2 chainring versus 3 chainring crank

General cycling advice ( NOT technical ! )
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The utility cyclist
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Re: 2 chainring versus 3 chainring crank

Postby The utility cyclist » 27 Aug 2019, 7:44pm

reohn2 wrote:
NetworkMan wrote:Please, please don't just buy any old road bike without being sure the gears will go low enough. As Reohn2 rightly points out many, many write in to this forum asking how they can get lower gears on a road bike with a compact double chainset. We virtually never get anyone complaining that their gears don't go high enough!

And I'll guess a vast majority of riders very,very rarely ever use the top three gears,particularly on road geared bikes.

but still having them isn't really hindering is it, even for those fairly new to cycling, it can also serve as a teaching tool for the future as to what one might or might not want/need.
I spin out on my hybrid (48-12) within a few hundreds metres of hitting the 7% slope on the way to the supermarket, I enjoy/prefer pedalling downhill whenever I can, I was going to swap cassettes or c/ring some years back but I'm too tight to change something that I can put up with. Not having a high enough gear, aside from racing isn't really a massive deal, just an annoyance/inconvenience, it's massively more preferable than not having a low enough gear for sure and why the triple wins out most of the time in terms of ease of providing that.

reohn2
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Re: 2 chainring versus 3 chainring crank

Postby reohn2 » 27 Aug 2019, 8:59pm

thelawnet wrote:
reohn2 wrote:
thelawnet wrote:
That depends on what the top three gears are, surely. There are plenty of MTB hybrids with relatively low top gears.

I beg to differ,my 29er MTB's top is 40x11 = 106inch,just about useable off a cliff!


Really?
This is about an average -0.7% gradient, I was in 40/11 for most of it (the first part is poorly surfaced, the rest is tarmac, and there's a hill at the end).

orly.png

MTB on road because not all the roads are surfaced here, so a MTB seems to be the most useful thing.

The more-or-less continuous downhill isn't steep enough to be visible to the naked eye, so it's not steep enough to coast, but it's enough of an aid to want a big gear.

You were in a 106inch gear at a cadence of 69rpm(which is slow)with a maximum speed of 42kph(?) And an average of 30kph(?).40x13=90inch is 'well under geared' then you are a slow cadence grinder.
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reohn2
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Re: 2 chainring versus 3 chainring crank

Postby reohn2 » 27 Aug 2019, 9:28pm

The utility cyclist wrote:
reohn2 wrote:
NetworkMan wrote:Please, please don't just buy any old road bike without being sure the gears will go low enough. As Reohn2 rightly points out many, many write in to this forum asking how they can get lower gears on a road bike with a compact double chainset. We virtually never get anyone complaining that their gears don't go high enough!

And I'll guess a vast majority of riders very,very rarely ever use the top three gears,particularly on road geared bikes.

but still having them isn't really hindering is it, even for those fairly new to cycling, it can also serve as a teaching tool for the future as to what one might or might not want/need.
I spin out on my hybrid (48-12) within a few hundreds metres of hitting the 7% slope on the way to the supermarket, I enjoy/prefer pedalling downhill whenever I can, I was going to swap cassettes or c/ring some years back but I'm too tight to change something that I can put up with. Not having a high enough gear, aside from racing isn't really a massive deal, just an annoyance/inconvenience, it's massively more preferable than not having a low enough gear for sure and why the triple wins out most of the time in terms of ease of providing that.

A 48x12,assuming a 700Cx32mm tyre is 109inch and is no use to me, 48x14 is jussttt about useful but only very occasionally.

I like to have a range of useful gears that get used efficiently and regularly,because they're efficient and useful,and I dislike 11t sprockets intnsely due to the vibration my feet feel from them through the drivetrain.

Anoher point is that to get the range needed starting with an 11t top sprocket even with a 10sp cassette and a triple,widens gaps between ratios that my knees don't like at all,especially in the cruising ratios in the middle of the cassette.

Of course YVMV.
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Sweep
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Re: 2 chainring versus 3 chainring crank

Postby Sweep » 28 Aug 2019, 8:35am

james01 wrote:+1 for triple. I've spoken to so many newbies who get persuaded to buy high-geared doubles ("...nobody uses triples any more, sir"), then get thoroughly demoralised when they do the walk of shame up a not-very-steep hill. And the simple answer to the difficulty in fine-tuning a triple to avoid front-mech rubbing is to revert to friction shifters - do we really need indexing at the front?

Flat bar indexing shifters are also available (not sure if still current but not hard to find on ebay as new) with an extra trimming click. Has solved any triple chain rub issue I have ever had. And that's despite me building up/cobbling together a few bikes.
Sweep

thelawnet
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Re: 2 chainring versus 3 chainring crank

Postby thelawnet » 28 Aug 2019, 8:50am

reohn2 wrote:
thelawnet wrote:
reohn2 wrote:I beg to differ,my 29er MTB's top is 40x11 = 106inch,just about useable off a cliff!


Really?
This is about an average -0.7% gradient, I was in 40/11 for most of it (the first part is poorly surfaced, the rest is tarmac, and there's a hill at the end).

orly.png

MTB on road because not all the roads are surfaced here, so a MTB seems to be the most useful thing.

The more-or-less continuous downhill isn't steep enough to be visible to the naked eye, so it's not steep enough to coast, but it's enough of an aid to want a big gear.

You were in a 106inch gear at a cadence of 69rpm(which is slow)with a maximum speed of 42kph(?) And an average of 30kph(?).40x13=90inch is 'well under geared' then you are a slow cadence grinder.


The wheel diameter is 27.2", so it's 99" and 84" respectively.

reohn2
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Re: 2 chainring versus 3 chainring crank

Postby reohn2 » 28 Aug 2019, 9:41am

thelawnet wrote:
reohn2 wrote:
thelawnet wrote:
Really?
This is about an average -0.7% gradient, I was in 40/11 for most of it (the first part is poorly surfaced, the rest is tarmac, and there's a hill at the end).

orly.png

MTB on road because not all the roads are surfaced here, so a MTB seems to be the most useful thing.

The more-or-less continuous downhill isn't steep enough to be visible to the naked eye, so it's not steep enough to coast, but it's enough of an aid to want a big gear.

You were in a 106inch gear at a cadence of 69rpm(which is slow)with a maximum speed of 42kph(?) And an average of 30kph(?).40x13=90inch is 'well under geared' then you are a slow cadence grinder.


The wheel diameter is 27.2", so it's 99" and 84" respectively.

It's still a high gear/slow cadence for a 30kph average,and a maximum of 42kph.But if youre a a big gear grinder that's your prerogative.
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thelawnet
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Re: 2 chainring versus 3 chainring crank

Postby thelawnet » 28 Aug 2019, 10:08am

reohn2 wrote:
thelawnet wrote:
reohn2 wrote:You were in a 106inch gear at a cadence of 69rpm(which is slow)with a maximum speed of 42kph(?) And an average of 30kph(?).40x13=90inch is 'well under geared' then you are a slow cadence grinder.


The wheel diameter is 27.2", so it's 99" and 84" respectively.

It's still a high gear/slow cadence for a 30kph average,and a maximum of 42kph.But if youre a a big gear grinder that's your prerogative.


TBH I'm quite often more like 59rpm than 69rpm. Perhaps this is wrong, it isn't completely clear.

reohn2
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Re: 2 chainring versus 3 chainring crank

Postby reohn2 » 28 Aug 2019, 10:16am

thelawnet wrote:
reohn2 wrote:
thelawnet wrote:
The wheel diameter is 27.2", so it's 99" and 84" respectively.

It's still a high gear/slow cadence for a 30kph average,and a maximum of 42kph.But if youre a a big gear grinder that's your prerogative.


TBH I'm quite often more like 59rpm than 69rpm. Perhaps this is wrong, it isn't completely clear.

If a slow cadence suits you then I can't criticise you for it,but you're in the minority and as I posted up thread,most people's better use of their energy is with a higher cadence rate.
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Samuel D
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Re: 2 chainring versus 3 chainring crank

Postby Samuel D » 28 Aug 2019, 11:04am

Cugel wrote:I've passed many a heaver going down hill whilst not pedalling myself. Many don't have much understanding of the huge difference it makes to get aerodynamically crouched upon the bicycle. In fact, their flapping knees and sticky out elbows, as they heave down hill in 53X11, is making them rather unslippery to all that air rushing over them!

But they never learn. "You must have better wheel bearings", declared one. "What tyres are those", asked another.

Aye, that’s the crux of it.

The utility cyclist mentioned that he likes pedalling down a 7% slope. I don’t doubt he does, but tucking and coasting is faster and of course easier. So there’s the double benefit of going faster down the hill and having more energy to climb the next hill or push on the flat, where your power can be put to much better use.

Although like Cugel I give regular demonstrations of this theory to my riding companions, some of them are not easily persuaded. They feel in their belly that nothing could be faster than manfully pushing a big gear down the hill, perhaps with force I couldn’t muster if I wanted to.

But if more theory is useful, plug the following into Bike Calculator while leaving the other options as default:

Grade: −7%
Position: Aerobar
Power: 0 watts


It returns a speed of 69.18 km/h. In reality a good downhill tuck is more aerodynamic than even an aerobar position, since there is no need to pedal. On this point, the best position for coasting is with knees level. This isn’t quite the same as pedals level. Obviously you should have your head low relative to your torso, knees crossed in against the frame, hands as close together as possible, back low and flat so your chin is bouncing off the bars (I sometimes rest my chin on my hands), etc.

Now switch to Position: Drops and drag the red Power/Speed slider until you match the coasting speed of 69.18 km/h. You’ll need 292 watts at the pedals. That’s anaerobic territory for most people. For Position: Hoods, maybe more representative of a big guy pedalling hard, you’d need somewhere in the 600 watt region.

Taking this into account makes gears over 100" unnecessary, at which point a carefully chosen double becomes a viable option for a lot of cyclists.

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Cugel
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Re: 2 chainring versus 3 chainring crank

Postby Cugel » 28 Aug 2019, 2:20pm

Samuel D wrote:
Cugel wrote:I've passed many a heaver going down hill whilst not pedalling myself. Many don't have much understanding of the huge difference it makes to get aerodynamically crouched upon the bicycle. In fact, their flapping knees and sticky out elbows, as they heave down hill in 53X11, is making them rather unslippery to all that air rushing over them!

But they never learn. "You must have better wheel bearings", declared one. "What tyres are those", asked another.

Aye, that’s the crux of it.

The utility cyclist mentioned that he likes pedalling down a 7% slope. I don’t doubt he does, but tucking and coasting is faster and of course easier. So there’s the double benefit of going faster down the hill and having more energy to climb the next hill or push on the flat, where your power can be put to much better use.

Although like Cugel I give regular demonstrations of this theory to my riding companions, some of them are not easily persuaded. They feel in their belly that nothing could be faster than manfully pushing a big gear down the hill, perhaps with force I couldn’t muster if I wanted to.

But if more theory is useful, plug the following into Bike Calculator while leaving the other options as default:

Grade: −7%
Position: Aerobar
Power: 0 watts


It returns a speed of 69.18 km/h. In reality a good downhill tuck is more aerodynamic than even an aerobar position, since there is no need to pedal. On this point, the best position for coasting is with knees level. This isn’t quite the same as pedals level. Obviously you should have your head low relative to your torso, knees crossed in against the frame, hands as close together as possible, back low and flat so your chin is bouncing off the bars (I sometimes rest my chin on my hands), etc.

Now switch to Position: Drops and drag the red Power/Speed slider until you match the coasting speed of 69.18 km/h. You’ll need 292 watts at the pedals. That’s anaerobic territory for most people. For Position: Hoods, maybe more representative of a big guy pedalling hard, you’d need somewhere in the 600 watt region.

Taking this into account makes gears over 100" unnecessary, at which point a carefully chosen double becomes a viable option for a lot of cyclists.


Hard data - always more persuasive than an anecdote, even mine. :-)

In days of yore, even the fittest racing cyclists had a top gear of 52X13. They also had smaller diameter wheels as the 700C rims often had 21 or even 19mm wide tyres on, which are correspondingly of a lesser diameter too. Yet this "low" top gear (by today's standard) still enabled ferocious sprints and chaingang speeds of 30mph. Even those super fast TT lads made do with a 13 sprocket albeit turned with a 55 toof chainring.

In my racing prime, I often used a schoolboy block with a small sprocket of 15. It enabled a 24 at the other end with relatively close ratios throughout the block, which in them days was merely 7 of the cog. Hilly circuits were thereby made a bit easier. It wasn't really possible to win a sprint, if it came to it, on 52X15; but going down the significant downhills at 40+ mph was still possible with nothing but gravity, so at least one could still get to the sprint. Perhaps the 24 cog might even help an escape in the uphill bits, as others heaved on 52X21.

Modern cassettes seem mad to me. Why not start at 15 (which most non-racing riders will find high enough with a 50 ring) and add some dinner plate cogs at the other end, all of which these same lads will find most useful when the slopes go up, along with the cream scone they just ate in the cafe if they've got nowt but a 39X23?

Cugel

djnotts
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Re: 2 chainring versus 3 chainring crank

Postby djnotts » 28 Aug 2019, 8:00pm

One more +1 for triples, reasons all covered above. Age/health demands c. 20" for even quite modest hills - and a 22 or 24 up front easiest and cheapest way to get it while having a 90" high without expense of dinner plate cassettes and 11 speed chains.

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Tigerbiten
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Re: 2 chainring versus 3 chainring crank

Postby Tigerbiten » 28 Aug 2019, 8:45pm

Cugel wrote:Modern cassettes seem mad to me. Why not start at 15 (which most non-racing riders will find high enough with a 50 ring) and add some dinner plate cogs at the other end, all of which these same lads will find most useful when the slopes go up, along with the cream scone they just ate in the cafe if they've got nowt but a 39X23?

Cugel

My understanding is .............

When cassettes got wider, I think it was 5->6, the smallest sprocket got closer to the dropout and there was a risk of it catching on the ends of the chain stays.
So it got smaller to give it more clearance.
Marketing then got on the bandwagon as smaller sprockets equals bigger gears which sell better.
Why do think the latest "best thing" is a cassette with a 10t sprocket.
I've just recently watched a video on a latest groupset which had a top gear ratio of 5:1.
The 135" top gear was supposed to be a good thing for coming down alpine descents.
It's just a pity there's none around here ......... :lol:

Plus it's harder to make a derailleur to work well with very big sprockets.
So it was easier to leave the big sprocket alone and shrink all the others vs leave the small sprocket alone and make all the others bigger.

What never happened was the chainring shrinking to match the shrinkage of the sprocket.
If that happened then 42-26 alpine doubles have taken the place of 50-34 compact doubles and gear ranges would be much more sensible.

YMMV ........ :D

Brucey
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Re: 2 chainring versus 3 chainring crank

Postby Brucey » 28 Aug 2019, 10:20pm

6s 126mm usually had enough clearance to the frame for a 14T sprocket to be used. Anyway the exact spacing wasn't standardised; it didn't have to be (friction shifting) so wheels could be respaced slightly if they wouldn't go in a particular frame.

The real crunch came with 7s 126mm, and then 8s 130mm. Suddenly it was possible (desirable, or necessary) to have more standardised spacing, to run the chain close to the dropout and if you had an older 6s style frame the ends of the stays might clash with the sprockets, either all the time or as the wheel came out of forward facing dropouts. Frames were redesigned to better accommodate the wider cassettes and reduced running clearances; smaller sprockets were just a small part of the problem.

Smaller sprockets are not a new idea; Sun Tour New Winner freewheels could be built 7s with a 12T sprocket as early as 1978, and maybe before then albeit with less availability/more difficulty . Very few people actually fitted such a sprocket mainly because they didn't need to. I used to TT with a 13up block and in most cases the 13T sprocket would be the first to go if I have to lose one.

cheers
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reohn2
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Re: 2 chainring versus 3 chainring crank

Postby reohn2 » 29 Aug 2019, 10:41am

FWIW,Ive been running 14 up cassettes in 8 and 9speed on a variety of frames with 160,145 and 135 oln for some 15 years including
Tandems
Thorn Discovery(145)
Santana Arriva(160)
Cannondale road (145)
Solos,all 135oln
Cannondale T800
Dawes Galaxy
Thorn Audax MK3
Salsa Vaya
Genesis Vagabond
All with no clearance issues.
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Cugel
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Re: 2 chainring versus 3 chainring crank

Postby Cugel » 30 Aug 2019, 12:34pm

reohn2 wrote:FWIW,Ive been running 14 up cassettes in 8 and 9speed on a variety of frames with 160,145 and 135 oln for some 15 years including
Tandems
Thorn Discovery(145)
Santana Arriva(160)
Cannondale road (145)
Solos,all 135oln
Cannondale T800
Dawes Galaxy
Thorn Audax MK3
Salsa Vaya
Genesis Vagabond
All with no clearance issues.


I used a 7-speed schoolboy block of 15-24 on a racing bike for nearly a decade (for most hilly races) and never had the 15 sprocket foul a chainstay. The frame was a typical Reynolds 531SL racing frame of the day with a fairly short wheelbase and chainstays, although I couldn't say the measurements. I do recall that the rear wheel OLN dimension was 126mm.

Cugel