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Fork spring replacement?

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by chipa, Oct 9, 2011.

  1. Bit of a back story first.

    OK, bike in question CBR250RR, 99 import, built 91.
    Bike has been through 2 friends and then myself since 2000, has done around 20,000 in that time (purchased with 5k on the clock), so currently has 25k, although who knows before 2000.
    I've been riding dirt bikes for about 15 years and got this bike to give me a transition to road bikes (plus I just moved to Sydney, so wanted a bike I was happier to drop in traffic while getting used to roadies)

    Now that I've established that I know at least a 'little' about bikes....

    The old bike has crap front suspension. I have replaced the oil with the original spec 10wt, I have also tried 15wt, but the sag under braking is quite annoying. Not being a suspension expert, i have no idea if the oil or the springs are what should control this aspect. My hope is that since the oil didn't make very much if any difference, than perhaps fixing the springs will help.

    If so, my question is this. Can you get fork springs reset? Or does it normally involve new replacements?

    I'll welcome any comments (aside from buy a new bike) :)

  2. You can do a quick and dirty, or get it done properly

    A quick and dirty involves putting a small spacer that the top of the spring. That'll limit the sag, but it won't give much better ride because all you'll be doing is artificially shortening the spring.

    There are a couple of suspension experts in Sydney who may be able to advise you

    Failing that, why not try and find a pranged CBR at a wrecker and get some cheap second-hand springs; it'd be a bit of a lottery, but you never know?
  3. I'm trying to remember the bloke's name... The shop is called 'shock treatment.' Glen Alerton gives him a big rap, and that's good enough for me.

    [edit] Terry Hay - that's his name.
  4. I don't think it's the springs entirely, and by putting in heavier rated springs you will not have your suspension working properly on little bits and stuff like that.

    I'm guessing these are old damper rod forks, so you will always have "sag" under braking. What is happening is that the braking is apply force and pushing the oil through the circuit, so it is slowly (relatively) going through your fork travel. when you come to a stop, it bounces back up.

    Most people went down the path of upgrading to NSR forks, that was supposed to be an easy upgrade, but I don't know what parts are needed.
  5. Terry is one of the best.
    Forks aren't as hard to play with as they use to be. Same as kegs.
    I grew up tapping the old kegs and trying not to get hit in the head with fork caps.
    If the springs are gone and quite well could be. The shims would be pretty average as well. Does it take ages to settle over bumps or throwing it into corners? Like take a couple of chews before it bites the line.
    You can pull your whole forks out and bubble wrap them and send them to Terry to be rebuilt to your specs. Weight, riding level.
    It's a lot of money for two fifty though.
    My advice is sell it and your sister and buy an R6
  6. Thanks for the advice everyone, I dare say I will give Shock Treatment a go.

    I'm about to upgrade my car, so I was hoping to hold off with swapping the bike for 9-12 months if possible. The bike is in great nick otherwise, and aside from the constant gear changing does what I want it to do.. for now :) Plus I'm also picky and don't like to have anything wrong, even if it is a smaller thing. I could just live with this, but I just don't work like that..

  7. measure your static and rider sags and go from there, does the cbr have any external adjusters?

    if you're bottoming alot, then either spring rate needs to go up and/or fork oil level needs an increase. depends on the severity, what your sags are and the feel of the fork everywhere else.
  8. i had this same problem initially with my own '22, but i found that with learning to ride better the suspension feels much more stable even though i've changed zilch
  9. I don't think it is (too much) my riding style. My older, more bashed around with similar k's XT550 had more controlled sag under braking than this. I've also ridding another MC22 that felt much better in the front end. Unfortunately whilst I'm quite good with working on drivetrain things, suspension is very much a black art to me. As I'm in Sydney I'll just get a professional opinion and hopefully get a better idea if I'm just crazy or if I'm actually right :)
  10. Mate just get new springs, go up a couple of ratings higher and new oil and you'll see a big improvement. Don't get me wrong it won't be ready for the race track, but having new springs on an old bike makes a huge difference.

    Otherwise google "cbr250rr 20c mod", that's preloading it as Hornet suggested. I did this to my gf's first cbr250 and it helped but still wasn't good enough. She's got another 250 now and I'm going to look at replacing the springs.

    Google racetech and see if they do springs for the mc22. My mate just put some racetechs in his old cbr900rr and the difference was day and night.
  11. Jimmy's on the right track. To judge whether you need a stiffer spring you need to measure the sag first.

    I suspect the cbr250 spring will be on the soft side, but I don't know your weight or riding style. The result is, to say, "just whack a stiffer spring in" is not the best advice you can get.

    After that, I suspect the entire front suspension needs TLC. Swapping a set of springs may be disappointing if the rest isn't right.
  12. The problem with that is that springs sag when they are old.. It's a 20 year old bike, they'll be sagged.. The measurements mean nothing in terms of trying to guage what spring to replace it with.

    Use the calculator on the racetech site and you'll probably find it'll recommend a spring "a couple of ratings higher".
  13. still its dumb not to do the measurements. and dont forget a change in rear preload will alter the front sag etc.
  14. Ok serious question, how do you determine what spring to purchase based on a measurement taken from a thrashed spring? I'm no suspension guru by any means, I'm not trying to be a smart ass. If your going to keep the same old springs and want to make relative adjustments to your setup then of course you'd want to measure. But if you later put in a brand new spring of the same part no the setup would be all wrong again (too stiff).

    I made the mistake adjusting my fork height based on pretty worn out tyres to get more turn in. It was great then when I put new tyres on it was a twitchy death trap and ended up reverting to the first setup.

    My Lesson learnt = trying to use worn parts as a benchmark is pissing into the wind.
  15. The easiest way would be to use the Racetech calc to determine the best spring for you weight & start from there. If it's same as standard & your standard spring is 20 years old, well, get a new one. It's ****ed anyway & who knows if it's stock...

    You can send your old spring to a suspension specialist for testing, but all that will give you is what the current spring rate is, bit pointless, especially seeing as you will more than likely replace it anyway.

    Edit: & correct me if I'm wrong, but Jimmyd is saying do the measurements to confirm you can't set the sag properly with the current springs.
  16. Yes that's a good point. On a cbr250rr (designed for midgets) with no adjustment and high chance of springs been sagged I think the chance is very low. Maybe with 40mm of spacers. It's a good rule of thumb. I need to respring both my bikes. My cbr600 is maxed out on the front preload at 36mm of sag, I want closer to 25mm being a track only bike. I'm going to take that to a pro and have it valved etc. But my firestorm I'll just order some racetech springs and run a thicker oil.

    I just checked the racetech site and cbr250 is not listed :/

    I really want to respring my gf's 250 and get it handling nice.
  17. Also why you would only need to do a static "measurement" and not a "rider on" to determine if the springs themselves are stuffed.
    The calculator is still only a guide and your riding style/ability will also factor into it.
    What bugs you more.
    A bike pattering across the road on corners a bit and jarring on some of our better road works.
    Or have it pogo into all the corners and never really bite?
    For a road bike your weight with gear on and a basic knowledge of your skill level, and you could have it done easy.
    A dirty is a lot more difficult because ability becomes a huge factor in spring rate.
  18. Bretto if that was directed at me by measurement I meant "static and rider sag measurements", not the length of the spring itself.