2 chainring versus 3 chainring crank

General cycling advice ( NOT technical ! )
bryonabike
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Joined: 8 Aug 2019, 11:13am

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.