21 Gears - How Come Only Four Have Any Purpose?

[woodface]

Help a newbie understand. New hybrid bike, 21 Shimano gears, three on crank / chainring, seven at rear. Wheels 700c.

What baffles me is that only the highest four gears have any purpose! With the chainring on '3' (the biggest), the comfortable, efficient rotation of the pedals on level ground is with the rear gears on '6' or'7'. (Going downhill I just freewheel - luckily I've no need for speed.)

If I need to climb a hill, '5' is perfect. Guess I might one day need '4' or '3' on a steep gradient, but anything below that and my legs would be spinning round like the rods on the Flying Scotsman! Even worse with chainring on the smaller '2' or'1'. (Chain rubs the middle ring if you do use ring '1' by the way)

I could understand if gears could somehow be wrongly adjusted, but surely these are fixed ratios which no bike shop could mis-adjust? Or adjust at all? While I follow that you don't need as many gears for flat or descent, I would have expected the 'sweet spot' for gears to be a bit more toward the middle range???

Spec: Shimano Acera - Rear Cassette (edit: Now realise not called a cassette but a screw-on arrangement) is marked 'SUPER-LOW 14-34T' Teeth seem to be 14,16,18,20,22,24,34. The only visible markings on the chainrings are '11 RING' on the smallest & '521-34-2' on the middle ring. The twist-grip Revoshift changers are marked 'SL-RS45' and '22.2'. Bike is a Merlin London hybrid with electric power-assist. (No, the over-ease of pedalling isn't the result of the motor's push. Switched off, 17 gears are still redundant. Only for road use - bought this hybrid solely due to price.)

Thanks.

[PT1029]

I interpret "'521-34-2" as meaning your chain rings are 42-32-22t. If that is the case, with a 14t top sprocket at the rear, your bike is very under geared in terms of gear ratios.
42 t outer rings are fine with cassette sprockets as these usually have 11t or 12t top sprockets which makes for a sensible top gear.
Assuming the motor is in the rear hub, you are stuck with the screw on rear sprockets (so 13 or 14t top sprocket) - cassette sprockets won't fit.
If you really need bigger gears, the way forward is probably to fit a 48/38/28 chainset - which may/may not need a different front gear - which are chain ring size specific, though some times you can get away with using the wrong one. If unlucky, you might possibly need a different length BB depending on crank model/designs and a few extra links in the chain.
I see quite a few bikes with your set up.
Chain rubbing on the front gear in 1 in theory can be cured by adjustment, but some times the chain rubs somewhere.

[pete75]

Assuming the motor is in the rear hub, you are stuck with the screw on rear sprockets (so 13 or 14t top sprocket) - cassette sprockets won't fit.

Not necessarily though I suspect a lowish priced ebike wouldn't use one of these -

[woodface]

Thanks for those replies. As I said, I'm new to all this, and Prof Google led me to think all rear gears were referred to as 'cassette'.

I hope this picture will display to make it clearer.



I don't think I would want to go changing BB or chainset - I'm only an occasional rider and as I said, I can manage with the curious current gearing - just wanted to learn a bit more about it.

Hmm. Image doesn't appear to be displaying, sorry. Perhaps not allowed as I'm new. On web at ibb.co/gMQdjQ

[gaz]

Click for image, which shows a screw on freewheel.
Ultimately you are the engine and, ignoring terrain for the time being, everybody is different. The gears you find comfortable may not be for someone else. On my own twenty one gear bike my regular commute rarely uses more than five of the gears. On other trips I am very grateful to have more but some are surplus to my requirements.

The number of teeth on the chainrings at the front end would be interesting to know in terms of comparing the gearing.

[hamster]

It's more efficient to spin your legs faster than to grind a big gear. If you look at seasoned riders they typically pedal at something like 90+rpm. You can ride slowly (say 10-12mph on the flat) turning the pedals slowly but it's pretty hard to do so at 18mph.

You cannot ride comfortably for long distances or ride fast with slow pedal rpm (cadence). As you get fitter you will probably increase your cadence - it will also reduce the loading on your knees.

[Mick F]

It's more efficient to spin your legs faster than to grind a big gear. If you look at seasoned riders they typically pedal at something like 90+rpm. You can ride slowly (say 10-12mph on the flat) turning the pedals slowly but it's pretty hard to do so at 18mph.

You cannot ride comfortably for long distances or ride fast with slow pedal rpm (cadence). As you get fitter you will probably increase your cadence - it will also reduce the loading on your knees.

Utterly incorrect.

.............. or at least for me.

I cannot be the only cyclist that doesn't like a high cadence.
When I had a cadence sensor, my average cadence was 67rpm. I find that anything over 80rpm is hard work and very very tiring.
Give me a nice high gear on the flat - 100+ gear inches at circa 15mph.

[hamster]

Well Mick, compared to somebody averaging 90rpm you are having to push 34% harder as work done = force x distance. This opens you up to much greater risk of injury, especially to the knees.

Yes, it does feel tiring (I cannot keep up 120rpm for long) but retraining yourself helps a lot, although I'm quite convinced that individuals vary hugely.
Pros used to push bigger gears and slower cadences until it was proved that faster pedalling was more efficient - if for no other reason than the increased number of contractions helped pump blood more efficiently through muscles, removing toxins and transporting more oxygen.

[meic]

The other gears would have a purpose if you were riding steeper hills, doing longer distance (more hills), carrying more weight (touring/shopping), didnt have an electric assist and were "spinning" the pedals rather than "grinding" them.

On this forum there is more call for lowering gearing to something like what you have from what you want, than for your problem of too low gears.

A different gearing system would be more appropriate for you, you already know what you dont like, now you have to try and figure out what you would like. Sounds like the once standard 39-52 front double road set up would suit you fine. Unfortunately it would probably require messing with too many other things to just fit as a replacement.

More likely that replacing the front rings or cranks with a much larger set (and accepting that the inner ring was there for only very, very occasional use) would be the more practical way to go.

I have to agree that while your electric assist is working, those low gears are pretty wasted, but if it was ever to fail, I would need them to keep the thing moving in my terrain.

[[XAP]Bob]

Well Mick, compared to somebody averaging 90rpm you are having to push 34% harder as work done = force x distance. This opens you up to much greater risk of injury, especially to the knees.

Yes, it does feel tiring (I cannot keep up 120rpm for long) but retraining yourself helps a lot, although I'm quite convinced that individuals vary hugely.
Pros used to push bigger gears and slower cadences until it was proved that faster pedalling was more efficient - if for no other reason than the increased number of contractions helped pump blood more efficiently through muscles, removing toxins and transporting more oxygen.

Pushing 34% harder, but having to push for 34% less distance...

In general I'd say that between 60 and 90 is a 'typical' range - there will be people at each end of the spectrum (I am at the top end, Mick is at the low end). Sporting cadences may well be more like 80-110...

We don't all run small petrol engines with twin turbos and MGU-H and MGU-K unit attached - because the requirement for sporting engines doesn't necessarily translate to the engines we need for daily transport.
Similarly the efficiency gains for a pro athlete do not necessarily translate to the far lower power output of even the strongest transport rider. Froome can output 400+W for 30 minutes (Ventoux, 2015).
I could probably hold 200W for that duration, but I can hold 150W all day long... What's efficient at 400+W is not necessarily efficient at 150W...

[Mick F]

Just come in from a ride and thinking about this subject ......... and knowing I'm not a high-revving 2stroke, but a low-revving 4stoke.

I was riding along a flat bit. Unusual to find anywhere flat round here, but there's a a good half mile flattish not far away.
I was doing 13 to 14 mph in top gear - outer 61t and outer 11t - on the Moulton = 101.5 gear inches which gives a cadence of 43 to 46 rpm.

Speed x 336 divided by Gear Inches = Cadence.

I could have kept that up all day. Very relaxing indeed.

I'm nearly 65 years old, and been cycling all my life. My knees are fine and I've never had a problem with them, so I don't buy this "bad for your knees" thing at all.

[Scunnered]

I'm not that much of a cyclist, but I'm reasonably fit from other sports. Before I knew any better, my cadence would be 60 or less and this did not tax my CV system in the slightest. Nowadays I aim for a higher cadence, roughly 90 or so. As a result my HR and breathing are a bit faster, so I know that I am generating more power. Whether it's more efficient or not, I haven't the slightest.

[horizon]

(No, the over-ease of pedalling isn't the result of the motor's push. Switched off, 17 gears are still redundant. Only for road use - bought this hybrid solely due to price.)

I was going to write that the gears are what other people use instead of a motor.

However, I'm not sure what cycling you do but as soon as you place a load on a bike (and a hybrid will take one), the gears become essential.You don't need the top gears often IME as you can coast down hills but just sometimes you get some lovely rolling countryside and the high gears carry you through beautifully.

[hamster]

Well Mick, compared to somebody averaging 90rpm you are having to push 34% harder as work done = force x distance. This opens you up to much greater risk of injury, especially to the knees.

Yes, it does feel tiring (I cannot keep up 120rpm for long) but retraining yourself helps a lot, although I'm quite convinced that individuals vary hugely.
Pros used to push bigger gears and slower cadences until it was proved that faster pedalling was more efficient - if for no other reason than the increased number of contractions helped pump blood more efficiently through muscles, removing toxins and transporting more oxygen.

Pushing 34% harder, but having to push for 34% less distance...

But for exactly the same duration.

[[XAP]Bob]

I'm not that much of a cyclist, but I'm reasonably fit from other sports. Before I knew any better, my cadence would be 60 or less and this did not tax my CV system in the slightest. Nowadays I aim for a higher cadence, roughly 90 or so. As a result my HR and breathing are a bit faster, so I know that I am generating more power. Whether it's more efficient or not, I haven't the slightest.

What you know is that you are consuming more oxygen - if your speed is the same then you are generating the same power, just less efficiently.
If your speed is faster then the maths becomes fairly tricky.



Efficiency is relatively hard to measure, and it will vary according to power output and speed. If your max power output is 100W then spinning at 100rpm is highly unlikely to be the most efficient way of providing that power.