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Load, inflation and...
 
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Question Load, inflation and speed rating

 

 Glenn
(@Glenn)
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Joined: 3 weeks ago
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I saw in your recent article a reminder of the normal speed rating of 65 mph on most ST tires.  Using my weights and the load tables for my GY Endurance tires, I determined that 65 PSI was appropriate with about a 20% load cushion, insteaond of the 80 PSI maximum.  What is the impact of speed on the inflation pressure?  I typically drive just under 70 on 75 mph Interstates.  Will a higher inflation pressure , for instance running at 80 PSI max, provide me with more of a cushion relating to speed, or does the inflation pressure only impact load?  

Thanks for helping us non-tire experts run safer!


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 Roger Marble
(@Roger Marble)
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Yes, Inflation can impact the ability of tires to handle higher speed.  Goodyear and other manufacturers of ST-type tires had Tech Bulletins that provided guidance for speeds above 65 mph that said.

Tires with the ST size designation may be used at speeds between 66 and 75 mph (106 and 121 km/h) by increasing their cold inflation pressure by 10 psi (69 kPa) above the recommended pressure for the rated maximum load.

Do not exceed the wheel's maximum rated pressure. If the maximum pressure for the wheel prohibits the increase of air pressure, then maximum speed must be restricted to 65 mph (104 km/h).

The cold inflation pressure must not exceed 10 psi (69 kPa) beyond the inflation specified for the maximum load of the tire.

Increasing the inflation pressure by 10 psi (69 kPa) does not provide any additional load carrying capacity.


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 Jim Rogers
(@Jim Rogers)
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Sorry to be a little stupid Rodger but does that mean my Goodyear endurance E-Class that says 80 psi does that mean I should put it at 80 psi or I put it sometimes around 79 not to be splitting hairs there but I kind of would like to know that also if there's any other question about this such as drive a grand design reflection 315 RS TS something like that real no that's rare living triple slide so it's rlts anyway I don't usually travel over 60 to 65 mph I'm kind of on the conservative side I've lived too long to take too many chances and I've had too many blowouts going down the interstates with cheaper tires in my estimation an answer would be great thank you Roger


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 Roger Marble
(@Roger Marble)
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Joined: 6 months ago
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1. Tires do not Blowout because they have too much pressure gain.

2. Tires are designed and tested when inflated to the pressure number molded on the sidewall. So we tire engineers know they increase in pressure.

3. Do you really think your hand gauge is accurate to +/- 0.5 psi?

4 79 or 80 psi is not going to make any real difference. I don't understand your concern with inflating to the inflation on the certification label


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 Roger Marble
(@Roger Marble)
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Joined: 6 months ago
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Posted by: @Glenn

I saw in your recent article a reminder of the normal speed rating of 65 mph on most ST tires.  Using my weights and the load tables for my GY Endurance tires, I determined that 65 PSI was appropriate with about a 20% load cushion, insteaond of the 80 PSI maximum.  What is the impact of speed on the inflation pressure?  I typically drive just under 70 on 75 mph Interstates.  Will a higher inflation pressure , for instance running at 80 PSI max, provide me with more of a cushion relating to speed, or does the inflation pressure only impact load?  

Thanks for helping us non-tire experts run safer!

Increased inflation impacts both load capacity and speed-related heat resistance.

 


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