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A while ago, we took 3 bikes to cramond all with 20" wheels - circe helios, islabike beinn and dahon islabike.
I noticed that even when the two grownups were coasting or pedaling slowly, the islabike rider often still had to pedal quite vigorously, even when she seemed to be in the right gear.
Is this something to do with gear ratios? Or something else? And is there anything we can do about it?
"Is this something to do with gear ratios?"
Probably
"Or something else?"
Perhaps
"And is there anything we can do about it?"
Depends
Is that a dumb enough ansa?
You seem to be saying top gear too low.
Make sure it was in top gear.
I'm assuming multigeared at the back. Smallest cog likely to be 14T. Cassette hub would allow smaller.
Or larger chainring/set at front - which may or may not be easier.
My first guess is plain old fashioned friction vs inertia.
I can confirm from having worn the Islabike rider as a shoecover and strolling around PY that she's very light, so even if the bike's hubs are in good order and it doesn't have knobbly or under-inflated tyres, she just doesn't have the mass to overcome the rolling resistance, or more accurately the rolling resistances which are largely independent of the weight of the rider.
Now, if it doesn't have slick, inflated tyres and smooth-running hubs, then that'll makes things worse.
Crank lengths might mean that what "seems" like the right gear in terms of selected ratios isn't infact correct.
Alternatively, what Bruce says, and add ballast?
thanks all.
the thing is, the reason it was a dumb question is that i don't 'get' gear ratios. is the reason they are different on small bike because it is designed to be more help going up hill?
not sure we can do much about mass - we're trying fatten her up! interesting point re cranks. i notice this when on the tandem with kiddie cranks on the back. but not quite clear on how this interacts with gears...
" i don't 'get' gear ratios"
You're not alone. But the fact that you pointed out that all the bikes had the same sized wheels is a step in the right direction. Many people don't understand gears and small wheeled bikes generally - "doesn't that mean you'll have to pedal faster?"
Many people don't even begin to get the concept of gear inches (method of measurement and comparison of gearing) that actually is straightforward (in a perverse sort of way - it's about comparison with High Ordinaries, which didn't have gears...)
"Unfortunately, the handwriting is on the wall for all inch-based measurement systems." (Says Sheldon)
But that's all a diversion - partly to cover comparisons where there are different wheel sizes.
The important part of the ratio is simply dividing the number of teeth on the front by those on the back.
If you have this one -
http://www.islabikes.co.uk/bike_pages/pdfs/product_specs/Beinn20_Small.pdf
Then the smallest at the back is a 12T (which is better than 14T for higher gears). The front is 32T - about the same as the smallest ring on a normal/adult triple chainset.
The gears on the 24" Islabike are the same
http://www.islabikes.co.uk/bike_pages/pdfs/product_specs/Beinn24.pdf
The bigger wheels increase the gearing.
You do say "even when she seemed to be in the right gear" - presume you are talking about top gear??
I too don't understand "still had to pedal quite vigorously, even when she seemed to be in the right gear" - do you mean her cadence was correct, but she had to keep pedalling while you coasted?
If so I think inertia is the simple answer. Your cross-section into the wind, relative to your weight, is much smaller than hers. When you stop pedalling the forces acting to slow you down are greater (because you're bigger) but acting on a much bigger mass (so you don't slow down as fast).
I imagine you would particularly notice this on downhills?
The value I'm interested in is how fast the bike goes when I'm turning the pedals at my minimum-grindy, comfortable-cruisy and maximum-spinny cadences.
Nowadays that's easy to determine, since the arithmatic is a doddle when you have a calculator. It's even easier with the web calculators like Sheldon's and the one PS linked to.
Back in the day, they didn't have them, so they used the value called gear inches because that is only has one division and one multiplication in it (both just involving integers) - easy to do with pencil and paper or even in your head if you're good at that kinda thing.
Front chainring's number of teeth, divide by back cog's number of teeth, and then multiply by diameter of wheel in inches.
Hey presto, you have a value that is directly proportional to how far the bike will go forward when the cranks turn, and therefore directly proportional to how fast the bike goes at the aforementioned cadences.
It's still perfectly sensible to use it today because not everyone's cadence is the same. Also, it's all directly proportional anyway; it could be based on a completely arbitary value and still be useful, so the way gear inches comes out in the humanly comfortable 20-130 range of numbers is a happy accident.
Note that wheel size is chewed up and spat out in neatly digested format by the gear inch equation - a Brompton and a Pashley Guv'nor will both go the same speed at the same cadence when at the same gear inches.
Pedant NB: the diameter of a tyre is rarely an integer, but meh.
+1 on the mass thing, but might also be worth just spinning the wheels to check that they're going round freely, check that the chain and cogs are in good nick & the tyres are well pumped up.
I often pedal going down hill, I just like to keep my legs moving even if I'm not pushing on the pedals very hard. I'll also try and speed up as much as I can on the easy bits to build up momentum for the uphill bits
I'm sure I remember something about tall gears being bad for younger people, as it encourages weird muscular/skeletal development?
Possibly islabikes have decided that gearing the bike down low to promote spinning is healthier?
May be making this all up...
I can answer the crank length bit though:
The crank acts as a lever on the front cogs. If I push on the pedal with a given force, the turning force which eventually ends up acting on the cog increases as the length of my lever (crank) increases. The whole 'give me a lever long enough and a suitable pivot and I will move the earth' idea. So longer cranks amplify your effort, making you appear stronger.
That has to be weighed against striking the cranks on the ground, the increased weight making them more effort to spin up, and the fact that pedaling cranks a metre in length doesn't fit very well with the way most folk's legs work.
"May be making this all up..."
All things are possible...
Having lower gears is always good for young people/beginners.
Islabikes has also taken decision to have a single chainring. Reduces confusion for people new to cycling (and reduces weight which Islabikes, correctly, things is important for small users).
In junior racing there used to (may still?) be a limit on top gear.
Crank length is also about matching leg length. Though it's a bit arcane. Some people say that variations from the fairly standard 165mm make a difference to them.
Probably more important for people with much shorter legs - eg children.
Also means bikes can have lower bottom brackets.
"So longer cranks amplify your effort, making you appear stronger."
I always prefer to explain lever-length things with something along the lines of "longer cranks allow you to input more metres and fewer Newtons to achieve the same work" but it relies upon having heard of the Nm.
"You do say "even when she seemed to be in the right gear" - presume you are talking about top gear??"
"do you mean her cadence was correct, but she had to keep pedalling while you coasted?"
We were on flat/downhill and she was in 7th or 8th gear (out of a possible 8), and her legs were still going round at twice the rate of mine. Which *i think* means her cadence is wrong?
What does she think?
Why don't you come for a ride with us and ask her?
You looking for a list of excuses?
"We were on flat/downhill and she was in 7th or 8th gear (out of a possible 8), and her legs were still going round at twice the rate of mine. Which *i think* means her cadence is wrong?"
In which case basically her top gear is lower than your top gear - presumably for reasons mentioned above, that for wee folk it's considered better to have lower gears.
Might be possible to put smaller cogs on the back or a bigger chainring on the front?
"I'm sure I remember something about tall gears being bad for younger people, as it encourages weird muscular/skeletal development?"
Quite right - there are pedantically enforced upper limits on gearing for youth track cyclists. And rightly so, as teenage knees have their limits.
(Slightly OT but there is a similar danger in fitting young feet into clipless pedals too soon).
"limits on gearing for youth track cyclists"
Is it just track now? Pretty sure used to be road too.
"And rightly so, as teenage knees have their limits"
And adults...
When I was a kid there was a certain macho 'necessity' to ride in top gear as much as possible.
But then a normal chainset was 52/49!
Californian mountains changed the world.
Ahhh. If chdot's link is the same bike, then she's on 18-49" of gear, which is teensy by adult standards and evidently too low for her.
She will, however, be able to develop a fast 'n smooth spinning style, which will count in her favour when she moves on to larger, higher geared bikes. :-) She could become an ace track sprinter.
"She could become an ace track sprinter"
But she'd have to move to Glasgow...
How about a velodrome in Harrison Park?
@chdot - can confirm that there's still a feeling among kids (sample size = 1, but another girl a bit older than miniSRD) that the higher a gear you can manage the better a cyclist you are. So maybe keeping the gears low is a good thing.
I suppose the main consideration would be whether she's finding it hard work keeping up, and isn't enjoying the ride so much as if she was turning a slightly bigger gear
App doesn't appear to deal with hub gears. There is one for Bromptons here:
It takes account of hub gearing
Nobody seems to have the 13/16 sprockets for the Brompton 6 speed at the moment so I'm about to fit a 12/16 combo on one of my 6 speeds. This is actually the set for the 2 speed. It will raise the gearing by about 8% on the smaller sprocket. Top gear will now be 108" and the jumps will not be quite as even as they should be.
<pet_peev> If it's chain driven it's a sprocket, not a cog. </pet_peev>
Did you happen to note the speed you were going at, SRD?
nope. not that fast. essentially our speed was limited by hers, and what struck me was that she was pedaling a lot more than we were. We felt that we were 'going slow' and here she was pedaling frantically. which is what led me to start this thread.
<pet_peev> If it's chain driven it's a sprocket, not a cog. </pet_peev>
'Cog' is synonymous and engineeringly interchangeable with 'tooth'.
However, the compound word cog-wheel entered the English language only about 200 years later in about 1420, and it took another 400 years for 'cog-wheel' to be considered comprising teeth rather than cogs. So when fervent bicyclists talk about the size of their cog, or being 'on the cog' or whatevever, it's probably only the vernacular.
Weefolding is however completely correct about sprocket being associated with a chain drive, or anything analogous such as the holes in a roll of film. That word didn't appear until the mid-18th century.
The Islabike has (as pointed out) a tiny big ring so to replicate her gearing you would probably be in gear 4 or 5 on the Helios (yours has Alfine so tricky to compare directly).
Bring the Islabike round to shop! We have rollers now so you can see how her bike compares with a multigeared ICE trike with 20" wheel.
Also.... Other thing we have done at school sessions was have a roll down event. Line up all the bikes on playground with slight slope and let each person roll on bike till it stopped. No pedalling. K's lesser mass would mean that she wouldn't go as far whatever bike she chose. Like a version of the Innocent Tunnel roll down.
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