Improvements z4m 18" to 19"csl's

[gav2612]

Some may have read my earlier posts regarding how I wasn't happy with the bouncy suspension on my z4m which I just bought a month ago(they all do that from the factory sir apparently)

Looks like I have managed to improve things although I'm not 100% sure why. I also have an e90 330d as my daily runner which I currently have 19" csl replicas on. Loving how the z4mc looks on csl's and not so much on the standard 18" oem wheels, I tried swapping them today. The bounce and unsettled feeling is much improved. The ride has now become a bit firmer and slightly more crashy over big bumps. I can live with that however for the more planted feeling it has given.

Now I'm wondering if anyone can explain the difference? Obviously the sidewalls are narrower, but the 18's weren't exactly a high profile tyre and most state the best handling balance comes from 18's. Interestingly the wheel tyre combo was actually 2.1kgs lighter on the 19" than the 18's which may be part of the reason? Tyre pressures on the 18's were spot on so shouldn't be that.

The car now looks great and feels much more planted, so I'm a happy but confused bunny!

[SBN]

I take it the csl's don't have rft fitted?

If not it's due to less tyre walls... Are the tyres exactly the same sizes on each car when you swapped the wheels over?

[Heathrow]

Could be due to a difference in alloy width?

[gav2612]

Both 18" and 19" are falken non run flats. Tyre widths and sizes are different as the originals were 8x18 and 9x18 and the csl reps 8.5x19 and 9.5x19. Can understand better grip with the wider lower profile tyres and that's what I would expect. It's the change in ride from bouncy and choppy to simply firm and sporty that is both surprising and pleasing. I was looking in to coilovers purely to try and sort out the bouncy ride as it was the one thing ruining the driving experience for me. It's still not as good as it could be, but it's now gone from something i couldn't live with if I was keeping the car long term to a minor irritation. The only explination I can come up with is the saving in un sprung weight.

[Top pup]

I have both the O.E wheels and CSL's for my Z4MC and I also think my car drives nicer on the CSL's, it's a little more crashy over pot holes and cats eyes but the actual ride is better, not sure why but most probably the weight as you say.
Bit of a sore topic though as others have made the change and switched back saying the ride was better on the 18"s.

[gav2612]

Exactly my thoughts. The 19s have defiantly made the ride harder, but I can live with that on a sports car. It's the bounciness over uneven surfaces which sapped my confidence in the car which has gone.

[gaz1234]

All in the head

[MOTK]

says chassis engineer gaz. thanks for the input yet again.