Hi, this is to answer your question and also to address someone who asked about winter driving with the Z4:
The regular Z4 3.0si has good ground clearance, especially if compared, for example, to the E46 M3 and it's very low front spoiler. The clearance in Z4 3.0si is about the same as the E87/1-series, in both you sit at about the same height and have practically the same ground clearance - clearly less than the normal E90 or E92 for example. This is with both having the optional sports suspension installed from the factory (15mm lowered suspension and much stiffer and harder, not to mention other major changes.) Without the sports suspension, your clearance is even better, but your handling will suffer quite a lot.
The Z4 M (Coupé or Roadster) has less clearance (due to having the much more lowered M Sports suspension by default), but still more than the old E46 M3 had, again mainly because of old M3's low front spoiler. You have to be careful in the wintertime not to scratch it on snow or ice. I've driven the Z4MC several times now during the winter and it's not a problem to drive as an everyday car (warm and comfy too, seat heaters warm up really fast) but you gotta be careful with icy and/or snowy parking lots and such, first to make sure that you don't hit hard ice with the bottom (luckily the Z4MC has excellent bottom insulation and protection), and second to make sure you don't scratch or ruin the front spoiler or the side panels by running into a spot with a high or thick pile of ice and/or snow on it. If you're careful, you don't have to worry about any more problems than you would with pretty much any other car -
it's an M car and to protect it you should drive it accordingly, carefully, and with respect, and most people do - this avoids 99% of winter problems. During the summer, you shouldn't have to worry about the clearance on either, Z4 regular or M - only if you have some really nasty potholes on the roads, road constructions or annoying stop-and-go type road obstacles, you need to be careful especially with the Z4 M to take them real slow to avoid ground contact. If you need to, stop and get out of the car to check, if you're not sure that the front spoiler can make it without touching the ground. It's worth those few extra seconds vs. the repair bill.
For winter with the Z4 M, 18" winter wheels and tires are a must to keep the clearance height, smaller ones would bring it down more (and 17" probably wouldn't even fit because of the large brake calipers - a good combo for the Z4 M (Coupé or Roadster) is 18" for winter, 19" for the summer.) In cold, icy and snowy climates such as all of Scandinavia, northern Canada etc, 18" studded winter tires are the best choice. The best winter tire by far on the market right now seems to be the Continental WinterViking 2 with it's non-symmetrical oval-shaped "brilliant" stud-technology. (It has won practically every winter tire test that it has been on, and it's also my experience that it is the best, having used it myself on multiple vehicles (and my own), including sessions of very hard test driving involving the new E70 X5s.) Nokian's HKPL5 comes close, but just can't match it for quietness in all conditions and traction in normal fall or spring conditions when there suddenly is no snow, but you still have the winter tires on.
(Unfortunately this is in Finnish language - but the pictures give you a slight idea of how the studs differ from traditional studs:
http://www.conti-online.com/coremedi...main01_fi.html)
Conventional winter tire stud vs. the WV2 brilliant stud technology demo:
http://www.conti-online.com/coremedi...main01_fi.html
The WinterViking2 is well available in large sizes such as 17" and 18". Some sizes are even available as SSR (Run-flat) models, even though I don't recommend Run-flat technology on any BMW for any tire, in any situation - when you buy new tires for a new BMW, summer or winter, get the BMW M tire puncture fix kit and get regular non-runflats (As far as summer tires, Pirelli P Zero Nero and ContiSport 2 (haven't tried CS3 enough to judge yet) are some of my favorites, depending on the purpose, with the Pirelli being the best general purpose every-day driver that still has enough grip on it to haul ass hard even under M BMW's and pull off 4.x 0-100km/h times.
The WinterViking2 is also the first winter tire along with the model year 2006 Nokian Hakkapeliitta 5 to have a speed rating of T (Which means sustainable top speed of 190km/h). Most studded winter tires used to have a top speed rating of Q previously, which meant only 160km/h of sustained speed, which was one of the reasons lot of people who really would have benefited from studded winter tires, went with stud-less high-traction winter tires instead, as they have always had higher speed ratings. But as far as winter tire features go, they are practically useless (and
deadly dangerous) in a cold enough climate, as winter tires, non-studded tires just don't stop your car on pure ice - at all, and are downright dangerous especially with RWD, and if you like to drive with the DTC turned off in the winter like I do (I like to turn just by hitting the gas, for one.)
Hopefully this has been somewhat helpful in the quest for Z4 ground clearance issues and on the other hand, Z4's winter-worthiness.
:rocks: (Jamming with my new SACD player playing true 1-bit, 2.8MHz+ sample rate SACD's and 24-bit 192kHz sample rate DVD-Audio discs in 5.1 surround mode... Jeez what a difference compared to shitty old regular CDs! - and not just the 5.1 surround, but the pure sound quality itself - hope they get a player in BMWs one of these years. I hate having to play just 44.1kHz .wav files from my iPOD right now.)
Best regards,
Jussi