Double VS triple. Sheldon gears say 1.9 VS 1.8. Comparable?

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RideToWorky
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Double VS triple. Sheldon gears say 1.9 VS 1.8. Comparable?

Postby RideToWorky » 1 Dec 2018, 10:38am

Hi all,

Long time not on this forum!

Back onto commuting up those steep hills in Bristol.

I see that double front ring setups have come a long way with gravel bikes becoming fashionable.

Looking at Sheldon’s gear ratio website. For the lowest gear available, I see the gear ratios are:
Double mring equals 1.9
Tripling equals 1.8

No idea what these numbers actually mean. But, does this mean a double front ring setup is now very much comparable to having a triple front ring?

I am comparing my current commuter bike triple with the lowest available gear for double front rings. See below, hope I filled in the Sheldon gearing site correctly. I am only concentrating on the lowest gear, to give an idea of how well I can get up those hills.

The Lowest gear setup for double fronted rings are:
Front - Praxis crankset – 44, 30
Rear - cassette – 11–34
Crank length – 165
Tires – 28, 700c


My current commuter:
Front - Smallest ring equals 28
Rear cassette = 11–32
Crank length – 165
Tires – 35, 700c

Hope you can advise

Cheers
Martin

Brucey
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Re: Double VS triple. Sheldon gears say 1.9 VS 1.8. Comparable?

Postby Brucey » 1 Dec 2018, 10:47am

the most common way of expressing gears in this country (and others) is in "inches". This is the gear ratio (as a fraction or decimal) that you (I think) have quoted multiplied by the rolling diameter of the wheel that you intend to use (which allows for tyre size variations as well). This gives an equivalent wheel diameter as if the cranks were directly attached to the wheel. It is one of several different ways of expressing gear ratios, familiarity being the major determinant between them.

You can set the Sheldon calculator to read gear inches. There are other gear calculators available; I like this one

http://ritzelrechner.de/

which again can be set to read gear inches, and allows a graphical presentation/comparison of two different setups.

You can of course buy all kinds of kit that allows you to have different gear ratios than the big manufacturers think you should be happy with. If you have an extant selection of gear ratios and want them different to that, do say; plenty of folk have experience of doing things differently.

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

PH
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Re: Double VS triple. Sheldon gears say 1.9 VS 1.8. Comparable?

Postby PH » 1 Dec 2018, 11:04am

RideToWorky wrote:H
No idea what these numbers actually mean. But, does this mean a double front ring setup is now very much comparable to having a triple front ring?

Comparable in what way?
Less gears means you either have a narrower range or bigger steps between some or all of your gears. You can quite easily get as low a gear as you like, or as high, or as close, but not all three. I have a triple on my only derailleur bike, for the time I spend in the top ring it could easily be changed for a double that didn't have the highest couple of gears but I would miss the bottom ones if I were to lose them.

Brucey
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Re: Double VS triple. Sheldon gears say 1.9 VS 1.8. Comparable?

Postby Brucey » 1 Dec 2018, 11:13am

RideToWorky wrote: The Lowest gear setup for double fronted rings are:
Front - Praxis crankset – 44, 30
Rear - cassette – 11–34
Crank length – 165
Tires – 28, 700c


My current commuter:
Front - Smallest ring equals 28
Rear cassette = 11–32
Crank length – 165
Tires – 35, 700c



your gears are compared here (assuming a 28,38,48 chainset for the triple)

http://ritzelrechner.de/?GR=DERS&KB=30,44&RZ=11,13,15,17,19,21,23,26,30,34&UF=2150&TF=90&SL=2.3&UN=MPH&DV=gearInches&GR2=DERS&KB2=28,48,38&RZ2=11,12,14,16,18,20,22,25,28,32&UF2=2185

Bottom gear is about the same with both setups. Tyre size difference is allowed for.

NB there are many other cranksets with small chainrings besides the praxis one.

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

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cycleruk
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Location: Lancashire

Re: Double VS triple. Sheldon gears say 1.9 VS 1.8. Comparable?

Postby cycleruk » 1 Dec 2018, 11:59am

Just looking at the lowest gears for hill climbing.
Double chainset:-
front ring = 30 and rear sprocket = 34
So 30/34 = 0.88

Triple chainset:-
Front = 28 and rear = 32
So 28/32 = 0.87

So virtually identical.

My information regarding tyre size circumferences :-
Double:- 700c x 28 = 213 cm.
Triple:- 700c x 32 = 216 cm.

So if my logic :roll: is correct then :-
Double - 0.88 x 213 = 187.4
Triple - 0.87 x 216 = 187.9
So again near enough identical as to see no real difference.
It might be that the little weight saving of the double and smaller tyre size could help with the climbing :?:

Is this sound thinking or just drivel. :?
You'll never know if you don't try it.

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Cugel
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Re: Double VS triple. Sheldon gears say 1.9 VS 1.8. Comparable?

Postby Cugel » 1 Dec 2018, 12:23pm

RideToWorky wrote:....
No idea what these numbers actually mean. But, does this mean a double front ring setup is now very much comparable to having a triple front ring?
....
Hope you can advise

Cheers
Martin


It depends on which double chainset is compared to which triple chainset. The chainsets available to you might be limited if you have, for example, a brazed-on front gear hanger, as they typically don't descend enough for ideal placement on big rings less than 50 teeth.

But it's true that you may be able to get the same low gear (and high gear) with a double as with a triple. However, the real advantage of a triple is to have a more idealised range of gears, if your ideal includes close ratios and the convenience of gear "sets".

For example, you could put a 12-34 cassette with a 50/34 chainset and have a bottom gear ratio of 1:1. Put on a 12-30 cassette with the same number of sprockets with a 50/39/30 chainset and you have the same top and bottom ratios but a set of rear gears that are closer in ratio than with a 12-34 cassette. Example 10 speed:

12-13-14-15-17-20-23-26-30-34
12-13-14-15-17-19-21-24-27-30

But perhaps more to the point, a triple chainset can provide you with three "sets" of gear ratios, for fast terrain (the big ring); for undulating terrain (the middle ring); for hilly terrain (the small ring). For example, with a 52/39/30 chainset I spend a lot of time in the 39, which can access all sprockets without a bad chainline, to go between about 10-20mph. When it's a fast section (flat or a good tailwind) the big ring will support 12-30mph. When it's generally going up the steeps, the 30 ring will do 5-12 mph. One avoids the biggest or smallest two sprockets respectively when using the big or the small ring.

Personally I find a 10 speed cassette of 15-16-17-18-19-20-21-24-27-30 with a 52/39/30 ideal - but I like lots of close ratios to support my preferred narrow cadence range, whatever the terrain. There are various other possibilities but the triple seems better at realising all the ratios and ranges you might want whereas the double can often force something of a compromise. A "one-by" seems very limiting.

Cugel

thelawnet
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Re: Double VS triple. Sheldon gears say 1.9 VS 1.8. Comparable?

Postby thelawnet » 1 Dec 2018, 2:14pm

RideToWorky wrote: I am comparing my current commuter bike triple with the lowest available gear for double front rings. See below, hope I filled in the Sheldon gearing site correctly. I am only concentrating on the lowest gear, to give an idea of how well I can get up those hills.

The Lowest gear setup for double fronted rings are:
Front - Praxis crankset – 44, 30
Rear - cassette – 11–34
Crank length – 165
Tires – 28, 700c


My current commuter:
Front - Smallest ring equals 28
Rear cassette = 11–32
Crank length – 165
Tires – 35, 700c


I don't find these gear sites helpful in the slightest.

Just consider these things as ratios.

Hardest gear on first bike is obviously 44/11 = 4, easiest gear is 30/34 = 0.88.
Second one (assuming 48/38/28), is 48/11 = 4.36 or 28/32 = 0.875 (0.88).

Crank length is not used typically (though if the crank length lengthens, then it gets that much harder)

The tyre sise makes a small difference, a 35mm tyre having 14mm wider diameter compared to a 28mm. However 14mm out of a nominally 700mm tyre is obviously not all that significantly (2% more-or-less), so it's not really necessary to worry about it.

Note that the Sheldon Brown calculator has numerous errors in the coding, including nearly all the wheel diameters, so will give you incorrect answers. And the giant dropdown list of wheelsizes and cassettes is confusing/poorly designed.

It's easiest to compare ratios as above. The newer bike has 9% easier/slower hardest gear, the easiest gears are the same, and because of the narrower tyre you end up with an 11% easier top gear.

thelawnet
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Re: Double VS triple. Sheldon gears say 1.9 VS 1.8. Comparable?

Postby thelawnet » 1 Dec 2018, 2:25pm

cycleruk wrote:My information regarding tyre size circumferences :-
Double:- 700c x 28 = 213 cm.
Triple:- 700c x 32 = 216 cm.

So if my logic :roll: is correct then :-
Double - 0.88 x 213 = 187.4
Triple - 0.87 x 216 = 187.9


It's not particularly important to know the circumference of the tyre as you know the diameter of the wheel (622mm for '700c' road bikes and '29"' MTB), so it's just 622 + 28*2 = 678mm, and 622 + 35*2 = 692mm. Not much sense in bringing π into it.

Personally I'd disregard tyre width as the difference it makes is sufficiently small as to be trivial. Much easier just to compare gears.

RideToWorky
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Joined: 23 Oct 2015, 1:14pm

Re: Double VS triple. Sheldon gears say 1.9 VS 1.8. Comparable?

Postby RideToWorky » 1 Dec 2018, 4:37pm

Hi all,

Thank you so much for the info!

Really good food for thought, it’s not just about the Lowest gear, it’s about the usability of the gears is well.

Thanks again

Martin

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cycleruk
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Location: Lancashire

Re: Double VS triple. Sheldon gears say 1.9 VS 1.8. Comparable?

Postby cycleruk » 1 Dec 2018, 4:44pm

thelawnet wrote:
cycleruk wrote:My information regarding tyre size circumferences :-
Double:- 700c x 28 = 213 cm.
Triple:- 700c x 32 = 216 cm.

So if my logic :roll: is correct then :-
Double - 0.88 x 213 = 187.4
Triple - 0.87 x 216 = 187.9


It's not particularly important to know the circumference of the tyre as you know the diameter of the wheel (622mm for '700c' road bikes and '29"' MTB), so it's just 622 + 28*2 = 678mm, and 622 + 35*2 = 692mm. Not much sense in bringing π into it.
Personally I'd disregard tyre width as the difference it makes is sufficiently small as to be trivial. Much easier just to compare gears.

True but did the OP realise that the difference in tyre sizes make little difference in this case?
He did ask for advice and only by giving the figures do you show that.
Normally I just compare "inches" to see for myself what effect the gears have.
You'll never know if you don't try it.

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Double VS triple. Sheldon gears say 1.9 VS 1.8. Comparable?

Postby Brucey » 1 Dec 2018, 4:52pm

with the triple setup I used for calculations (see link upthread) you would -when 'tapping along'- be using both a larger chainring and a larger sprocket (for the same gear ratio) than with the double setup. This is more efficient, smoother running, and longer lasting than a setup using a smaller sprocket/chainring.

As it happens there wasn't a lot to choose between them in terms of chainline in (what I would imagine are) the most-used gears; if you spend a lot of time running cross-chained the transmission can also be less efficient and faster-wearing than it would be otherwise. All things being equal you are more likely to be able to choose a gear with a good chainline when using a triple setup rather than a double. You can buy triples with almost any ratios you care to imagine eg from Spa cycles. They are not even particularly expensive.

One thing that is distinctly lacking in modern bike parts is an alpine double transmission with a decent sized big ring and a top gear that isn't too big. This is mainly because the component manufacturers don't do a wide-ratio cassette that starts with a 13 or 14T sprocket; you have to make those yourself. This is a PITA but it opens the door to easier chainset purchase; for example if you have a 13-36T cassette, this gives the gears you probably want even when using a readily available 50,34T chainset.

The ratios so developed for a 13-36 (10s) cassette with a 50,34 chainset are

http://ritzelrechner.de/?GR=DERS&KB=34,50&RZ=25,13,15,17,19,21,23,28,32,36&UF=2161&TF=90&SL=2.6&UN=MPH&DV=gearInches

this way you can do most of your riding using a good chainline and on sprockets 19-25 instead of with a bad chainline and much smaller sprockets with systems that use a smaller chainring/sprocket combination. FWIW the slight weight increase of a setup like that is more than paid back in increased efficiency, even up steep hills.

cheers
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andrew_s
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Re: Double VS triple. Sheldon gears say 1.9 VS 1.8. Comparable?

Postby andrew_s » 2 Dec 2018, 2:32pm

RideToWorky wrote:Looking at Sheldon’s gear ratio website. For the lowest gear available, I see the gear ratios are:
Double mring equals 1.9
Tripling equals 1.8

No idea what these numbers actually mean. But, does this mean a double front ring setup is now very much comparable to having a triple front ring?

The numbers are "gain ratio".

1.8 means that the rear wheel moves 1.8 times as far at the rim as the pedal does, or, ignoring friction, that you have to supply at the pedal 1.8 times the force exerted on the road.

Sheldon was fond of gain ratio because it takes crank length into account, which gear inches or development ignore (crank lengths don't vary much anyway).

Whilst it is true that, as sold, the bottom gear on a compact double is similar to the bottom gear on a triple, if you should subsequently decide that you want an even lower gear, it's considerably cheaper and easier if you bought a triple in the first place.
The flip side is that a double is easier to get set up well with STI levers.

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Chris Jeggo
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Re: Double VS triple. Sheldon gears say 1.9 VS 1.8. Comparable?

Postby Chris Jeggo » 2 Dec 2018, 5:10pm

On my elderly Roberts touring bike with a Stronglight Impact chainset I used to have a triple: 46-34-24t, but I found myself changing between outer and middle rings too often, so I removed the outer and changed the middle to a 40t (which remained aligned with the centre sprocket of my 9-speed 11-34t standard cassette because I did not change the BB axle). I use the central seven sprockets (13t to 30t) with this ring giving gears of 82" to 35" with no serious chain misalignment. When the road really tilts up I can go from 32" down to 19" using the five biggest sprockets (20-34t) with the inner ring. Some people would hate the jump from 17t to 20t; I find it a bit big, but not a problem - part of the price I pay for not faffing about with custom cassettes. I tried that once and decided that, for me, the benefits did not outweigh the disadvantages. The other price I pay is always carrying about that stupid 11t sprocket that I virtually never use. Yes, I am effectively using a 2x8 Alpine setup, but with smaller chainrings than Brucey suggested above. It is also, in effect, the Spa Cycles compact touring double without the outer chainguard and, I think, slightly different chain alignment.

On another, much more modern bike I have a 42-32-22t triple driving a 12-36t 9-speed cassette operated by STI levers. I like that too, particularly in that changing down from the outer ring does not give such an enormous drop in gear ratio. Also, the ratios of the 12-36t cassette are a bit better than those of the 11-34t one, so I think that at some point in the future I will put one of those on the Roberts and go back to a triple with 42-32-24t rings. Easy to do with a 110-74mm BCD triple chainset and separate gear and brake controls.

Valbrona
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Re: Double VS triple. Sheldon gears say 1.9 VS 1.8. Comparable?

Postby Valbrona » 2 Dec 2018, 6:08pm

I want four chainrings.
I should coco.

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Chris Jeggo
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Re: Double VS triple. Sheldon gears say 1.9 VS 1.8. Comparable?

Postby Chris Jeggo » 2 Dec 2018, 6:31pm

Valbrona wrote:I want four chainrings.

Old hat. Velocio built a bike with four chainrings over 100 years ago. There were two on each side, also two chains and two sprockets on each side, with gear selection by clutches.