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Ohlins DFV 16kg

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Old 03-19-17, 08:47 PM
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Ohlins DFV 16kg

Just finished installing a set of Ohlins DFV revalved for 16kg springs from the factory. At 7 clicks out the overall ride quality is similar to the Bilsteins they replaced which were 8kg front and 6kg rear. The increased spring rate is noticeable over large bumps and undulations but is otherwise relatively comfortable.

The chassis is much more tightly controlled, reacts to inputs faster and has very little understeer. Overall the car feels smoother and easier to drive. I will post some more thoughts on the handling when I've had a chance to go for a longer drive.

Here are the dyno graphs for the front and rear shocks showing 0, 7 and 20 clicks from full stiff. The left axis is in Kgf.



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Old 03-26-17, 05:43 AM
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I did a few hours of driving today, hopefully this feedback will be useful.

Through uphill hairpins, the inside rear wheel spins more easily. I expect this is due to the reduced droop travel.

There are several mid corner bumps that used to bottom out the car quite violently. The rear is now stiff enough to resist this but the front tyres still touch the inner fenders over the biggest hits. Does removing the inner fender liners give much extra clearance?

It's hard to give feedback on the balance of the car as the grip level with semi slicks is high. Through slower corners it rotates a little better and turns in more sharply. At low speed the car feels more agile, however in longer bends the reduced roll angle gives less feedback.

In terms of comfort, for the most part I find the spring rate easy to forget, and the bucking from the driveline is less irritating now that it is more strongly damped. I wouldn't recommend them for a daily driver over rough roads, but for a weekend street and track car I think they are acceptable.

I will add some more comments after I have been to the track.
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Old 03-31-17, 05:02 AM
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Interested in the update after track use.

Also, how may miles have you had with these shocks for now?

Are they properly run in yet?

Thanks,
Konstantinos.
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Old 03-31-17, 10:38 AM
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*You should remove your fender liners and relocate the wiring harnesses up above the unibody sheetmetal level if you haven't done this already. The wire harness just hangs on top of the plastic fender liner stock and gets rubbed through.* I put my liners back in after. My RX-8 is missing a liner and you don't want to run that way. Trimmed would be fine, but missing fills the unibody, fender and door jamb with rocks and leads to more damage.

Does removing the inner fender liners give much extra clearance?

It depends on where the tire is contacting the fender liner on how much extra travel you will "gain" (a big bump will blast your tire into the plastic hard enough to push it against the metal behind it).

On my set-up (18x11 +45 w/ 295/30-18) the tire rubs the fender liner where it is hanging down between the upper two outboard mounting points. If your tire is rubbing in this outer area because of its rounded shape or being unsupported (as in my case) you can just trim the liner back.

If your tire is rubbing the very top deepest part of the fender liner removing the liner won't gain you much travel.




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Old 03-31-17, 09:29 PM
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Originally Posted by Nabu View Post
Interested in the update after track use.

Also, how may miles have you had with these shocks for now?

Are they properly run in yet?

Thanks,
Konstantinos.
I've done about 300km on them.

Originally Posted by BLUE TII View Post
*You should remove your fender liners and relocate the wiring harnesses up above the unibody sheetmetal level if you haven't done this already. The wire harness just hangs on top of the plastic fender liner stock and gets rubbed through.* I put my liners back in after. My RX-8 is missing a liner and you don't want to run that way. Trimmed would be fine, but missing fills the unibody, fender and door jamb with rocks and leads to more damage.

Does removing the inner fender liners give much extra clearance?

It depends on where the tire is contacting the fender liner on how much extra travel you will "gain" (a big bump will blast your tire into the plastic hard enough to push it against the metal behind it).

On my set-up (18x11 +45 w/ 295/30-18) the tire rubs the fender liner where it is hanging down between the upper two outboard mounting points. If your tire is rubbing in this outer area because of its rounded shape or being unsupported (as in my case) you can just trim the liner back.

If your tire is rubbing the very top deepest part of the fender liner removing the liner won't gain you much travel.
Thanks mate, I removed the fender liners and tucked the harness above the sheetmetal. The liners are only a few millimetres thick where the tires are rubbing so I'll definitely put them back in.

I have done some measuring and by my calculations the front bumpstop needs to be spaced down quite a bit in order to be effective. At a ride height of 25.5" I have 30mm of droop, 70mm of bump before hitting the fender liner and at that point there is still another 30mm before the bumpstop would be engaged.

I will have to double check these figures but I've attached my spreadsheet with the rough calculations. I will likely put a 42.5mm spacer in the front and a 10mm spacer in the rear so that both bumpstops are engaging at around the same time.

I estimated the behaviour of the bumpstop using data from another Ohlins bumpstop of a similar size.
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Shocks.xls (38.5 KB, 18 views)
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Old 04-01-17, 12:56 AM
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What front tire are you running?
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Old 04-01-17, 01:33 AM
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255/40r17
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Old 04-01-17, 11:40 PM
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That is the correct diameter tire...

And you calculated the suspension motion ratio into it when seeing how much travel there was to the bumpstop?

So, not just like "I have 2" from top of tire to top of fender and 2.5" from top of shock body to bumpstop." type of eye-balling?

Hard to see how Ohlins would F that up you know...
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Old 04-04-17, 12:35 AM
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At full droop I measured 3.25" shaft travel before the bumpstop. Dividing by the motion ratio of .63 gives roughly 5" travel at the wheel. Unless I'm mistaken, if you have less than 5" travel from the wheel to the inner fender, the bumpstop won't engage. I will remove the springs so I can confirm these measurements.
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Old 04-29-17, 06:13 PM
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Last night I removed the springs from the shocks to check my measurements and they are pretty close.

With a 44mm spacer, there is 35mm above the tire when the shock touches the bumpstop. The tire hits the sheet metal before the bumpstop goes solid.

With a 47mm spacer, the bumpstop goes solid with a couple of millimetres between the tire and the sheet metal.
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Old 04-30-17, 06:33 AM
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Worth noting that going from 255/40-17 to 245/40-17 would give you 4mm and I don't think would cost much in terms of performance, if anything...
I went from 255/40-17 front NT01s to 235/40-17 (8.5" wheels) and did not notice any particular loss of front grip.

Last edited by ZDan; 04-30-17 at 06:38 AM.
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Old 04-30-17, 08:06 PM
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Originally Posted by ZDan View Post
Worth noting that going from 255/40-17 to 245/40-17 would give you 4mm and I don't think would cost much in terms of performance, if anything...
I went from 255/40-17 front NT01s to 235/40-17 (8.5" wheels) and did not notice any particular loss of front grip.
Good idea, I think I'll do that when I next order tyres.

In the meantime, I am not sure whether I should simply maximize front and rear travel or whether it's more critical to have the front and rear bump stops engaging at the same time. What do you guys think?

I'll probably buy a number of different spacers so I can try some different combinations.
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Old 05-02-17, 06:16 AM
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Originally Posted by mrselfdestruct1994 View Post
I did a few hours of driving today, hopefully this feedback will be useful.

Through uphill hairpins, the inside rear wheel spins more easily. I expect this is due to the reduced droop travel.
Try using some helper springs.
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Old 05-19-17, 07:02 PM
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Last night I removed the standard 10mm spacers from the front shocks and replaced them with a set of 1", 3/4" and 1/2" spacers from Allstar Performance for a total of 56mm. I used the split collar spacers from this 14mm kit. The dust boots had to be removed for clearance.

I measured 30mm of droop travel, 30mm of bump travel before touching the bumpstop and another 40mm before the bumpstop was solid. I measured from the rim to the guard so there will be some error being introduced from the camber curve of the suspension. There is approximately 10mm between the tire and the inner fender sheet metal which will be closer to 2.5-5mm with the inner fender liner installed.
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Old 05-21-17, 08:40 PM
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Originally Posted by mrselfdestruct1994 View Post
Last night I removed the standard 10mm spacers from the front shocks and replaced them with a set of 1", 3/4" and 1/2" spacers from Allstar Performance for a total of 56mm. I used the split collar spacers from this 14mm kit. The dust boots had to be removed for clearance.

I measured 30mm of droop travel, 30mm of bump travel before touching the bumpstop and another 40mm before the bumpstop was solid. I measured from the rim to the guard so there will be some error being introduced from the camber curve of the suspension. There is approximately 10mm between the tire and the inner fender sheet metal which will be closer to 2.5-5mm with the inner fender liner installed.
Shock shims? Them's called packers where I'm from..

Wait, why are you using packers to *reduce* stroke?
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Old 05-22-17, 04:31 PM
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Originally Posted by Valkyrie View Post
Shock shims? Them's called packers where I'm from..

Wait, why are you using packers to *reduce* stroke?
The front shocks have too much shaft travel and never engage the bumpstops. This allows the front tyres to hit the inner fenders in some situations. The 56mm spacer still allowed a tiny amount of scrubbing so I've also raised the front ride height to 25.5", I expect this will give sufficient clearance now.
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Old 05-22-17, 05:56 PM
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Originally Posted by mrselfdestruct1994 View Post
The front shocks have too much shaft travel and never engage the bumpstops. This allows the front tyres to hit the inner fenders in some situations.
There is no such thing as too much travel.

The 56mm spacer still allowed a tiny amount of scrubbing so I've also raised the front ride height to 25.5", I expect this will give sufficient clearance now.
This is how it's supposed to be done. Or you could get stiffer front / softer rear springs.

BTW, scraping the fender liners isn't the end of the world as long as you aren't burning holes in them.
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Old 05-22-17, 06:56 PM
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@_@

Finally dawned on me why you had too much compression travel.

Going from 11K to 16K springs you have less spring compression at rest, so to get down to the 25.5" ride height at the fender you probably had to shorten the lower shock mount beyond the amount recommended by Ohlins.

Alternately, you could have kept the shock lower mount at the recommended height and dropped the spring lower perch down to the point you were at the ride height you wanted and preserved the same droop to compression ratio Ohlins engineered. But the spring would have been loose at full droop without a tender spring.

Which is what you are doing now by lowering the spring top perch, but you are sacrificing shock stroke to do it.
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Old 05-22-17, 07:41 PM
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Originally Posted by BLUE TII View Post
@_@

Finally dawned on me why you had too much compression travel.

Going from 11K to 16K springs you have less spring compression at rest, so to get down to the 25.5" ride height at the fender you probably had to shorten the lower shock mount beyond the amount recommended by Ohlins.

Alternately, you could have kept the shock lower mount at the recommended height and dropped the spring lower perch down to the point you were at the ride height you wanted and preserved the same droop to compression ratio Ohlins engineered. But the spring would have been loose at full droop without a tender spring.

Which is what you are doing now by lowering the spring top perch, but you are sacrificing shock stroke to do it.
Protip: If you get stiffer springs, they have to be proportionately shorter or your ride height will be way too high.

I made this mistake with my MR2 once.

OTOH, I don't think full-length adjustable coilovers particularly care where you set the ride height adjustment so long as you achieve the right ride height without letting the springs flop around at full droop. Unless you run out of ride height adjustment (which he probably did assuming the springs are the same length).

You definitely want helper springs on an FD with 16kg springs, especially in the rear, because it doesn't weight enough to compress the springs enough to achieve sufficient droop travel if the springs are preloaded.

BTW, what is the front/rear recommended ride height for Ohlins coilovers?

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Old 05-22-17, 08:04 PM
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I went for the lowest recommended setting by Ohlins and with the 11K stock springs my car measures 25.25" to the top of the front fender arch and 25.5" to the top of the rear fender arch with a mostly stock weight FD on 25" tall tires.

If a front corner weight is 318Kg (700Lbs) on an 11K spring it will compress the spring 28.9mm and it will only compress a 16K spring 19.9mm.

This alone doesn't seem to account for the troubles the OP is having since he is at 25.5" ride height.
Still, by increasing the shock and lower mount length and putting tender springs in or letting the spring clank around the OP could stop the tire from hitting the top of the fender liner without sacrificing any stroke with spacers shortening the shock shaft.

Basically, compression stroke into droop stroke to preserve the correct ratio.
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Old 05-22-17, 08:33 PM
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Originally Posted by BLUE TII View Post
I went for the lowest recommended setting by Ohlins and with the 11K stock springs my car measures 25.25" to the top of the front fender arch and 25.5" to the top of the rear fender arch with a mostly stock weight FD on 25" tall tires.

If a front corner weight is 318Kg (700Lbs) on an 11K spring it will compress the spring 28.9mm and it will only compress a 16K spring 19.9mm.

This alone doesn't seem to account for the troubles the OP is having since he is at 25.5" ride height.
Still, by increasing the shock and lower mount length and putting tender springs in or letting the spring clank around the OP could stop the tire from hitting the top of the fender liner without sacrificing any stroke with spacers shortening the shock shaft.

Basically, compression stroke into droop stroke to preserve the correct ratio.
I can't even imagine how you could be hitting the fender liners with 16 kg springs if you're running the recommended ride height for 11 kg springs. They're so much stiffer I don't see why you'd even need full-length bump stops.

Unless the tires/wheels are badly fitted.

Are they definitely hitting the top of the fender liners? Because if they're hitting anywhere, it's more likely they're hitting the sides near the fender lip, where the liners are slightly lower.

What size are the wheels/tires?
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Old 05-22-17, 09:58 PM
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With the standard setup there is roughly 4.13" shaft travel before the bumpstop is solid. That is about 6.5" at the wheel. That is probably enough travel for the wheel to go through the bonnet.

I don't see this as a problem, the bumpstop just needs to be shimmed correctly for the ride height and spring rate.

They only engage over very big dips and bumps so it is probably not going to be an issue for most people.
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Old 05-22-17, 11:16 PM
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Originally Posted by mrselfdestruct1994 View Post
With the standard setup there is roughly 4.13" shaft travel before the bumpstop is solid. That is about 6.5" at the wheel. That is probably enough travel for the wheel to go through the bonnet.

I don't see this as a problem, the bumpstop just needs to be shimmed correctly for the ride height and spring rate.

They only engage over very big dips and bumps so it is probably not going to be an issue for most people.
That's pretty much a textbook case of needing a shorter spring and a tender/helper spring.

You don't want to be picking your tires off the ground if you can help it. Theoretically you have less than an inch of droop stroke.

You could be gaining droop stroke equivalent to the thickness of your packers.

25.25" to the top of the front fender arch and 25.5" to the top of the rear fender arch
I assume the tops of the fenders aren't exactly the same height. How does that look in terms of actual rake (based on, say, the angle of the frame rails, rather than the aero bits). I've been told on good authority that FDs don't like rake and if anything are faster with the front higher (unless you've got a lot of rear aero).
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Old 05-22-17, 11:38 PM
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I assume the tops of the fenders aren't exactly the same height. How does that look in terms of actual rake (based on, say, the angle of the frame rails, rather than the aero bits). I've been told on good authority that FDs don't like rake and if anything are faster with the front higher (unless you've got a lot of rear aero).
That is 140mm to the jacking rail in front and 150mm in the rear.
I have the Top Fuel spoiler, which doesn't do as much as a GT wing, but feels more planted over 90mph than 1993 stock.



In stock class form with stock springs and GAB Super R shocks my FD had quite a bit more rake. I would say closer to 25mm higher in the rear.
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Old 05-23-17, 01:00 PM
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Originally Posted by BLUE TII View Post
If a front corner weight is 318Kg (700Lbs) on an 11K spring it will compress the spring 28.9mm and it will only compress a 16K spring 19.9mm.
Gotta account for motion ratio! FD front springs are higly leveraged, MR ~0.61

Say 300kg front corner (with unsprung mass subtracted), the force on the spring is going to be 300kg/MR or ~300kg/0.61 = 492 kg, so 11kg/mm spring compresses 45mm and 16kg/mm spring compresses 31mm (which jibes with the 30mm droop that mrselfdestruct measured).

To get droop travel at the wheel, you have to divide by motion ratio again. With zero preload, 11kg at front will have 74mm of droop travel at the wheel, and 16kg have 51mm.

TBH I didn't even measure any of this stuff when I installed my DFVs or when I went to 13kg/mm fronts, but thinking about it now it does seem like there is entirely too much travel available in the bump direction, leading to ventilated inner fenders...
I also bottom out way too easy, would prefer to hit bumpstops first. So I might do something to reduce my bump travel as well...

No adjustment changes the fact that if you want a given ride height with a given tire size, there's only so far the wheel/tire can move upward before contact. Only way around it is to either run a higher ride height or limit bump motion at the shock.
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