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 Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

 12-16-04, 02:45 PM #1 BostonFixed Banned. Thread Starter   Join Date: Oct 2004 Bikes: Posts: 4,416 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) More information about # of skidding spots with gearing... Headache inducing... http://www.dartmouth.edu/~ccatalan/skid.html
 12-16-04, 02:51 PM #2 dolface Iguana Subsystem     Join Date: Nov 2004 Location: san francisco Bikes: Posts: 4,016 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) that rocked! hooray for math-geek cyclists!
 12-16-04, 03:02 PM #3 ink1373 nothing: lasts forever     Join Date: Aug 2004 Location: minneapolis Bikes: Posts: 1,502 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) 43 teeth here i come!
 12-16-04, 03:03 PM #4 TimArchy Senior Member     Join Date: Jun 2003 Location: Atlanta Bikes: Zeus (Razesa) tarck, Giant TCR road, Eddy Merckx road, Fuji Touring Series IV for everything else Posts: 1,155 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) that page seems to make it a lot more complex than it needs to be. 48/16 = 3/1 = 3 so the back wheel goes around three times with each crank rotation and ends up in the same place. so if you always skid with the same foot forward, you always hit the same spot. this is true for all ratios that are whole numbers. 45/18 = 5/2 = 2.5 now the crank has to go around two times to get the rear wheel back in the same position so you have two places on the wheel. 48/15 = 16/5 = 3.2 here, the crank has to go around 5 times to get back to the same spot on the rear wheel so you've got 5 spots to hit. 48/17 = something with a lot of decimals. it won't reduce so the crank has to go around 17 times to hit the same place on the rear wheel. easy formula: reduce your ratio to the smallest denominator (chainring/cog). the denominator will tell you how many places you will skid on the rear wheel. (if you skid with either foot forward, double the number) much easier right? a month ago I taught a lesson to a 6th grade math class about ratios using my fix. tim
 12-16-04, 03:04 PM #5 adamkell 72 & Sunny     Join Date: Oct 2004 Location: Brooklyn Bikes: '93 Yamaguchi Pursuit track bike, Alan Super Record Posts: 1,103 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) nice use of applied math with the kiddies
 12-16-04, 03:11 PM #6 TimArchy Senior Member     Join Date: Jun 2003 Location: Atlanta Bikes: Zeus (Razesa) tarck, Giant TCR road, Eddy Merckx road, Fuji Touring Series IV for everything else Posts: 1,155 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) yeah, my mentor teacher liked it a lot. I'm teaching high school geometry and algebra next spring. I'm trying to think of lessons using cycling that I can use on them. tim
 12-16-04, 03:36 PM #7 HereNT 無くなった     Join Date: Mar 2004 Location: Sci-Fi Wasabi Bikes: I built the Bianchi track bike back up today. Posts: 5,073 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) 44/14 = 3.1428571428571428571428571428571 - dammit - I almost had the fabled pi gearing!!!! According to the last paragraph, taking the highest denominator (2) I have 7 patches to skid on... I don't see how he connects Sheldon with brakeless though... __________________ My thoughts on life. Minneapolis Bike Love.
 12-16-04, 03:44 PM #8 dolface Iguana Subsystem     Join Date: Nov 2004 Location: san francisco Bikes: Posts: 4,016 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) HereNT, he doesn't connect scheldon with brakeless; Though Sheldon Brown, the laws of several states and plain old common sense urge otherwise, many fixed gear riders choose to pilot their machines without brakes.
 12-16-04, 03:46 PM #9 HereNT 無くなった     Join Date: Mar 2004 Location: Sci-Fi Wasabi Bikes: I built the Bianchi track bike back up today. Posts: 5,073 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) Dang, losing that contact lens earlier must be affecting my eyesight or something. Found it again, but everythings kind of blurry out of that eye... __________________ My thoughts on life. Minneapolis Bike Love.
 12-16-04, 03:49 PM #10 BlastRadius Direct Hit Not Required     Join Date: Nov 2003 Location: San Bruno, CA Bikes: Leopard DC1, Ridley X-Fire, GT Zaskar 9r Posts: 6,193 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 1 Post(s) I'm glad I found that elusive 43 tooth 118bcd chainring on Ebay.
 12-16-04, 05:25 PM #11 TimArchy Senior Member     Join Date: Jun 2003 Location: Atlanta Bikes: Zeus (Razesa) tarck, Giant TCR road, Eddy Merckx road, Fuji Touring Series IV for everything else Posts: 1,155 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) damn... this thread's been Pi-jacked
 12-16-04, 05:32 PM #12 gh-ap BxTS     Join Date: Nov 2004 Location: Santa Rosa, CA Bikes: 1987 Centurion Dave Scott Ironman, 1988 Giant Kashmir, 1989 Trek 660 Posts: 280 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) what's 52-17, for a math ******?
 12-16-04, 05:38 PM #13 dolface Iguana Subsystem     Join Date: Nov 2004 Location: san francisco Bikes: Posts: 4,016 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) you've got 17 patches, since 17 is a prime number.
 12-16-04, 07:18 PM #14 gh-ap BxTS     Join Date: Nov 2004 Location: Santa Rosa, CA Bikes: 1987 Centurion Dave Scott Ironman, 1988 Giant Kashmir, 1989 Trek 660 Posts: 280 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) hooray!
 12-17-04, 06:47 AM #15 ephemeralskin as you wish, skeletor.     Join Date: Feb 2003 Location: Freiburg, Deutschland Bikes: Posts: 753 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) yup i think trevor worked all this out for us a while back. totally awesome. and now as of last week my new chainring is 43t. i also changed to a 3/32" drivetrain. hopefully ill take some pics in a week or so..
12-17-04, 10:15 AM   #16
Jumbo
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Quote:
 Originally Posted by BostonFixed Headache inducing... http://www.dartmouth.edu/~ccatalan/skid.html
Fan-diddely-tastic. Now i'm gonna translate this into my native language and put it in our magazine and pretend that i figured it out myself

 12-17-04, 11:39 AM #17 Gravityhatesme natural born loser   Join Date: Sep 2004 Bikes: Posts: 22 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) *drool*
12-17-04, 01:10 PM   #18
TimArchy
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Quote:
 Originally Posted by dolface you've got 17 patches, since 17 is a prime number.
it wouldn't matter if 17 was a prime number. if you ran a 51/17, you'd only have one skid patch since 51/17 = 3/1 = 3. whole number = one skid patch.

52/17 indeed gives 17 skid patches, but it's because 52 and 17 are mutually prime.

tim

 12-17-04, 01:34 PM #19 bostontrevor Retrogrouch in Training     Join Date: Sep 2004 Location: Knee-deep in the day-to-day Bikes: Posts: 5,484 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) relatively prime. edit: hey, lookit that, indeed "mutually prime" is also an acceptable term. I don't think I've ever heard it called thaht.
 12-17-04, 01:54 PM #20 dolface Iguana Subsystem     Join Date: Nov 2004 Location: san francisco Bikes: Posts: 4,016 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) heh heh, i was gonna point that out too, nice to know that both are correct. btw, TimArchy, thanks for correcting my comment. nice catch
 12-17-04, 02:08 PM #21 TimArchy Senior Member     Join Date: Jun 2003 Location: Atlanta Bikes: Zeus (Razesa) tarck, Giant TCR road, Eddy Merckx road, Fuji Touring Series IV for everything else Posts: 1,155 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) mutually prime, relatively prime... I can't remember which is correct. I took abstract algebra twice, but it was two years ago I figured that since they were prime relative to each other... tim
 12-17-04, 02:53 PM #22 BlastRadius Direct Hit Not Required     Join Date: Nov 2003 Location: San Bruno, CA Bikes: Leopard DC1, Ridley X-Fire, GT Zaskar 9r Posts: 6,193 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 1 Post(s) A prime chainring is what you want. Otherwise you'll need to do the calculation at the bottom.
 12-17-04, 03:02 PM #23 dolface Iguana Subsystem     Join Date: Nov 2004 Location: san francisco Bikes: Posts: 4,016 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) you don't need a prime chainring OR cog as long as they're prime relative to each other
 12-17-04, 03:14 PM #24 BlastRadius Direct Hit Not Required     Join Date: Nov 2003 Location: San Bruno, CA Bikes: Leopard DC1, Ridley X-Fire, GT Zaskar 9r Posts: 6,193 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 1 Post(s) Yes, but what is most flexible is a prime chainring. Then you can run pretty much any size cog and not have to worry.
12-17-04, 05:06 PM   #25
ryan_c
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Quote:
 Originally Posted by BlastRadius Yes, but what is most flexible is a prime chainring. Then you can run pretty much any size cog and not have to worry.
For anyone wondering, the prime chainrings of reasonable size would be 41, 43, 47, 53.
Justification of reasonable size: 37 seems a bit small, 61 a bit big. Certainly a good spread though.