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BigJimnyMeet (North) 2024 (12 Jan 2024)


BigJimnyMeet 2024

14th July 2024
Parkwood Nr. Leeds

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Re:Tyre Pressure for 215/75/R15 ?

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24 Oct 2022 12:46 - 24 Oct 2022 12:46 #245557 by fordem

As it's a gen4 the offset of the factory wheels is actually negative 22 

Factory alloys on a gen 4 have an ET/offset of positive 5
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Last edit: 24 Oct 2022 12:46 by fordem. Reason: typo

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24 Oct 2022 17:26 #245561 by Lambert
Yes we found that out a while ago. I thought I had rectified all the mention of the 22 offset.

Temeraire (2018 quasar grey automatic)
One of the last 200ish of the gen3s, probably.
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24 Oct 2022 19:13 #245562 by Soeley

Yes we found that out a while ago. I thought I had rectified all the mention of the 22 offset.
You did somewhere, must have been a different topic.
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25 Oct 2022 12:36 - 25 Oct 2022 12:44 #245576 by jadatis
Ideal tirewidth (section width) for 7 inch is 245/75 or 255/75
But 205/75 is minimum adviced by the tiremakers.
So your 215/75 is within what they allow.
Max section width " allowed" is 285/75.
Made calculator for that, after contact with a tyremaker, and is also dependend on Hight/Width division, called Aspect ratio.

Needed cold pressure for onroad use is depended on load on tyre and speed used. All to not overheat any part of tyre when driving that reference-speed constantly.
Reference-speed for Q R S T H V speedcode is 160kmph/99mph.

If you give of that tyre next, I will make a pressure/axleload list for you.
1. Maximum load or loadindex.
2. Kind of tyre to determine the reference-pressure
Standard load personscartyre AT 36psi
XL/reinforced/extraload AT 42psi.
Given on sidewall the maximum allowed cold pressure between 44 and 51 psi, and an ocacional XL// 60psi.
C-tyres and LT-tires almost always give reference-pressure behind AT on sidewall
3. Speedcode, less important, have my own system for that.

Then also give if you want it in KG or LBS, and in psi or bar or kPa.

Then you "ONLY" have to determine the axleloads acurate, the most tricky part in it all, and your responsibility.
Carmakers use max permissable axleloads for that, if they not give it higher for energy-saving or responcibility reasons.

End 2007 this " pigheaded Dutch selfdeclared tyrepressure specialist" got hold of the officially used formula and system for calculating needed tyre-pressure, and went running with it.

I have old list of Michelin, in wich pressure loadcapacity list for a specific tyre, for 110 kmph ( K speedrated) down to 20kmph onroad, and for mud/sand about 50% of pressure for 20kmph( 12.5mph) onroad, wich then is maximum allowed speed.
For on track about 80% of the pressure for 65kmph onroad, wich then is max allowed speed.
I write " about" because that is what I made of the lists, would like to know the real system the tyremakers use for that.
Last edit: 25 Oct 2022 12:44 by jadatis. Reason: Typing errors

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