Re: 20" vs 24" for sloping trail, and crank length question
On Tue, 30 Apr 2002 23:37:35 -0500, teachndad
>Into muni, huh. Glad to hear it. What hills are there in The
>Netherlands - forgive me if I am wrong about your local.
We have some decent hills in the Netherlands, our highest point is 321
m (just over 1000 ft - don’t laugh). I’m in the flatter western part
of the country but still we have some park areas within unicycling
distance which are technical, at least for me. I plan to make some
photos this weekend (weather permitting) and put them up.
>I think there is more to just comparing the ratios to the two unis you
>describe. The 20" just seems like you would be spinning way to much
>over any distance like a short mile or 2km. While the ratios are
>compatible, the distance covered per revolution is quite different.
I realise that, and I wouldn’t want a 20" muni. I was just wondering
if 150’s on my 24" would permit equally technical stuff. I think to
just try 150’s on my Sem 24" is a good idea, thanks for the hint.
>Go with the 150’s on the 24 to get the hang of stuff, then buy a real
>muni. I think you will be really happy with a 2.6 tire. The Gazz 2.6
>is a great tire if your frame can’t take the 3.0.
Would the Sem XLW take a 3.0 tyre? I love Semcycle generally.
On Wed, 1 May 2002 02:35:30 -0500, john_childs
>A 24" wheel with 150mm cranks has a Ct/Cp ratio of 2
>A 20" wheel with 125mm cranks has a Ct/Cp ratio of 2
>So a 24" wheel with 150mm cranks will feel about the same as a 20" wheel
>with 125mm cranks.
That was my calculation too (can do it without spreadsheet, just my
grey cells), and from the answers I gather it is approximately true
also in practice.
On Wed, 1 May 2002 07:53:31 -0500, U-Turn
>Also on the slopes, the 20" will not handle irregularities in the slope
>nearly as well as the larger wheels, even if the leverage is the same. A
>bump on the hill may be twice as steep locally as the surrounding slope.
>A larger wheel with lower pressure has a smaller sense of “local”.
Good point but almost ambiguously phrased. You mean the sensitivity of
the 24" to locality is smaller. Conversely, the length scale with
which the 24" looks at locality etc is larger.
On Wed, 1 May 2002 09:31:13 -0700, John Foss <firstname.lastname@example.org>
>> Wheel and crank combinations with the same ratio will give
>> you the same mechanical advantage.
>That covers the math.
I have a mathematical argument that a 20" with 125’s would give a bit
more leverage than 24" with 150’s. I would need a lot of words to
explain. I’m happy to do so if anyone wonders.
On Wed, 01 May 2002 17:21:35 GMT, “Joe Marshall”
>Yes, but if you have the same crank length to wheel size ratio you should be
>able to go just as fast, as your legs have to move at the same speed to go
>the same distance. Hence why a 24" wheel with 90mm cranks is much faster
>than a 26" wheel with 150mm cranks. Spinning very fast on short cranks is
>just as easy as spinning normal speed on normal length cranks.
I believe your example, and in general your assessment that shorter
cranks give increased speed. However, I would say that this would not
be the same ratio, i.e. cranks shorter by 20% would give less than a
20% speed gain because you still have to muster the rotational speed.
And I believe wheel larger by 20% would also give less than 20% speed
gain, but closer to 20% than in the crank length example.
Thanks for all the responses!
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