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Ohlins DFV's - Review

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Old 12-08-2014, 12:24 PM
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I can confirm that stock DFV fronts do have hysteresis at the stiffest settings. I don't know about the stock rears (didn't get mine dynoed prior to the valve). Pretty sure my re-valved rears don't have any hysteresis.
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Old 12-08-2014, 01:30 PM
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Every shock will exhibit some hysteresis. From the testing I've done, hysteresis appears to be a function of how much the shims are being exercised. This, in turn, is a function of piston velocity, shim stack design and adjustment settings. For the Ohlins TTX25 design, seal friction doesn't appear to play a part in the hysteresis. Only the adjuster settings and the piston velocity. At full soft, I did not see any notable hysteresis, which would imply the seal drag has a minimal effect.

EDIT: the plots below are from an Ohlins TTX25 damper (really a Cane Creek damper), not a S2k Ohlins DFV

Here's the range of adjustment. Blue is every adjuster (4-way adjustable) at full stiff. Green is every adjuster at full soft. You can see the green damper curve doesn't show any hysteresis while the blue curve exhibits notable hysteresis below 6 in/sec.


Here's the same damper at a given setting, overlaying CVPs for 0-1 in/sec, 0-2 in/sec, etc.... all the way up to 10 in/sec. You can see that the hysteresis is lowest (I know it's tough to see in there) for the 0-1 in/sec curve. The 0-10 in/sec curve exhibits the most hysteresis.


FYI, the overlay of the 10 incrementing velocity curves is how you manually generate a PVP.
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Old 12-08-2014, 01:52 PM
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Originally Posted by nmrado View Post
Here's the same damper at a given setting, overlaying CVPs for 0-1 in/sec, 0-2 in/sec, etc.... all the way up to 10 in/sec. You can see that the hysteresis is lowest (I know it's tough to see in there) for the 0-1 in/sec curve. The 0-10 in/sec curve exhibits the most hysteresis.
So is it correct to interpret that at this setting, hysteresis is the least when the piston is changing direction from having been moving at a slower speed? As in, there is some residual effect from super high-speed movements that tends to induce hysteresis on the return movement?
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Old 12-08-2014, 02:08 PM
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Originally Posted by thomsbrain View Post
So is it correct to interpret that at this setting, hysteresis is the least when the piston is changing direction from having been moving at a slower speed? As in, there is some residual effect from super high-speed movements that tends to induce hysteresis on the return movement?
Yes... mostly. A better way to think about it is: the hysteresis is a function of the fluid velocity (or mass flow rate because oil is considered incompressible) through the piston and shim stack. Fluid velocity through the piston/shims is affected by piston velocity and adjuster settings. If a rebound adjuster (typically a bleed style) is fully open, more fluid will flow through the adjuster orifice and less fluid will flow through the piston and shims, resulting in a lower fluid velocity through the piston/shims.
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Old 12-08-2014, 03:09 PM
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Originally Posted by nmrado View Post
Originally Posted by thomsbrain' timestamp='1418079178' post='23430979
So is it correct to interpret that at this setting, hysteresis is the least when the piston is changing direction from having been moving at a slower speed? As in, there is some residual effect from super high-speed movements that tends to induce hysteresis on the return movement?
Yes... mostly. A better way to think about it is: the hysteresis is a function of the fluid velocity (or mass flow rate because oil is considered incompressible) through the piston and shim stack. Fluid velocity through the piston/shims is affected by piston velocity and adjuster settings. If a rebound adjuster (typically a bleed style) is fully open, more fluid will flow through the adjuster orifice and less fluid will flow through the piston and shims, resulting in a lower fluid velocity through the piston/shims.
That makes sense. I think where I was confused was that there was less hysteresis at a given piston speed if the overall dyno sweep was slower. So 1 in/sec on a 0-1 sweep seemed to have less hysteresis than 1 in/sec on a 0-10 sweep. Or am I reading the graph wrong?
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Old 12-08-2014, 03:15 PM
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Originally Posted by thomsbrain View Post
That makes sense. I think where I was confused was that there was less hysteresis at a given piston speed if the overall dyno sweep was slower. So 1 in/sec on a 0-1 sweep seemed to have less hysteresis than 1 in/sec on a 0-10 sweep. Or am I reading the graph wrong?
Correct, because the shim stack is being exercised much less by the 1 in/sec peak velocity vs. the 10 in/sec peak velocity.

EDIT: sorry to derail your review thread, Terrible01.
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Old 12-08-2014, 03:32 PM
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Originally Posted by nmrado View Post
Originally Posted by thomsbrain' timestamp='1418083796' post='23431045
That makes sense. I think where I was confused was that there was less hysteresis at a given piston speed if the overall dyno sweep was slower. So 1 in/sec on a 0-1 sweep seemed to have less hysteresis than 1 in/sec on a 0-10 sweep. Or am I reading the graph wrong?
Correct, because the shim stack is being exercised much less by the 1 in/sec peak velocity vs. the 10 in/sec peak velocity.

EDIT: sorry to derail your review thread, Terrible01.

It's still on topic in my eyes. I'm even learning a bit here. lol
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Old 12-08-2014, 04:45 PM
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So given the dyno plots that are shown, I'm asking the more knowledgeable guys what you think the max spring rate is that could be run on these with off the shelf valving. For the all purpose use that I'm after I don't see the need to have them revalved and was looking most towards a 650/550lb setup or 12/10k setup.

I recently ran mine on the off the shelf rates at an autocross and found 2 from stiff up front and 6-7 from stiff out back worked very well for me. I haven't tried running them at full stiff but also haven't felt like they needed it. I was running the fronts a little stiffer to make up for the lack of massive front sway. If I had a little more bar I'd likely run them a tad softer.
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Old 12-08-2014, 06:02 PM
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[attachment=70482::] DFV makes an average of 325 lbs of rebound damping force at 2"/sec on full stiff

If you look at the national competitor's rear penske's 8300 dyne plot, controlling 750lb springs, middle setting is 180 lbs at the same speed. Softest is 60 lbs and stiffest is 300. I've attached the pic but again, it is failing to show (on desktop anyway)

[attachment=70483::]
Attached Thumbnails Ohlins DFV's - Review-image-3551858384.jpg  
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Old 12-09-2014, 12:47 AM
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Originally Posted by //steve\\ View Post
So given the dyno plots that are shown, I'm asking the more knowledgeable guys what you think the max spring rate is that could be run on these with off the shelf valving. For the all purpose use that I'm after I don't see the need to have them revalved and was looking most towards a 650/550lb setup or 12/10k setup.

I recently ran mine on the off the shelf rates at an autocross and found 2 from stiff up front and 6-7 from stiff out back worked very well for me. I haven't tried running them at full stiff but also haven't felt like they needed it. I was running the fronts a little stiffer to make up for the lack of massive front sway. If I had a little more bar I'd likely run them a tad softer.
+1

I would like to know this as well
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