Hi all, just got my DFV yesterday and found an issue in its mounting instructions about the rear spring preload, the manual calls for 7mm for the 8k spring, and in the table right after it says 20mm. I wonder which one should I use? The car will be 99% street driven.
I checked sakebomb's posting about the rear preload, looks like 20 is more appropriate, if that's the case, what's the distance between the spring adjuster and height adjuster should be for this setup? Thanks

 

Go 15-20mm <peload> and measure , have 15mm on mine with 105nm iirc if car is too low adjust at lower fork only.

 

What alignment specs you would recommend for 99% street driving with the ohlins?

 

Have a chat with your supplier they may have more xp than myself

 

Don't use someone else's custom specs. They may not work for you for a million reasons.

Desired alignment spec depends so much on your actual preferences and your own setup. You should research what each setting does and how you'd like to use it.

Or...if not, then using the factory specified ranges is just fine. The AP2 spec is a good one to use. They're meant to work well enough in all situations. If you plan to change something, find out why you're changing it first.

 

If you wanted to run 20 mm preload I think you could theoretically ball park it off of the 7 mm measurements by taking off the difference (13 mm) for the spring length (total 180 mm), and add the difference to the distance between the height adjuster and fork (total 25mm). I'm not sure how static vs active compression of the shock will factor but this will get you into the ball park. I would also note that in general I take the manual settings and measurements as ball park recommendations anyway as there's so much variance from car to car, components, and individual preferences. For example, not all of the springs I got from Ohlins were exactly 200mm so I had to do some additional math. Chances are when you first mount the shocks to the car not all 4 corners will be exactly the same ride height so you will need to do some adjusting anyway and likely the spacing between the collars will vary from the manual once you're done.

I agree with others that anywhere from 15-20mm is acceptable. I think with 20 mm the ride height at the rear may be some what limited with the stock shock forks however that may be fine if you aren't aiming to be too low. For a street driven car I would stick to OEM alignment.

 

So according to the diagram the spring is 193mm and the distance between the adjuster is 22mm. To maintain the same ride height at 20mm preload, the spring will be 13mm shorter, and the distance between the adjusters will be 22+13=35mm. My understanding is once I mount it on the car, the spring will be compressed to the same length no matter the preload, so to maintain the same ride height, I would need 22mm between the adjusters as well. Same for the case if I want 15mm preload. I'm not 100% sure, let me know if you agree. Thanks

 

I might have had a stroke when I wrote that. I think I made 2 logical mistakes. (1) I failed at math and 22+13 is indeed 35 and not 25 and (2) I agree that the shock fork adjuster should likely move up with the spring perch adjuster (and not downward) to maintain ride height. I agree that the spring should theoretically compress the same amount from its static position regardless of preload. However with the higher spring perch position you get with higher preload I believe this should also raise your ride height. That is why aftermarket forks are available for the Ohlins as the OEM forks do not allow adequate lowering when running high preloads. Thus you must move the shock fork position upward correspondingly to maintain ride height.

I think I have it right this time? I guess that's part of the reason why I didn't go into engineering.

 

Step 1.
Delete complexity.

Lets use 20mm of preload for the example at hand.
And lets say you want to use Ohlins' recommended ride height settings.

Measure the spring when you take it out of the box. Before you put it onto the shock.

They should measure about 198mm. Don't send them to NASA to measure via space shuttle laser beam. Just use a tape measure.


Put the shock together with all the measurements that Ohlins recommends. Measure everything they recommend to measure.

Measure the distance between spring and bottom perches. Write it down as "thread distance". Or call it whatever you want.




Now.
Spin the spring perches up so that the spring is compressed and 20mm shorter than you started when you took them out of the box.
198-20 = 178mm

Then.
Spin the BOTTOM perches upward so that the "Thread distance" is the same as what you measured and wrote down.

Step 2.
Put them on the car.
Enjoy.

 

Thank you for your picture and explanation, I think we are on the same page, the factory diagram calls for 22mm thread distance, and I will make it 22 whatever preload I use