Rear suspension newbie questions.

punkyguy
punkyguy Posts: 4
in MTB workshop & tech
I bought an old cheap full suspension mountain bike locally for £50 ($65) to have some occasional fun with.

I'm completely new to suspension. On the rear it has a coil shock absorber, I can't see anywhere to add air and haven't removed it.

I'm 125kg (275lbs) and when I sit on the bike the spring pretty much compresses fully or at least continually bounces on it. I've adjusted the nut I think to both extremes but it didn't seem to make much difference. It has a 400lb/in spring but I don't know if it's because I need a stronger spring due to my weight or it's right for me but just worn out. I'm trying to use calculators but struggling to work out the measurements they ask for like stroke and wheel travel. Trying to research this is sending my down endless rabbit holes.

I want to keep fixing cheap so I don't worry so much about theft or damage but still want something I can enjoy in the woods.

All suggestions much appreciated.



Comments

  • steve_sordy
    steve_sordy Posts: 2,453
    I am not an expert on coil springs, but that looks like a cheap undamped coil shock. It is not worth spending ANY money on it. A new spring could cost several times more than you paid for the bike. And you will still be bouncing about like Zebedee!

    Stroke is how far the spring compresses, it will only be a few inches maybe 2"-2.5". That stroke is multiplied by the suspension geometry and results in the wheel travel. You will need a heavy friend to help you and also a tape measure. You will have to compress the bike so that the spring is fully compressed. Measure where the saddle is from one extreme to the other. The difference is the wheel travel. (Strictly speaking, you are supposed to turn the bike upside down and measure the axle movement, but measuring the saddle is easier to do, if not quite as accurate). It is easier with an air spring, you just let out the air!

    The wheel travel will be several times the stroke, in the region of 2-2.5 times, more or less.
  • mully79
    mully79 Posts: 904
    Spring is far too light for your weight but you havent any options other than to sell the bike.

    I used to get away with a 650lb spring when i was 100kg but 125kg is another 25% heavier and it gets a bit expensive going much above 650lb.

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