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Tire pressures

Alloy wheels and tyre discussion
Drjcb198
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Tire pressures

Post by Drjcb198 » Fri Jan 13, 2012 9:55 pm

Any one know what the pressures should be on the 2.0l z4 with 18 inch rft on it, handlings not great so thik will check th pressures
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Tire pressures

Post by ranski » Fri Jan 13, 2012 9:56 pm

30 / 32 or 32 / 35 is quite common


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Tire pressures

Post by Adamski » Fri Jan 13, 2012 9:58 pm

I run 32F 36R. I'm on non RFTs though. Dropping the pressure a little may help with RFTs :thumbsup:


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Re: Tire pressures

Post by bat1959 » Fri Jan 13, 2012 10:00 pm

Owners handbook or next to the drivers door lock. All the info you need. :driving:
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Re: Tire pressures

Post by Drjcb198 » Sat Jan 14, 2012 5:41 pm

So I pumped the tires up to 30/ 32 as suggested, the were 33 at the rear and front right 27 left 28 made a huge difference to the handling, would have thought when I bought the car dealers would have checked this as only bought it 3 months ago
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Re: Tire pressures

Post by ranski » Sat Jan 14, 2012 5:48 pm

:thumbsup:
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Re: Tire pressures

Post by Bing » Sat Jan 14, 2012 5:51 pm

32 front 36 rear sounds correct - but the label on the driver door shut next to the lock will tell you as pinted out. THB, if you haven't put air in the tyres for three months :o then they were probably right when you got it, the air has just slowly leaked. I drive mine every day, and try to remember to check them once a week - I'd suggest every couple of weeks as a minimum would be best, if only because if you don't you'll go through tyres at a rate of knots, and your fuel consumption will drop :thumbsup:
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Re: Tire pressures

Post by Finisterre » Sun Jan 15, 2012 1:06 pm

I tend to have the tyre pressure the same front and back. 32psi

I have heard that BMW have slightly higher rear tyre pressure to encourage oversteer but I am uncertain what the benefits is. (Unless it is safer to go through hedges backwards!) Does anyone know if this is why they have decided a 50:50 weight distribution car should have a smaller contact patch at the rear?
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Re: Tire pressures

Post by sars » Sun Jan 15, 2012 1:10 pm

Finisterre wrote:I tend to have the tyre pressure the same front and back. 32psi

I have heard that BMW have slightly higher rear tyre pressure to encourage oversteer but I am uncertain what the benefits is. (Unless it is safer to go through hedges backwards!) Does anyone know if this is why they have decided a 50:50 weight distribution car should have a smaller contact patch at the rear?
As the car accelerates the weight distribution changes to the rear, so the rears have a higher pressure to compensate
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Re: Tire pressures

Post by Herminator » Sun Jan 15, 2012 1:57 pm

BMW and all manufacturers will tend to keep things on the side of understeer, it's much better to go through the hedge pointing forwards :?

I believe the higher pressure on the rear is partly because they're wider, there's more "unsupported" tyre tread.
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Tire pressures

Post by Adamski » Sun Jan 15, 2012 2:04 pm

I thought the higher pressures were due to it being RWD?


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Re: Tire pressures

Post by Bing » Sun Jan 15, 2012 4:22 pm

In every car I have ever driven, the drive wheels are higher PSI than the non-drive wheels - irrespective of whether it's FWD or RWD, and the Z4 is the first car that I have had that has a staggered set-up. My car says 2.3 bar on the front, 2.6 bar on the back, which works out at 33 / 38 psi I think. I was surprised the rears are so high, but there's lots of power, the weight shifts as Sars says, and perhaps the wider rears also have something to do with it.

However, IMHO you should look at the door shut plaque showing the pressures and do what it says, because someone brainier than me has worked it out already. If you then want to adjust the pressures that's your preference - i've just never bothered playing around. As my winters are all the same size I've dropped the back by 2 psi to 36, but that's only for fear of them exploding. Irrational, I know, but it's my head and I have to live with it :D

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Last edited by Bing on Sun Jan 15, 2012 6:23 pm, edited 2 times in total.
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Re: Tire pressures

Post by sars » Sun Jan 15, 2012 4:38 pm

Herminator wrote:I believe the higher pressure on the rear is partly because they're wider, there's more "unsupported" tyre tread.
I have 225/45/17's all round and the tyre pressures are different 2.4 Bar front and 2.9 Bar rear so I don't believe that to be the reason, also when you break you want the fronts to deform and get flatter to increase surface contact, this may be another reason for the difference :idunno:
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Re: Tire pressures

Post by Ewazix » Sun Jan 15, 2012 5:12 pm

I've played around with the pressures on my non-RFTs and settled on 32F/34R, much lower makes it feel 'baggy' on the turn in, much more starts to make it unsettled on bumpy bends.

Tyres generally lose a minimum of 1 ft/lb per month, and need seasonal adjustment to take account of ambient temperatures. You lose/gain roughly 1ft/lb of pressure for every 10 deg F so they will be a few pounds down in cold weather and need a top-up.
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Re: Tire pressures

Post by RCT_Z4Coupe » Sun Jan 15, 2012 5:38 pm

Ewazix wrote:I've played around with the pressures on my non-RFTs and settled on 32F/34R, much lower makes it feel 'baggy' on the turn in, much more starts to make it unsettled on bumpy bends.

Tyres generally lose a minimum of 1 ft/lb per month, and need seasonal adjustment to take account of ambient temperatures. You lose/gain roughly 1ft/lb of pressure for every 10 deg F so they will be a few pounds down in cold weather and need a top-up.
Is that on 18's? I was disappointed in the handling and ride of my car when I had my RFTs on the manufacturer recommended pressures (33/39). I lowered to 32/35 which really made the car feel settled with less dramatic tramlining. Made a significant difference.
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