2 chainring versus 3 chainring crank

General cycling advice ( NOT technical ! )
bryonabike
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2 chainring versus 3 chainring crank

Postby bryonabike » 8 Aug 2019, 11:22am

Does anyone have any wisdom to share about the plus and minus points of a 2 crank setup over a 3 crank on a hybrid bike? I am new to cycling and want to cover longer distances than my current 7-speed mountain bike allows but also be able to tackle hills and long gradients. I have read that 2 crank setups can be as efficient but less problematic and less technically troublesome.
Last edited by Graham on 8 Aug 2019, 11:28am, edited 1 time in total.
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whoof
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Re: 2 chainring versus 3 chainring crank

Postby whoof » 8 Aug 2019, 12:15pm

This is the most recent musings on double/triple that I can find.

viewtopic.php?f=5&t=131772&hilit=triple+double

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Tigerbiten
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Re: 2 chainring versus 3 chainring crank

Postby Tigerbiten » 8 Aug 2019, 12:50pm

First off I'll say, I'm old school and I like triples ..... :D

Triples give you the options of either a wider range of gears and/or more gears in the same range.
With a wider range you can get lower gears while still keeping a standard high top gear.
As for why more gears in the same range. It makes it easier to find the absolutely correct gear to match conditions. If you know what gears you like/need then you can also fine tune your gears to suit you. Even going to the stage of splitting and combining two cassette to make an ideal one.

But if you're using indexed shifters at the front then a double is probably the way to go as it can be tricky to setup an indexed triple.
With the right choice of cassette and chainrings you don't lose out that much to a triple for the gain in simplicity.

YMMV ........ :D

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TrevA
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Re: 2 chainring versus 3 chainring crank

Postby TrevA » 9 Aug 2019, 9:16am

I’m another fan of triples and have them on all of my bikes. The granny ring is not used very often but it’s great to have it there when it is needed. I spend most of my time in the middle ring, which does wear out quicker than the other 2 so it’s worth getting a chain set than has replaceable rings. I live in a reasonably flat area but there are steep hills nearby, so that’s when the triple comes in useful - the granny ring for going up them and the big ring for coming down.

I have no trouble setting up the indexing on the front rings on any of my bikes.

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andrew_s
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Re: 2 chainring versus 3 chainring crank

Postby andrew_s » 9 Aug 2019, 10:53am

Most doubles have a small chainring that's limited to 34T or larger, and on 7/8/9-speed the normal limit is a largest sprocket of 34T or 36T. That limits the lowest gear to 25-27 inches.
Whether that's low enough depends on how strong you are, how tired you are, how much weight you are carrying, how long the hill is, and how steep it is. It's often OK for unladen day rides in the UK for a cyclist that's used to 50-80 mile rides, unless the ride includes some of the more notable passes, such as those in the Lake District. However, almost all tourists, and most of those who start on Alpine rides, will want something lower, as will those who haven't got trained up on steep hills.

Lower gears can be obtained whilst continuing to use a double chainset by either going 10 or 11 speed, which allows rear sprockets up to 50T, or by using an "alpine double" chainset with chainrings like 28/44 or 24/42.
Alpine doubles are the cheapest option, but they are rare, other than those that are just using the middle and inner chainring positions of a triple, and if you find one that is designed as such, you've got to check for non-standard chainrings (expensive to replace when worn). Some people may find the top gear too low too (I just pedal faster, being OK up to about 140-150 rpm as a result of having spent about 3 years riding 65" fixed).
Large (40-50T) cassettes are expensive (starting at around £35-£40) compared to 7 or 8 speed (£10), don't last any longer, and will require a matching rear mech.
Using doubles can also result in larger steps between gears, and also in finding yourself riding at a speed where you end up having to swap chainrings, and hence have to make simultaneous front/rear changes, relatively frequently.

Triples are the traditional touring solution. You get a full range of gears without restriction at either the low end or the high end, or expensive parts, and they are usually more restful to pedal on as you can select a chainring appropriate to the general terrain and do most of the changing at the rear.
The disadvantages are that the choice of shifters is relatively limited, and that front changing will never be as slick, so you'll have to anticipate the need to front change on a hill, so you can change at a point where you are still pedaling relatively fast and can ease off on the pedal pressure during the change. An unexpected steep hill can result in failure to make the change and either having to walk the rest of the hill, or make the change whilst stationary (lifting the back wheel) and starting off again.

FWIW, I use a triple (20/36/46 to 11-32 8sp) with bar-end shifters. Suits me.
The 20T chainring doesn't get much use (generally only for touring luggage or one of the steeper hills up the Cotswold escarpment), but I wouldn't want to be without it.

boblo
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Re: 2 chainring versus 3 chainring crank

Postby boblo » 10 Aug 2019, 12:50pm

Yeah, I'm using 22/32/44 to 11-34 9 speed. Luggage, hills and consecutive days means the lower gears avoid undue fatigue as the last thing I want to do when touring is honk up hills. I use a 20 on the tandems as well to counter the extra weight.

rmurphy195
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Re: 2 chainring versus 3 chainring crank

Postby rmurphy195 » 10 Aug 2019, 7:41pm

TrevA wrote:I’m another fan of triples and have them on all of my bikes. The granny ring is not used very often but it’s great to have it there when it is needed. I spend most of my time in the middle ring, which does wear out quicker than the other 2 so it’s worth getting a chain set than has replaceable rings. I live in a reasonably flat area but there are steep hills nearby, so that’s when the triple comes in useful - the granny ring for going up them and the big ring for coming down.

I have no trouble setting up the indexing on the front rings on any of my bikes.


Ditto
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shobo
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Re: 2 chainring versus 3 chainring crank

Postby shobo » 11 Aug 2019, 3:31pm

Andrew s, can u suggest a supplier for the alpine double chainset please ? Also the 50t cassette. The only ones i can find are the SRAM designed for single chainrings, what are they 42t ?

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TrevA
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Re: 2 chainring versus 3 chainring crank

Postby TrevA » 11 Aug 2019, 5:27pm

Spa Cycles will do an Alpine double chain set with something like 40-24 chainrings.

RH20
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Re: 2 chainring versus 3 chainring crank

Postby RH20 » 25 Aug 2019, 7:21pm

My opinion would be go for a three ring setup. If you don’t need the third ring it’s there, but get to a big hill and the third ring can be manner from heaven. I have a bike with a compact double and a commuter bike with a triple ring. Living in an area where there are big hills I welcome the granny ring. I used to commute on the double but now over seventy I love the third ring It is the difference between peddling square and peddling at a reasonable cadence on the hills.

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The utility cyclist
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Re: 2 chainring versus 3 chainring crank

Postby The utility cyclist » 25 Aug 2019, 11:15pm

For me the only bike I use with a double is my lightest, most efficient/highest spec carbon bike, I know the routes that I ride on it I can manage (for now) with the gearing I have and one that does not compromise me with respect to big jumps between the ratios. That for me is the big rub with regards to using dinner plate cassettes with a double so that you can gain the lowest ratios you need to get you up the slopes and get you home/to your destination.
There's no real downside to having a triple, well set up flat or drop STI gear shifters should give you no problem shifting from anything as small as a 24T up to a 52T ring.
I have used and still have fitted a super compact double currently a 48/28, this is using the old 86mm BCD of Stronglight chainset but finding the rings is harder and harder, IF you really want to go for an 'alpine' double then the cheapest method is to simply use a triple chainset and only use the middle and inner chainrings, you could then look at older 130/74mm chainsets which have gone out of favour but the rings are still available.

Jamesh
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Re: 2 chainring versus 3 chainring crank

Postby Jamesh » 25 Aug 2019, 11:28pm

Gearing won't really help you go faster or longer.
A new set of lighter weight tyres would help to improve the speed of a bike.

Or if your flushed a new road bike would be better still.
At this time of year there will be bargins to be had new and used.

Cheers James

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Tigerbiten
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Re: 2 chainring versus 3 chainring crank

Postby Tigerbiten » 26 Aug 2019, 12:01am

Jamesh wrote:Gearing won't really help you go faster or longer.

It depends on how close the gears match your riding style.

Get it right and you don't waste any energy by being able to keep close to your ideal cadence.
Get it wrong and you'll have bad jumps between gears and/or not a low enough first gear to match the hills you meet.

But that only really shows you when you get towards your limit distance/speed wise.

YMMV ........... :D

Brucey
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Re: 2 chainring versus 3 chainring crank

Postby Brucey » 26 Aug 2019, 7:46am

IME if you are new to cycling then the most important thing is that you have a range of gears that allows you to tackle the routes you want to ride. That will vary with the rider, the bike, the terrain and the load being carried. If you are new to cycling then you won't know what gears you need for sure; indeed even experienced cyclists are often surprised by the range of gears that they need when they change something.

This being the case the most sensible thing is to either

a) start out with a range of gears that is far wider than you will probably need or
b) start out with a set of gears that you can change (easily/cheaply) as your particular needs become apparent.

There are secondary considerations such as efficiency; for example it is not at all uncommon to find that, with a so-called 'compact double' setup, you are commonly running 'cross chained' in your most favoured gears, i.e. either small chainring -small sprocket or large chainring-large sprocket. A suprising amount of people put up with this, but their transmissions wear out prematurely and in terms of raw efficiency you may as well have set the brakes to rub or something.

Anyway for various long and mostly boring reasons IME a 3x9 transmission will usually come closest to meeting both the a) and/or the b) requirement.

A 2x10 or 2x11 tranmsission can be modfiied to give a different range of gears but this will often require a substantial/expesnvie change to the bike, such as changing the chainset.

cheers
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peetee
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Re: 2 chainring versus 3 chainring crank

Postby peetee » 26 Aug 2019, 8:52am

If you are not technically minded and want the simplest solution then I would have to advocate a triple. That may sound counter intuitive but hear me out.
You will most likely need a wide spread of gears. This is achievable on double chainring road bikes but the big drawback is the big gear ratio difference between the two chainrings. When you do this change your pedalling rate instantly speeds up or slows down and many people find this quite hard work or detrimental to maintaining a reasonable pace or effort. Most experienced riders get around this problem by doing a double shift, i.e. changing gear with both hands and operating both shifters at the same time therefore changing the gear ratio at the back to reduce the overall difference in ratio but this can be difficult to judge if you are not a frequent rider. It also increases the possibility of a mechanical problem as the chain can be put under greater strain with some systems and can overshift, jam or fall off the cogs.
A triple has a full complement of gears and each change is of a smaller difference in ratio so double shifts are not necessary.
I have just returned to cycling after nearly 10 years off. I used to ride quite close ratios on my road bike but now I am thankful for a triple because my power output is drastically reduced and every slight gradient change requires a different gear so I can maintain a comfortable pedal rate. Unfortunately, my 'pure' road bikes will be staying in their boxes for a while. :roll: :cry:
Current status report:
Latter side of fifty and feeling less than nifty.
Too many bikes on pegs and too few miles in the legs.