Quote:
Originally Posted by parthpatel1
Nice write-up. Out of curiosity, does anyone know when the OEM suspension usually needs to be replaced in terms of mileage on the F15's? I have lowering springs on my stock suspension and trying to decide if I should just buy coilovers now if I am going to have to replace them soon.
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Quote:
Originally Posted by jmack123
I believe if I recall correctly, most people cite between 50-75k miles.
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I agree with jmack123. 50-75k is about right for most street dampers dual-tube units. Bilsteins monotube units seem to last longer than that and maintain good dampening characteristics.
There is a range of what dictates actual replacement. Technically, shocks are still 'good' if they are not leaking, but the reality is the damping force reduces over time even if they are not leaking. The oil within the shock wears out as do the metal shims and seals. This leads to decreased performance overall and it happens slowly over time.
For example, most high-end coilovers that are serviceable generally recommend rebuilding in the 25-50k mile range to maintain optimum performance.
True race shocks needs rebuilds after "x" number of hours - an incredibly short amount of time.
Street shocks/dampers generally start to degrade noticeably above 50k miles. This depends on a variety of factors... how they're used, where they are used, and the temperatures in which they are used.
Every BMW I've owned or a family member has owned the shocks and bump stops are pretty much worn out by 75k miles.
Bumpstop Rant
The one thing I've learned about later series BMWs, say E90 and newer, is that they rely heavily on the bumpstops to act as a secondary spring. So, the performance improvement of new OE BMW bumpstops is large. They have a massive effect on the ride smoothness in tandem with the shocks. Also, in my previous BMWs I bought many other brand bump stops to see if there was a viable alternative to OE as they are relatively expensive ($30+ each) and I have not found an alternative that was visually extremely similar. For that reason, I stick with OE BMW brand for this component as it plays a big role in how the car rides and this part also time/labor intensive to replace (aka, PIA to replace). Not worth it to go aftermarket for that piece from what I've seen.