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· Climbs like a sprinter...
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Discussion Starter · #1 · (Edited)
I happened to catch a Semi cresting an overpass last night so I went for a little drafting action. I maxed out at 44.49 mph before I spun out my 50x12 (109.5 gear inches w/700x23c tires and 172.5 cranks) but I'm trying to figure out how many RPM I was turning. I'm trying to figure out the formula to get the number but I are stoopid. As a side note - I drafted a farm truck earlier in the season and hit the exact same 44.49 mph.
 

· 'brifter' is f'ing stupid
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all i know is that crank arm length won't matter...other than that i have the same math handicap you do. but...according to the nifty app on my iphone, you'd be at roughly 136-137 rpm at about 44.4mph. nice! that would be a 10.1 200m, which on a 250m track would qualify you for a world cup sprint field any day! you'd have to lose the semi, tho:thumbsup:
 

· Climbs like a sprinter...
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Discussion Starter · #7 ·
pretender said:
Use a tape measure and some chalk to measure how far one revolution of the cranks at 50x12 carries you. Some 8th grade algebra, et voila.
109.5 inches. I'm a HS drop out and my algebraic skillz be lacking.
 

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2 and a quarter ...ish revolutions per second. I made a little crude calculator a while back when I had my fixie.

By the way, you were a spinning fool. I know that when I used to spin 2.5 revs per sec, I felt like my legs would fly out of sockets.
 

· Climbs like a sprinter...
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Discussion Starter · #11 ·
mechelaar said:
2 and a quarter ...ish revolutions per second. I made a little crude calculator a while back when I had my fixie.

By the way, you were a spinning fool. I know that when I used to spin 2.5 revs per sec, I felt like my legs would fly out of sockets.
So my cadence was around 135. Thanks. I'm used to it from years of BMX racing but I was only there for a couple of seconds and it was pretty sketchy.
 

· waterproof*
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bmxhacksaw said:
I've been there but don't see where to figure out cadence for a given gear ratio/speed.
you can back into it via the menu for "gear units"

so it gets 32.6mph at 100 rpm, and 39.1 mph at 120 rpm, so a little division and you get 137.7 rpm at 44.49

not such a fast cadence, really.
 

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Here, it's VERY crude but it works. You have to manually play with the revs per second to get the final speed to where you need it with the gear ratio you had the bike in.

http://www.cottonwoodfx.com/Gearing-Cadence-calculator.xlsx

I created it to figure out the gearing on my fixie to see what the top speed would be at the limit of my being able to spin but since I no longer care about that, I quit messing with it. By the way, right now it is set to 700X25 tire size. I think for 700X23 you have to change 215.5 to 209.6 in the cell A9 it is in centimeters so you have to move a decimal point one place to the left from the charts for the tire diameter that you get with the bike speedometers.

Edit: I changed it to the 700X23 tire size so you don't have to.
 
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