Non runflat tyre sizes - implications?

Specific discussion about the E89 2009 Z4 (sDrive35is, sDrive35i, sDrive30i, sDrive23i)
DR-Z
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Non runflat tyre sizes - implications?

Post by DR-Z » Thu Jul 11, 2019 5:49 pm

Even though I have practically new RFTs, I'm going to take the (expensive) plunge to go to normal tyres.   My 19" 326 wheels are currently crack-free, and I'd like to keep it that way. Also would be nice to soften the ride a little. 

Reading around,  seems likes the optimum tyre sizes will be 235/35 front and 255/35 rear. That will increase the diameter a little on the fronts, and quite a lot (an inch) on the rears. Apart from the benefits of a better ride, there appear to be a few other implications of upping the tyre size:

• Speedo will read lower - but as it reads a bit high at the moment, should be OK. 
• Wider tyres may give a bit more grip
• ..but greater rolling resistance of the wider tyres could affect mpg (which is already pretty poor) 
• The car will sit 1/2 inch higher at the rear on the stock Msport suspension.  Those of you who have done this, it's this noticeable? (I don't particularly want to start messing with the springs).
• Larger rears will also reduce acceleration - not sure how noticeable this would be.  

Not sure if I've missed anything significant. Any views on the above?
Z4 28i (E89 2014) - mineral grey
530d (F11)
Previous (most recent first)
BMWs: 330D, Z4 2.5si (2007), 535D; Marlin Sportster (M3 engine, self-build); 330D Coupe; 123D coupe; 520i; 523i.
Also: Audi A6 2.7tdi; Audi TT 225; Audi 100 avant; Porsche 944S

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Non runflat tyre sizes - implications?

Post by Busterboo » Thu Jul 11, 2019 6:11 pm

Use the BMW specification. Mummy knows best.
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Non runflat tyre sizes - implications?

Post by DR-Z » Thu Jul 11, 2019 9:59 pm

Busterboo wrote:
Thu Jul 11, 2019 6:11 pm
Use the BMW specification. Mummy knows best.
You mean keep the runflats specified by BMW?
Z4 28i (E89 2014) - mineral grey
530d (F11)
Previous (most recent first)
BMWs: 330D, Z4 2.5si (2007), 535D; Marlin Sportster (M3 engine, self-build); 330D Coupe; 123D coupe; 520i; 523i.
Also: Audi A6 2.7tdi; Audi TT 225; Audi 100 avant; Porsche 944S

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Non runflat tyre sizes - implications?

Post by Busterboo » Thu Jul 11, 2019 11:13 pm

DR-Z wrote:
Thu Jul 11, 2019 9:59 pm
Busterboo wrote:
Thu Jul 11, 2019 6:11 pm
Use the BMW specification. Mummy knows best.
You mean keep the runflats specified by BMW?
You asked about sizes, not disasters. :wink:
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Non runflat tyre sizes - implications?

Post by Pbondar » Fri Jul 12, 2019 9:20 am

DR-Z wrote:
Thu Jul 11, 2019 5:49 pm
Even though I have practically new RFTs, I'm going to take the (expensive) plunge to go to normal tyres. My 19" 326 wheels are currently crack-free, and I'd like to keep it that way. Also would be nice to soften the ride a little.

Reading around, seems likes the optimum tyre sizes will be 235/35 front and 255/35 rear. That will increase the diameter a little on the fronts, and quite a lot (an inch) on the rears. Apart from the benefits of a better ride, there appear to be a few other implications of upping the tyre size:

• Speedo will read lower - but as it reads a bit high at the moment, should be OK.
• Wider tyres may give a bit more grip
• ..but greater rolling resistance of the wider tyres could affect mpg (which is already pretty poor)
• The car will sit 1/2 inch higher at the rear on the stock Msport suspension. Those of you who have done this, it's this noticeable? (I don't particularly want to start messing with the springs).
• Larger rears will also reduce acceleration - not sure how noticeable this would be.

Not sure if I've missed anything significant. Any views on the above?
Given the wide range of wheels/tyres fitted over the life of the car in simple terms your changes are all like it to have a minimal impact save that of changing from runflats to nonrunflsts..imho

I’ve now tried 17 18 and 19 in different widths, asymmetrical and symmetrical with cheap and premium tyres.

On stock m sport suspension the best ride comfort/subjectively best road oriented handling was asymmetrical 17” wheels running 235 fronts and 255 rears in premium rubber...
2012 E89 20i MSport Auto Atacama Yellow, Fully loaded in its day.. Changes (Re-map/Wheels/Tyres/Spoiler/Steering Wheel/Shock Absorbers/ARB/Rear Diffuser/Brakes/Speakers/Amps/ASD delete) Upcoming changes (Quaife LSD) Full Whippy here!

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Non runflat tyre sizes - implications?

Post by Mister T » Fri Jul 12, 2019 11:23 am

255/35 is way too tall for the rear, you'd be better with a 265/30 if you're desperate to move away from the standard sizes.

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Non runflat tyre sizes - implications?

Post by ZedConvert » Fri Jul 12, 2019 11:43 am

If you're just going for comfort I'd agree with Pbondar,
I on the other hand went for looks, and it's far from comfortable, but transformed the car :driving:
235/35/19 - 265/30/19

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Non runflat tyre sizes - implications?

Post by David-H » Fri Jul 12, 2019 2:08 pm

I ran 235/35/19 and 265/30/19 on my 326 wheels on my E89 and was very happy with the result and the improvement in the ride. :)
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Non runflat tyre sizes - implications?

Post by DR-Z » Fri Jul 12, 2019 2:12 pm

My main aim is to protect the flimsy rims, although any improvement in comfort would be a bonus. But I don't want to compromise handling. As expected, I get mixed messages when i read this and other forums, but these seem to be favoured options:

• Standard is 225/35 and 255/30 - keeping this but with non RFTs may be more forgiving to the wheels.
• 225/40 and 255/35 - increases both wheel sizes by an inch - maximum forgiveness
• 235/35 and 265/30 - a slight increase in diameter for both, plus some extra width
• 235/35 and 255/35 - bigger increase in diameter for rears than front.
Z4 28i (E89 2014) - mineral grey
530d (F11)
Previous (most recent first)
BMWs: 330D, Z4 2.5si (2007), 535D; Marlin Sportster (M3 engine, self-build); 330D Coupe; 123D coupe; 520i; 523i.
Also: Audi A6 2.7tdi; Audi TT 225; Audi 100 avant; Porsche 944S

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Non runflat tyre sizes - implications?

Post by del_tl1000r » Fri Jul 12, 2019 2:19 pm

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This is my Zed. Non M sport with standard suspension. I've got 235 x 35s front and 255 x 35 rears and in my opinion they fill the arches nicely. On level ground the gaps around the tyres and arches are spot on. I don't think the rears are too tall. The car does sit approx. 15mm higher at the rear but I don't find it an issue.
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Non runflat tyre sizes - implications?

Post by PinkPineapple44 » Fri Jul 12, 2019 2:28 pm

Mister T wrote:
Fri Jul 12, 2019 11:23 am
255/35 is way too tall for the rear, you'd be better with a 265/30 if you're desperate to move away from the standard sizes.
On the contrary, 255/35 is the perfect size for 326 rears imo.

I've been running 225/35 and 255/35 non runflats for a good while now and I'd go the same again next time too

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Non runflat tyre sizes - implications?

Post by ZedConvert » Fri Jul 12, 2019 2:36 pm

del_tl1000r, Not to highjack the thread, but mines on non-Msport suspension too, but rides much higher, any ideas why?
I'm sporting 235/35/19 - 265/30/19
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Non runflat tyre sizes - implications?

Post by DR-Z » Fri Jul 12, 2019 2:56 pm

del_tl1000r wrote:
Fri Jul 12, 2019 2:19 pm
I've got 235 x 35s front and 255 x 35 rears and in my opinion they fill the arches nicely. On level ground the gaps around the tyres and arches are spot on. I don't think the rears are too tall. The car does sit approx. 15mm higher at the rear but I don't find it an issue.
Looks really good. My msport suspension will be a little lower than yours (10mm?), but I think this may only be at the front. No issues with having 1/2" larger diameter rears than fronts?
Z4 28i (E89 2014) - mineral grey
530d (F11)
Previous (most recent first)
BMWs: 330D, Z4 2.5si (2007), 535D; Marlin Sportster (M3 engine, self-build); 330D Coupe; 123D coupe; 520i; 523i.
Also: Audi A6 2.7tdi; Audi TT 225; Audi 100 avant; Porsche 944S

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Non runflat tyre sizes - implications?

Post by del_tl1000r » Fri Jul 12, 2019 3:29 pm

DR-Z wrote:
Fri Jul 12, 2019 2:56 pm
del_tl1000r wrote:
Fri Jul 12, 2019 2:19 pm
I've got 235 x 35s front and 255 x 35 rears and in my opinion they fill the arches nicely. On level ground the gaps around the tyres and arches are spot on. I don't think the rears are too tall. The car does sit approx. 15mm higher at the rear but I don't find it an issue.
Looks really good. My msport suspension will be a little lower than yours (10mm?), but I think this may only be at the front. No issues with having 1/2" larger diameter rears than fronts?
DR-Z wrote:
Fri Jul 12, 2019 2:56 pm
del_tl1000r wrote:
Fri Jul 12, 2019 2:19 pm
I've got 235 x 35s front and 255 x 35 rears and in my opinion they fill the arches nicely. On level ground the gaps around the tyres and arches are spot on. I don't think the rears are too tall. The car does sit approx. 15mm higher at the rear but I don't find it an issue.
Looks really good. My msport suspension will be a little lower than yours (10mm?), but I think this may only be at the front. No issues with having 1/2" larger diameter rears than fronts?


I originally had 225 x 17 runflats all round. The only thing I can say I noticed was that my average mpg is around 3mpg less.
23i
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CDV deleted
LED halo bulbs
LCI side repeaters
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Non runflat tyre sizes - implications?

Post by del_tl1000r » Fri Jul 12, 2019 3:42 pm

ZedConvert wrote:
Fri Jul 12, 2019 2:36 pm
del_tl1000r, Not to highjack the thread, but mines on non-Msport suspension too, but rides much higher, any ideas why?
I'm sporting 235/35/19 - 265/30/19

IMG_1798.jpg
Do you mean the car sits higher or the gap between the arch and the tyre looks bigger? If your car originally had 17s it will sit higher at the rear. The overall diameter of 17s is 634mm compared to 642mm for the tyres you have but it should only be half the difference higher i.e 4mm.
23i
Msport seats
CDV deleted
LED halo bulbs
LCI side repeaters
Stubby
Brushed stainless exhaust tips
Focal speakers
Pioneer amp
Kicker sub
M4 style wheels

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