Another tyre thread! But I have done a search first!

C

Captain Vimes

Member
Hi all

I have been the proud owner of a 2013 sDrive20i MSport for three months now and loving it!

I always intended swaping the 19 inch Potenza run-flats it came with for 'normal' tyres when they need chaning, however they are nearly new! It's my only car and I do about 15k miles a year, 75% on the motorway. So now I am thinking about swaping sooner, and indeed dropping down to 18 inch wheels for better comfort and lower road noise. I use it as an everyday car, so not so concerned about looks.

I've not driven a Z4 on anything other than 19 inch run-flats so my question is, how much does it improve the noise level? Not too worried about comfort, it's OK as it is although it would be a bit nicer to have more give in the tyres, it is very much about the noise at 70 to 80mph.

Can anyone enlighten me?

JB
 
I changed the runflats to Cooper non-runflats on my 2.5 and the difference in noise is marvellous. Especially noticeable on the M25 near Heathrow where the surface is concrete, I think
 
Move away from RFT's and you'll definitely notice extra give in the tyre walls as the tyres now make more of a contribution to your car's suspension.

I chose to stay on 19's but had similar objectives in mind to yourself when I swapped. I had a significant expectation in terms of noise reduction which was only partly met. Subjectively, tyre noise does seem a little less (even commented on by my wife - without any prompting) but it's not a night and day change. Running 18's may be different.

I think it was Maniac who pointed out on another thread that your ears are pretty close to the rear axle and road wheels, so noise attenuation may not be huge. It'll never be like driving a saloon car. Plus of course, the road surface you're driving on is the biggest variable.

And then there's the question of what pressures to run them on - a subject well covered on the forum...............
 
Cheers.

Fully realise it will not be a quite as my 'old' Mondeo, but want to make sure I make the most suitable changes to get the best out of the car for the purpose I will use it the most
.
 
I did not notice any difference going from 18" run flats to 19" run flats. Both sets were running the same Bridgestone RE050.
You will probably hear a bigger difference going from run flats to normal tyres.

Chris
 
Go for Michelin Pilot Sport 4, amazing tyre, very highly rated. I run these and they are TRULY amazing..
 
Thanks for the responses so far. I'm feeling pretty confident that switching from 19 inch run-flats to 18 inch normal wheels and tyres should give me a noticeably quieter ride.

Now I just need to find the right wheels and tyres! Tyre advice aplenty on here, but I need to research wheels next.

And apart from here and eBay, any ideas where I might be most successful in selling the current 19 inch wheels? They are 326Ms with nearly new Potenzas all round.

Cheers

Vimes
 
Captain Vimes said:
Here's the motor in question! I was thinking dark grey wheels.....?

file.php
Click to expand...

The VO + black roof is superb.

If you keep the 326s, just check they're not cracked before you put new tyres on them.
 
Ta! Waited nearly a year to get one! Had to have the black roof..... 8)

The potential cracking issue is one other reason I'm going to change. I know with non run-flats there is less chance, but I'm still taken by the idea of 18's with more sidewall for comfort.
 
Captain Vimes said:
... but I'm still taken by the idea of 18's with more sidewall for comfort.
Click to expand...

Remember that one of the holy grails of tyre design was wall stiffness, not least because it contributes significantly to agility & steering accuracy, which was why designers went to big wheels with shallow-walled tyres at high pressures that were stiffer than 'normal' tyres. (Big wheels & liquorice-strip tyres were/are also 'cool', but that's an entirely different game, isn't it?)

Ironically, RFTs also have stiff walls & high pressures, of course - it's part of how they work - but, as you know, some people find their performance problematic, which brings us to your 18"s and "more sidewall for comfort" ...

Several of the major manufacturers are now producing their 18" tyres in Z4 sizes as 'XL' - for heavier load and, yep, with stiffer sidewalls. (Here, "load" relates to power & performance, of course, and not only to 'driven by a big guy, with his large wife in the passenger seat & the boot full of luggage'.)

So, it may well be that, in some very good 2017 18" performance tyres, you won't find the comfort you seek. Mind you, you can always let 10psi out ... :wink:
 
Note that the 326 style wheels are also quite susceptible to cracking so:

1) You will find plenty of eager buyers on Ebay with cracked wheels wanting a replacement.
2) Fitting non-run flats will help in preventing cracking in the first place due to the far higher compliancy.
 
Whatever alloys you choose most definitely go for NRF's I run 18" alloys with Michelin PS4's outstanding for grip and low noise as well as comfort.
 
OK, I have chosen my wheels (below) so one final question on tyre size.



IMG_2971.JPG

The standard tyre size for 18" wheels is 225/40 and 255/35.

Is it OK to go to 225/45 and 255/40 on the standard Msport suspension? This should soften and quieten the ride a little more I think, as well as filling the wheel arches better.

I've found a couple of threads for increasing the profile on 19" wheels that suggest this should fine, so any reason why I should not?

Vimes
 
If you are after a quieter tyre check out the dB ratings, your Potenzas are notionally 72 dB, the PS4's 71 dB whereas something like the Eagle ASy 3 are a low 68 dB. Remembering that decibels are a non-linear logarithmic scale a fall of 3 dB = a 50% reduction in audible noise 'pressure' (expressed another way a rise of 10 dB = 10 x louder) so it's quite a difference. Whilst raw dB's are not the full picture in terms of 'annoying frequencies' and these are 'drive-by' measurements, not interior where sound is presumably transferred according to the suspension and structure, they are a useful comparison between tyres.
 
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