How bad did I get screwed by my Ohlin vendor

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You ordered a progressively-wound spring?<BR><BR>

Uh...no. I thought Ohlins had progressive springs. Sounds like I'm wrong. Sorry to add to the confusion.

And to continue the confusion, can someone 'splain to me how increasing pre-load would reduce bottoming out? It's a linear spring with, as far a I can tell, a neutral rate linkage.

It seems to me that the only thing the pre-load should be used for is to keep the front/rear ride heights correct.

BTW VR, I can't find my sag measurements for the bike-alone case, but with me on it (and my trusty metrologist - I mean 13yo daughter making the measurements), I got this:

Stock Showas w/ 40K miles

Front A-C=60mm
Rear A-C=60mm

With the Ohlins initially I had

Front A-C=45mm
Rear A-C=45mm

As I noted in your other thread, I ultimately reduced the preload in the rear by about 4 or 5 turns because I felt that the bike had a little too quick of turn-in and required a bit more corrections mid-turn. I don't know how much pre-load it has now - not much I suspect.

Cheers,

Ben

If you put 100-lb of spring preload on a shock, it won't move until after 100-lb of force are applied. Then it moves at the same rate it did without preload based on the spring rate. Wtih preload, it takes 100-lb more force to bottom the shock. Thus, bottoming out is reduced.

- Mark

Hmm. But the spring is compressed by the amount of the pre-load so there is less of it left before bottoming out?!

Sorry, I still don't get it.

Ben

If the "bottoming out" is caused by coil bind, then you're right, there would be less travel. But for a properly set up shock, bottoming out is caused by hitting a rubber stop on the shock rod with the spring coils still free and able to compress further.

IOW, a shock with and without preload has the same total travel. Preload just changes the load required to start the shock compressing. With no preload, it starts compressing with the very first pound of force. With 100 lb of preload, it does essentially nothing for the first 100 lb and then starts compressing on the 101st lb.

- Mark

<BR>An interesting aside about bottoming the suspension - - Most usually, bottoming is caused from the mass of the bike accelerating into the shock. And not the other way round. By that meaning, suspension bottoming usually cannot be caused by the wheel accelerating the suspension arm into the shock.

A suspension has 2, ahh . . 'sides' call it. The wheel is on one side of the suspension, and the bike is on the other. And either side can push on the shock.

The wheel is limited in how hard it can push on the shock. It is limited to the weight of the bike, you know? The wheel can only push so hard on the shock before the bike begins to rise.

Visualize riding over a elevated bump in the road, like a tree branch. At some point a large enough bump begins to loft the mass of the bike, instead of compressing the shock.

But when the bike is accelerating into the shock, like when landing a jump say, well there's no limit. The bike has the ground to push against.

- - -

The suspension has two 'sides'. The 'bike' side and the 'wheel' side. And the shock deals with accelerations from both 'sides'.

And the 2 simple examples. A bike landing a jump is an example of the bike accelerating into the shock. And striking a large tree branch in the road is an example of the wheel accelerating into the shock.

The suspension can be tuned to work well for either event. But more often one capability is unwittingly sacrificed in pursuit of the other.

- - -

And I'm finally around to it. Ben your intuition is correct. The spring preload does not reduce the incidence of bottoming, in an A/B comparison over the same terrain say.

A really good experimental picture is formed if you imagine dropping two bikes onto their wheels, from three feet off the ground.

Say that neither bike has any suspension damping. Both bikes have only their springs. And one bike has a 100N/mm spring, and the other a 50N/mm. And to start, image both springs as having zero preload.

A spring rate of 100N/mm will arrest the fall in half the distance of a spring with 50N/mm rate.

Experiment with changing preload and you'll see that if a particular spring rate will not arrest the fall, then no amount of preload can change that.

- - -

A higher spring rate reduces suspension travel, and that's one way to reduce bottoming. But shocks have damping, and that makes it look like there are two ways to go about reducing suspension travel and bottoming.

Increased spring rate reduces compression travel. And increased damping reduces compression travel.

But here's the thing, using increased damping as the method of arresting the acceleration of the bike toward the ground has negative handling and comfort side effects.

In blind taste tests, increasing damping to fix the problem of bottoming out makes the ride very uncomfortable or sharp. Road bumps feel sharper because due to the high suspension damping the wheel can move the bike more.

Increased spring rate can be used to reduce bottoming with a positive impact on comfort and handling. Less damping means the wheel travel is less restricted when hitting road bumps. So instead of lofting the bike a little when hitting a bump, the bike stays put and the suspension arm moves.

- - -

An extreme example to visualize. Start with two identical bikes, one with a much higher rate spring, but equal compression damping curves.

Now, remove the damping altogether. The bikes will both ride very smooth. But the lighter-rate-springed bike will feel less controlled because the suspension will 'pogo' over a greater distance of suspension travel.

Yes sure, a feeling of control can be 'simulated' with increased damping. The ride generally suffers but that's not the worst of it. More importantly, the 'feeling of control' that's created with high damping is really more of a simulation and illusion.

The increased damping creates the illusion of a higher rate spring by reducing suspension travel, but here's the kicker. For every bit that the wheel doesn't move when hitting a bump, the bike moves instead.

Increased damping reduces wheel movement, but increases bike movement. And increased bike movement erodes traction and control.

Nothing says controlled ride like a high rate spring. And nothing lands a jump without bending parts like a high rate spring.

Nothing reduces ride comfort more than increased compression damping. Nothing bends suspension parts like high compression damping. And nothing erodes traction and control like bike movement from bumps caused by high compression damping.

- - -

Then what the heck good is damping? Well I think the best way to answer that is to understand damping. A basic philosophy that leads to understanding is, springs are for the bike, damping is for the wheels. Or another way, springs keep the bike from moving, damping keeps the wheels from moving.

- Jim<BR><BR>

Damn Jim, my suspension understanding just doubled!

Thanks!

Jim