Fork Spring Rate

Discussion in 'Trials' started by lamotovita, Jul 2, 2013.

  1. lamotovita

    lamotovita Ageing Adventurer

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    Can you tell me what a is typical spring rate, or range of spring rates for a modern trials bike?
    I'm working on a trail bike and just looking for another reference point. I can't recall seeing a spring rate published anywhere.
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  2. klx_dude

    klx_dude Been here awhile

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    Go onto racetech site and click on there spring rate calculator. Gives standard rates for the bike u select

    Sent from my GT-I9300T using Tapatalk 2
    #2
  3. lamotovita

    lamotovita Ageing Adventurer

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    Not Trials bikes.
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  4. mung

    mung Been here awhile

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    My 04 Raga had .30 springs stock and now I use .40 mountain bike springs for my 250 pounds.Look at Beta USA under BYOB in the suspension section and it suggests spring rates for your riding weight.
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  5. motobene

    motobene Motoing for 44 years

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    Trials bikes are interesting as compared to my years of setting suspension up on fast off road bikes. Modern trials bike base settings tend to apply across a very wide range of riders, so spring rates tend to fall out of relevancy. Modern bikes generally have stiff enough springs to get by with, even with heavier riders. What is super relevant, however, is the affect setup has on steering characteristics.

    The role of spring rate and preload, front and rear in handling characteristics, is often not well understood, and riders, thinking the rear end should sit up higher for more travel, will crank up rear spring preload and end up messing up the bike's steering characteristics. Then they wonder why they take so many points zigzagging in sections. "I just need to get better", they'll say to themselves.

    The last three used bikes I helped set up were a Beta Rev 3, a 4RT, and a Beta 300 4T. All were jacked up in rear preload, causing over steer. Over steer from ground reaction torques wanting to suck the bike deeper into turns by decreasing the turn radius. It has to do with rake and trail and bike lean... all to complex to write about here. But you've all felt those bikes that felt hyper and wanted to tuck under in turns?

    I set up bike attitude (pitch)/steering feel first making sure the grip position (bar rotation) is correct to modern trials, that is, more forward so the rider's body isn't being pushed back, but not so far forward as to increase over steer (grip position and steering action and reaction torques are related). Then I ride the bike on flat concrete to feel steering reaction torques. If you lean into a turn and the bike wants to steer into a decreasing radius and even tuck under, that's over steer.

    I set rear preload and fork preload and position in triple clamps for close-to-neutral reaction torques. Often I leave the shock preload alone unless it's been messed with (the factories center on ~80kg rider -180 pound riders). When I find over steer, which is more often than not, I increase fork spring preload and/or put the fork caps level with the top of the triple clamps. Then I observe riders turning to make sure I'm matching the settings to their weight and style.

    I set bikes up with a very slight tendency to over steer during good bit of lean in a turn, but otherwise on flatter turns I prefer neutral steering or even some under steer. Under steer is when a bike wants to steer slightly out of a turn and straighten up. Much less crazy to track the steering that way than when the bike isn't trying to steer itself into turns, acting hyper, and adding points to your game.
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  6. Sting32

    Sting32 Trials Evangelist

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    When I was NOT as "good a rider" I wanted stiffer springs, this mean I could keep my skidplate off of things, even though I was heavier than others on same bike (years are important, at least with Gasgas IMHO). We're talking about 1 inch or so, that I could sag the rear, not as much affected by fronts, more than my dad who weighed at least 60lbs less than I DID. We both would increase the pre-load on the front fork springs, up until about the 2008 Raga we got.

    Dad didnt need to add spacers anymore on the front, he never used the stiffer rear springs. I on the other-hand, I being semi athletic (yet fat but pretty heavy even for my size) nearly 275lbs, at the highest point. So I bought 2 forks springs from Lewissport, which were supposedly 10% stronger each. 2 almost was too stiff. Plus I had the stiffer spring for the rear Sachs shock, that I had rebuilt and revalved. Anywho, I recall I sold one of the pair of fork springs, to a buddy. He as at least 250, novice rider heading to amature on a short fuse (riding well).

    THen I also started to lose weight, but the time I lost 25 lbs, the spring was still WAY too stiff. BUT! Here's the deal, You don't notice too stiff so much, especially since the old days I always wanted the front to not sag hardly at all. I didn't realize how stiff the front had become, until I was competing in winter on very slippery rocks and mud, I mean SLIPPERY STUFF! On dry ground and rocks with traction, I was beating my peers just fine, never felt there was any problem with my setup per se. you hit a pebbel sized rock on the mud path, it stopped you because shocks didnt compress at all, etc.

    Now I weigh in at 199lbs. I have even recently had to reduce preload on rear shock spring preloads (stock shock spring on the 2011 Reiger) compared to what I started with a few months ago, when I was above 210, and I haven't modified the front forks from stock since I left that 08 raga.

    You want the softer suspension IMHO, as long as it doesn't BOTTOM out or BIND up suspension at full compression, on a 2ft or 3 ft drop of any kind, IMHO. if it hits bottom of travel, things are not right, and IMHO you can find yourself bending and breaking things that are then given a lot harder "tug" on or against when this happens

    Even with Raga being a light guy, in comparison, the bike at stock settings sould hold a 180-230lb rider without much mods, other than adding turns to the rear spring preloader, and maybe adding 1/4 - 1/2 inch to the spacers in the front spring setup. what I we used to DO, was take original spacer out, replace with ones that were longer, made from PVC pipe. I dont do this anymore but if I was above 220 I might I dunno, I like softer setup now. ALSO, there was a limit to how much you can add from stock spacer length though, I cannot recall that VALUE, better ask JSE or someone at Trails Central for that kind of technical info, I know I never added more than 1/2 inch per side... when you add that much, there is a BIG difference if the springs are not SHOT!
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  7. neilking

    neilking Been here awhile

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    This is the best explanations I have ever read! As far as on topic, I can only think of a couple things to add. I can really only comment on stock Beta spring rates specifically. I set rear preload and bar rotation as a compromise between traction and turning characteristics. I find rolling the bars forward increases foot pressure and rear sag, too far forward and steering gets twitchy, too far back puts too much pressure on the front and makes drop offs harder. I find that the one size stiffer (8.0kg) rear spring works well for me(185lb). This way I can run less preload actually making the initial action of the rear shock softer than stock, then it stiffens up nicely further in the stroke helping prevent bottoming out. I'm able to rotate my bars a little more forward to get more weight on the pegs.

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  8. neilking

    neilking Been here awhile

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    Forgot to say, I pretty much leave the front alone, just add a couple clicks of damping from zero. Aso add a little to the rear to keep it planted, much more important than having it off the ground.
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  9. neilking

    neilking Been here awhile

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    This is the best explanations I have ever read! As far as on topic, I can only think of a couple things to add. I can really only comment on stock Beta spring rates specifically. I set rear preload and bar rotation as a compromise between traction and turning characteristics. I find rolling the bars forward increases foot pressure and rear sag, too far forward and steering gets twitchy, too far back puts too much pressure on the front and makes drop offs harder. I find that the one size stiffer (8.0kg) rear spring works well for me(185lb). This way I can run less preload actually making the initial action of the rear shock softer than stock, then it stiffens up nicely further in the stroke helping prevent bottoming out. I'm able to rotate my bars a little more forward to get more weight on the pegs.

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  10. lamotovita

    lamotovita Ageing Adventurer

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    Thanks for the info. The Beta site lists springs in the .8-.9 range, so I'm guessing that Beta either rates their springs as a pair, or only uses one spring. Anybody know?

    I've never changed fork spring rate on a Trials bike even though I frequently change them on other bikes. That's why I don't know what rates are used. I'm working on softening up the front end of a trail bike and just want to compare the rate of Trials bike springs to what I'm using.
    #10
  11. DrKayak

    DrKayak Retro Rider

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    My new Evo only uses one spring on the front. Just got the Evo. I rode a stock Techno for 2 years. I never touched the suspension, just rode it. Did hard trail riding too and it never bottomed.

    This Evo came with 3 sets of springs. I would have left it stock after my Techno experience. Now I have too many choices. The previous owner has the stiffest spring in it Rated to 250+ rider. I am 190lbs. Still I get a ton of movement in the suspension, does not feel that stiff and it does not seam to over steer as motobeam describes. Guess I will leave it as is for now.
    #11
  12. neilking

    neilking Been here awhile

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    Sorry for the double postong. Don't know how that happened.
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  13. motobene

    motobene Motoing for 44 years

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    Well, thanks, Neil! Motobene is me, your friendly, shorts-wearing, gimpy competitor :ear

    I was reminded recently just how important bike setup is. I had my former Econo here as well as the 'new' `11 Raga. I think I mentioned in my post about the affect grip placement (bar rotation) has on bike attitude and handling.

    Riding the two bikes back and forth, I just could not get the Raga to thread as precisely through rocks and turns as well as the Econo. Given the money I spent on the Raga, it was disturbing me because any one of us can trade places in our class with just a few points. I thought it might have been the bike pitch/attitude/front-rear preload), but those seemed right for my weight, stance, and other variables. What was causing me to lose a touch of steering acuity?

    I found it was grip position (bar rotation). Grip position and angle interact with preload and bike pitch (attitude) which affects steering. I was somewhere between one and two degrees of error, bars rotated back. I thought it was just the Raga bend. The error created slight under steer and vagueness.

    When I made the minor correction it was eye opening. I could stay on line like the Econo. I might not have caught that without a long term well set up bike to compare to.
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  14. Sting32

    Sting32 Trials Evangelist

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    Bar rotation makes a good bit of difference for sure, for us who aren't experts (hopping and big objects). When I rotate forward I find I can hop rear over easier, then struggle a slow-normal *line*... amazes me to see master's with bars even farther forward than I have even *tested* lol. My issue is strenght I thought but absolutely not sure.

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  15. Twin-shocker

    Twin-shocker Long timer

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    Bar position does make an awful lot of difference, and in many cases moving the bar mounts themselves forward a little will improve a bike enormously.

    The stock position is a compromise, and means its often necessary to move the bars forward to help improve control. Factory riders have bar mounting position adjusted to suit them perfectly, but this is something thats relatively easy to do, if you use S3 adjustable clamps.
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  16. motobene

    motobene Motoing for 44 years

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    I used to cut the angled back TY350 mounts and re weld them pointing up in a much more modern position. It was a huge help to the steering.

    Hold a 1" cylinder rod in the hands with your arms hanging down and you will see a natural up angle toward the outside. When the bars are rotated too far back the bar ends are too flat or even angled down, which is contrary to the natural hand grip axis. That's very uncomfortable, and it pushes the body mass back too far. I call it the floppy-eared effect, whereas trials is more an upright and alert-ears sport. A bad experience for me is to hop on a typical fast off road rider's bike with bars rotated back, bar ends angled dawn, and levers angled down. I feel like a lead blanket is smothering me down and back on the bike. It's exhausting to ride that way. For them it is normal because they tend to ride glued to the seat all the time.

    The important thing is the position AND compound angle of the grips relative to the rest of the bike and your particular body. How you get there is less important than where the bars are mounted. Where they are mounted - how backward or forward on the triple clamp - is simply an enabler to get to your ergonomic goals at the grips.

    I'm tall and have long arms. For me the typical modern bar bends and standard triple clamp handlebar clamp positions work out well. If I were to slide the bar mounting forward, I'd lose up angle at the bar ends when the grips are where they should be.

    And then there is that last bit about clutch and brake lever in-out position and angle. For me, once the grips are where they should be, I end up with a slight down angle to the levers, but more up angle than the reservoir caps being level with the ground. All of it together is complicated. A picture is worth a thousand words. The following shows the 280 Econo's ergos. Too many angles and positions to be captured in a photo, but it's perhaps helpful to see what works for me.

    https://docs.google.com/file/d/0B9eLpPW6KxzjbHV2eTBzalZNVGs/edit?usp=sharing
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  17. mud

    mud I just wander.....

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    Be careful with this one. I have ridden both trials and dirt bikes that have their bars forward on the clamps for more room and they don't handle right. Yes, they are comfortable, but you get the bars to much forward of the steertube and the bars have to swing instead of turn. It looses its neutrality.

    If your bars are much higher and/or forward of the factory boys, think twice....
    #17