Conference noted::bicycle

2039.0. "Technology strikes again......." by IDEFIX::HEMMINGS (Lanterne Rouge) Wed Aug 14 1991 10:17

Hey, you computing and gear ratio freaks........

I just bought a book about "Cols of the Southern Alps", which contains 
profiles and maps of the majority of cols together with info about road 
conditions, plus feeding and watering places en route.  Absolutely 
fascinating...

It also gives details of a service available through Minitel (3615 TOTEM for 
those who can get it), whereby you can get recommendations on gear ratios, 
speeds and rpm for chosen percentages.

The idea is that you enter the speed you can keep up for some time on the flat 
(I think an earlier version recommended a flat 100 km trip), and the combined
weight of yourself and velo.  This gives you your power output, from which 
they make some assumptions about friction and air resistance and optimum rpm.

For myself, I put in 88 kg and a level speed of 30 kph, which gave a power 
output of 214 watts.  They then suggested gearing of 32/42/52 by 
14,16,18,20,22,24 and the following table:(I added 28 kph for good measure) -

30 kph and 88 kg =214 watts	28 kph and 88 kg =182 watts	
---------------------------	---------------------------
 %  Vkph     Gear   RPM		 %  Vkph     Gear   RPM
 3  19    42x20(57)  71		 3  17    42x20(57)  63
 4  16,5  42x22(52)  68		 4  14    42x22(52)  59
 5  14    42x24(47)  64		 5  12    42x24(47)  54
 6  12,5  42x24(47)  56		 6  11    42x24(47)  49
 7  11    32x20(43)  55		 7   9,5  32x20(43)  47
 8  10    32x20(43)  49		 8   8,5  32x20(43)  42
 9   9    32x22(39)  49		 9   7,5  32x22(39)  42
10   8    32x24(36)  48		10   7    32x24(36)  41
11   7,5  32x24(36)  46		11   6,5  32x24(36)  38
12   7    32x24(36)  41		12   6    32x24(36)  36

Before anyone jumps in to say "Hey, I can roll up 5% on 52x12 with no 
trouble", you should realise that these figures are designed for long climbs, 
not 100 yard bursts, so we are talking about 10 km at a time......  I was very 
gratified to recall that on the Coll'Agnello (up to 2700m with last 10 at 10%) 
I was using 32x24 and my speedo registered 8 kph - can't say it was 
comfortable however.

Over the weekend I hope to get over to Entrevaux via the Col de Bleine, Col de 
Buis and Col des Felines - should be a chance to test out the figures a bit 
more, I just need to stick this table plus the profiles on my bars.....

    What are the numbers in parentheses?
    
    ed

	Sorry, the original was French style ie: metres/pedal rev, so I divided
by pi and multiplied by 39,3 to give the equivalent diameter of the front wheel
of an Old Ordinary....... (see some notes back).

    So the  numbers  in parens are in "gear inches", as they're called
    in the States.

    I was  interested  to see the low cadences. I try to keep above 80
    on  most  climbs  and always above 70, so I found it odd that they
    would  use  a  71  cadence  on a 3% climb all the way down to a 40
    cadence on a 12% climb (ouch).

    I know  I  tend  toward lower gears than most people, but I didn't
    realize  my  gearing was that much lower. I would certainly want a
    27"  gear  for  serious hills. I have a 20" gear on both my bikes,
    but  rarely  use it on hills that I normally ride. A long 10% hill
    will get me in it everytime.

--David

    
    I'd like to see what they would recommend with the constraint
    of a double (rather than triple) chain-ring.  That's what I use
    in the Alps, Rockies, etc. ... and I'm one of those rogue non-spinning
    gear pushers (tho' down to a 42x24 on Wolf Creek Pass a couple weeks ago).
    
    -john

    NEVER MIND