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Re: Will Dinan Springs from an M5 fit my 540i?
Marinakorp, keep in mind he's considering Dinan "lowering springs"...not OEM M5 springs. Some stock M5's have a higher ride height than a 540i sport, especially in the front. M5's generally sit 1/2" higher than my 540i sport. My stock 540i sits the same height as an M5 with H&R's 29441 spring. I agree that installing stock OEM M5 springs on an early 540i car (that weighs about 250lbs less) will result in a higher ride height than OEM 540i. But....I would not use this logic to predict ride heights between Dinan M5 lowering springs & OEM 540i sport springs, when installed on the same car.
The Dinan suspension for M5 has extremely low ride height...too low in the rear, IMO. The difference in axle weights is not going to affect the ride height much with higher rate Dinan springs. I would expect an early 540i car to sit about 1/4" to 1/2" higher than an M5 with the Dinan springs. If you have a lighter '97 or '98 car, the weight differential (between M5) will have a similar effect to removing one 150# passenger in the front seat and one 150# passenger in the rear. My car hardly moves when I add or remove passengers. Guessing...this Dinan spring setup should put the car somewhere between 13-1/2" to 14" from fender lip to roundel. The rear might be lower than that because some M5's with these springs slam to under 13". When I bought replacement BMW componentry for my 540i suspension, I discovered that later M5 & 540i bumpstops and spring cushions were identical. IMO, it should still be as low or lower than OEM sport 540i springs. Even more significantly, the Dinan front camber plates add about 3/8" to the ride height. If you're not using them, the car may sit lower than a Dinan'd M5 with the plates. Last but not least, the later-year 540i cars are heavier, as they installed more gizmos and safety hardware. A loaded 2001 and newer 540i comes with M5 springs, direct from BMW. Same part#'s.
This seems like a decent upgrade, if it's under $400 & you want stiffer front springs or lower ride height. I don't want either because I'm more concerned about two things: 1) neutral handling and 2) adequate jounce travel. I intend to drive at 100% on a rough road/track without touching bumpstops at 80+ MPH. You can't do this with a soft, slammed setup. Even 3200# Corvettes with stock ride height & standard suspension have problems doing this & they run 2x spring rates compared to M5. I have serious doubts whether the Dinan rear springs are stiffer than OEM rears. They have the same free (uncompressed) length as OEM (around 13-1/2"), yet their compressed length is shorter by an inch. Rough calculations indicate their spring rate is almost 10-20% lower. On a positive note, the Dinan M5 setup on your lighter car will have a little more jounce travel than folks get when installing them on an M5. IMO, the stiffer Dinan front springs & softer rear springs will promote understeer. You may need a bigger rear bar and camber plates to compensate. Of course...that Dinan mystique may provide a placebo effect. In conclusion, I wouldn't bother. To each his own.
If you want better street handling, get a set of Konis, swaybars & maybe camber plates....forget the spring swap. Any spring swap on the OEM Boge struts and shocks is a mistake. This equally applies to M5 or 540i/6.
Last edited by Lscman; 5th August 2004 at 17:12.
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