Tyre pressure

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Wrinkley
Joined: Fri 25 Jun, 2010 20:11
Posts: 103

  Z3 roadster 2.8
Location: Beverley

Tyre pressure

Post by Wrinkley » Tue 19 Oct, 2010 14:17

Sorry if it's been asked lots before but despite google and searches on various sites I cannot find what pressure my tyres should be at.
I would be grateful if someone could advise me.

Tyres are Falken FK452 235/40ZR18 95Y. 97 2.8 Z3

Many thanks,

Steve

Frank.A
Joined: Mon 20 Jul, 2009 22:15
Posts: 875

  Z3 roadster 2.8
Location: Twixt York and Hull

Post by Frank.A » Tue 19 Oct, 2010 14:33

Hi Steve,

Mine is 2000 2.8 with 225/45 17 front and 245/40 17 rear.

I have found that 32psi all round gives best results,and is the recommended tyre pressure in the Owner Handbook for 16" or 17" wheels on a 2.8 roadster.
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2000 Topaz 2.8 Individual.

Youth would be more useful if it came later in life!

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TitanTim
Joined: Mon 23 Jun, 2008 19:56
Posts: 5488

  Z3 roadster 1.9i
Location: Stafford

Post by TitanTim » Tue 19 Oct, 2010 15:19

On mine FK452s on 8.5x18s ............fronts 225/40/18 = 32psi Rears 255/35/18 = 36psi

Tim.
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2001 Z3 1.9 Roadster Sport - 2012 Z4 sDrive 2.0 M Sport

Mike Fishwick
Joined: Fri 19 Jun, 2009 11:27
Posts: 1991

  Z3 roadster 2.8
Location: Daglan, France

Pressures

Post by Mike Fishwick » Tue 19 Oct, 2010 17:37

The factory pressures are always on the low side - I use FK-452 in seventeen inch sizes, and find 2.4 bar is the optimum.

Wrinkley
Joined: Fri 25 Jun, 2010 20:11
Posts: 103

  Z3 roadster 2.8
Location: Beverley

Post by Wrinkley » Tue 19 Oct, 2010 21:47

Many thanks,

Steve

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komis
Joined: Wed 01 Dec, 2004 11:18
Posts: 475

  Z3 roadster 2.8

Re: Pressures

Post by komis » Wed 20 Oct, 2010 09:39

Mike Fishwick wrote:The factory pressures are always on the low side - I use FK-452 in seventeen inch sizes, and find 2.4 bar is the optimum.
I'm on the same tyres, I tend to overinflate by 10% and use 2.2 front and 2.4 for the rear instead of the manual's stated 2.0 and 2.2... The manual's stated figures seem to make the tyres feel somewhat under-inflated.
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Mike Fishwick
Joined: Fri 19 Jun, 2009 11:27
Posts: 1991

  Z3 roadster 2.8
Location: Daglan, France

Difference

Post by Mike Fishwick » Wed 20 Oct, 2010 12:04

On FK-452 at least, there is a huge difference between 2.2 and 2.4 bars, in terms of virtually no understeer, reduced tyre noise, and lighter, more responsive steering.

I tried increasing to 2.5, but could not reaaly detect any difference, so returned to 2.4 all round.

I've been using this for years, and after dropping back the factory pressures the car felt awful, then increasing to 2.2F and 2.3 R it felt a bit less awful, but nowhere near its normal self on 2.4 F & R.

Even with a Butt Strut, Body Brace, Bilstien/Eibach suspension, rear cross member bush inserts, and poly bushes, higher pressures all round are the icing on the cake, particularly on alpine passes with lots of hairpin bends and adverse cambers.

Try it and see.

Frank.A
Joined: Mon 20 Jul, 2009 22:15
Posts: 875

  Z3 roadster 2.8
Location: Twixt York and Hull

Post by Frank.A » Wed 20 Oct, 2010 12:48

I will up them to 2.4 all round to see if there is a difference,it might even improve mpg although that has been constant at 33mpg according to posts of a previous owner,apart from a trip to S of F where it averaged around 37mpg.

The biggest improvement in handling for me has been changing directional tyres by Goodyear and Falken for asymmetrics by Falken.Goodyear have stopped producing there F1 directional in favour of asymmetric.

Incidentally Falken recommend 2.0 all round with 1 occupant and 2.1 front and 2.3 rear fully loaded for a 2.2 on 17" rims.
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2000 Topaz 2.8 Individual.

Youth would be more useful if it came later in life!

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komis
Joined: Wed 01 Dec, 2004 11:18
Posts: 475

  Z3 roadster 2.8

Re: Difference

Post by komis » Wed 20 Oct, 2010 16:43

Mike Fishwick wrote:
I've been using this for years, and after dropping back the factory pressures the car felt awful, then increasing to 2.2F and 2.3 R it felt a bit less awful, but nowhere near its normal self on 2.4 F & R.

Try it and see.
Mike does yours have staggered front/rear 17" rims? I'll give it a try tomorrow, I've got a longish run to make so it'll be interesting to see how it behaves.
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Mike Fishwick
Joined: Fri 19 Jun, 2009 11:27
Posts: 1991

  Z3 roadster 2.8
Location: Daglan, France

Rims

Post by Mike Fishwick » Thu 21 Oct, 2010 08:55

Yes - I have the usual 8.5 inch rears.

The factory pressures are usually specified to produce an understeer chracteristic, by running the fronts a little on the soft side - hence the improvement when inflated a little more.

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Adam
Joined: Sat 21 Jul, 2007 19:43
Posts: 334

  Z3 roadster 2.8
Location: Newport
Contact:

Post by Adam » Thu 21 Oct, 2010 10:35

I normally run with 2.0bar front, 2.2bar rear on the 17" staggered as stated on the door sill of the car.

I understand where Mike is coming from regarding the feel of the tyres being under inflated and the feel when turning in. This morning I have amended my pressure to 2.4bar all around and will test it on varied roads and conditions this weekend.

From just driving the mile and a half from the air pump to my work which is mainly a dual carriageway and a couple of roundabouts I have noticed a more responsive turn in on the roundabouts. It just feels a little sharper. Lets see what its like over the weekend.

The other thing that I'm thinking regarding changing pressures is...what effect on tyre wear people are getting? positive or negative on wear?

Thats probably opened up another can of worms.

Mike Fishwick
Joined: Fri 19 Jun, 2009 11:27
Posts: 1991

  Z3 roadster 2.8
Location: Daglan, France

Wear

Post by Mike Fishwick » Thu 21 Oct, 2010 11:14

I have been using 2.4 all round for years, and did not find any effect on tyre wear. I normally had 30k from the fronts, and 20k from the rears on my 2.8, the inner edges of the rears wearing more than the outer edges.

Accurate toe-in adjustment is more important for the front tyres than small pressure increases such as this.

Since fitting the Strong-Strut Butt Strut and Body Brace I now get at least 25k from the rears, as they now wear evenly across the tread area, so extending the effective life of the tyre.

I could probably get a bit more life from the rears, but as tyres are a lot cheaper in the UK, and French tyre fitters cannot balance such wide rims, I always replace the tyres when visiting the UK, when there is still some useful life left in the tyres.

Frank.A
Joined: Mon 20 Jul, 2009 22:15
Posts: 875

  Z3 roadster 2.8
Location: Twixt York and Hull

Post by Frank.A » Thu 21 Oct, 2010 16:54

It's worth remembering to check tyre pressures regularly and in particular the effect of temperature,which is approximately 10kpa(0.1bar)/10degC.
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2000 Topaz 2.8 Individual.

Youth would be more useful if it came later in life!

jimplops
Joined: Sat 03 Jul, 2010 18:37
Posts: 13

  Z3 roadster 2.8
Location: Lancaster

Post by jimplops » Thu 21 Oct, 2010 20:43

Having just read this, it's worth noting for those that use garage air lines that these may not be very acurate and it's worth investing in a quality analogue pressure gauge, and to also check tyre pressures when cold. And as already stated ( even though I'm new to zeds) they are very sensitive to tyre pressures, and having spent plenty of time getting pressures that "feel" right when driving on my other cars did the same with the zed and settled on 36psi.

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komis
Joined: Wed 01 Dec, 2004 11:18
Posts: 475

  Z3 roadster 2.8

Post by komis » Fri 22 Oct, 2010 07:44

Happy to report that upping tyre pressures to 2.4 bars all around resulted in slightly crisper handling, better behaviour over bumps and potholes and, dare I say it, mildly better fuel economy (38mpg on the trip computer instead of my usual 37 on that trip, that's a 50 mile drive at a steady 60-70mph).

I think I'll keep it this way, thanks Mike :)
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