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Thread: Tire pressure

  1. #11
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    Quote Originally Posted by Basic View Post
    I wont completely bash that post that Flatbroke shared, but I will just tell you that as a Tire Engineer, it is littered with inaccuracies... OP means well though. His contact patch discussion is relevant, however he explains it poorly (actually just plain wrong) He vaguely says Manufacturer Recommended Inflation, but doesn't clarify is he if referencing the Door Placard or the Tire Sidewall, etc etc etc...
    So 39 PSI would Be fine, I guess? for a tire that says max 51. mitsu door panel recomends 33 psi...


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  2. #12
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    Quote Originally Posted by flatbroke View Post
    ..however, the technical approach seemed to be absent and recommendations were offered without a technical disclosure of the elevation of risk. Increasing fuel economy by trading off safety is, in this writer’s opinion, a fool’s economy.
    There was a study which found that increasing pressure slightly increases static and slightly reduces sliding grip. Changes were really minor ~5% or so.
    Last edited by cyclopathic; 05-10-2016 at 05:15 PM.

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  3. #13
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    Quote Originally Posted by Basic View Post
    I wont completely bash that post that Flatbroke shared, but I will just tell you that as a Tire Engineer, it is littered with inaccuracies... OP means well though. His contact patch discussion is relevant, however he explains it poorly (actually just plain wrong) He vaguely says Manufacturer Recommended Inflation, but doesn't clarify is he if referencing the Door Placard or the Tire Sidewall, etc etc etc...
    So what are your thoughts on overinflation?



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    I've ran my front tires at 50 and rears at 45, which did great for reducing rolling resistance, but now I'm finding the traction to be less than acceptable with my half-worn tires. Dropped the pressure to 44 front and 40 rear, which feels like a good compromise. They're gripping a bit more without too much of a hit with rolling resistance.

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        click to view fuel log View my fuel log 2014 Mirage DE 1.2 manual: 49.2 mpg (US) ... 20.9 km/L ... 4.8 L/100 km ... 59.1 mpg (Imp)


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    Quote Originally Posted by Basic View Post
    I wont completely bash that post that Flatbroke shared, but I will just tell you that as a Tire Engineer, it is littered with inaccuracies... OP means well though. His contact patch discussion is relevant, however he explains it poorly (actually just plain wrong) He vaguely says Manufacturer Recommended Inflation, but doesn't clarify is he if referencing the Door Placard or the Tire Sidewall, etc etc etc...
    From a pure safety standpoint cars function at their optimum point when the tire pressure matches what is on the door placard, as long as the rest of the vehicle hasn't been altered. People want better mileage, although we are doing quite well already, but it shouldn't come at a risk of reduced safety. This is magnified greatly by the size of the Mirage. "He was getting great MPG" shouldn't be on a tombstone.

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  7. #16
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    Quote Originally Posted by flatbroke View Post
    From a pure safety standpoint cars function at their optimum point when the tire pressure matches what is on the door placard, as long as the rest of the vehicle hasn't been altered. People want better mileage, although we are doing quite well already, but it shouldn't come at a risk of reduced safety. This is magnified greatly by the size of the Mirage. "He was getting great MPG" shouldn't be on a tombstone.
    Look this subject is just touchy period... placard recommendations have gotten people killed before too. One case is famously recognizeable.
    Resident Tire Engineer

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        click to view fuel log View my fuel log 2014 Mirage ES 1.2 manual: 44.4 mpg (US) ... 18.9 km/L ... 5.3 L/100 km ... 53.3 mpg (Imp)


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    Quote Originally Posted by Basic View Post
    Look this subject is just touchy period... placard recommendations have gotten people killed before too. One case is famously recognizeable.
    please be specific....

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    From the wheels/ca website....Q: If I were to increase the inflation pressure of my tires to improve fuel economy, what considerations should I be aware of? Can I run at the maximum pressure marked on the sidewall?

    A: There has been much bunk posted on the Internet about how easy it is to save fuel by over-inflating the tires on a vehicle. The people never mention the downside: driver safety.

    I have canvassed all the major tire companies and not one was willing to recommend deviating from what the vehicle manufacturer’s placard recommends.

    Michelin, in particular, noted, “Michelin’s recommendation is, and always has been, that the correct and only inflation pressure for your vehicle is that which is specified by the OE vehicle manufacturer, either on the placard (inside the driver’s door jamb) or owner’s manual.”

    Are the tire companies part of the cabal that killed the 100-mpg carburetor and just want you to wear out your tires faster?

    In short, no. The thing that kills fuel economy and increases tire wear is underinflation. Driving with tire pressures 10 per cent too low will increase fuel consumption by 4 per cent. And the tires will give 30 per cent less mileage before wearing out.

    The tire pressure numbers on the placard are not just a random whim by the car company. A lot of research went into choosing the tire size, type, speed rating and pressures for your car. The pressures have to take into account passenger comfort, vehicle grip, vehicle load, tire life, rolling resistance and fuel economy.

    All car manufacturers would like to increase the fuel efficiency of their cars. But in dealing with tires, for everything you gain, you lose something elsewhere on the product map.

    That’s why tire performance charts are spider graphs. The perfect tire would have a perfect circle graph to show its performance, but that never happens. The charts end up looking like spider webs.

    The area where the tires touch the ground is the contact patch. By increasing tire pressure, the contact patch shrinks.

    According to Michelin, “The first thing to understand is the tire’s interaction with the pavement is through contact-footprint forces, which are significantly affected by inflation pressure. Altering these contact-footprint forces from the intended design with an inflation increase will vary by vehicle and inflation pressure, but generally results in less than optimal performance for the tire application on the vehicle.”

    Jon Bellissimo, Goodyear’s director of consumer tire technology, states, “On wet surfaces, lower inflation pressure generally produces slightly higher braking traction – until the onset of hydroplaning.”

    On the lateral-grip (how well the car holds in the corner) aspect of overinflation, Bellissimo concludes,

    “If pressures are increased without the corresponding increase in load (adding weight), lateral grip will generally decrease. For vehicles in the market place, the placard inflation generally provides optimum handling.”

    The Michelin engineering team ran a computer simulation on a family car with pressures increased to 44 psi from the proper 35 psi.

    They report, “Increasing inflation pressure can negatively affect performances such as handling, wear life, worn appearance and braking traction. For instance, our modeling simulations predict, with an increase from 35 to 44 psi, up to 6-per-cent degradation in stopping distance can occur on wet/dry surfaces.”

    To put that in context, a Chevy Cobalt travelling at 110 km/h takes about 49.8 metres to stop. An increase of 6 per cent adds another 3 metres to the distance – three-quarters of a car length.

    The Michelin report concludes, “The key learning is that inflation pressure affects the tire-vehicle interaction, and the only correct inflation pressure for proper balanced performance is what is specified by the vehicle manufacturer on the placard. Never exceed the maximum inflation pressure, as branded on the sidewall of the tire.”

    - See more at: http://www.wheels.ca/news/over-infla....eqDZXFID.dpuf

  10. #19
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    So I guess that kinda wraps it up and puts a bow on it, unless your smarter than Michelin and Goodyear, run the pressure on the door sticker unless you feel you don't need that extra 4 or 5 feet you might need in an emergency. I've had a few close ones in my time. I would rather have as much of a buffer as I can get.

  11. #20
    Senior Member strawboss's Avatar
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    Quote Originally Posted by Basic View Post
    Look this subject is just touchy period... placard recommendations have gotten people killed before too. One case is famously recognizeable.
    Are you referring to the Firestone fiasco where the Ford door placard recommended a low tire pressure to (hopefully) prevent their Explorers from rolling at low speed in an abrupt maneuver?


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        click to view fuel log View my fuel log 2015 Mirage ES Plus 1.2 automatic: 37.9 mpg (US) ... 16.1 km/L ... 6.2 L/100 km ... 45.6 mpg (Imp)


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