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Speed & Temperature ratings vs cold PSI #4111292 05/31/16 09:52 AM
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badtlc Offline OP
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If you buy tires with a different speed or temperature rating than the OEM, is the manufacturer cold PSI rating supposed to be adjusted accordingly?

If so, how do you figure this out/calculate it?


2007 Ford Escape XLS 2.3L ATX, M1 AFE 0W20, Fram TG, 167k
2015 Chrysler T&C, 95k+, M1 5W30, Wix OF
2018 Forester Premium 10k+, M1 5W30, EcoGard Syn OF, ST 75W90
Re: Speed & Temperature ratings vs cold PSI [Re: badtlc] #4111301 05/31/16 10:04 AM
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Quattro Pete Offline
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No.

But just fyi, you are not supposed to mount tires with lower speed rating than what came from the factory, so hopefully you are going up in speed index and not down. There are some exceptions.


2002 530i   2015 Q5 3.0T   2018 Charger SRT
Re: Speed & Temperature ratings vs cold PSI [Re: badtlc] #4111308 05/31/16 10:11 AM
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901Memphis Offline
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Did you change the size too?


2012 Chevy Cruze LT 1.4T - 69k - M1HM 5w30 + Fram Ultra
2002 Buick Century 147k - Built 4T65e(Maxlife) - GTX 5w30 + Fram XG3980
Re: Speed & Temperature ratings vs cold PSI [Re: 901Memphis] #4111313 05/31/16 10:17 AM
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badtlc Offline OP
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Originally Posted By: 901Memphis
Did you change the size too?


no


2007 Ford Escape XLS 2.3L ATX, M1 AFE 0W20, Fram TG, 167k
2015 Chrysler T&C, 95k+, M1 5W30, Wix OF
2018 Forester Premium 10k+, M1 5W30, EcoGard Syn OF, ST 75W90
Re: Speed & Temperature ratings vs cold PSI [Re: badtlc] #4111435 05/31/16 01:13 PM
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jadatis Offline
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Temperature rating is only to be compared for the same brand and series of tires, so I once read.
Speedrating thoug is another thing .
Most car tires are Standard Load or XL/reinforced/Extraload, and have speedrating above Q ( maxspeed 160km/99m/h) and above Q the maximum load is calculated for that speed, and higher speed needs higher pressure .
Will give picture of the system , in wich you see the exceptions to this rule , and that is R,W.Y-speedrating.
For V.W.Y 30 km below max even the maximum load has to be reduced.


But my idea is that this officially used system , has to be chanched.
This because a W or Y speedrated tire with same sises and tirekind ( SL or XL) have same maximum load given, and to my conclusion the W and Y need to give lower maximum load because they give it for higher speed.

Tires must have maximum speed ( speedrating) that is the same or higher then the maximum technical car speed ( max given in the books, even in practice you never make that speed).
At least thats law in The Netherlands where I live, but in some country's ( Belgium) the tires need to be homogolised by the car maker, before you may put them on the car.


So short answer after this long explanation.
Temp rating and speedrating doens not need other psi.
Other speed though need other psi.

Here the picture, hope you can maker something of it.

Re: Speed & Temperature ratings vs cold PSI [Re: badtlc] #4111591 05/31/16 04:01 PM
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slacktide_bitog Offline
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The pressure spec is the same for any tire of that size smile

Re: Speed & Temperature ratings vs cold PSI [Re: slacktide_bitog] #4112102 06/01/16 06:19 AM
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badtlc Offline OP
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Originally Posted By: slacktide_bitog
The pressure spec is the same for any tire of that size smile


I assumed as much but I thought maybe speed and temperature ratings might have different stiffness to the sidewall. I wasn't sure if a stiffer sidewall would require a lower PSI level to prevent increased center tread wear and vice versa.


2007 Ford Escape XLS 2.3L ATX, M1 AFE 0W20, Fram TG, 167k
2015 Chrysler T&C, 95k+, M1 5W30, Wix OF
2018 Forester Premium 10k+, M1 5W30, EcoGard Syn OF, ST 75W90
Re: Speed & Temperature ratings vs cold PSI [Re: jadatis] #4112142 06/01/16 07:20 AM
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Originally Posted By: badtlc
Originally Posted By: slacktide_bitog
The pressure spec is the same for any tire of that size smile


I assumed as much but I thought maybe speed and temperature ratings might have different stiffness to the sidewall. I wasn't sure if a stiffer sidewall would require a lower PSI level to prevent increased center tread wear and vice versa.


Actually, sidewall stiffness is NOT related to speed or temperature ratings - except to say that higher speed rated tires tend towards higher handling and therefore tend to have a stiffer sidewall. That is not to say that lower speed rated tires can not have stiff sidewalls. Those 2 things are not cause and effect sorts of things.

Further, tire manufacturers spend a lot of time trying to get their tires to wear evenly in spite of those things that cause uneven wear, but sidewall stiffness, speed ratings, temperature rating, traction ratings, and wear ratings are not among those things that affect EVENNESS of wear. This is a footprint geometry kind of thing.

Originally Posted By: jadatis
Temperature rating is only to be compared for the same brand and series of tires, so I once read. ......


Sorry, but speed ratings, temperature ratings, traction ratings, and wear ratings are all based on standardized tests and CAN be compared to each other.

- HOWEVER -

That is not to say that sometimes tire manufacturers won't under rate their tires as there is no law against doing that. For example, a tire manufacturer MIGHT want to rate their best wearing tire 25% better than their next best wearing tire, and since they can't artificially boost the better one's ratings, they'll lower the other one.

Last edited by CapriRacer; 06/01/16 07:21 AM.

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Re: Speed & Temperature ratings vs cold PSI [Re: badtlc] #4112166 06/01/16 07:34 AM
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IndyIan Offline
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Originally Posted By: badtlc
Originally Posted By: slacktide_bitog
The pressure spec is the same for any tire of that size smile


I assumed as much but I thought maybe speed and temperature ratings might have different stiffness to the sidewall. I wasn't sure if a stiffer sidewall would require a lower PSI level to prevent increased center tread wear and vice versa.

Stiffer side walls in LT tires need more pressure than P tires at equal loading. The LT sidewall will overheat run at P tire pressures even at lower loading.
Between different P tires though, I don't think sidewall stiffness is a huge factor. I put some BFG sport comp2 on the Focus and they do advertise a special sidewall stiffener section, so they may generate extra heat in the sidewall at lower pressures. I went down a size and load rating so I run them at 35 psi and they stay cool on the highway. Maybe some of the higher profile high performance SUV tires might have stiff enough sidewalls that you could get overheating if you ran them at door pressure with a full load?


07 Focus ZXW, 5spd manual, 245km M1 5W30
18 Outback 2.5 CVT 35km 0W20
Re: Speed & Temperature ratings vs cold PSI [Re: jadatis] #4112341 06/01/16 10:34 AM
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Originally Posted By: jadatis

Tires must have maximum speed ( speedrating) that is the same or higher then the maximum technical car speed ( max given in the books, even in practice you never make that speed).
At least thats law in The Netherlands where I live, but in some country's ( Belgium) the tires need to be homogolised by the car maker, before you may put them on the car.



No, the law is the same in Belgium as in Holland. However you can only vary the tyre/wheel size a small amount from the homologation sizes. (-2% to +1.5% circumference, +/- 2% track width).

http://www.goca.be/nl/p/ak-pa-banden


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