Advertise on Bikeforums.net



User Tag List

Page 1 of 2 12 LastLast
Results 1 to 25 of 50
  1. #1
    Aluminium Crusader :-)
    Join Date
    Apr 2004
    Location
    Melbourne, Australia
    Posts
    9,872
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)

    Steering is too twitchy, what can I do?

    Will a longer raked fork make a big difference?

    How long do rakes get (or "trail", or whatever it's called)?

  2. #2
    Senior Member Don Cook's Avatar
    Join Date
    Sep 2003
    Location
    Memphis TN
    My Bikes
    Raleigh, Benotto, Schwinn, Trek
    Posts
    816
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Take a look at this site :
    http://www.phred.org/~josh/bike/trail.html

  3. #3
    cycles per second Gonzo Bob's Avatar
    Join Date
    Oct 2003
    Location
    Minnesota
    My Bikes
    Vitus Aluminum, DiamondBack Apex, Softride Powerwing 700, "Generic" Ishiwata 022, Trek OCLV 110
    Posts
    1,790
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by 531Aussie
    Will a longer raked fork make a big difference?

    How long do rakes get (or "trail", or whatever it's called)?
    I believe that if you want to increase stability, you want to *decrease* rake, not increase it. Actually, you want to increase the trail, but if you consider head tube angle and tire size fixed, decreasing rake is the only way to do this.

  4. #4
    Senior Member Retro Grouch's Avatar
    Join Date
    Feb 2004
    Location
    St Peters, Missouri
    My Bikes
    Rans Enduro Sport, Hase Kettweisel Tandem, Merin Bear Valley beater bike
    Posts
    23,718
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by 531Aussie
    Will a longer raked fork make a big difference?

    How long do rakes get (or "trail", or whatever it's called)?
    Before you do anything, check your headset adjustment. The handlebar should flop from side to side by itself if you lean your bike over. A too tight headset will handle very twitchy.

    If that's not it, then you need to get a "straighter" fork to relax your steering.

  5. #5
    don d.
    Guest
    What is the head angle of the bike? It is impossible to determine if a shorter or longer fork will make your bike less "twitchy" without considering the head angle and geometry of the bike.

    Of course it could be a mechanical problem, and you should eliminate those variables first.
    Last edited by don d.; 07-13-04 at 09:57 PM.

  6. #6
    ÖöÖöÖöÖöÖö Dannihilator's Avatar
    Join Date
    Oct 2002
    Location
    Annandale, NJ.
    My Bikes
    2014 Surly Steamroller, 1977 Puch Pathfinder
    Posts
    18,787
    Mentioned
    20 Post(s)
    Tagged
    1 Thread(s)
    Stable equals low BB height there for you need less rake or you should work on your riding position.
    Strike like an eagle and sacrifice the dove.
    Words and Stuff.

  7. #7
    Aluminium Crusader :-)
    Join Date
    Apr 2004
    Location
    Melbourne, Australia
    Posts
    9,872
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by don d.
    What is the head angle of the bike? It is impossible to determine if a shorter or longer fork will make your bike less "twitchy" without considering the head angle and geometry of the bike.

    Of course it could be a mechanical problem, and you should eliminate those variables first.
    Not sure about the head tube angle. Someone's looking at it today

  8. #8
    Senior Member bg4533's Avatar
    Join Date
    Jul 2003
    Location
    OH
    Posts
    634
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Is this a new bike? If so, maybe you need more time to get used to it. I found my road bike too twitchy after I first got it, but over the course of a few hundred miles I am now finding it perfect.

  9. #9
    Aluminium Crusader :-)
    Join Date
    Apr 2004
    Location
    Melbourne, Australia
    Posts
    9,872
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by bg4533
    Is this a new bike? If so, maybe you need more time to get used to it. I found my road bike too twitchy after I first got it, but over the course of a few hundred miles I am now finding it perfect.
    Yeah, it's new, but I bought a frame only -- no fork, so I'm not sure what fork is the ideal match.
    I've been riding it for a week, and it still feels a bit unstable, especially if I relax my hands on the bars, or take one hand off.

  10. #10
    Aluminium Crusader :-)
    Join Date
    Apr 2004
    Location
    Melbourne, Australia
    Posts
    9,872
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    What if I put on an Ouzo Pro with a 50mm rake?

  11. #11
    Senior Member
    Join Date
    Dec 2003
    Posts
    1,295
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by 531Aussie
    What if I put on an Ouzo Pro with a 50mm rake?
    Suggest you do a google search for rake and trail. Then you'll know "what" and you won't have to guess. 50 mm sounds pretty extreme and very unstable. Try 43 mm for a 72 to 73 degree head tube.

    Al

  12. #12
    don d.
    Guest
    Quote Originally Posted by 531Aussie
    What if I put on an Ouzo Pro with a 50mm rake?
    To obtain what is called "neutral" steering, a 50mm fork would work well with a 72 deg head angle. Neutral steering means that the bike will respond to deliberate input you put into the front end instead of having a tendency to oversteer when you make subtle changes in your position like reach for a water bottle or take your hands off the bars. Some people consider neutral steering "slow" because the bike only does what you tell it to do.

    A bike with a 73 deg head angle achieves neutral with a 45 mm fork rake, and the steeper the head angle, the shorter the rake as a rule, so a 74 likes a 40, so on and so on. Of course a few millimeters may not have a huge difference on handling, but the difference between a 40 and a 50 mm fork can be quite pronounced on a bike.

    In general, the shorter you make a fork in relation to the head angle, the longer the trail. The longer the trail, the less likely a bike is to oversteer, or be twitchy. If you make the trail too long, the bike will be slow to turn at low speed, stable at high speed, but not very quick handling at high speed. If you make the trail too short, it will be quicker handling at low speed and very sensitive to rider input at high speed(twitchy). So if you put a long rake(50mm) on a steep head angle(74), you will shorten the trail and you will get a twitchy front end.

    The other measurement to consider is the measurement from the fork crown race seat to the front axle center. A bike is designed to sit at it's correct head angle with a specific fork crown race/axle center dimension. If you buy a fork that is 5mm longer than what a frame is designed to accomodate, the front end will sit higher, which effectively reduces the head angle some. If you buy a fork that is 5mm shorter, the front end will sit lower, which effectively increases the head angle some.

    The Reynolds Ouzo Pro with a 50mm rake has a 372mm fork crown race to axle center dimension. You can measure the fork that came with your bike and see what it is to see if it is the same.

    Notice the dimension "F" on this frame specification chart. This dimension is the fork length. That is the dimension I'm referring to. As you can see, these frames were designed to take a fork 367mm long to maintain the designed head angle.

    http://cbike.com/colnagospecs.htm

    Just a word of caution: 9 out of 10 bike mechanics will look at you like you are speaking Inuit if you ask them these questions. Be prepared to do the measurements or research them yourself.

  13. #13
    Senior Member Nessism's Avatar
    Join Date
    Jun 2004
    Location
    Torrance, CA
    My Bikes
    Homebuilt steel
    Posts
    2,324
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by don d.
    The other measurement to consider is the measurement from the fork crown race seat to the front axle center. A bike is designed to sit at it's correct head angle with a specific fork crown race/axle center dimension. If you buy a fork that is 5mm longer than what a frame is designed to accomodate, the front end will sit higher, which effectively reduces the head angle some. If you buy a fork that is 5mm shorter, the front end will sit lower, which effectively increases the head angle some.

    The Reynolds Ouzo Pro with a 50mm rake has a 372mm fork crown race to axle center dimension. You can measure the fork that came with your bike and see what it is to see if it is the same.

    Notice the dimension "F" on this frame specification chart. This dimension is the fork length. That is the dimension I'm referring to. As you can see, these frames were designed to take a fork 367mm long to maintain the designed head angle.

    http://cbike.com/colnagospecs.htm

    Just a word of caution: 9 out of 10 bike mechanics will look at you like you are speaking Inuit if you ask them these questions. Be prepared to do the measurements or research them yourself.

    Seeing as how we're picking nits here regarding fork lengths and such...Reynolds, along with most other fork manufactuers, measure fork length parallel to the steerer tube. This is different than Colnago's "F" dimension which discribes fork length from the crown to the axle. A Colnago fork is actually 364.5 mm when measured the same way Reynolds does.

    Sorry to pick, the post is very good overall. Fork length is one of my pet peeves and I've done a lot of study on the lengths of various aftermarket forks.

    Ed

  14. #14
    don d.
    Guest
    Quote Originally Posted by Nessism
    Seeing as how we're picking nits here regarding fork lengths and such...Reynolds, along with most other fork manufactuers, measure fork length parallel to the steerer tube. This is different than Colnago's "F" dimension which discribes fork length from the crown to the axle. A Colnago fork is actually 364.5 mm when measured the same way Reynolds does.

    Sorry to pick, the post is very good overall. Fork length is one of my pet peeves and I've done a lot of study on the lengths of various aftermarket forks.

    Ed
    This has always been a pet peeve of mine as well. The whole fork as component concept leaves me cold. It just has to much to do with handling and ride for me to consider it something other than an integrated part of the frame.

    But when you say that Reynolds measures parallel to the steerer tube, do you mean the center/axis of the steerer tube? If so, this would put the measurement to an imaginary line drawn from the ctr of the frt axle at what angle? 90 deg to the fork blade ctr? or 90 deg to the steerer axis? Just curious because I contacted Reynolds recently and asked them for the dimension from the fork crown race seat to the frt axle ctr in a straight line on their 50mm fork and they told me it was 372mm.

  15. #15
    Senior Member Nessism's Avatar
    Join Date
    Jun 2004
    Location
    Torrance, CA
    My Bikes
    Homebuilt steel
    Posts
    2,324
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by don d.
    This has always been a pet peeve of mine as well. The whole fork as component concept leaves me cold. It just has to much to do with handling and ride for me to consider it something other than an integrated part of the frame.

    But when you say that Reynolds measures parallel to the steerer tube, do you mean the center/axis of the steerer tube? If so, this would put the measurement to an imaginary line drawn from the ctr of the frt axle at what angle? 90 deg to the fork blade ctr? or 90 deg to the steerer axis? Just curious because I contacted Reynolds recently and asked them for the dimension from the fork crown race seat to the frt axle ctr in a straight line on their 50mm fork and they told me it was 372mm.

    Measurement is per the diagram shown below.

    For some good info regarding how fork length affects head angle, check out the following link. http://www.sheldonbrown.com/rinard/forklengths.htm

  16. #16
    Aluminium Crusader :-)
    Join Date
    Apr 2004
    Location
    Melbourne, Australia
    Posts
    9,872
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    this is it!

    The old Kinesis fork is the third fork in a week. I've also tried the Profile-Design BSC and the locally made alu.

    Today I put in a heavier stem (12cm 3ttt) and bars (old ITM Pro 260) which I think has made more difference than anything.

  17. #17
    Fat Hack
    Guest
    Does the BSC fork have very little rake, or is it just a bad photo?

  18. #18
    Senior Member Nessism's Avatar
    Join Date
    Jun 2004
    Location
    Torrance, CA
    My Bikes
    Homebuilt steel
    Posts
    2,324
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Fat Hack
    Does the BSC fork have very little rake, or is it just a bad photo?

    Profile forks such as the BSC and BRC have 43 mm of rake, or offset if you prefer.

  19. #19
    don d.
    Guest
    Quote Originally Posted by Nessism
    Measurement is per the diagram shown below.

    For some good info regarding how fork length affects head angle, check out the following link. http://www.sheldonbrown.com/rinard/forklengths.htm
    Ok. Actually this measurement is a little unwieldy for the LBS or the home mechanic. You need to mount the fork in a fixture, ideally on an alignment table to be sure it's level, then locate a vertical line off the fork crown race seat and off the front axle using machinist squares, then measure that . This is good in the frame shop if you're prefitting unbrazed blades to a crown in a fixture and trimming at the top for correct length.

    I think Colnago's method is much more end user friendly, although it may not be the industry standard. But then, when did the industry do anything just because it made things more end user friendly?

    Thanks for the link.

  20. #20
    Sweetened with Splenda
    Join Date
    Sep 2003
    Location
    Brooklyn, Alabama
    My Bikes
    Too many 80s roadbikes!
    Posts
    2,335
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by don d.
    To obtain what is called "neutral" steering, ...(snip)...yourself.
    Great explanation, Don D - thanks!

  21. #21
    Fat Hack
    Guest
    Quote Originally Posted by Nessism
    Profile forks such as the BSC and BRC have 43 mm of rake, or offset if you prefer.
    It's disappointing that the Profile-Design web-site does have rakes (well, I couldn't find them).
    In my opinion, a lot of these companies don't appreciate what total "gear geeks" we are. I cannot get enough information on something I wanna buy.

    Infact, I think most companies are of the opinion that we're more impressed with 'dazzle and bull' than cold hard facts; you've just gotta check the Scapin site (http://www.scapin.com). All those jazzy pictures take ages to load....blah blah........what was I talking about? Oh yeah, light steering. Hmmm.

  22. #22
    Senior Member late's Avatar
    Join Date
    Oct 2002
    Location
    Southern Maine
    Posts
    8,248
    Mentioned
    18 Post(s)
    Tagged
    0 Thread(s)
    Get a larger tire with a round profile.

  23. #23
    Aluminium Crusader :-)
    Join Date
    Apr 2004
    Location
    Melbourne, Australia
    Posts
    9,872
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    I just want my thread back up the top of the list

  24. #24
    Senior Member meatwad's Avatar
    Join Date
    Nov 2003
    Posts
    216
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by 531Aussie
    Will a longer raked fork make a big difference?

    How long do rakes get (or "trail", or whatever it's called)?

    It's your bars. Youve got them at a bizzare angle.

  25. #25
    Aluminium Crusader :-)
    Join Date
    Apr 2004
    Location
    Melbourne, Australia
    Posts
    9,872
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by meatwad
    It's your bars. Youve got them at a bizzare angle.
    It's not a good photo, and the wheel is slightly turned; the bottoms of the drops are 'dead' parallel with the top tube
    Last edited by 531Aussie; 07-16-04 at 01:36 AM.

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
  •