New wheels, tyre help please!!

[Mos6689]

Ok read through about 2 hours worth of threads now & it’s a great help. My understanding has improved. I’m getting new wheels in the post tomorrow & they’re:

19x8.5 et 35
19x10 et 22

To be put on a Z4MC. I can see on here some have run very similar setups, so I know they’ll work but I’m now looking at tyres and not quite sure what to go for? I plan to lower the car 10mm rear & 20mm front but don’t want to be messing about with rolling the fenders to avoid rubbing. Any experts about to help? Mr Wilks, your reputation is second to none!

Thinking at the moment to run 235/35 on the fronts, as this increases ride height 5mm, so allows me to lower the 20mm without being too slammed. Hoping this won’t look stretched? 245/35 seems to be the general consensus but worried the extra diameter will mean rubbing?

On the rears I’m stuck between going 265/35 or 275/30? Leaning towards the 265/35, because I’m thinking the extra 5 between the 30 & 35 will be the difference between being crashy and bone shattering to acceptably comfortable. Am I right in thinking this? Use the car as a daily so don’t want to ruin my experience in it.

Thanks in advance for any help/insight anyone’s able to give.

 

[Mos6689]

Ok so had some feedback on Zpost, which has baffled me even more. So general consensus on wheels this size are 245/35 fronts & 275/30 rears. I was told go with this or 235/35 fronts & 265/30 rears. This maintains rolling diameter. So went back to will they fit.com and did the numbers on rolling diameter:

So OEM setup is:

18x8 225/40 RD (rolling dia) 637.2mm fronts
18x9 255/40 RD 661.2mm rears

OEM difference fronts to rears + 24mm

Stock they’re both running 40 and the rears are wider. So there’s a difference front to rear in the rolling diameters from stock. So I was looking to get as close to the difference between the rolling diameters from stock as possible.

Back to my initial thoughts on sizes, taking RD into consideration and here’s stats on them:

19x8.5 235/35 RD 647.1mm fronts
19x10 265/35 RD 668.1mm rears

Difference fronts to rears +21mm

What general consensus is suggesting:

19x8.5 235/35 RD 647.1mm fronts
19x10 265/30 RD 641.6mm rears

Difference fronts to rears - 5.5mm

OR

19x8.5 245/35 RD 654.1mm fronts
19x10 275/30 RD 647.6mm rears

Difference front to rears -6.5mm

Am I misunderstanding something? Is it better to match RD as close to eachother as possible? Opposed to matching to OEM. The other thing that I don’t like about this is speedo readings are thrown way off +\-2.5%.

 

[Anonymous]

OEM set up according to

https://www.wheel-size.com/size/bmw/z4/2008/

is 225/45 18 8J ET42 and 255/40 9J 18 ET30

 

[mr.tourette]

I run 235/35/19 and 265/35/19 on my e89..ride comfort is very good on Dunlop sportsmaxx rt2 tyres, I wouldn't want to run 30's on the rear, tyres don't look stretched at all but rim protection is not quite as good as on 18s tyre sizes, speedo reading is much more accurate too, about +2 mph at all speeds

 

[Mos6689]

OEM set up according to

https://www.wheel-size.com/size/bmw/z4/2008/

is 225/45 18 8J ET42 and 255/40 9J 18 ET30

Ah! That’s helpful! Previous owner must have gone for lower profile on a tyre change. Automatically assumed because they were 224’s they were original sizes.

I run 235/35/19 and 265/35/19 on my e89..ride comfort is very good on Dunlop sportsmaxx rt2 tyres, I wouldn't want to run 30's on the rear, tyres don't look stretched at all but rim protection is not quite as good as on 18s tyre sizes, speedo reading is much more accurate too, about +2 mph at all speeds

That’s good to hear! What widths are your wheels?

 

[Anonymous]

OEM set up according to

https://www.wheel-size.com/size/bmw/z4/2008/

is 225/45 18 8J ET42 and 255/40 9J 18 ET30

Ah! That’s helpful! Previous owner must have gone for lower profile on a tyre change. Automatically assumed because they were 224’s they were original sizes.

I run 235/35/19 and 265/35/19 on my e89..ride comfort is very good on Dunlop sportsmaxx rt2 tyres, I wouldn't want to run 30's on the rear, tyres don't look stretched at all but rim protection is not quite as good as on 18s tyre sizes, speedo reading is much more accurate too, about +2 mph at all speeds

That’s good to hear! What widths are your wheels?

FWIW..

The rolling radius difference of front and rear tyres should be less than 2% and ideally less than 1.5% to avoid confusing the DCS system!

 

[Mos6689]

OEM set up according to

https://www.wheel-size.com/size/bmw/z4/2008/

is 225/45 18 8J ET42 and 255/40 9J 18 ET30

Ah! That’s helpful! Previous owner must have gone for lower profile on a tyre change. Automatically assumed because they were 224’s they were original sizes.

I run 235/35/19 and 265/35/19 on my e89..ride comfort is very good on Dunlop sportsmaxx rt2 tyres, I wouldn't want to run 30's on the rear, tyres don't look stretched at all but rim protection is not quite as good as on 18s tyre sizes, speedo reading is much more accurate too, about +2 mph at all speeds

That’s good to hear! What widths are your wheels?

FWIW..

The rolling radius difference of front and rear tyres should be less than 2% and ideally less than 1.5% to avoid confusing the DCS system!

Thanks that sounds very useful but you’ve lost me a little. The rolling radius between eachother or individually?

Just worked it out again based on the ACTUAL front OEM tyres. Basically only have 2 choices really:

Stock is
225/45 fronts RD 659.7mm
255/40 rears RD 661.2mm
Difference of +1.5mm front to rear

CHOICE 1
235/40 fronts RD 670.6mm - Arch gap decrease by 11mm. Speedo -1.6%
265/35 rears RD 668.1mm - Arch gap decrease by 7mm. Speedo -1%
Difference of -2.5mm RD

CHOICE 2
245/35 fronts RD 654.1mm - Arch gap increase by 5.6mm. Speedo +0.9%
275/30 rears RD 647.6mm - Arch gap increase by 13.5mm. Speedo +2.1%
Difference of -6.5mm RD

My main reason for wanting to lower is purely to get rid of the crap rear springs the car comes with. No one does like for like replacements & the closest to stock is eibach -10mm rear & -20mm front.

Prefer the specs on choice 1. Closest to OEM spec but concerned the decrease in the arch gap, between tyre & fender, is going to be a problem when I lower it.

 

[mr.tourette]

OEM set up according to

https://www.wheel-size.com/size/bmw/z4/2008/

is 225/45 18 8J ET42 and 255/40 9J 18 ET30

Ah! That’s helpful! Previous owner must have gone for lower profile on a tyre change. Automatically assumed because they were 224’s they were original sizes.

I run 235/35/19 and 265/35/19 on my e89..ride comfort is very good on Dunlop sportsmaxx rt2 tyres, I wouldn't want to run 30's on the rear, tyres don't look stretched at all but rim protection is not quite as good as on 18s tyre sizes, speedo reading is much more accurate too, about +2 mph at all speeds

That’s good to hear! What widths are your wheels?

8.5 front 9.5 rear

 

[Anonymous]

The rolling radii of the fronts and rear should be ideally under 1.5% for later E85s and all E89s..2% tops!