How much faster and I supposed to go?

Remember those threads about crank length and speed?

http://tinyurl.com/3295x
http://tinyurl.com/2kmng

Well, recently, I decided to try getting more speed by changing the
crank length. With that I ordered 145mm cranks. What I found out was
surprising:
I only went a tad faster with 145mm cranks. I rode around a .60 paved
loop - as fast as I could - 4 times.

The result, my average speed and top speed were less than 1 mph faster
with the 145mm cranks - and I didn't have *much* more endurance. In
other words, I peddled as fast as I could - even when it hurt. Top speed
was slightly faster (.6 mph) on the 145mm cranks.

My average speed with 145mm was 7.35 mph
My average speed with 170mm was 7.00 mph

How much faster am I supposed to go with the shorter cranks?
(I wasn't paying attention in math class to learn how to make this basic
calculation)


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ChangingLINKS.com - member

Wishing you Happiness, Joy and Laughter,
Drew Brown
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Ok, i'm far far from an expert, but I had some thoughts when I read
this.

I have a 24 inch and a 36 inch unicycle. I've been riding the 24 for
awhile, so i'm pretty good at riding, forwards anyways. I got the Coker
recently, so I haven't been riding for awhile. I haven't timed myself,
but I think I probably don't go a lot faster on the Coker, than my other
one. I think the reason it cause i'm just not used to going fast on a
unicycle, I pedal a lot slower on the coker than my 24. Now If I ride
the Coker more and more and get used to it, i'll probably fly compared
to my 24.

So your shorter cranks i'm thiking are kinda the same, just maybe not as
big as a difference, but your still kinda pedaling less, or at least
making a smaller circle. Maybe your muscles need to adjust to the
difference and get more used to the motion of a smaller circle. I don't
know how long you've been practicing, but i'd say compare the times
later when you've practiced more.

Like I said i'm just hypothesizing, it makes sense to me, but I could be
wrong, have a good day.

Andrew


--
KJ-52 - unicycler

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Note this e-mail is baKsed oJn -a sto5ry a2nd mIay bSe fictKional oEr
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I believe you are correct KJ-52.
However, my question is:
How much faster SHOULD I go IF I pedal at the same speed?



I am not afraid of the speed I go with the 145mm (whereas I WOULD be
afraid peddling that fast on a Coker). I am going "the same speed" and
working "just as" hard. I expected to go at least 1 mph faster with the
shorter cranks. What I have found so far is that I gain little speed
and lose abilities like getting into idling, going backwards and
forwards, stopping, descending, etc.
I am hoping someone like newtouni will calculate how much faster I
"should go" (on flat pavement). Seems like there are a lot of people who
can calculate it on this forum.


--
ChangingLINKS.com - member

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Drew Brown
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We'll base these calculations on the constant foot speed hypothesis.
This hypothesis is based on the idea that your foot speed turning the
cranks will stay constant for different crank lengths. Foot speed is
calculated based on how fast your foot is moving in a circle. When
spinning 170 mm cranks at 100 rpm your foot speed is going to be faster
than when spinning 145 mm cranks at 100 rpm.

So we can figure out what your foot speed is with 170 mm cranks when
going 7 mph. Then we can work backwards and figure out what speed you'd
need to go to get the same foot speed with 145 mm cranks.

This is a job for 'UniCalc' (http://tinyurl.com/2lekq). Plug in the
numbers and use trial and error to find the results.

Figure for a 24x3 muni your wheel diameter is about 25 inches.

Going 7 mph your cadence is going to be 94 rpm and your foot speed with
170 mm cranks is going to be 5.49 ft/sec.

Now we'll figure out how fast you'll need to go with 145 mm cranks to
keep your foot speed at about 5.5 ft/sec.

Experiment with the numbers in UniCalc and you find that you'll be
pedaling at 110 rpm and have a speed of 8.18 mph with the 145 mm cranks
while maintaining the 5.5 ft/sec foot speed.

So you can figure to gain 1.18 mph by switching to 145 mm cranks.
Assuming that the constant foot speed hypothesis is true.

Of course there is more to it than just constant foot speed. It depends
on how smoothly you can spin the pedals. How much wasted effort you
have in making balance corrections (by varying your pedal speed). And
other factors. If you're a perfectly efficient unicyclist then the
constant foot speed hypothesis is probably closer to the truth. If
you're not quite a perfectly efficient unicyclist yet then the constant
foot speed hypothesis is not going to be as close to reality.


--
john_childs - Guinness Mojo

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It's much simpler than that.

NEW CRANKS DIVIDED BY OLD CRANKS, MULTIPLIED BY SPEED.

If you accept the basic idea that your feet move at the same speed, then
shorter cranks mean your feet can do more revolutions per second, whilst
moving at the same speed.

If your cranks are half as long, your feet have half as far to go, so
they can do twice as many rpm.

If you do twice as many rpm, then you go twice as fast.

So, say you went from 6 inch cranks to 3 inch cranks, you'd be halving
your cranks and doubling your speed.
6/3 is the same as 2/1. (Just do 6 divided by 3 = and you will get the
answer 2)

So, going from 170 top 145, you use the same formula: original cranks
divided by new cranks:

170 divided by 145 = 1.17

Your new speed will be 1.17 x whatever it was before.

Or, if you went the other way, 145 divided by 170 = 0.85, so cahnging
back makes your speed 0.85 x whatever it is on the shorter cranks.

So, to calculate the approximate change of speed:

NEW CRANKS DIVIDED BY OLD CRANKS, MULTIPLIED BY SPEED.

That's all there is to the maths.

But what is speed? Maximum speed? Cruising speed? Average riding
speed over a mixed terrain journey? Shorter cranks will not affect all
of these identically, because other factors like skill, control,
acceleration/deceleration, and nerve come into it.

The "constant footspeed hypothesis" is a jokey name we give to a rough
and ready rule of thumb. I have ridden wheels sized 20, 24, 26, 28 and
36, and have used various lengths of cranks including 89, 102, 110, 125,
150, 170, and have put some effort into making comparisons. The
constant footspeed hypothesis is no more than an approximation, and only
really works for adjacent crank lengths (say 125 and 150) with all other
things being equal (wheel, tyre, terrain, rider etc.) and when the rider
is confident and in control.

The rider and cranks are the engine. The wheel is the gear. Choose the
cranks to suit the rider (we are all different sizes) and the wheel to
suit the speed or terrain. A big wheel is the way to go fast, a small
wheel is the way to go up hill.


--
Mikefule - Roland Hope School of Unicycling

Well, it all depends on what you mean by "semantics".
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On Sun, 30 May 2004 18:00:18 -0500, "ChangingLINKS.com" wrote:

How much faster am I supposed to go with the shorter cranks?
(I wasn't paying attention in math class to learn how to make this basic
calculation)

Andrew's advice is spot on, practice more. This is not a simple math
thing so paying attention in math classes wouldn't have helped you
much.

If the rotational speed of the cranks stays the same, you don't gain
any speed at all.

If the footspeed stays the same, you would do 7.00 x (170/145) = 8.21
mph.

In practice, you are likely to be between 7.00 and 8.21.

Klaas Bil - Newsgroup Addict
--
be sure to remove the saddle and simply sit on the seat post. this is far more comfortable - tennisgh22 on the comfort of Savage unis

From a lot of riding on my muni with 150s and 29-er with 125's, with
some minor experimentation with a muni with 125's and 29-er with 110's;
my conclusions about crank length in regard to speed a -

* a bigger wheel size has more affect on speed than crank length

* the speed/smoothness benefits of a bigger wheel/shorter crank manifest
mainly in constant cruising i.e. I can go as fast on the muni for short
bursts, but for going fast for a sustained longish distance the 29-er is
much better

* I'm much happier going full blast on the muni, as I know I'll be OK if
something goes wrong; on the 29-er I have little desire to go at max
speed because it will be problematic if I come off while doing it

* in terms of getting somewhere fast (and I'm not the first to point
this out), sometimes the slower uni can work out faster. For example,
for a ride to the shopping center in Sheffield, the 29-er should be
fastest, but, on the muni I can utilise it's greater control to make
full use of pavements/short cuts and be very confident around
pedestrians; whereas, with the 29-er, it's either struggle on the
pavements, with lots of dismounts, or go on the roads, with traffic
lights etc.

Similarly, people with Cokers often point out that, on rougher terrain,
150's work out faster than 125's because of more control and less UPDs.


--
onewheeldave - Semi Skilled Unicyclist

"He's also been known to indulge in a spot of flame juggling - but it's
the Muni that really fires him up."

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ChangingLINKS.com wrote:
Remember those threads about crank length and speed?

http://tinyurl.com/3295x
http://tinyurl.com/2kmng

Well, recently, I decided to try getting more speed by changing the
crank length. With that I ordered 145mm cranks. What I found out was
surprising:
I only went a tad faster with 145mm cranks. I rode around a .60 paved
loop - as fast as I could - 4 times.

The result, my average speed and top speed were less than 1 mph faster
with the 145mm cranks - and I didn't have *much* more endurance. In
other words, I peddled as fast as I could - even when it hurt. Top
speed was slightly faster (.6 mph) on the 145mm cranks.

My average speed with 145mm was 7.35 mph
My average speed with 170mm was 7.00 mph

How much faster am I supposed to go with the shorter cranks?
(I wasn't paying attention in math class to learn how to make this
basic calculation)

How long were your old cranks?