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      04-21-2011, 11:42 AM   #1
kmarei
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Exclamation great table to check tire pressure/load rating



assume we're talking about the 18" OEM wheels
the fronts are 93Y and the rears are 97Y
and you just changed the tires to something else
so what do you adjust your tire pressure to?
OEM specs are 33 Psi front, and 35 Psi rear
so 93Y front tires at 33psi means 1178lb
so you find the correct pressure for your new tires by going along the load rating line for your new tire till you find the closest number to 1178

in my case i replaced the OEMs with 255/35 and 275/35 PS2s
their load rating is 96Y Front, and 100Y Rear
so the correct pressure for the new tires is 30 Psi front, and 31 Psi rear


NOTICE
this is not the optimum pressure, nor the one for people who like their tires super firm
this is the correct pressure to keep it as close as possible to OEM spec

so my new tires at 30/31psi should feel the same as the OEM tires at 33/35psi
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      04-21-2011, 02:49 PM   #2
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You can also calculate it with spreadsheet , in wich I use the same system , that is used to make these lists. Once got hold of it and worked it out.
How do they come to the 42 psi? I suppose this list is for XL , Extra load, reinforced tires that work with a reference pressure of 2,9 bar wich is 42 psi ( I estimate). This is for up to 220km/h , for higher speeds there is a system for highgening up this reference pressure.
http://cid-a526e0eee092e6dc.office.l...0tyre-pressure
In this map the spreadsheets and examples for re-calculating the advice pressures for non oem tires , but also to check the original and see if you can go lower for sertain conditions.
Download and open the spreadsheets in Excell or likewise programm to work with it, the browser will try to open it but cant handle the protection and data-validation I used in it. If this message appears, click on the name of the spreadsheet at the line above to go to a page where you can download it.

I checked the list and it calculates with the right save European calculation for normal car tires. But if you fill in the advices of the car , they are made for up to maximum speed of the car with the original speedcode of the tires.
This could make the conversion to other tires like you do insecure.
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      04-21-2011, 02:59 PM   #3
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I once heard a description of, “the perfect solution to a non-existent problem.” With all respect, there is just too much good Kentucky bourbon to be drunk to spend time reading tire pressure charts. But I'm sure that's a character flaw on my part.
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      04-21-2011, 03:11 PM   #4
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Quote:
Originally Posted by elh0102 View Post
I once heard a description of, “the perfect solution to a non-existent problem.” With all respect, there is just too much good Kentucky bourbon to be drunk to spend time reading tire pressure charts. But I'm sure that's a character flaw on my part.
it may be boring
but if you are not running the OEM tires AND you have too little or too high pressure
it might cut your Kentucky bourbon drinking days
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      04-22-2011, 08:17 AM   #5
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Quote:
Originally Posted by kmarei View Post
it may be boring
but if you are not running the OEM tires AND you have too little or too high pressure
it might cut your Kentucky bourbon drinking days
Absolutely true in the literal sense. And, for someone shopping for bargain tires, the chart could be useful. But, if you look at all summer high performance tires in the OE sizes, you will find that all significantly exceed both the real world load rating and speed capability of the car. One would have to run at speed for a considerable distance on significantly underinflated tires to experience a pressure-related problem. But, you can never be too careful where safety is concerned. For example, my favorite bourbon comes with a cork, not a screw cap, lest I could cut myself in the process of operation. We all have our risk tolerance.
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      04-22-2011, 11:51 AM   #6
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Quote:
Originally Posted by elh0102 View Post
Absolutely true in the literal sense. And, for someone shopping for bargain tires, the chart could be useful. But, if you look at all summer high performance tires in the OE sizes, you will find that all significantly exceed both the real world load rating and speed capability of the car. One would have to run at speed for a considerable distance on significantly underinflated tires to experience a pressure-related problem. But, you can never be too careful where safety is concerned. For example, my favorite bourbon comes with a cork, not a screw cap, lest I could cut myself in the process of operation. We all have our risk tolerance.
it's not about bargain tires
the Michelin PS2 i am using are not bargain
but they are a different size/load rating than the stock rating
if i put 33/35 (oem pressure) they will be too firm and uncomfortable
and they will wear too much in the middle
hence the need for the chart

if a tire exceeda the load rating of the oem size
you would need to LOWER the pressure
so your example still needs to check the table for the correct pressure
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      06-02-2012, 05:56 PM   #7
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Quote:
Originally Posted by jadatis View Post
How do they come to the 42 psi? I suppose this list is for XL , Extra load, reinforced tires that work with a reference pressure of 2,9 bar wich is 42 psi ( I estimate).
Good point. I found this chart for SL tires, which is what I have:
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      06-02-2012, 06:00 PM   #8
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This seems to be the source for those charts:
http://www.falkentire.com/template.php?page=technical
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      06-03-2012, 03:01 PM   #9
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Quote:
Originally Posted by Drifty// View Post
Good point. I found this chart for SL tires, which is what I have:
Removed the image from the quote, to keep my post shorter.
But this list is calculated with the right formula , The European way.
Only thing is they have calculated it in Kg and steps of 10 kPa/0,1 bar.
After that it is conversed to PSI and LBS. No problem , because they first rounded the KG down to 10 kg then made the list on PSI and angain rounded after conversing to LBS rounded again only for the higher loadindexes.
Also the list does not go lower then 26 psi wich is usual in the old american system, In Europe they go as low as 1,5 bar/21,75 psi.

But for higher speed the reference-pressure ( here 36 psi) has to be highened up with a sertain system , depending on the speedcode letter of the tire.
Made a picture of it.
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