Quote:
Originally Posted by fe1rx
So you can see from the above that the lower shock mount is not particularly flimsy.
An interesting point that is not visually apparent because of the dust boot normally covering the top of the OE shock - the 135i rides on its rear bump stop at normal ride height. The bump stop is very soft and fairly linear in its initial stiffness, but it adds to the total spring rate at the rear and means that the rear has a progressive total rate, even with a linear spring.
Attachment 1138821
Any load going into the bump stop also loads the shock upper mount, so that thing gets a good workout. You can see how soft this upper mount is simply by jacking the suspension and watching it move. I plan on measuring the actual stiffness of this mount also, but have to make another fixture.
In contrast to the OE suspension my Ohlins suspension at ride height has about 27 mm of shock travel from ride height before the bump stop engages. This is "normal" for a performance oriented suspension, where a linear spring rate is desirable in the steady state working range of travel.
Attachment 1138822
I am planning on installing Powerflex upper mounts to stiffen up the upper mount. I will measure the actual stiffness of this configuration before I install it also.
I think the soft upper mount chosen by BMW is an inexpensive way of softening the damping under high frequency low amplitude inputs. Any large amplitude input would immediately bottom out the upper mount and bring the shock into play. With a good shock, I don't believe this gimmick is necessary. |
Hello fe1rx,
Can you please tell me the length of the Ohlins Bump Stop and his P/N?
Thank you for your help and your science!
BR.