Anyone who owns any of these cars is extremely fortunate. I hope you realize that I understand just how fortunate I am to be able to drive either of these fantastic automobiles. I am sharing my experiences that I wrote on a different BMW board a few months ago to provide a comparison.
Before I begin my quote- I have to say this- there is absolutely no body flex on the Z8. I have also some experience with the M Roadster, and there is some on that. The Z8s handling, in my opinion is better than the M5 in terms of feel; but in terms of limits, the M5 sticks to the road better. The reason is probably a more forgiving suspension plus a longer wheelbase.
So heres what I wrote (Im making a few edits as I re-read it):
The big question- how does it handle compared to the M5? Who wins? The answer is: it depends.
"Handling" is such a subjective word. For me it is more complicated than just sticking to the road. While the g-force a car can pull is important to me, its not all of it.
If youre looking for which car will stick to the road better, its the M5.
The Z8, due to its shorter wheelbase, doesnt like turns that have expansion joints. the car doesnít become totally unglued, but it skips over them (so that the rear kind of slides out a little), while the M5 pretty much keeps on going.
In terms of steering, the Z8 is more communicative and accurate- the M5 almost feels numb by comparison. The Z8s steering feel is very close to E36 M3- maybe a little better, maybe a little worse- its hard for me to tell. This is likely due to the rack & pinion setup vs the recirculating ball on the M5. The steering feel is a little heavier than the M5 with sport mode activated, and much heavier than the M5 with sport mode off. The sport mode on the Z8 only affects the throttle, not the steering, as some people in the print media have errorenously reported (Autoweek).
The Z8's steering feel is more "linear". The M5's steering seems to exhibit a bit of a dead spot on center and also seems to be a little vague around this area. The sport mode helps with this though. Never the less the Z8s steering is just better.
on the downside, with the Z8s steering one also feels the tires tramlining more, whereas with the M5 this sensation is mostly absent.
The Z8 has much less body roll and almost no dive or squat. Going through a turn quickly in the M5 you can sense the mass of the car, while the Z8 has a more nimble feel- although its not a small car it feels as if it shrinks when you make quick turns.
The M5 rides much better over rough pavement and road conditions. But the Z8 is supposed to be more of a pure sports car. Both cars feel like bank vaults as far as chassis rigidity. The Z8's passenger seat rattles ever so slightly when one drives over bumpy roads, this is enough to be a little annoying though. The M5 has a few rattles (sunroof, rear deck) as well.
The shifter in the Z8 is essentially that of the m5, but the throws feel shorter and the shifter is much smoother. It has a great feel.
In terms of braking- The feel of the brakes in the Z8 is very crisp and powerful- while those in the M5 feel a little mushy. However, Ive had to make a panic stop in the M5 (~65-0 mph) and I can tell you the brakes work extremely well. I would expect the Z8 to do even better. For daily driving though, the Z8s brakes feel sharper.
On acceleration. The Z8 feels faster, and the exhaust note is more pronounced. The sound from 4500 RPM + is really something to enjoy- it almost becomes addictive. The M5 makes a nice exhaust note, but as many have noticed, its not quite as pronounced as an enthusiast would like. I think the M5 gives you the right amount of engine noise in the cabin and the same is true of the Z8. The Z8s normal throttle mode is a bit quicker than the sport mode in the M5. The sport mode on the Z8 is kind of like what a "hyper" sport button would provide on the M5. With less weight the ability of the engine to launch one from 0- whatever speed you desire is truly scarey. There seems to be no end to the torque. As the speed builds you expect it to run out of power- but it doesnt!
So thatís handling- my conclusion, the M5 might be capable of higher handling numbers, but Ill take the Z8 on feel.
On to driving experience- well, youíd expect a sedan and roadster to be different- and they are. The M5 is a truly refined sedan capable of mind-boggling performance for a 4,000 lb machine. This is the ultimate daily driver for an enthusiast.
The Z8 is fantastic luxury roadster also capable of really mind boggling performance. This is the ultimate "toy" for an enthusiast. It is capable as a daily driver, the ride is good enough for that- even on bumpy roads- but this car was designed for the weekends and summer time road trips in mind.
On the whole, the Z8 is a much more involving experience. As good as the M5 is, it makes the M5 feel a bit numb. It feels as if it out accelerates the M5 by a considerable amount- even though we all know this is not true. Itís just that youíre closer to the action.
Whereas the M5 offers you the ultimate mix of sportiness and refinement, with the Z8 the sensation is of just you, the wind, and the open road. Nothing in front of you except the long hood- it takes a couple of minutes to get used to this, but once you do- you donít want to let it go.
Also, the gauges in the middle is something thatís very easy to get used to and IMHO is not awkward at all. Itís a little bizarre the first time you look out and thereís no gauge cluster in your view.
The first time I drove the Z8, I was looking for the consumption data and other data that Ive seen in every BMW. Many of those read outs are not there! I had gotten so acoustomed to knowing my gas mileage, this was actually a little troubling.
Thats when I realized this car isnít about gauges or data, itís about feel. It gives the emotional feel of what like what one would expect a classic roadster to feel like, but with modern performance and all the modern conveniences (ABS,etc)- thereís even somewhat of a cup holder (but I think its an afterthought for us Yankees).
The Z8 is unlike anything Ive ever experienced, and Ive driven a Ferrari F40 (ok- it was a very short drive- but I did get to drive it!). I had recently driven the new 360 hardtop. I liked it very much! However, for me they are too flashy- now thats a personal preference thing so Im not knocking Ferrari because parts fell out or something like that.
The Z8 is a very user friendly "supercar". and it would make anyone who enjoys driving very happy.
If I had to pick one for a daily driver, the M5 wins easily. If I had to pick one as a weekend fun car, the Z8 wins easily.
[This message has been edited by MEnthusiast (edited 07 February 2001).]