Shock problem.... solved!

[tommy]

Having alot of problems with my shock. Kept shooting me out of my seat over every bump. Put it down to me being a light weight.
So I went to bike garage near me (Total Traction) to see if my sag was right
After 5 minutes, he discovered the problem....
NO GAS!!!

Hence the spring had no damping, and the spring was catapulting back

So hopefully next week if funds are right, i'll be heading down to MC Technics to get it refurbed
and fingers crossed, no more sore arse and nuts!!!!!!!

[Willopotomas]

Wonder if this is where my problem lies.. as that sounds like what happens on my bike.. but I've not had a good enough play with the back end yet.. it's getting the time to do these things ye see..

[HowardQ]

Depends on the shock you are using.
Many Falcos with the original Blue Spring shock have preload set well up to both lift the ride height slightly and compensate a bit for lack of damping as the shock deteriates. In the early days it aint to bad, (better than many cheap bikes), but it is then pretty hard and will try and launch you out of the seat on bumpy roads.
As it gets older and looses more (or most) of the damping, then the spring will Boinng you out of the seat, (especially with the preload turned right up), as it will be pretty stiff.
When I fitted a (good) White Spring shock off a Mille, it surprised me as I thought it would be much stiffer. No it was much better over the bumps and better damped, so performed much better overall. If you fit an Ohlins the ride is even better!

[Nooj]

Preload won't affect the hardness of the ride, only adjusting damping or changing the spring or the dogbones will do that. Preload adjusts the position of the bike in relation to the wheels, which in turn affects rake and trail, it's nothing to do with comfort.

[tommy]

Depends on the shock you are using.
Many Falcos with the original Blue Spring shock have preload set well up to both lift the ride height slightly and compensate a bit for lack of damping as the shock deteriates. In the early days it aint to bad, (better than many cheap bikes), but it is then pretty hard and will try and launch you out of the seat on bumpy roads.
As it gets older and looses more (or most) of the damping, then the spring will Boinng you out of the seat, (especially with the preload turned right up), as it will be pretty stiff.
When I fitted a (good) White Spring shock off a Mille, it surprised me as I thought it would be much stiffer. No it was much better over the bumps and better damped, so performed much better overall. If you fit an Ohlins the ride is even better!

Im using an ohlins shock off an early rsvr, it turns out the preload and sag was spot on for me. Just had naff all damping, was being launched right out of the seat, sometimes up to 6 inches or so. I swear there must be imprints of my nuts on the tank, haha
On some roads i had to actually ride with my arse off the seat jockey style just to make it bearable

Will be getting a full refurb on it, and hopefully I'll start enjoying riding again

[HowardQ]

Preload won't affect the hardness of the ride, only adjusting damping or changing the spring or the dogbones will do that. Preload adjusts the position of the bike in relation to the wheels, which in turn affects rake and trail, it's nothing to do with comfort.

Agreed,
but as well as raising the ride height slightly, it does tend to compress the spring a bit more, hence a very slightly harder ride.

[anzacinexile]

Preload won't affect the hardness of the ride, only adjusting damping or changing the spring or the dogbones will do that. Preload adjusts the position of the bike in relation to the wheels, which in turn affects rake and trail, it's nothing to do with comfort.

Agreed,
but as well as raising the ride height slightly, it does tend to compress the spring a bit more, hence a very slightly harder ride.

...only if the shock is against its stops - not a normal situation.

If its not on the stops then winding the pre-load will have no effect on the spring rate.

[mangocrazy]

Preload won't affect the hardness of the ride, only adjusting damping or changing the spring or the dogbones will do that. Preload adjusts the position of the bike in relation to the wheels, which in turn affects rake and trail, it's nothing to do with comfort.

Agreed,
but as well as raising the ride height slightly, it does tend to compress the spring a bit more, hence a very slightly harder ride.

...only if the shock is against its stops - not a normal situation.

If its not on the stops then winding the pre-load will have no effect on the spring rate.

Are you sure about that? A spring rate is quoted in either lbs/inch or kg/mm (I'm forgetting about Newton metres at the moment). So if you take a spring rated at (say) 800 lbs/in, that is its rate when uncompressed. When you compress it (as in preloading it), the effective spring rate increases, dependent on the amount of preload applied. This is clear from the way spring rates are measured; i.e. pounds per inch or kilograms per mm. Ask anyone who's tried to compress a valve spring by hand whether the effective spring rate increases the more you try and compress it. The answer is yes.

So with our 800 lb/in spring, the effective spring rate would increase by 800 lb for each inch of travel (or preload) applied. The big problem here is that it's very easy to preload a spring that is too soft for its intended application to the point where the spring becomes coil-bound before the full travel of the shock is used. When that happens it's like hitting the bump-stop on a shock - there's nothing graceful about it, just a hard jolt as the spring coils contact each other and momentarily lock.

I agree there is no substitute for having the correct spring rate, but jacking up the preload can be a short-term solution of sorts. It will also undoubtedly bugger up the static sag, of course.

[D-Rider]

I believe anzac is correct .... unless you are using progressive rate springs

[mangocrazy]

Don't believe so - progressive rate springs merely alter the rate of change; i.e. the curve. Linear springs are just that; the rate of increase is linear.

There's a good explanation here:

http://www.sportrider.com/tech/146_9510_tech/index.html

The point we're discussing is addressed here:

When you tighten the adjusting collar on a shock or increase the preload length by tightening the adjuster on the fork, you are indeed increasing the initial force exerted by the springs. This decreases sag, making the bike ride higher. It does not, however, increase the spring rate.

Increasing the preload cannot alter the spring rate as that is fixed at the point of manufacture, what it does is move the starting point further up the 'curve' (or the straight line in the case of a linear spring).

[anzacinexile]

Difficult to explain in words but I'll have a pop.

Yes, springs are rated in compression or tension but that's when they're moving - i.e. working.

Consider a bike resting on its suspension with its spring under some compression. Its load doesn't change (the weight of the bike) so if you move its seat up or down (the pre load collar), the only effect will be to move the bikes suspension in sympathy - i.e. lower or raise the ride height. The spring doesn't compress or relax when you move the collar (the weight hasn't changed, the spring can be considered as a solid tube) therefore its compression rate doesn't alter either.

As I said, the only time the pre load adjuster would have an effect on the "stiffness" is if the shock is on its stop. Tightening the collar would have the effect of needing more force to start the spring compressing but in a normal situation, a shock shouldn't be against its stops. Try lifting the rear of your bike and it moves without lifting the rear tyre of the ground - right?

[mangocrazy]

Difficult to explain in words but I'll have a pop.

Yes, springs are rated in compression or tension but that's when they're moving - i.e. working.

Springs are rated as force required to compress the free length a certain distance. They have the same rate whether they're moving or static.

Consider a bike resting on its suspension with its spring under some compression. Its load doesn't change (the weight of the bike) so if you move its seat up or down (the pre load collar), the only effect will be to move the bikes suspension in sympathy - i.e. lower or raise the ride height. The spring doesn't compress or relax when you move the collar (the weight hasn't changed, the spring can be considered as a solid tube) therefore its compression rate doesn't alter either.

Sorry, but the spring DOES compress when you move the collar. That's the whole point. You are effectively shortening the spring and moving the 'starting' rate up the spring rate 'curve'. You are also raising the ride height, of course. When you dismantle a shock, the first thing you do is to measure the assembled length of the spring on the shock (with the shock off the bike). Once the preload collar has been wound off you can then compare the free length of the spring with the preloaded length, and work out how much preload to apply to the spring when re-assembling (assuming you want the same preload length as before).

As I said, the only time the pre load adjuster would have an effect on the "stiffness" is if the shock is on its stop. Tightening the collar would have the effect of needing more force to start the spring compressing but in a normal situation, a shock shouldn't be against its stops. Try lifting the rear of your bike and it moves without lifting the rear tyre of the ground - right?

I'm not sure what you mean by the shock being on its stop. The bump stop rubber (is that what you're referring to?) is there to limit shock travel when fully compressed, without damaging the shock internals.

Under normal circumstances, if you lift the rear of your bike, you will be taking up the static sag. If the static sag is minimal or non-existent (i.e. if you have applied excessive preload) you WILL be able to lift the back of the bike off the ground (assuming you're strong enough).

[anzacinexile]

Difficult to explain in words but I'll have a pop.

Yes, springs are rated in compression or tension but that's when they're moving - i.e. working.

Springs are rated as force required to compress the free length a certain distance. They have the same rate whether they're moving or static.

Consider a bike resting on its suspension with its spring under some compression. Its load doesn't change (the weight of the bike) so if you move its seat up or down (the pre load collar), the only effect will be to move the bikes suspension in sympathy - i.e. lower or raise the ride height. The spring doesn't compress or relax when you move the collar (the weight hasn't changed, the spring can be considered as a solid tube) therefore its compression rate doesn't alter either.

Sorry, but the spring DOES compress when you move the collar. That's the whole point. You are effectively shortening the spring and moving the 'starting' rate up the spring rate 'curve'. You are also raising the ride height, of course. When you dismantle a shock, the first thing you do is to measure the assembled length of the spring on the shock (with the shock off the bike). Once the preload collar has been wound off you can then compare the free length of the spring with the preloaded length, and work out how much preload to apply to the spring when re-assembling (assuming you want the same preload length as before).

As I said, the only time the pre load adjuster would have an effect on the "stiffness" is if the shock is on its stop. Tightening the collar would have the effect of needing more force to start the spring compressing but in a normal situation, a shock shouldn't be against its stops. Try lifting the rear of your bike and it moves without lifting the rear tyre of the ground - right?

I'm not sure what you mean by the shock being on its stop. The bump stop rubber (is that what you're referring to?) is there to limit shock travel when fully compressed, without damaging the shock internals.

Under normal circumstances, if you lift the rear of your bike, you will be taking up the static sag. If the static sag is minimal or non-existent (i.e. if you have applied excessive preload) you WILL be able to lift the back of the bike off the ground (assuming you're strong enough).

Not going to get into a bun fight over this but WHY should the spring compress if you tighten the collar, the load on the spring hasn't changed UNLESS the shocks fully extended and against its stop.

...and no, when I said against its stop I meant extended, not compressed and when you say "taking up the static sag" you are demonstrating that the shock ISN'T against its stop - where's the travel coming from, you have taken weight off the spring but yes, if you keep lifting the wheel will come of the ground only when the shock has hit its stop and cant extend any further

[mangocrazy]

Not going to get into a bun fight over this but WHY should the spring compress if you tighten the collar, the load on the spring hasn't changed UNLESS the shocks fully extended and against its stop.

The spring has to compress. The shock has a fully extended length (i.e. what you refer to when you say it's against its stop), so it cannot extend any further. As you tighten the preload collar the only piece of the shock which can yield or deform is the spring. This is the same whether the shock is off the bike or on it. The only difference is that when the shock is on the bike, adding preload has the effect of raising the ride height and reducing the static sag.

...and no, when I said against its stop I meant extended, not compressed and when you say "taking up the static sag" you are demonstrating that the shock ISN'T against its stop - where's the travel coming from, you have taken weight off the spring but yes, if you keep lifting the wheel will come of the ground only when the shock has hit its stop and cant extend any further

Now I understand what you mean when you speak of the shock being against its stop. If you continue to add preload to the shock on the bike you initially take up the static sag and then, when all the static sag is used up, you take the bike into a 'topped out' condition, whereby you actually have to add weight to the bike (normally sit on it) to induce any sag or movement in the suspension.

GP125 racers are like this; they run with zero (or negative) static sag because the bikes are so light. In order to have the correct sag with the rider sat on the bike, the spring has to be preloaded so that the bike is topped out with no rider on board.

[HowardQ]

What have I started??
Still reckon that it does as Mango says, as well, as raise the ride heght, but hey, it's no major argument.