Going to ditch the RFTs - should I get smaller wheels too?

[WayOfTheGinja]

Loving my E89, but much like my E86 the ride is… “firm” on the run flats.

I switched to Eagle Asymmetrics 5s on the E86 and it was a massive difference (in road noise as well as comfort and handling). Now planning on doing the same on my E89 (it has stock Bridgestone Potenza RFTs).

I’ve got 19 inch 326M wheels currently. I love the look of them but am wondering if it is worth seeking out a set of 18s (probably the 325Ms, if I can find a decent second hand set). This would mean the tyres would be a bit cheaper and the cracking risk goes. Also, a bit more sidewall = a bit more comfort, maybe?

I guess the disadvantage is that it would be more of a pain to sort, more expensive overall (at least unless I could sell the 326Ms) and of course, wouldn’t have those 19 inch looks!

My question is - any thoughts on whether the 19 to 18 swap would have that much impact on ride? Or will the switch from RFTs to non-RFTs be more than enough improvement? And how is the cracking risk on 326Ms once the RFTs are gone?

 

[Panta Rhei]

One thing is certain. OE tyre sizes on e89 are joke. 255/30/19 - I mean for real? On 9J?
E60 or F10 got 9Jx19 rear wheel and they got 275 and here BMW thought it would be okay to put a lay's chip tyre ona wheel.
I am a meaty tyre combo fan.
You can always run upsized profiles or wider tyres:
245/35 + 275/30 or 255/40 + 255/35
Better ride
Better looks
Smaller wheel arch gap

 

[tiglon]

One thing is certain. OE tyre sizes on e89 are joke. 255/30/19 - I mean for real? On 9J?
E60 or F10 got 9Jx19 rear wheel and they got 275 and here BMW thought it would be okay to put a lay's chip tyre ona wheel.
I am a meaty tyre combo fan.
You can always run upsized profiles or wider tyres:
245/35 + 275/30 or 255/40 + 255/35
Better ride
Better looks
Smaller wheel arch gap

It's hardly a joke that a 5 series has different sized tyres to a Z4.

255 is pretty standard on 9J...

 

[mr.tourette]

I run 19s Dunlop sportsmaxx RT2 on my e89..they are known to give a more comfortable ride due to their construction..to me there was very little difference to the previous Michelins on 18s..my car does have SE suspension though which helps..not sure I'd have gone to 19s on msport suspension, I should imagine the dunlops on 18s with a bigger sidewall would be pretty comfortable on the e89

 

[Panta Rhei]

One thing is certain. OE tyre sizes on e89 are joke. 255/30/19 - I mean for real? On 9J?
E60 or F10 got 9Jx19 rear wheel and they got 275 and here BMW thought it would be okay to put a lay's chip tyre ona wheel.
I am a meaty tyre combo fan.
You can always run upsized profiles or wider tyres:
245/35 + 275/30 or 255/40 + 255/35
Better ride
Better looks
Smaller wheel arch gap

It's hardly a joke that a 5 series has different sized tyres to a Z4.

255 is pretty standard on 9J...

I am not questioning the difference in wheel + tyre setup.
This is just my opinion, this look silly

 

[WayOfTheGinja]

One thing is certain. OE tyre sizes on e89 are joke. 255/30/19 - I mean for real? On 9J?
E60 or F10 got 9Jx19 rear wheel and they got 275 and here BMW thought it would be okay to put a lay's chip tyre ona wheel.
I am a meaty tyre combo fan.
You can always run upsized profiles or wider tyres:
245/35 + 275/30 or 255/40 + 255/35
Better ride
Better looks
Smaller wheel arch gap

So could I just put non-RFT 225/40 (front) + 255/35 (rear) on the current 19s? Would the larger tyre cause any issues rubbing on the arch with stock M suspension?

 

[WayOfTheGinja]

Or even 225/35 and 255/35??

 

[Chippie]

From what I’ve read on previous posts it’s ok to go up one tyre size on the width on 19” and also one size up on the profile, it’s better not to increase more on the rear as the discrepancy in rolling circumference can upset the DSC.

 

[WayOfTheGinja]

From what I’ve read on previous posts it’s ok to go up one tyre size on the width on 19” and also one size up on the profile, it’s better not to increase more on the rear as the discrepancy in rolling circumference can upset the DSC.

That's very reassuring, thank you.

I can see the benefit of increasing profile (more cushioning), but what would the advantage be of adding a bit of extra width? I assume that means more contact area so better handling but also more road noise. I am mostly in the market to soften the ride and reduce the likelihood of cracked wheels.

 

[biZ4rreMids]

I’ve been running goodyear eagle f1 asymmetric 5 tyres on 326m alloys with a slightly increased tyre profile on the rear (255/35) for the last couple of years without issue. A wider tyre with the same profile eg. 265/35 will give you a bit more profile as well as a bigger contact area. Also experimenting with tyre pressures can improve ride quality and performance, I’m currently running 34psi front and 36psi rear.

 

[WayOfTheGinja]

I’ve been running goodyear eagle f1 asymmetric 5 tyres on 326m alloys with a slightly increased tyre profile on the rear (255/35) for the last couple of years without issue. A wider tyre with the same profile eg. 265/35 will give you a bit more profile as well as a bigger contact area. Also experimenting with tyre pressures can improve ride quality and performance, I’m currently running 34psi front and 36psi rear.

Perfect, thank you.

I’ve just ordered four Eagle F1 Asymmetric 6s (just released!!) for fitting on Monday. £600 from RAC tyres (cheaper than Black Circles this time).

 

[jenniferlouise]

When I discussed tyres with my BMW Specialist - Bartlett’s in Cambridgeshire - I was instantly advised against changing the tyre profile, as I’m told it can affect the differential (as the wheel circumference is no longer as it was set up to manage). Just passing it on. I’m sticking with the 255/30 on the rear for now.

 

[B21]

When I discussed tyres with my BMW Specialist - Bartlett’s in Cambridgeshire - I was instantly advised against changing the tyre profile, as I’m told it can affect the differential (as the wheel circumference is no longer as it was set up to manage). Just passing it on. I’m sticking with the 255/30 on the rear for now.

Have to say that is complete rubbish…changing tyre sizes may effect many things but affect the differential in any way is not logical Jim….

Having tried 255/30 19, 265/35 18, 275/30 19 I’ve never seen any faults or issues and I’ve never heard of anyone have a differential issue on any E89 related to size of tyres..

It is true that with a gross mismatch on front and rear rolling radius tyres you can have DSC related issues but that’s nothing to do with the differential

 

[sars]

Never understood why you would increase the width of the tyres unless you need the extra traction, a wider tyre has a larger contact patch and therefore noise and rolling resistance increases, that is compared against the same tyre with a lower width. As many have said previously just increase the profile not the width or buy a tyre with a bias towards comfort rather than performance. Also note that increasing the wheel diameters will negatively effect performance and fuel economy.

As B21 stated, the differential comment makes no sense, the whole point of a differential is to counter different inner and outer wheel rotational speeds as you corner.

 

[Panta Rhei]

Probably because 245/35/19 has got similar diameter (0,8 mm difference) as 225/40/19. Wider tyres affect tyre height by the definition of a profile.
So you have got two ways to achieve your goal - wider tyre and same profile or same tyre width with higher profile.
And if you have 8,5 + 9,5 you will not buy 225 and 255 tyres on such wheels as it would be irresponsible

I was instantly advised against changing the tyre profile

Those SPeciAlistS also recommend changing oil every 20k miles, because BMW said so and they won't change GBX oil - it is lifetime by BMW so no further discussions!!!11one, great advice :fuelfire:
Ask him what tyre should you buy for a 10x19 rim at the back. 255/30? :rofl:

 

[WayOfTheGinja]

Tyres fitted at F1 Autocentre in Cowley, Oxford. Can recommend them - good service, nice chaps, genuine interest in cars.

First impressions of the Asymmetric 6s are good, manhole covers are more of a gentle bump than a shock to the spine!