Results 1 to 13 of 13
  1. #1
    1946:2006:2066
    Reputation: FireDog46's Avatar
    Join Date
    Jan 2004
    Posts
    1,455

    Wink Mountain Bike Spring Rate Calculator V5.0


    A Brief History:

    Last fall I converted my bike to coil suspension. I bought a Fox Vanilla RC and, on the recommendation
    of both Fox and Rocky Mountain, an 800# spring. This seemed high to me, but I deferred to the 'experts?'.
    Turned out the ride was too firm. I decided to do my own research to come up with a calculator that would
    provide some insight into what would be a more appropriate spring rate for different riding conditions. Also,
    my bike has three travel settings and I needed to know the effect of moving from one setting to another with
    the same spring or what alternate springs I might need.

    This calculator, the latest ( final? ) is the end result of that research. I have added units in inches or
    millimetres, three travel settings in one calculation, optional spring rates for varying degrees of preload
    and a couple of extra useful links. Being honest about your riding style ( weight distribution, sag level
    and preload ) in the input parameters is key to finding the correct spring rate. Also, it is a common practice
    to have more than one spring.

    There will always be some controversy over what is a correct spring rate. This calculator has helped me to
    better understand what would be a single compromise spring rate for all three travel settings and what three
    unique spring rates would be appropriate for each of those travel settings.

    I now understand where that 800# recommendation came from and why I didn't like it. I prefer about 30% sag
    and a 600# spring with about 2 turns of preload works well in the 4.5" travel setting. However, I prefer the
    geometry of the 4.0" travel setting but ordering multiple springs from the Canadian Fox distributor was just
    too expensive. Luckily, Cambria still had some Mountain Speed rear springs in my sizes at only $25 USD.

    To any web designer: My apologies for the less than elegant coding. I had to find a way of keeping the whole page
    under 100K bytes. That's the limit for mtbr posts. I had to load the page into Visual C++ and remove all the indenting.
    This reduced the page by 30%! To restore the formatting load the page into Frontpage and save.

    michael
    -->
    Code:
    -->
    
    
    
    
    Mountain Bike Spring Rate Calculator V5.0
    
    
    
    
    
    
    
    
    
    
    Mountain Bike Spring Rate Calculator V5.0
    Total Riding Weight: (pounds) includes the rider and anything else added to the bike: lock, water bottles, etc.
    Rear Weight Bias: (percent) The standard formula is based on a 60:40, Rear to Front weight distribution. A more accurate way would be to use a bathroom scale under the rear wheel and a 2x4 under the front wheel to determine the true sprung weight at the rear wheel. Position your body according to your riding style. Enter this value for total weight and 100 for Rear Weight Bias. Alternatively use 55=XC, 65=FR, 70=DH, all others use the standard 60.
    Rear Wheel Travel & Shock Stroke: (inches or millimetres)
    Shock Sag: (percentage of shock stroke) The standard formula uses the Fox Shox recommended 25% of shock stroke. However, this tends to calculate too high a spring rate for the majority of riders. A more appropriate starting point would be 30% to 35%.
    Preload Adjuster: (number of turns) The standard formula ignores the effect of applying preload and tends to calculate too high a spring rate. Usually 1.0 is required to lock the spring to the shock body. Choose a preload value that will allow some plus or minus adjustment consistent with your required sag level and re-submit. A zero preload spring rate is found, then preload is applied to find an alternate spring rate taking into account the preload spring tension. Calculation is based on a linear progression.
    End-Coil Effect: (percent) Closed/Ground compression springs have a typically lower spring rate in their initial deflection range. The suggested value is a best guess of the effect ECE will have on preload adjustment. It is a percentage of the overall spring rate used in calculating the spring tension for the specified number of turns of the preload adjuster.
    Input Parameters: inches or millimetres
    Total Riding Weight: pounds
    Rear Weight Bias: percent
    Rear Wheel Travel: in or mm
    Shock Stroke: in or mm
    Shock Sag: percent
    Preload Adjuster: turns
    End-Coil Effect: percent
    Output Parameters: Travel Setting Three
    Leverage Ratio: travel divided by stroke
    Zero Preload Spring Rate: lbs per in
    Alternate Preload Spring Rate: lbs per in
    Suggested Spring Rate: lbs per in
    Suggested Spring Rate Preload Sag: percent

    Optional Spring Rates Constant Preload
    ( target preload as entered above )
    ( sag value is calculated from optional spring rate )
    ( never exceed spring preload limit - if unknown, never use more than 2.0 turns )
    ( more than 4.0 turns is not recommended )
    Preload Travel Setting One Travel Setting Two Travel Setting Three
    Travel:    Ratio:  Travel:    Ratio:  Travel:    Ratio: 
    Rate Sag Sag Rate Sag Sag Rate Sag Sag

    Optional Spring Rates Constant Sag
    ( target sag as entered above )
    ( optional spring rate is calculated from preload value )
    ( never exceed spring preload limit - if unknown, never use more than 2.0 turns )
    ( more than 4.0 turns is not recommended )
    Preload Travel Setting One Travel Setting Two Travel Setting Three
    Travel:    Ratio:  Travel:    Ratio:  Travel:    Ratio: 
    Rate Sag Sag Rate Sag Sag Rate Sag Sag

    Correction For Suspension Progression
    -----------------------------------
    The calculator assumes a linear suspension progression.
    For any deviation plus or minus <7% use the calculated spring rate.
    -----------------------------------
    Rising Rate ( 7% - 15% ) - Subtract 50 lbs.
    ( may require more preload )
    Extreme Rising Rate - rare ( 15% - 25% ) - Subtract 100 lbs.
    ( may require considerably more preload, possibly with a longer stroke spring )
    -----------------------------------
    Falling Rate ( 7% - 15% ) - Add 50 lbs.
    ( may require less preload )
    Extreme Falling Rate - common ( 15% - 25% ) - Add 100 lbs.
    ( may require as little preload as possible )
    ( extreme falling rate suspension bikes should be using an air shock )
    -----------------------------------
    ( or simply ride with the calculated spring rate and let personal preference decide )

    Correction For Stable Platform Shocks
    -----------------------------------
    If you have already corrected for suspension progression
    try a 50 pound lighter spring, otherwise try a 100 pound lighter spring.
    -----------------------------------
    One nameless publication suggests as much as 50% lighter but you stand the chance
     of blowing through your travel when the stable platform compression filters open up.
    -----------------------------------
    ( or simply ride with the calculated spring rate and let personal preference decide )

    Preload Precautionary
    -----------------------------------
    Preload adjusters apply about 1mm or .039" per turn.
    If the spring is not marked as to its real stroke never use more
    than 2.0 turns on the preload adjuster to avoid coil binding,
    or install a spring with a longer stroke ( if you can find one that will fit ).
    -----------------------------------
    Preload does not change the spring rate. It does change the load capacity,
    hence the ability to vary sag levels with the judicious application of preload.
    The calculator factors in the effect of preload to arrive at an alternate spring rate.
    -----------------------------------
    Even though you may be well within the limits for avoiding coil binding,
    ( as in having installed a spring with a much longer stroke than the shock )
    using too much preload stresses the shock, possibly leading to premature failure.

    Reference Links
    "A Bicycle Rear Suspension Analysis Method" by Ken Sasaki
    http://www.mtbcomprador.com/pa/english/
    "Linkage V2.0 Bicycle Suspension Simulation Program" by Gergely Kovacs
    http://www.extra.hu/linkage/
    http://www.engineersedge.com/spring_terms.htm
    http://www.engineersedge.com/spring_general.htm
    http://www.engineersedge.com/spring_comp_calc_k.htm
    http://www.engineersedge.com/spring_comp_calc.htm
    http://www.rpmnet.com/techart/spring.shtml

    Mountain Bike Spring Rate Calculator V5.0
     
    Copyright (C) 2004 Michael R Young ( mrdy )
     
    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License as
    published by the Free Software Foundation; either version 2
    of the License, or (at your option) any later version.
     
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty
    of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
    See the GNU General Public License for more details.
     
    http://www.gnu.org/copyleft/gpl.html

    This page is best viewed in Microsoft Internet Explorer Version 6.0 or higher.

    Roll Your Own
    -----------------------------------
    From The Menu Bar: View -> Source
    Within your text editor: Save As "mtbSpringRateCalculatorV5.htm"
    Search for "INIT--mtbSpringRateCalculatorV5"
    Delete everything above this line.
    Search for "FINI--mtbSpringRateCalculatorV5"
    Delete everything below this line.
    Save again.
    voila
    your own calculator
    ( if this, or any alternative method, fails, message-via-email me to receive a copy of the original )
    -----------------------------------
    Anyone wishing to post this on their own web site is welcome to.
    Simply delete this "Roll Your Own" portion, specific to this forum.
    Leave everything else intact, particularly the Copyright and Disclaimer.
    -----------------------------------
    If you respond to this post, please remove the [QUOTE]'d data.
    Otherwise the thread will become cluttered with multiple calculators.

    -->

  2. #2
    mtbr member
    Reputation:
    Join Date
    Mar 2005
    Posts
    46

    Good work!

    just tried it out...results I got confirmed real-world experience for setting a long travel bike up for a very light rider.

    Recommend to any interested in trying it out that they take the time to play with the variables. It might not work for every setup, but it definitely illustrates the effect of changing suspension setup parameters.
    Last edited by biker dad; 05-10-2005 at 09:01 PM.

  3. #3
    1946:2006:2066
    Reputation: FireDog46's Avatar
    Join Date
    Jan 2004
    Posts
    1,455

    thanks...

    Unfortunately, the one posted here doesn't work in Firefox.

    The corrected one can be found here http://www.theride.ca/guru/spring-calc.htm

    michael
    "Be not afraid of going slowly but only of standing still." - Chinese Proverb

  4. #4
    jrm
    jrm is offline
    mtbr member
    Reputation: jrm's Avatar
    Join Date
    Jan 2004
    Posts
    10,156

    That rocks....

    [QUOTE=mrdy]
    A Brief History:

    Last fall I converted my bike to coil suspension. I bought a Fox Vanilla RC and, on the recommendation
    of both Fox and Rocky Mountain, an 800# spring. This seemed high to me, but I deferred to the 'experts?'.
    Turned out the ride was too firm. I decided to do my own research to come up with a calculator that would
    provide some insight into what would be a more appropriate spring rate for different riding conditions. Also,
    my bike has three travel settings and I needed to know the effect of moving from one setting to another with
    the same spring or what alternate springs I might need.

    This calculator, the latest ( final? ) is the end result of that research. I have added units in inches or
    millimetres, three travel settings in one calculation, optional spring rates for varying degrees of preload
    and a couple of extra useful links. Being honest about your riding style ( weight distribution, sag level
    and preload ) in the input parameters is key to finding the correct spring rate. Also, it is a common practice
    to have more than one spring.

    There will always be some controversy over what is a correct spring rate. This calculator has helped me to
    better understand what would be a single compromise spring rate for all three travel settings and what three
    unique spring rates would be appropriate for each of those travel settings.

    I now understand where that 800# recommendation came from and why I didn't like it. I prefer about 30% sag
    and a 600# spring with about 2 turns of preload works well in the 4.5" travel setting. However, I prefer the
    geometry of the 4.0" travel setting but ordering multiple springs from the Canadian Fox distributor was just
    too expensive. Luckily, Cambria still had some Mountain Speed rear springs in my sizes at only $25 USD.

    To any web designer: My apologies for the less than elegant coding. I had to find a way of keeping the whole page
    under 100K bytes. That's the limit for mtbr posts. I had to load the page into Visual C++ and remove all the indenting.
    This reduced the page by 30%! To restore the formatting load the page into Frontpage and save.

    michael
    -->
    Code:
    -->
    
    
    
    
    Mountain Bike Spring Rate Calculator V5.0
    
    
    
    
    
    
    
    
    
    
    Mountain Bike Spring Rate Calculator V5.0
    Total Riding Weight: (pounds) includes the rider and anything else added to the bike: lock, water bottles, etc.
    Rear Weight Bias: (percent) The standard formula is based on a 60:40, Rear to Front weight distribution. A more accurate way would be to use a bathroom scale under the rear wheel and a 2x4 under the front wheel to determine the true sprung weight at the rear wheel. Position your body according to your riding style. Enter this value for total weight and 100 for Rear Weight Bias. Alternatively use 55=XC, 65=FR, 70=DH, all others use the standard 60.
    Rear Wheel Travel & Shock Stroke: (inches or millimetres)
    Shock Sag: (percentage of shock stroke) The standard formula uses the Fox Shox recommended 25% of shock stroke. However, this tends to calculate too high a spring rate for the majority of riders. A more appropriate starting point would be 30% to 35%.
    Preload Adjuster: (number of turns) The standard formula ignores the effect of applying preload and tends to calculate too high a spring rate. Usually 1.0 is required to lock the spring to the shock body. Choose a preload value that will allow some plus or minus adjustment consistent with your required sag level and re-submit. A zero preload spring rate is found, then preload is applied to find an alternate spring rate taking into account the preload spring tension. Calculation is based on a linear progression.
    End-Coil Effect: (percent) Closed/Ground compression springs have a typically lower spring rate in their initial deflection range. The suggested value is a best guess of the effect ECE will have on preload adjustment. It is a percentage of the overall spring rate used in calculating the spring tension for the specified number of turns of the preload adjuster.
    Input Parameters: inches or millimetres
    Total Riding Weight: pounds
    Rear Weight Bias: percent
    Rear Wheel Travel: in or mm
    Shock Stroke: in or mm
    Shock Sag: percent
    Preload Adjuster: turns
    End-Coil Effect: percent
    Output Parameters: Travel Setting Three
    Leverage Ratio: travel divided by stroke
    Zero Preload Spring Rate: lbs per in
    Alternate Preload Spring Rate: lbs per in
    Suggested Spring Rate: lbs per in
    Suggested Spring Rate Preload Sag: percent

    Optional Spring Rates Constant Preload
    ( target preload as entered above )
    ( sag value is calculated from optional spring rate )
    ( never exceed spring preload limit - if unknown, never use more than 2.0 turns )
    ( more than 4.0 turns is not recommended )
    Preload Travel Setting One Travel Setting Two Travel Setting Three
    Travel:    Ratio:  Travel:    Ratio:  Travel:    Ratio: 
    Rate Sag Sag Rate Sag Sag Rate Sag Sag

    Optional Spring Rates Constant Sag
    ( target sag as entered above )
    ( optional spring rate is calculated from preload value )
    ( never exceed spring preload limit - if unknown, never use more than 2.0 turns )
    ( more than 4.0 turns is not recommended )
    Preload Travel Setting One Travel Setting Two Travel Setting Three
    Travel:    Ratio:  Travel:    Ratio:  Travel:    Ratio: 
    Rate Sag Sag Rate Sag Sag Rate Sag Sag

    Correction For Suspension Progression
    -----------------------------------
    The calculator assumes a linear suspension progression.
    For any deviation plus or minus <7% use the calculated spring rate.
    -----------------------------------
    Rising Rate ( 7% - 15% ) - Subtract 50 lbs.
    ( may require more preload )
    Extreme Rising Rate - rare ( 15% - 25% ) - Subtract 100 lbs.
    ( may require considerably more preload, possibly with a longer stroke spring )
    -----------------------------------
    Falling Rate ( 7% - 15% ) - Add 50 lbs.
    ( may require less preload )
    Extreme Falling Rate - common ( 15% - 25% ) - Add 100 lbs.
    ( may require as little preload as possible )
    ( extreme falling rate suspension bikes should be using an air shock )
    -----------------------------------
    ( or simply ride with the calculated spring rate and let personal preference decide )

    Correction For Stable Platform Shocks
    -----------------------------------
    If you have already corrected for suspension progression
    try a 50 pound lighter spring, otherwise try a 100 pound lighter spring.
    -----------------------------------
    One nameless publication suggests as much as 50% lighter but you stand the chance
     of blowing through your travel when the stable platform compression filters open up.
    -----------------------------------
    ( or simply ride with the calculated spring rate and let personal preference decide )

    Preload Precautionary
    -----------------------------------
    Preload adjusters apply about 1mm or .039" per turn.
    If the spring is not marked as to its real stroke never use more
    than 2.0 turns on the preload adjuster to avoid coil binding,
    or install a spring with a longer stroke ( if you can find one that will fit ).
    -----------------------------------
    Preload does not change the spring rate. It does change the load capacity,
    hence the ability to vary sag levels with the judicious application of preload.
    The calculator factors in the effect of preload to arrive at an alternate spring rate.
    -----------------------------------
    Even though you may be well within the limits for avoiding coil binding,
    ( as in having installed a spring with a much longer stroke than the shock )
    using too much preload stresses the shock, possibly leading to premature failure.

    Reference Links
    "A Bicycle Rear Suspension Analysis Method" by Ken Sasaki
    http://www.mtbcomprador.com/pa/english/
    "Linkage V2.0 Bicycle Suspension Simulation Program" by Gergely Kovacs
    http://www.extra.hu/linkage/
    http://www.engineersedge.com/spring_terms.htm
    http://www.engineersedge.com/spring_general.htm
    http://www.engineersedge.com/spring_comp_calc_k.htm
    http://www.engineersedge.com/spring_comp_calc.htm
    http://www.rpmnet.com/techart/spring.shtml

    Mountain Bike Spring Rate Calculator V5.0
     
    Copyright (C) 2004 Michael R Young ( mrdy )
     
    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License as
    published by the Free Software Foundation; either version 2
    of the License, or (at your option) any later version.
     
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty
    of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
    See the GNU General Public License for more details.
     
    http://www.gnu.org/copyleft/gpl.html

    This page is best viewed in Microsoft Internet Explorer Version 6.0 or higher.

    Roll Your Own
    -----------------------------------
    From The Menu Bar: View -> Source
    Within your text editor: Save As "mtbSpringRateCalculatorV5.htm"
    Search for "INIT--mtbSpringRateCalculatorV5"
    Delete everything above this line.
    Search for "FINI--mtbSpringRateCalculatorV5"
    Delete everything below this line.
    Save again.
    voila
    your own calculator
    ( if this, or any alternative method, fails, message-via-email me to receive a copy of the original )
    -----------------------------------
    Anyone wishing to post this on their own web site is welcome to.
    Simply delete this "Roll Your Own" portion, specific to this forum.
    Leave everything else intact, particularly the Copyright and Disclaimer.
    -----------------------------------
    If you respond to this post, please remove the
    'd data.
    Otherwise the thread will become cluttered with multiple calculators.

    -->
    Now only if someone could come up with a calculator for rear air shock Psi....

  5. #5
    "El Whatever"
    Reputation: Warp's Avatar
    Join Date
    May 2004
    Posts
    18,676
    Quote Originally Posted by mrdy
    Unfortunately, the one posted here doesn't work in Firefox.

    The corrected one can be found here http://www.theride.ca/guru/spring-calc.htm

    michael
    mrdy... a dumb question. I have a 600 spring for a 2.00 travel shock. I need a 400-450 spring. Is this lower rate spring going to be shorter or longer than my 600 for the same stroke??

    Is -15mm (600 longer 15mm than 450) an acceptable variation?? Where can I find more info on this. Thanks!
    Check my Site

  6. #6
    mtbr member
    Reputation:
    Join Date
    Sep 2004
    Posts
    121
    Quote Originally Posted by jrm
    Now only if someone could come up with a calculator for rear air shock Psi....
    Yea, I wish Fox, manitou, and 5th would give numbers for piston area, and volume (full and at bumper) of their shocks. Otherwise it's a guessing game.

  7. #7
    mtbr member
    Reputation:
    Join Date
    Mar 2005
    Posts
    46
    Quote Originally Posted by Warp2003
    mrdy... a dumb question. I have a 600 spring for a 2.00 travel shock. I need a 400-450 spring. Is this lower rate spring going to be shorter or longer than my 600 for the same stroke??

    Is -15mm (600 longer 15mm than 450) an acceptable variation?? Where can I find more info on this. Thanks!
    A softer spring with the same stroke capacity needs more winds, so if it is wound out of the same stock, it will be longer. Usually all springs in a series are wound out of the same stock, however, if it is wound out of lighter stock, the length could be similar or even shorter.

  8. #8
    "El Whatever"
    Reputation: Warp's Avatar
    Join Date
    May 2004
    Posts
    18,676
    Quote Originally Posted by biker dad
    A softer spring with the same stroke capacity needs more winds, so if it is wound out of the same stock, it will be longer. Usually all springs in a series are wound out of the same stock, however, if it is wound out of lighter stock, the length could be similar or even shorter.
    Thanks... the one I'm getting gotta be lighter stock then, as it's actually shorter than current.
    Check my Site

  9. #9
    mtbr member
    Reputation: LonesomeCowboyBert's Avatar
    Join Date
    Apr 2008
    Posts
    251
    Well, using the preset 60% rear weight bias the result I get for my 6.6SS is quite a bit off, it recomends 315 lb for my 150lb rider weight
    In real life I use a 350lb which is a little soft and a 400lb which is a tad stiff (swap em on type of riding im doing), the mojo calculater gave me 388lb, iirc, so seems far more accurate for this particular bike

    I suspect the discrepency is in the 60% rear weight bias figure that is default on the calculator, this may only be right for a cross country bike, only problem being I (and I suspect most others) have no idea what my front to rear bias is, it would be a total guess (I dont have 2 bathroom scales)

  10. #10
    mtbr member
    Reputation:
    Join Date
    Aug 2008
    Posts
    54
    THANK YOU!! I have been trying many different calcs to see what spring I need for my first coil shock (I'm coming off an air shock), and this is consistent with other calc's results as well as real world experiance, yet its also FAR more in-depth and comprehensive then any other clac I've yet seen.

    Great work! More people should see this.

  11. #11
    Australia = phun
    Reputation:
    Join Date
    Sep 2010
    Posts
    405
    Bump: This should be a sticky

  12. #12
    mtbr member
    Reputation:
    Join Date
    Mar 2013
    Posts
    1
    Another calculator for Fox Shox.
    Been trying to figure what spring I need for my Van RC.
    Mountain Bike Spring Rate Calculator

  13. #13
    1946:2006:2066
    Reputation: FireDog46's Avatar
    Join Date
    Jan 2004
    Posts
    1,455
    Quote Originally Posted by Rannelator View Post
    Another calculator for Fox Shox.
    Been trying to figure what spring I need for my Van RC.
    Mountain Bike Spring Rate Calculator
    and who do you think wrote it...but it's out of date...
    there is a version 7.0...but i don't hang out around here any more
    damn fox racing...they have no shame
    no accreditation
    Last edited by FireDog46; 07-17-2013 at 08:03 PM.
    "Be not afraid of going slowly but only of standing still." - Chinese Proverb

Similar Threads

  1. If you need to know this.
    By KevinVokeyJ24 in forum General Discussion
    Replies: 14
    Last Post: 12-24-2004, 08:40 AM
  2. Lance's Austin "29er" revealed
    By ncj01 in forum 29er Bikes
    Replies: 3
    Last Post: 08-28-2004, 08:14 PM
  3. Help. MTB speech for school.
    By jonowee in forum General Discussion
    Replies: 17
    Last Post: 06-16-2004, 02:25 AM
  4. For fun: Dirt Rag's Monkey review
    By ncj01 in forum 29er Bikes
    Replies: 5
    Last Post: 04-27-2004, 10:38 AM
  5. Buying first mountain bike this spring
    By Newrider in forum Beginner's Corner
    Replies: 9
    Last Post: 03-27-2004, 09:02 PM

Posting Permissions

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