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M2 Technical Topics > Suspension | Brakes | Chassis > Ohlins R/T Advice Needed

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      11-15-2019, 06:29 PM   #23
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Quote:
Originally Posted by Megator View Post
I meant 40mm of preload ie compressing the spring by 40mm from its resting position.

I did pick this value from the one being discussed as it seems like an easy mistake to make and to wrongly set the preload to 40mm. I was asking if doing so would lead to your bolded statement above and whether this might be the culprit for the poor ride and suggested this should be checked.

What seems to be missing from Ohlins instructions is what the rear preload should be.

If the car compresses the springs by 16mm due to its weight then as I understand it you only have 16mm of extension if the preload is set to 0. Further increasing the preload would lead to an extension of the shock for the same applied weight which reduces the available extension travel.

This would seem to lead to traction problems over bumps and potholes as the suspension can only decompress so little and compressing requires overcoming the "excess" preload.

To summarise it would seem that the spring rate might be too high (not enough compression due to the weight) or the preload is to high, which leads to not enough extension (rebound? not sure on the term if it is from rest out) travel.

Or? and thanks for your reply
I would imagine it'd be pretty difficult/nearly impossible to set 40mm of preload. If you set the height adjuster to have 40mm of pre load before installing it and the spring it'd be impossible to jack up the lower camber arm to align it into the subframe or knuckle (depending on which side you disconnect to take the OE spring out) since the car would raise before those points aligned. If you tried to set 40mm of preload after the spring was already installed using your typical cheap and narrow coilover wrenches you'd have to put a crazy amount of rotational force in there to get the perch to spin.

16mm of spring movement is like 27mm at the wheel.
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      11-15-2019, 08:20 PM   #24
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Just enough preload to keep the sprig in place with an unloaded suspension is all you really need.

We haven't run into these issues you are having at our shop. Our last customer running 90 and 190 rates at 20+ clicks actually thinks it's still on the soft side. Large bumps didn't upset the car or sent its passengers off of their seats.
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      11-15-2019, 09:35 PM   #25
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Something isn't right. I have the M2 Ohlin set up as you do, and at 15 clicks, the ride borders on plush. I've had my ride height set and professionally corner balanced.
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      11-15-2019, 10:12 PM   #26
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Quote:
Originally Posted by HP Autosport View Post
Just enough preload to keep the sprig in place with an unloaded suspension is all you really need.

We haven't run into these issues you are having at our shop. Our last customer running 90 and 190 rates at 20+ clicks actually thinks it's still on the soft side. Large bumps didn't upset the car or sent its passengers off of their seats.
Quote:
Originally Posted by gsrbri View Post
Something isn't right. I have the M2 Ohlin set up as you do, and at 15 clicks, the ride borders on plush. I've had my ride height set and professionally corner balanced.
I would say there is an installation issue with mine but after the tech couldn't setup the rear properly, I told him to put everything back to what it says in the manual. In fact, he couldn't even break the adjuster on the rear shock loose. So all he did was to set the spring perch 40mm from the vehicle body, which is what the manual says. I watched him do it in front of me and I also double checked the spring perch measurement myself as well. Unless he somehow messed up the shock height (even though he told me he couldn't break it loose), I don't think there is an installation error that I can see. I highly doubt it but maybe I got a defective unit. Btw, mine is corner balanced as well.

Also, just to clarify, it doesn't push me out of my seat in every bump or dip. For the most part, it's just stiff with 18clicks in the rear. However, when there is a bit serious bump or a dip, the rear is literally super jumpy. I can even feel the difference between my front and rear going over speed bumps at very low speeds. The front just beautifully handles it even at speed but for the rear I almost have to come a complete stop otherwise it just skips over the bumps as if there is no suspension in the rear.

Here's another example... After my last track day, I changed my rear to 16clicks (normally run 18-20clicks for the street) just to see the difference. Didn't even say a word to my wife about this change, after a 2-minute ride in the car, her first reaction was "What did you do to your car? It's super bumpy". Just for reference, she never said a single word about the ride quality on my M4 which had MS lowering springs paired with its adaptive suspension (it was a bad choice).

Anyways... Looks like I need to make an appointment and get it checked by someone who is more experienced.
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