do. For Audax I use 28" to 111" on a double crank; I'd like to change this to c.25" to 100-105" on a triple. Very unfashionable these days but sensible for me on 300km plus rides, esp. in hills, wind, heat, or rain—which about covers most rides.
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by BNA » Mon Sep 02, 2013 10:46 am

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Re: Gear inches

Postby CW83 » Mon Sep 02, 2013 10:46 am

PS: My 1980s touring bike—still going strong—is equipped with an OFMEGA 24-44-48 crankset (144/74 BCD) running a 13-28 six speed freewheel. Half-step gearing—great, but the double changes can get tedious, tho' in practice when loaded I tend to stay on just one chainring. (It used to have a 44-40-26 TA crankset, which worked well but IMO was ugly. And French.) I have used a 12-28 10-speed cassette wheel on it, which yields quite a few overlapping gears. If I changed that to an 11-34 I'd have a fairly sweet c.116-18, but again in half steps. My audax bike has 34-50 x 12-32, which is ok, but I don't like the gaps between gears.
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Re: Gear inches

Postby snafuspyramid » Thu Sep 05, 2013 6:57 pm

I've got a similar issue (or strictly speaking, my partner has). I built up my own bike myself, so used the lowest gears I could get my hands on - full MTB gearing with a granny gear of 22 on the front and 34 on the back. However, my girlfriend's bike is an off-the-rack Kona Sutra with a 48-36-26 triple on the front. In my opinion, that's much too heavy for a touring bike, especially for a wee person.

I want to extend the range of the gears into a lower range. The easiest way to do that would be to buy a more sensible front crankset - the Deore cranks are made in a 44-32-22 (altogether more sensible in my opinion). However, I'm loathe to spend $100 to replace a virtually brand new part, so am planning to just shell out $20 and replace the inner ring with a 22. (The rear casette is an 11-32, which is acceptable).

Will the drop from a 36 to 22 front chainring cause any issues? I've never seen a crankset that drops more than ten teeth in a shift - this will drop fourteen.
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Re: Gear inches

Postby RonK » Thu Sep 05, 2013 7:04 pm

snafuspyramid wrote:I've got a similar issue (or strictly speaking, my partner has). I built up my own bike myself, so used the lowest gears I could get my hands on - full MTB gearing with a granny gear of 22 on the front and 34 on the back. However, my girlfriend's bike is an off-the-rack Kona Sutra with a 48-36-26 triple on the front. In my opinion, that's much too heavy for a touring bike, especially for a wee person.

I want to extend the range of the gears into a lower range. The easiest way to do that would be to buy a more sensible front crankset - the Deore cranks are made in a 44-32-22 (altogether more sensible in my opinion). However, I'm loathe to spend $100 to replace a virtually brand new part, so am planning to just shell out $20 and replace the inner ring with a 22. (The rear casette is an 11-32, which is acceptable).

Will the drop from a 36 to 22 front chainring cause any issues? I've never seen a crankset that drops more than ten teeth in a shift - this will drop fourteen.

I doubt you'll be able to get a 22T chainring for that crankset - 24T is the smallest you can likely go with the BCD of the crank she's using.

Happy wife - happy life. Bite the bullet and buy her the Deore chainset. Get her the right gears and a crankset that is not likely to cause her dropped chains.
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Re: Gear inches

Postby snafuspyramid » Thu Sep 05, 2013 8:18 pm

I am fairly confident that all the Deore cranks use the 104/64mm standard bolt circle diameter, and there's certainly a 22T Deore chainring available in 64mm BCD.

I am more interested in the dropped chain issue. I vaguely recall being told that sixteen is the max, and a random Google search seems to confirm that advice: http://www.bentrideronline.com/messageb ... hp?t=87353 . However, that advice comes from a recumbent forum, and as we all know, contraption captains are not to be trusted with machines :)

As far as the general gear spread goes, I don't think there would be enough difference to warrant purchasing an entire new crankset simply for the benefit of reducing the gap between the granny and middle ring?

EDIT: Of course, I should first have referred to the work of the late great S. Brown: http://sheldonbrown.com/gear-theory.html . The discussion seems to suggest that a fairly large gap is acceptable (such as a "half-step plus granny"), but I do want to find a solid figure.
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Re: Gear inches

Postby snafuspyramid » Thu Sep 05, 2013 8:26 pm

Aha, here we are: http://janheine.wordpress.com/2012/11/0 ... hainrings/

"One big rule is that the difference between adjacent chainrings ideally should not be larger than 16 teeth. You can use a larger difference – I once tested a classic René Herse bicycle with a 52-26 double – but your shifting will not be ideal. For example, a 48-32 (16 tooth difference) will shift fine with most front derailleurs, but a 48-30 (18 tooth difference) may require trimming of the front derailleur after each front shift. A large chainring difference also can result in the chain rubbing on the large chainring when you ride in the small chainring in the front and on one of the smaller cogs in the rear."
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Re: Gear inches

Postby }SkOrPn--7 » Thu Sep 05, 2013 9:40 pm

RonK wrote:I doubt you'll be able to get a 22T chainring for that crankset - 24T is the smallest you can likely go with the BCD of the crank she's using.


A 20T or 22T will fit Ron on that BCD

Ricky
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Re: Gear inches

Postby }SkOrPn--7 » Thu Sep 05, 2013 9:44 pm

Snufu drop a 20T granny on it if you want to give her a low end and maybe drop a 36 sprocket on the back end.

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Re: Gear inches

Postby RonK » Thu Sep 05, 2013 10:03 pm

snafuspyramid wrote:I am fairly confident that all the Deore cranks use the 104/64mm standard bolt circle diameter, and there's certainly a 22T Deore chainring available in 64mm BCD.

I am more interested in the dropped chain issue. I vaguely recall being told that sixteen is the max, and a random Google search seems to confirm that advice: http://www.bentrideronline.com/messageb ... hp?t=87353 . However, that advice comes from a recumbent forum, and as we all know, contraption captains are not to be trusted with machines :)

As far as the general gear spread goes, I don't think there would be enough difference to warrant purchasing an entire new crankset simply for the benefit of reducing the gap between the granny and middle ring?

EDIT: Of course, I should first have referred to the work of the late great S. Brown: http://sheldonbrown.com/gear-theory.html . The discussion seems to suggest that a fairly large gap is acceptable (such as a "half-step plus granny"), but I do want to find a solid figure.

I was thinking the Sutra had a road crankset with a 74mm BCD.

Upshifts could perhaps be rough or slow and maybe drop the chain sometimes - I don't think this would bother me or you either probably, but the point I was making is will your girl be happy if the shifting is a bit rough. You'll have to try it to find out.

But it wouldn't cost much more to change the 36T ring to a 32T ring as well. She probably won't use the 48T ring anyway so it won't be a problem.

I toured Tasmania on an LHT with the standard 26T chain ring, and it just wasn't low enough, particularly for the hillier western side.
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Re: Gear inches

Postby snafuspyramid » Fri Sep 06, 2013 8:42 am

RonK wrote:I was thinking the Sutra had a road crankset with a 74mm BCD.

Upshifts could perhaps be rough or slow and maybe drop the chain sometimes - I don't think this would bother me or you either probably, but the point I was making is will your girl be happy if the shifting is a bit rough. You'll have to try it to find out.

But it wouldn't cost much more to change the 36T ring to a 32T ring as well. She probably won't use the 48T ring anyway so it won't be a problem.

I toured Tasmania on an LHT with the standard 26T chain ring, and it just wasn't low enough, particularly for the hillier western side.


I decided to go with the 22T. I don't think it's a sufficient drop to cause shifting issues, and she's fairly careful not to cross the chain too much and not to downshift at the front under load. In fact, I noticed that she rarely bothers to change the front chainring at all, probably because it involves fiddling with bar-end shifters. Since she only ever uses the front ring for climbing anyway, I'm hoping that lowering its range a fair bit won't cause too much disruption to her riding style. By contrast, I'm constantly shifting rings and tend to change the front and rear at the same time - I'd find the 14 tooth jump extremely annoying.

It's a good suggestion on changing to 36T to a 32T. I'll see how things run on our next tour and then consider forking out - that would still equal less than half the cost of purchasing an entire crankset, even with the usual CRC/Wiggle et al discounts.
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