Tire Speed Rating Question

Hi jadatis;

I am answering your message in another topic entitled At what psi can I travel 65-75mph?.

HTH;
John

Once read for ST tires that for higher speed a percentage higher pressure then acording to the lists, and for better handling quality , also a percentage highening up.
If then the new pressure came above maxloadpressure, pressure needed for the maximum load , so reference-pressure, it may not be more then 10 psi.
So my calculation of 44psi + 10% =48,5 psi already has that percentage , wich I mean to remember 2 x 5% , higher then acording to the list,in this case my extra save list, and so stays under the 50+10 psi , and is allowed.
You are also allowed to drive with 60 psi , thoug it would not be good for grip and keeping the screws in the wood of the TT.

You can even stay at normal rubber valves, wich are allowed a cold pressure of 65 to 70 psi ( depending on the brand) with 26 psi extra for higher temperature in the tire, to the mildest american standard.
This 26 psi makes it possible to fill at 65dgr F a pressure of 70 psi and if the inside tire temperature gets boiling point of water ( 100dgr C/200dgrF?) , wich it can incidentialy get by the heat of the brakes, transported trough the rims, the pressure stays below that 96 psi.
High pressure snap in valves wich are alowed for 90 psi maximum cold pressure , or metal valves for over 150 psi.

I run 70# and whatever the speed limit is. Good luck.

Good luck with that !!!!!!!!!!

We have our reply from

Goodyear wrote:





From: goodyear_cr@goodyear.com on 07/25/2013 01:13 PM

Sent by: Goodyear Tire & Rubber Company Consumer Relations 728 1144 East
Market Street Akron, OH 44316 Voice #: 800.321.2136 Fax #:
330.796.6829

Mr. ,

The max load is 1,360lbs at max 50psi.

Industry standards dictate that tires with the ST designation are speed
rated at 65 MPH (104 km/h) under normal inflation and load conditions.
• Based on these industry standards, if tires with the ST designation are
used at speeds between 66 and 75 mph (106 km/h and 121 km/h), it is
necessary to increase the cold inflation pressure by 10 psi (69 kPa) above
the recommended pressure for the rated maximum load.

Do not exceed the maximum pressure for the wheel.

Jennifer - Consumer Relations



From: on 07/24/2013 01:11 PM AST




From:


To: goodyear_cr@goodyear.com
cc:
Subject: Contact Us request from www.goodyear.com



A Goodyear website user has submitted a request through the corporate
contact form. Please address the concern accordingly.

Name:
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, 0
Message:
Looking for ST trailer tires. What is the status of your Document PSB
#2011-13 with Subject: Tires for Trailer Use Only: General Information ?
What is the max load and psi of your Marathon 175/80/R13 between 66 and
75mph?

If you are not the correct recipient, please notify the Goodyear Global Web
Operations team of the email error and we will update our website contact
list.

This is the same as the contents of Goodyear's PSB #2011-13 which we have discussed beforehand. I believe we can say the PSB is in effect.

... at speeds between 66 and 75 mph:

Tire: Add 10 to 50psi means inflate to 60psi.

Wheel: Dexstar 17-229 is rated 1660lbs 65psi.

HTH;
John

jadatis wrote:


... and that would prove your 45 psi used is ok. But correct me if I am wrong.

Thank you for those calculations. Yes, the data I gave was accurate.

I am sending an e-mail to Goodyear with

message wrote:


HTH;
John

A couple of thoughts:

First, I am of the opinion that trailer manufacturers don't do a good job of sizing the tires on their trailers. I think they need to use tires that have at least a 15% unused capacity (in other words, no more than 85% of the tire's rated load).

So I don't think the vehicle tire placard for trailers is such a good stand alone value. I certainly wouldn't use anything less than what is there.

Second, the tables showing load vs inflation pressures are MINIMUMS!! You can NOT take that value by itself and use it. You SHOULD increase the inflation pressure ABOVE the value indicated - I think 15% more load carrying capacity - and I think that is 10 psi.

Third, I do not know of any vehicle tire placard that indicates a speed restriction for the vehicle. I think that is a good idea. I also think that speed restrictions should be plain and obvious - and they are usually just the opposite. Another shortcoming of trailer manufacturers.

And lastly, the 10 psi more to increase the speed restriction from 65 mph to 75 mph is on top of the load carrying capacity. So if you take my 15% and add 10 psi, you get 20 psi.

PS: One more thought: The burst pressure of tires is many times the maximum indicated on the sidewall of the tire. Put another way, tires do NOT fail because of the increased pressure (or at least the 10 psi values we are discussing. Please note, I am NOT advocating grossly over inflating tires, but within the limitations published by the tire manufacturers and tire standardizing organizations (which is what we are discussing), there are no failure issues involved.

fj12ryder wrote:
Not to hijack this thread, at least not too much :), but how exactly will "low tire pressure" be proven to be the culprit? It's pretty much impossible to tell "after the fact" so any speculation is just that: speculation.

You can tell if a tire was operated over-loaded / under-inflated by the impressions left by the rim on the beads of the tire - commonly called "bead grooving".

full_mosey wrote:

CapriRacer wrote:
Just an FYI,

There's a provision that isn't well publicized about ST tires (LT tires, too) that you can over-inflate them 10 psi and that allows you to run up to 75 mph. If you also reduce the load by 10%, then you can run up to 85 mph.

So, yes, it is permissible to exceed the inflation pressure written on the sidewall - but only by 10 psi.

Can you do the math for me?

I have a single axle with ST175/80R13 50psi 1360lb rated tires. My heaviest wheel is 1060lbs. I run the psi from 45-50 now.

What pressure would allow me to travel at 65-75mph?

HTH;
John

Strange thing of your ST tires is that mostly they are allowed to carry more load because they may deflect more at lower speed, and this gives higher maximum load at the same reference-pressure ( that 50 psi , wich is not the maximum pressure) , then for a LT tire with same sises.
But searched with google for LT tire with same sises and 50 psi , and could not find.
Only found European 6pr tire wich needs 55psi in that system with load index 94 and speedcode P wich is up to 150km/90m/h.
If you calculate that back , to the 50 psi and 1360 , you come to the same load to carry. So probably your ST tire has not that extra load to carry as for most ST tires is done for more deflection at lower speed. They did not use this extra at your tires , and this makes them better then most ST tires, so positive.

Both tires filled in in my Traveltrailertirepressurecalculator, give and advice of 43 psi for your ST and 44 for the Falken 175/80R13 94P.
This is already with reserve for things like , pressure-loss in time, unequall loading R/L, little misjudging of load and misreading of pressure and load-scales.
So if your loads are weighed , and you are sertain that you never go over that load you gave, for savety you could add the 10% to the pressure for higher speed and better handling, but will come to max 48.5 psi wich is still under the reference-pressure , and you dont have to use the 10 psi extra above that wich is allowed. With the TT loaded to 2400 lbs and tonge-weight of 10% so 240 leaves 2160 axle load /2=1080 lbs per tire. Then a weightdifference of 240 lbs L/R possible before one tire reaches the damage border at higher speed.

So endconclusion, if the data you gave where right , you dont have to use 60 psi pressure , these tires have all the reserves at 50 psi.
You probably never had any problems with these tires, and that would prove your 45 psi used is ok. But correct me if I am wrong.

fj12ryder wrote:
Not to hijack this thread, at least not too much :), but how exactly will "low tire pressure" be proven to be the culprit? It's pretty much impossible to tell "after the fact" so any speculation is just that: speculation.

A tire forensics expert such as Dr. John Daws (Daws Engineering) can almost always determine the causes of tire failures.

FastEagle