Few tricks on adjusting the rear shock

Discussion in 'Technical' started by ray23, Nov 16, 2010.

  1. ray23

    ray23 Ol'Timer

    Took it to the Mechanic I normally use, to change the shock to a new one. Didn't even look at it, in a way I can't blame him you have to really tear it down to even see the shock to check the sitting you have to have it out.

    The down side we are talking about a bike that is 17 years old, will there be adjustment left. No way to tell till you get it off. If I can't then the hunts on. I know where there is a new one but we are taking $750

    Well it's the next day I was right and there was room to adjust the shock and lots of it, Instead of buying a new one. Everything went very smoothly, one problem one of the mechanics stole the shock spanner wrench from the tool kit. Learned a trick take bailing wire on bother sides of the spring twist it takes the pressure of the adjustment point and you can easily do it with two screw drivers.

    The other thing we used the jack and a block of wood to line up the last bolt hole. Not the Thai way of hammers and four guys at your bike with pry bars.
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  3. johngooding

    johngooding Ol'Timer

    Hi Ray, I hope others more knowledgeable will correct me if wrong, but I think the adjustment on the rear shock is to adjust for the normal rider weight. It precompresses the spring so there is still some movement when the machine is loaded.
    Normally set by measuring the ride height with no one on the bike and then sitting on and getting someone to check again. Should be around 20 to 30mm depending how soft you like your ride. If you just tighten down from the proper adjustment to correct a tired spring, you will not have much movement left. The spring should be replaced. If your shock is not damping the spring movement, up and down then maybe the oil is leaking due to bore, seal or piston wear.
    Hope someone else will add to this. Cheers, John
  4. ray23

    ray23 Ol'Timer

    Thanks John I went by the shop- manual for that part, But they do weaken with time and require adjustment. I know you wouldn't know that since you don't buy 17 year old bikes LOL JUST KIDDING; :happy2:

    Life would have been much easier if the spanner had not been stolen.

    This works if you find yourself in the same position
  5. brian66

    brian66 Ol'Timer

    If you use just the pre load adjuster with the intention of making suspension of the bike feel better, unfortunately you will not gain any better suspension feel.
    Springs are made to a “Rate”

    That is, that the spring has strength in the wire coil that requires a certain weight to compress it a certain length.
    The spring fitted to your bike 17 years ago would have been rated at some average ratio to support the bike and a rider. And probably would have been a linear spring rate. The shock and spring may have about 90 mm of stroke before the coils bind.

    Let’s say the spring required 9.5 kilograms of load to compress 1mm. a 9.5 spring is for a heavy person (90 to 110) kilograms) on an average weight bike.
    For each additional mm of compression travel it would require another 9.5 kilogram of load.

    Over time the strength in the wire coil of the spring would diminish slightly and the spring may only require, say, 9 kilograms of load to compress 1mm.
    Or over 17 years of time there may even be a small section of the wire coil that is fatigued and would compress and extend with much less force than 9 kilograms.

    If the spring has lost all of its strength the suspension should be compressed or sagged would be a better word and the bike would look very low and there will be nothing to adjust.
    Apart from the possible situation in the last paragraph, the spring would still work even though it is 17 years old.

    When you compress a spring to a certain point the energy required to do that would work in the opposite direction and the spring would start to extend and it would begin a cycle of compression and extension until it slowed down. This pogo motion would make the bike unrideable unless we have the shock section.

    The shock absorber piston and cylinder part of the suspension is to dampen out this pogo motion and allow the spring to come to its neutral loaded position from either compression or extension in only one stroke and at a controlled speed. If it takes more than one stroke to stop the pogo affect the shock is bad.

    The adjuster you are now trying to use as a way to make your shock work better is only there to pre load your spring. The only thing that adjuster will do is shorten the usable stroke of the spring and shock and change the height geometry of the bike. Nothing more.
    It will not change the way the bike will absorb bumps or smooth out the suspension in any way what so ever.

    If you removed the spring from the shock the spring would be at rest and have no stored energy. If you installed it on the bike with the adjuster not applying any force and slightly compressing the spring even with the rider on the bike also, the spring would not work smoothly over the initial movement and you would have a very sharp kick from the suspension as the spring takes the initial load.

    That adjuster is there to load some tension into the spring so that it is not at its resting position and to set the correct ride height.
    If you turn that adjuster in to create some compression to the spring, the spring’s ratio will stay the same (9.5 kilograms required to compress 1mm) but you will lose some of the stroke. You will raise the rear of the bike a little which should not be noticeable in the handling.

    So if you have a poor ride now, just using the adjuster will not make the ride better.
    The main problem will be in the shock absorber section of your shock. If it has never been rebuilt it will be shot and it needs to be replaced.

    There are 4 different types of shock and fork springs. Linear, Progressive, Digressive and dual rate.
    Each has their own advantages and disadvantages. To understand those different types of springs would require another long explanation.

    I hope this helps Ray, to understand about the suspension a little better.
  6. ray23

    ray23 Ol'Timer

    Thanks it was bottoming out on hard bumps, if I have taken care of that I will be happy. It was on the third notch proper sitting for 150 Lbs, been a long time since I weighed that 200 would be more like it. 85 Ibs for the wife 25 lbs for accessories.

    Not disputing anything you have said I'm sure you know a lot more about it then I do. But, I have shocks adjusted in the past and my problems stopped.

    I will let you know how it works out, right now I'm using the opportunity to clean those hard to get places while I have it torn down.

    The bike is 17 years old the shock isn't/ I was just teasing John
  7. johngooding

    johngooding Ol'Timer

    I know what you mean about old shocks Ray, mine are now 62 years old and definately not as flexible as when they were a lot younger.
  8. ray23

    ray23 Ol'Timer

    Kids :lol-sign:
  9. ray23

    ray23 Ol'Timer


    What I adjusted was the pre load setting, worked fine bounce in is gone and no bottoming out.

    The original idea was to show a different way to do the adjustment if you don't have the proper tools. If you ride older bikes getting a complete tool kit with them is rare.
  10. Hoghead

    Hoghead Ol'Timer

    I tend to start with preload at 25% of the total suspension range on a road bike.
    Unload the suspension for the baseline reading, Ie the weight right off the springs, then sit on it. the difference in the two readings is sag and preload the spring to achieve the 25% figure. Naturally with a pillion, or luggage you will need to increase preload as well as tyre pressure.

    Just did this on Dave's BMW 800 GS (rear only) the other day and he was amazed at the difference in tarmac performance. The bike was set for a 65 Kg rider and he is 125 Kg. This required the spring to be cranked all the way up and achieved 30% rear at this setting. Interestingly the front is not adjustable and it was factory set at 25% with his weight. Perhaps the GS is more biased towards the dirt than I am used to and I now wonder if I got it right?

    My new Versys was set for a 68 Kg rider and no amount of explaining at Kawi could change their minds that it needed adjusting for my size. A simple matter to do at home, but makes me wonder how he bikes are set up for the less technically inclined.

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