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High Tire PSI = Better Performance

  1. Sep 29, 2009 #1
    Hello,

    I am a tactical driving instructor and a precision/stunt driver. For more than 15 years I use high PSI tire inflation method on my family car, tactical training courses or stunt performance cars.

    Namely, if on the side wall of the tire manufacturer is indicating that maximum PSI 41, I inflate my tires at 51 PSI.

    Different law enforcement agencies are using the same high PSI tire inflation technique, and the method is endorsed and recommended by highly qualified EVOC instructors and dedicated precision/stunt trainers.

    One of the people endorsing the use of high PSI tires is, Bobby Ore, a veteran driver, with over 30 years of stunt driving experience, 13 world driving records, many standing to this day.
    He is a law enforcement certified instructor, training for 25 years federal agents like FBI, CIA, Secret Service and other numerous Law Enforcement agencies to drive in extreme tactical circumstances. In regards of driving I believe he is the most qualified driver I ever had the pleasure to meet and learn from.

    Yet the amateur driving community in general is regarding the high PSI tire inflation method as a dangerous practice and any discussion on this topic in the automotive forums encounters a lot of resistance and reluctance, (flames) but none of the writers have neither experimented nor sat down and take the physics and/or tire dynamics in consideration.

    The main counter-argument to high PSI tire inflation method is lack of tire traction leading to a poor handling, higher distance braking, danger of tire "explosion" and uneven tire wear in the middle. However in my personal experience none of those concerned are valid.

    Is there anyone that can help me to find a way to validate the physics and tire dynamics, of what I know for fact, due to my real world experience it works, the high PSI tire inflation method?

    Thank you anticipated for your time and effort.
     
  2. jcsd
  3. Sep 30, 2009 #2
    Well as with all things car related.... it depends.

    High pressures do give lower traction and poorer steering responce and feel, as it prevents the sidewall and carcass of the tyre of deflecting. This is mostly to do with tyre temperature though.

    On saying that on the road this doesnt really make a hell of a lot of difference, you'd be hard pressed to tell. On the track where speeds and cornering forces tend to be higher, you centraily can tell the drop off of grip.

    In wet conditions higher inflated tyres will be more resistant to aquaplaning. Also properly inflated tyres decrease rolling resistance and improve fuel consumption.

    However, severe over inflation can acutally be dangerous. It leads to the tyre's contact patch not sitting flat with the floor, giving uneven wear and having the tendancy to 'snap' near the limit of adhesion. i.e the grip falls away suddenly you also do run the risk of rapid deflation if there are any flaws in the carcass.

    You'll probably be fine 10psi over, but you've got to remember that manufacturers specifications are there for a reason. They have done thousands of man hours of testing and designed the tyre to work optimallly at their spcified pressure. Not only this, but the pressure further increases as you drive but to the temperature in the carcass of the tyre rising. So 50 psi may be fine for heavy laden low speed town driving, but can drive the pressures way up with extended high speed driving.

    Put it this way, if a winch is specified for a ton, you'd never dream of consistently overloading it by 25%.


    Most important thing is that it probably wont make a jot of difference on the road. Only very high pressures and very low pressures will make the difference.


    There really is no need to experimentally determine this, as thats all been done many many times and is well documanted in lots of books. The only thing that needs to be determined by testing is how pressure changes affects your set up.



    EDIT: i've been thinking about this and i've come up with a nice tldr version of the above.

    Correct PSI for set up = Best performance. On the road high PSI = slighty less performance but more consistent over the range of road conditions.

    I'd suspect thats the reason why they tend for higher pressures.
     
    Last edited: Sep 30, 2009
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