after-market limited slip differential

There are so many different ratios for the Z4. But one is some kind of special. Did you know there is a difference in ratios between 3.0Si Roadster and Coupe. Both manual, the ratio of the Roadster is 3.15 if I remember correct. The Coupe is 3.46!
So the coupe should feel torquer on low rpms..
 
1:3.46 is a very common ration for bmw's.
A lot of automatics have that ratio. For example the 3.0i auto (so the pre facelift one) and also in e46. So that diff is very easy to get hold of.
The roadster 3.0si has 1:3.23.
You can get it as high as 1:3.64 and probably as low as 1:2.35 (from an e46 diesel obviously)

It's important that you choose the ration on power, and mainly first gear. You're not getting any faster away if you keep spinning in 1st.
My first gear is already pretty useless. 2nd is still ok.
Ideally you want to change gearbox ratio's, not diff ratio's, but that's very expensive.
 
Guido! You are right, it is 3.23 on the roadster. But still, why do the 3.0si roadster and coupe have different gear ratios?

When doing 0-62mph tests om my 3.0si Coupe, I have to change up to 3rd gear at approx 57mph. This ruins a really good 0-62 time. Could it be so that the roadster can use their second gear up to 62mph? Then they will have a faster 0-62 time!!
Still the Coupe will have more low down torque tho :)
 
Yes when you're in the same gear you have more torque
but you have to change gear earlier, and at that point you have less torque until the other one changes gear. So it's not an advantage all the time. In the end it's faster but just a little bit. It's way more complicated than some people think that you have (ratio1)/(ratio2)x100% torque all the time. Just part of the time and the other part you're way slower ;)
I guess they wanted the coupe to feel a bit wilder, a bit more raw. And when you're pulling away and your tires light up just that little bit easier, you can get that feeling more quickly. For bmw to change diff ratio's is easy. Changing gearbox ratios is very complicated.

It's not all about 0-62 times, it's also a first impression that sells cars to customers. Just like they sometimes change steering rack ratio's. That gives the impression that the car is more manouvreable/agile (but it makes absolutely no difference), or that they do a different throttle mapping. Some people actually think the sportsbutton makes their car faster and that it does something to the engine. That is how strongly the senses can be fooled.
 
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