Advertise on Bikeforums.net



User Tag List

Page 1 of 2 12 LastLast
Results 1 to 25 of 34
  1. #1
    Beausage is Beautiful Fugazi Dave's Avatar
    Join Date
    Oct 2003
    Location
    Chicago, IL
    My Bikes
    2006 Langster, which I actually like.
    Posts
    5,456
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Skid patch comparison chart...

    So....someone should make a chart in Excel or something with cog sizes on the x axis, chainring sizes on the Y axis, and # of resulting skid patches for corresponding ratios.

    I could do this myself, but I've already fallen asleep twice at my desk tonight. Time for bed.

  2. #2
    live free or die trying humancongereel's Avatar
    Join Date
    Oct 2005
    Location
    where i lay my head is home.
    My Bikes
    bianchi pista workhorse, cannondale r1000, mountain bike fixed conversion
    Posts
    6,999
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    it's been done already. ****ing wish i could remember what thread it's in.
    have:ea50 flats, black, light, stiff.
    144 bcd 3/32" 49t sugino track chainring, possibly 75.

    want: risers, light, stiff, 1", black if that can be
    144 bcd 46t or 47t chainring any kind or width

  3. #3
    live free or die trying humancongereel's Avatar
    Join Date
    Oct 2005
    Location
    where i lay my head is home.
    My Bikes
    bianchi pista workhorse, cannondale r1000, mountain bike fixed conversion
    Posts
    6,999
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    WTF are "skidpatches"?

    okay, down the page halfway. some nerdy math about skid patches courtesy of shants and someone else who was talking in math terms waaaaaaaaay above this dude's head.
    have:ea50 flats, black, light, stiff.
    144 bcd 3/32" 49t sugino track chainring, possibly 75.

    want: risers, light, stiff, 1", black if that can be
    144 bcd 46t or 47t chainring any kind or width

  4. #4
    shadybikes jacobpriest's Avatar
    Join Date
    Feb 2006
    Location
    Waco/Plano/Dallas/Brooklyn, Texas
    Posts
    1,141
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    i have it... hold on

  5. #5
    shadybikes jacobpriest's Avatar
    Join Date
    Feb 2006
    Location
    Waco/Plano/Dallas/Brooklyn, Texas
    Posts
    1,141
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

  6. #6
    ROBOTS... Spor's Avatar
    Join Date
    Nov 2005
    Location
    Berkeley, CA
    Posts
    169
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Code:
    
    function skidpatchchart(),
    
    gears = [30:66];
    cogs = 4:30;
    fprintf('    cogs');
    for k = 1:length(cogs);
        fprintf('%4d',cogs(k));
    end
    fprintf('\ngears\n');
    for j = 1:length(gears),
        fprintf('%4d    ',gears(j));
        for k = 1:length(cogs),
            fprintf('%4d',skidpatch(gears(j),cogs(k)));
        end
        fprintf('\n');
    end
    
    function sp = skidpatch(g,c),
    % this is totally non optimal code, but i had fun writing it
    
    primes = setdiff(1:100,unique(repmat(2:50,49,1).*repmat([2:50]',1,49)));
    primes = primes(2:end);
    
    sp = c;
    while (g>primes(1)),
        if g/primes(1) == floor(g/primes(1)) & sp/primes(1) == floor(sp/primes(1)),
            sp = sp/primes(1);
            g = g/primes(1);
        else
            primes = primes(2:end);
        end
    end
            
    
    
        cogs   4   5   6   7   8   9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30
    gears
      30       2   1   1   7   4   3   1  11   2  13   7   1   8  17   3  19   2   7  11  23   4   5  13   9  14  29   5
      31       4   5   6   7   8   9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30
      32       1   5   3   7   1   9   5  11   3  13   7  15   1  17   9  19   5  21  11  23   3  25  13  27   7  29  15
      33       4   5   2   7   8   3  10   1   4  13  14   5  16  17   6  19  20   7   2  23   8  25  26   9  28  29  10
      34       2   5   3   7   4   9   5  11   6  13   7  15   8   1   9  19  10  21  11  23  12  25  13  27  14  29  15
      35       4   1   6   1   8   9   2  11  12  13   2   3  16  17  18  19   4   3  22  23  24   5  26  27   4  29   6
      36       1   5   1   7   2   1   5  11   1  13   7   5   4  17   1  19   5   7  11  23   2  25  13   3   7  29   5
      37       4   5   6   7   8   9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30
      38       2   5   3   7   4   9   5  11   6  13   7  15   8  17   9   1  10  21  11  23  12  25  13  27  14  29  15
      39       4   5   2   7   8   3  10  11   4   1  14   5  16  17   6  19  20   7  22  23   8  25   2   9  28  29  10
      40       1   1   3   7   1   9   1  11   3  13   7   3   2  17   9  19   1  21  11  23   3   5  13  27   7  29   3
      41       4   5   6   7   8   9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30
      42       2   5   1   1   4   3   5  11   2  13   1   5   8  17   3  19  10   1  11  23   4  25  13   9   2  29   5
      43       4   5   6   7   8   9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30
      44       1   5   3   7   2   9   5   1   3  13   7  15   4  17   9  19   5  21   1  23   6  25  13  27   7  29  15
      45       4   1   2   7   8   1   2  11   4  13  14   1  16  17   2  19   4   7  22  23   8   5  26   3  28  29   2
      46       2   5   3   7   4   9   5  11   6  13   7  15   8  17   9  19  10  21  11   1  12  25  13  27  14  29  15
      47       4   5   6   7   8   9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30
      48       1   5   1   7   1   3   5  11   1  13   7   5   1  17   3  19   5   7  11  23   1  25  13   9   7  29   5
      49       4   5   6   1   8   9  10  11  12  13   2  15  16  17  18  19  20   3  22  23  24  25  26  27   4  29  30
      50       2   1   3   7   4   9   1  11   6  13   7   3   8  17   9  19   2  21  11  23  12   1  13  27  14  29   3
      51       4   5   2   7   8   3  10  11   4  13  14   5  16   1   6  19  20   7  22  23   8  25  26   9  28  29  10
      52       1   5   3   7   2   9   5  11   3   1   7  15   4  17   9  19   5  21  11  23   6  25   1  27   7  29  15
      53       4   5   6   7   8   9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30
      54       2   5   1   7   4   1   5  11   2  13   7   5   8  17   1  19  10   7  11  23   4  25  13   1  14  29   5
      55       4   1   6   7   8   9   2   1  12  13  14   3  16  17  18  19   4  21   2  23  24   5  26  27  28  29   6
      56       1   5   3   1   1   9   5  11   3  13   1  15   2  17   9  19   5   3  11  23   3  25  13  27   1  29  15
      57       4   5   2   7   8   3  10  11   4  13  14   5  16  17   6   1  20   7  22  23   8  25  26   9  28  29  10
      58       2   5   3   7   4   9   5  11   6  13   7  15   8  17   9  19  10  21  11  23  12  25  13  27  14   1  15
      59       4   5   6   7   8   9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30
      60       1   1   1   7   2   3   1  11   1  13   7   1   4  17   3  19   1   7  11  23   2   5  13   9   7  29   1
      61       4   5   6   7   8   9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30
      62       2   5   3   7   4   9   5  11   6  13   7  15   8  17   9  19  10  21  11  23  12  25  13  27  14  29  15
      63       4   5   2   1   8   1  10  11   4  13   2   5  16  17   2  19  20   1  22  23   8  25  26   3   4  29  10
      64       1   5   3   7   1   9   5  11   3  13   7  15   1  17   9  19   5  21  11  23   3  25  13  27   7  29  15
      65       4   1   6   7   8   9   2  11  12   1  14   3  16  17  18  19   4  21  22  23  24   5   2  27  28  29   6
      66       2   5   1   7   4   3   5   1   2  13   7   5   8  17   3  19  10   7   1  23   4  25  13   9  14  29   5

  7. #7
    shadybikes jacobpriest's Avatar
    Join Date
    Feb 2006
    Location
    Waco/Plano/Dallas/Brooklyn, Texas
    Posts
    1,141
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    damn! 60x30 only has one. i was gonna switch to that until now!

  8. #8
    live free or die trying humancongereel's Avatar
    Join Date
    Oct 2005
    Location
    where i lay my head is home.
    My Bikes
    bianchi pista workhorse, cannondale r1000, mountain bike fixed conversion
    Posts
    6,999
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    yeah, 64x4 only has one, so i've changed my mind about switching to that.
    have:ea50 flats, black, light, stiff.
    144 bcd 3/32" 49t sugino track chainring, possibly 75.

    want: risers, light, stiff, 1", black if that can be
    144 bcd 46t or 47t chainring any kind or width

  9. #9
    ROBOTS... Spor's Avatar
    Join Date
    Nov 2005
    Location
    Berkeley, CA
    Posts
    169
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by jacobpriest
    damn! 60x30 only has one. i was gonna switch to that until now!
    Quote Originally Posted by humancongereel
    yeah, 64x4 only has one, so i've changed my mind about switching to that.
    glad i could be of service

  10. #10
    live free or die trying humancongereel's Avatar
    Join Date
    Oct 2005
    Location
    where i lay my head is home.
    My Bikes
    bianchi pista workhorse, cannondale r1000, mountain bike fixed conversion
    Posts
    6,999
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    ha ha...while i was joking about it, i think that the wide range of combinations that chart affords is really nice.
    have:ea50 flats, black, light, stiff.
    144 bcd 3/32" 49t sugino track chainring, possibly 75.

    want: risers, light, stiff, 1", black if that can be
    144 bcd 46t or 47t chainring any kind or width

  11. #11
    don't pedal backwards... MacG's Avatar
    Join Date
    Jul 2005
    Location
    Minneapolis
    My Bikes
    Surly Long Haul Trucker set up for commuting and loaded touring, old Sekine road frame converted to fixed-gear, various beaters and weird bikes, waiting on the frame for my Surly Big Dummy build
    Posts
    754
    Mentioned
    0 Post(s)
    Tagged
    1 Thread(s)
    this does ratios, gear inches, skid patches, mph@rpm, rpm@mph, etc:

    http://grit.homelinux.net/gi/
    from Minneapolis, with bike love

  12. #12
    Frozen in carbonite Grimlock's Avatar
    Join Date
    Oct 2004
    Location
    Ottawa
    My Bikes
    '85 Full Cycle Cycle.
    Posts
    801
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Does it make sense to anyone else that the 30x30 combination has 5 skidpatches? Why wouldn't that have just 1?

  13. #13
    無くなった HereNT's Avatar
    Join Date
    Mar 2004
    Location
    Sci-Fi Wasabi
    My Bikes
    I built the Bianchi track bike back up today.
    Posts
    5,073
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I think if you're running 30x30, you could pretty much skid anywhere in the rotation. It should be 8 skid patches, but laid down on it's side...

  14. #14
    Frozen in carbonite Grimlock's Avatar
    Join Date
    Oct 2004
    Location
    Ottawa
    My Bikes
    '85 Full Cycle Cycle.
    Posts
    801
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I was just wondering if the math was right. If that combination wasn't true, are there others that don't work?
    Mind you, if you're going to ride a 1:1 ratio, 47 tooth cogs are really the way to go.

  15. #15
    Senior Member
    Join Date
    Nov 2004
    Posts
    2,544
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Grimlock
    Does it make sense to anyone else that the 30x30 combination has 5 skidpatches? Why wouldn't that have just 1?
    Yeah 30x30 would have one skid patch.

    Basically you you take your gear ratio as a fraction, reduce it and take the reduced cog - that's your number skid patches. For example, I ride 46x16.

    As a fraction: 46/16
    Reduced: 23/8

    I have 8 skid patches.

  16. #16
    don't pedal backwards... MacG's Avatar
    Join Date
    Jul 2005
    Location
    Minneapolis
    My Bikes
    Surly Long Haul Trucker set up for commuting and loaded touring, old Sekine road frame converted to fixed-gear, various beaters and weird bikes, waiting on the frame for my Surly Big Dummy build
    Posts
    754
    Mentioned
    0 Post(s)
    Tagged
    1 Thread(s)
    any time you run a gear ratio that comes out to an even integer (1:1, 2:1, 3:1, 4:1, etc.) you will get exactly one skid patch. With a 1:1, when the pedals are in the position used to skid, the tire will always be in exactly the same position. With a 2:1, the same thing happens, but the tire went around an extra time in the mean time. #:1 gives you two extra rotations before it stops at the same spot again.

    The most skid patches you can ever have is the same as the number of teeth on your cog. The best combinations are ones in which the cog tooth count and ring tooth count are relatively prime with regards to eachother. Using Yoshi's example, this would be any instance where you cannot reduce the fraction at all.
    from Minneapolis, with bike love

  17. #17
    Al noisebeam's Avatar
    Join Date
    Jun 2004
    Location
    AZ
    My Bikes
    Cannondale SuperSix, Lemond Poprad. Retired: Jamis Sputnik, Centurion LeMans Fixed, Diamond Back ascent ex
    Posts
    13,964
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by jacobpriest
    Thanks for posting it!

    Al

  18. #18
    i am sure that i hate you spud's Avatar
    Join Date
    Aug 2005
    Location
    703
    My Bikes
    'Cha-ruzu Fosuta Orusan Kein' Fuji Track (2005), Schwinn Tank MTB (?), Fuji Royale (1979)
    Posts
    3,230
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    you can get a few more in most situations if you can learn to skid with your other foot too
    putting the pi back in pirate!
    Itís an upstanding member of the solar system
    Apply the laws of earth and make it a victim
    Of Proposition 187

  19. #19
    Senior Member
    Join Date
    Aug 2005
    Location
    Albany, CA
    Posts
    144
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Whenever I see this great table, I've always wondered what the yellow highlighting is supposed to indicate. Any ideas?

  20. #20
    i am sure that i hate you spud's Avatar
    Join Date
    Aug 2005
    Location
    703
    My Bikes
    'Cha-ruzu Fosuta Orusan Kein' Fuji Track (2005), Schwinn Tank MTB (?), Fuji Royale (1979)
    Posts
    3,230
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    he was highlighting the combinations that were 3.0 or slightly below, and then checking the skid patches
    putting the pi back in pirate!
    Itís an upstanding member of the solar system
    Apply the laws of earth and make it a victim
    Of Proposition 187

  21. #21
    Al noisebeam's Avatar
    Join Date
    Jun 2004
    Location
    AZ
    My Bikes
    Cannondale SuperSix, Lemond Poprad. Retired: Jamis Sputnik, Centurion LeMans Fixed, Diamond Back ascent ex
    Posts
    13,964
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by spud
    he was highlighting the combinations that were 3.0 or slightly below, and then checking the skid patches
    That was basically the intent. To mark which ratios are close to 3.0, which is a good starting ratio for most flatlanders who use 700 wheels. The yellow on both charts just makes it easier to quickly x-reference ratios with skid patches.

    I also bolded skid patches that were 7 or above as this roughly keeps the wear evenly distributed. (A skid patch often nds up being about a 1/8th circumference on the tire as most folks are not static in the skid, but of course the wear is concentrated in the center of that patch.)

    Yes, this assumes singled sided skidding only. If your ambi then double the number of skid patches.

    Al

  22. #22
    i am sure that i hate you spud's Avatar
    Join Date
    Aug 2005
    Location
    703
    My Bikes
    'Cha-ruzu Fosuta Orusan Kein' Fuji Track (2005), Schwinn Tank MTB (?), Fuji Royale (1979)
    Posts
    3,230
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    thanks for the chart, its pretty useful
    putting the pi back in pirate!
    Itís an upstanding member of the solar system
    Apply the laws of earth and make it a victim
    Of Proposition 187

  23. #23
    無くなった HereNT's Avatar
    Join Date
    Mar 2004
    Location
    Sci-Fi Wasabi
    My Bikes
    I built the Bianchi track bike back up today.
    Posts
    5,073
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Huh, I just went from 8 skid patches to, um 8 skid patches. I guess not much is different from 46x16 to 42x16, except that I'm going to be spinning a lot more...

  24. #24
    i am sure that i hate you spud's Avatar
    Join Date
    Aug 2005
    Location
    703
    My Bikes
    'Cha-ruzu Fosuta Orusan Kein' Fuji Track (2005), Schwinn Tank MTB (?), Fuji Royale (1979)
    Posts
    3,230
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    get a 17t cog
    putting the pi back in pirate!
    Itís an upstanding member of the solar system
    Apply the laws of earth and make it a victim
    Of Proposition 187

  25. #25
    無くなった HereNT's Avatar
    Join Date
    Mar 2004
    Location
    Sci-Fi Wasabi
    My Bikes
    I built the Bianchi track bike back up today.
    Posts
    5,073
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    DA doesn't make 17t cogs, do they?

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •