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VTR250 Rear Shock

Discussion in 'Technical and Troubleshooting Torque' started by Sith Lord, Feb 17, 2008.

  1. Just bought a VTR250. The rear shock seems quite soft. Are they all soft? How hard should they be to bounce down? How far should they bounce down? Are they adjustable?

    Thanks for any thoughts.


  2. well yeah they arent exactly hard. if there is no dampning you may have a problem. preload is adjustable, a c spanner can do it as can a drift. you'll need to remove the subframe to do it. check the lock nut at the top of the shock, if they are right up the top then it could do with some firming up.
  4. How Your Suspension Works

    How Your Suspension Works

    Honda suspension is usually quite soft. When you bounce the suspension up and down it will move smoothly and easily.

    This can have a downside. Well, two to be precise.

    If the springs are too soft, the suspension will move too far when you hit a bump and bottom. This happens on the forks - a short spacer of about 10-15 mm can be useful.

    The rear is good, plenty of travel and enough spring capacity to carry me (90kg) and the Princess (I cannot say, I am a gentleman, but it's a number somewhere between 63 and 65, I reckon) without too much trouble. We seldom bottom on the bike.

    It is easiest to measure suspension movement with 2 people, one to measure while you sit on. Otherwise, just ride it and enjoy. :)

    If you have adjustable rear suspension, you turn the threaded collar on the top of the shock unit up or down, to vary the static (loaded) height. Remember that with the rider on board, the shock should take up somewhere between 1/4 and 1/3 of its travel.

    Note: adjusting the preload in the front or rear shocks does not make them stiffer! It just changes the ride height of the bike, and changes the amount of weight required to achieve a particular amount of suspension travel.

    Suspension stiffness depends on the thickness and diameter of the spring coils, and the number of turns in the spring. Cut a spring shorter and you make it stiffer. Amazing, isn't it, and some folks in here don't believe it, either. Once upon a time even I didn't realise this. We all have to be taught sometime...

    Preloading the spring changes the weight required to move the suspension to the same point of travel as before. It does not stiffen the spring. It's not just semantics.

    The second issue to consider is damping. A steel spring will bounce repeatedly when it is struck. The forks and shock contain oil which is forced through a very narrow opening (a valve) both on compression and rebound, to slow down the movement and stop the bounce.

    There needs to be more damping on rebound than compression, by at least 3 or 4 times more. They design the valves to allow for this.

    Here is how you check the damping, which can get too weak.

    Front: Hold the brake on lean on the forks a little, then push the forks down. At the bottom of the stroke (you push as hard as you can) remove your weight to allow the forks to rebound quickly and at the top of the stroke you just lean on the bars as you did at first..

    The forks should return to their original position when the damping is correct. If they travel higher and then sink a little under your weight the damping is too little.

    If they return slowly and don't want to even come back to their original position you have either put on weight in the last 2 seconds, or the damping is too strong.

    How to alter: The forks use 10w oil as a damping medium. This is usually too light after 10,000 km, so use 15w instead, after first draining the original oil!

    After 30,000 km we should be using 20w but I haven't got around to it yet.

    You need to put the correct amount of oil in - this does not affect the damping, but the spring rate, since a different height of oil is a little like converting the fork into an air suspension unit.

    Remember that the volume of air inside the fork (and its pressure) changes as the fork leg moves in and out, so adding oil will make it stiffer towards the end of its travel. Too much and you could end up with a hydraulic lock and blown fork seals!

    Checking rear damping: This works the same as the front, but get your mate to bounce the back end up and down while you are seated on the bike. With just your weight at the finish (he doesn't need to apply pressure at the end like you do with the forks) the rear end should go down and then return to its original position.

    It won't, though. It will rise and then drop down to where you started, because Honda don't build enough damping in, well, not after 10,000 km. Now for the sad bit - you cannot, yourself, change the rear damping. The shock needs to be sent away to a suspension specialist who can rebuild these non-rebuildable units.

    On the road too little damping results in a "bouncing floating" feeling - when you hit a bump the bike will rise up and then return to its normal position. When the damping is right you might feel a shock as you hit the bump, but the bike does not rise and then fall. Too little damping can be a real problem for some bikes at high speed when cornering - they feel like they have a hinge in the middle.
  5. Right on Trev.

    Take it to a coffee night and get one one of the lads to have a bounce up and down on it or a ride around the block, if you're really stressed about it.
  6. Thanks for everyones input. Handing over the cash tonight, so I'll check it out again beforehand. It is a 2003 model with tacho, so presumably adjustable. If it seems majorly wrong I'll get it checked out professionally. Cheers
  7. This would make a good 'sticky'

    Thanks Trev ! :wink:
    This is the problem I have. I assumed it may be the rear spring preload ( I adjusted it months ago to suit my height, or lack thereof :wink: ) I now realise that adjusting preload may not help.. Any advice would be appreciated
  8. Have you done the static bounce test yet?

    Because the rear is much stiffer than the front it is not easy, especially for a n00b to suspension tweaking, to work out clearly what is happening.

    Just get anyone, even a casual passerby ;-) to sit on it while you "bounce" the back end down.

    The front is just as annoying when the damping is low...you will rise up over a bump instead of having it "absobed".


    Trevor G
  9. Nope, not yet
    Thanks Trev .. will try to do so today ;-)