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Non Runflat Tyre Pressures

Specific discussion about the E89 2009 Z4 (sDrive35is, sDrive35i, sDrive30i, sDrive23i)
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sunnydays
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Non Runflat Tyre Pressures

Post by sunnydays » Wed Jun 28, 2017 9:57 am

Hey all,

Switching over to Michelin Pilot Sports 4S on my 35IS from the stock runflats.

The default tyre pressure is relatively high, everything I have read suggests that tyre pressure is vehicle dependant not tyre so I am leaning towards running the BMW defined pressures of 44 / 34 psi (off the top of my head)

Any thoughts guys?

Cheers

Busterboo
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Non Runflat Tyre Pressures

Post by Busterboo » Wed Jun 28, 2017 11:07 am

You're right. But, for the 35iS, it's 44 rear and 36 front. :)
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Non Runflat Tyre Pressures

Post by Busterboo » Wed Jun 28, 2017 11:10 am

You're also right that tyre pressures are vehicle dependent.

They're also size & profile dependent.

They are not RFT dependent. On the same car, RFTs and non-RFTs have the same pressures.
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Non Runflat Tyre Pressures

Post by Busterboo » Wed Jun 28, 2017 11:13 am

If anyone wants to argue these facts, just refer them to BMW itself or Michelin, Pirelli, Goodyear ...
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Non Runflat Tyre Pressures

Post by Busterboo » Wed Jun 28, 2017 11:17 am

BMW also put a convenient little sticker on their cars, of course, to confirm the tyre pressures for the vehicle in question. :)
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R.E92
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Non Runflat Tyre Pressures

Post by R.E92 » Wed Jun 28, 2017 4:55 pm

I found that running the stock pressures makes the car feel unsettled.
I now run 40 rear and 34 front. Best for both the PSS and PS4S. Nice even wear too.

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Non Runflat Tyre Pressures

Post by Garvin » Wed Jun 28, 2017 7:03 pm

Busterboo wrote: Wed Jun 28, 2017 11:10 am You're also right that tyre pressures are vehicle dependent.

They're also size & profile dependent.

They are not RFT dependent. On the same car, RFTs and non-RFTs have the same pressures.

and

If anyone wants to argue these facts, just refer them to BMW itself or Michelin, Pirelli, Goodyear ...
Facts? Where did you get these facts from?

Pressures are tyre dependent - the pressures given by BMW are, at best, linked to the RE050A RFTs they fit to the Z4 or, at worst, a compromise across a range of RFT tyres.

Below are the tyre pressures from the F355 handbook where Ferrari bothered to test the F355 with each of its recommended tyres - same size (non-RFTs) but significantly different pressures for each tyre brand.

Image

It's a bit experimental but when I fitted (same size) MPSS to the F355 the best tyre pressures turned out to be 34psi front and 36 psi rear. Over 40psi for rear non-RFTs on something the size of the Z4 seems a tad high to me!
Considering Ordered Received 35is - Melbourne Red / Ivory White with lots of bells & whistles. Deep Sea Blue replacement 35is now also departed. Replaced by something more brash, more powerful and American!

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Non Runflat Tyre Pressures

Post by Busterboo » Wed Jun 28, 2017 8:36 pm

Garvin wrote: Wed Jun 28, 2017 7:03 pm Over 40psi for rear non-RFTs on something the size of the Z4 seems a tad high to me!
Actually, 44 & 36 are a tad low.

The correct conversion into psi of the bar figures is higher. :)
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Non Runflat Tyre Pressures

Post by Busterboo » Wed Jun 28, 2017 8:44 pm

Garvin wrote: Wed Jun 28, 2017 7:03 pm Over 40psi for rear non-RFTs on something the size of the Z4 seems a tad high to me!
And the "non-RFTS" element is irrelevant.

Both RFTs & non-RFTs of the same size are inflated to the same pressures. :)
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Non Runflat Tyre Pressures

Post by Smartbear » Wed Jun 28, 2017 9:00 pm

Busterboo wrote: Wed Jun 28, 2017 8:44 pm
Garvin wrote: Wed Jun 28, 2017 7:03 pm Over 40psi for rear non-RFTs on something the size of the Z4 seems a tad high to me!
And the "non-RFTS" element is irrelevant.

Both RFTs & non-RFTs of the same size are inflated to the same pressures. :)
Then how do you explain the manufacturers table above? It shows tyres of the same size inflated to different pressures.
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e89 Sdrive 20i, plenty of mumbo & good economy-the thinking bears z4
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Non Runflat Tyre Pressures

Post by R.E92 » Wed Jun 28, 2017 10:49 pm

I'm with Garvin on this. Different tyres need different pressures.

I think the construction of the tyre will determine the contact patch at different pressures. RFTs have wildly different construction to proper performance tyres.

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Non Runflat Tyre Pressures

Post by Busterboo » Wed Jun 28, 2017 11:43 pm

Smartbear wrote: Wed Jun 28, 2017 9:00 pm Then how do you explain the manufacturers table above? It shows tyres of the same size inflated to different pressures.
Rob
I cannot explain the Ferrari data above, Rob.
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Non Runflat Tyre Pressures

Post by warmasice » Wed Jun 28, 2017 11:59 pm

sunnydays wrote: Wed Jun 28, 2017 9:57 am Hey all,

Switching over to Michelin Pilot Sports 4S on my 35IS from the stock runflats.

The default tyre pressure is relatively high, everything I have read suggests that tyre pressure is vehicle dependant not tyre so I am leaning towards running the BMW defined pressures of 44 / 34 psi (off the top of my head)

Any thoughts guys?

Cheers
Could you let us know your thoughts on the ride comfort please?
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Non Runflat Tyre Pressures

Post by Busterboo » Thu Jun 29, 2017 10:17 am

Busterboo wrote: Wed Jun 28, 2017 11:43 pm
Smartbear wrote: Wed Jun 28, 2017 9:00 pm Then how do you explain the manufacturers table above? It shows tyres of the same size inflated to different pressures.
Rob
I cannot explain the Ferrari data above, Rob.
That said, car makers do recommend tyres & pressures, of course. BMW - Bridgestone, Porsche - Pirelli P Zero Rosso N~ for the 911, and so on.
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Non Runflat Tyre Pressures

Post by Busterboo » Thu Jun 29, 2017 10:24 am

R.E92 wrote: Wed Jun 28, 2017 10:49 pm I'm with Garvin on this. Different tyres need different pressures.

I think the construction of the tyre will determine the contact patch at different pressures. RFTs have wildly different construction to proper performance tyres.
Tyre manufacturers will tell you that tyre pressures are vehicle dependent. If you don't believe me, contact them and ask.

Many 2017 tyres by the major manufacturers are coming as 'XL' - with stiffened walls for higher loads and do not have "wildly different construction" from RFTs.
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