What will 42 lb of tire pressure do to my Prius suspension?

Discussion in 'Gen 2 Prius Main Forum' started by ystasino, May 2, 2007.

  1. ystasino

    ystasino Active Member

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    I read that the tire can take the extra pressure and that gas mileage will be reduced but what will the extra pressure do to our car's suspensions?
     
  2. tripp

    tripp Which it's a 'ybrid, ain't it?

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    it should increase your MPG. The ride will be somewhat bumpier. It shouldn't affect the suspension in any adverse way.
     
  3. Bill Merchant

    Bill Merchant absit invidia

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    It will do nothing to the suspension itself. Increasing the pressure will improve MPG, improve tire wear, make the ride "stiffer", and perhaps change the tire's grip on the road for better or worse.

    Remember that the front tires should be 2 psi higher than the rear tires. Always fill and check your tire pressure on a cold tire, not driven 5 miles to the gas station. It's easy to adjust tire pressure with a portable compressor and a good guage. Get a good digital guage and use your guage for pressure testing since the accuracy of one guage will differ from another, i.e., your 42 psi might be 40 psi on a different guage.

    Use the pressure that feels good, a balance between comfort, MPG, and safety.
     
  4. ekpolk

    ekpolk What could possibly...

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    Search around some. There have been consistent reports about overinflation impacting the stability of the car, in particular, inducing over-steer in situations where it is both unexpected and (of course) unwelcome. Oversteer is a classic issue for rear-engined, butt heavy cars. It is the issue that has haunted the Porsche 911 series of cars throughout their existence. In a rear engine car, the classic pattern would be to enter a turn too fast, lift off the gas causing the rear to lose traction, and then the rear would swing out, sometimes with such force that you could not recover it. Obviously, the Prius doesn't have a big lump of engine out back, but still, an unexpected oversteer could cause a loss of control.

    I ran my tires hard for a while, but ultimately backed off, both to improve ride, and because I was not seeing that much improvement in mpg (I now run them a few pounds up from standard, but not to the sidewall max). And it's not as if the Prius has big tires that are exacting a huge penalty in drag at the outset. Most of the tires you'd put on this car are LRR (to some extent) in the first place, and the size is relatively small to boot. Personally, I'd recommend just working up from standard in steps to see if you're gaining any real-world benefit, and add no more pressure if you're not.
     
  5. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    I have been consistently over inflating the tires in my wife's car and she hasn't yet noticed.

    I've noticed that my ride seems a little stiffer and I can feel more of the bumps. I'm running 52f/50b
     
  6. tochatihu

    tochatihu Senior Member

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    In 2001 Prius, I have used 'higher than Toyota' tire inflations since very early. It is reasonable to suspect that the resultant 'hard ride' might be tough on the balls joints and struts/shocks. Even so, having carefully inspected mine, they are working fine at 105 k miles.

    Your experience may vary. But pay close attention to the suspension bits, and your car will not fail you at difficult times.

    ystasino, I know no evidence that fuel economy would be reduced with a bit more air in your tires.
     
  7. ystasino

    ystasino Active Member

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    <div class='quotetop'>QUOTE(Bill Merchant @ May 2 2007, 01:25 PM) [snapback]434062[/snapback]</div>
    And which would those be?

    Thanks
     
  8. Boucher187

    Boucher187 New Member

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    I have made the change from standard when I bought the car up to 42/40.
    The ride is stiffer but I can see a slight change in MPG. And from what I hear the tires will last longer.
    That is something that I am looking forward to.
     
  9. philmcneal

    philmcneal Taxi!

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    <div class='quotetop'>QUOTE(ystasino @ May 2 2007, 11:01 AM) [snapback]434097[/snapback]</div>
    i got my DIGITAL pressure gauge with LED light for only 10 bucks at canadian tire, it was 20 bucks off! what a steal!

    i run 57 front 55 rear, been 60 psi guy for years. As long as you take advantage of the coasting and drive with "performance" in mind there should be no problem. If your double thinknig about it FORGET IT and go back to your cushy soft ride if you don't feel you can handle the extra "boucnce" from bumps.

    But as for mpg, I'm scoring low 60 mpg, but I coast a lot and hard tires is what I need when I coast like a mad man.

    Although I think toyota's door recommendation (35/33) psi is too low for my taste, that kind of psi for the weight of the prius has (think eco tires but with midsize sedan weight....) its just overkill in terms of tread and coasting ability. 40 is the bare min for the prius IMO and I would die if it was any lower.

    But hey that's just me, I'm so used to high psi pressure I cannot live without it. To each and their own, keep asking questions good luck.
     
  10. pinball

    pinball New Member

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    I'm on 44/42 psi.
    Yes you get a little better mpg and yes your tyes will wear a little better but also you will feel the bumps a whole lot more (I swear today the car jumped) :eek:
    But most of all I've found it will rattle more ....!
    I HATE Rattles ! :angry: :angry:
     
  11. darelldd

    darelldd Prius is our Gas Guzzler

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    Hard tires are your friend.
     
  12. daniel

    daniel Cat Lovers Against the Bomb

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    <div class='quotetop'>QUOTE(TonyPSchaefer @ May 2 2007, 10:36 AM) [snapback]434075[/snapback]</div>
    Are you serious? Are your tires rated for that? I run 42/40 because that's what john1701a recommended way back when I began reading PriusChat, and John is my authority on all things Prius.
     
  13. jamarimutt

    jamarimutt New Member

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    I have settled on 36/34. For me, 42/40 produces a bumpier ride and may produce additional rattles.
     
  14. darelldd

    darelldd Prius is our Gas Guzzler

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    <div class='quotetop'>QUOTE(daniel @ May 2 2007, 02:45 PM) [snapback]434277[/snapback]</div>
    He's serious (at least in this matter, I'm pretty sure).

    I know somebod else (ahem) who runs similar pressure.
     
  15. philmcneal

    philmcneal Taxi!

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    <div class='quotetop'>QUOTE(darelldd @ May 2 2007, 03:53 PM) [snapback]434314[/snapback]</div>

    hahah believe me, some of us have pressures in the high 50's like me or for some low 60's. I used to use low 60's for the classic prius, but their tires are rated 51 psi max. For this NHW20 prius these tires are only 44 psi max so I only push it to mid 50's.

    john1710a may be a prius guy but I highly doubt he gets the fuel economy I'm getting ;) let alone having the patience to do so... I mean hey if you can live with 20 mph average speeds for the whole tank by all means prove me wrong in that department ;)

    but hey if your happy with the mileage and ride quality by all means just stick with what works (usually 42 front 40 rear) but if you want the peformance its there... just don't be driving like the way you are if you do decide to jack up the pressure.

    In other words, if your going to jack up your pressure beyond tire limits, TAKE ADVANTAGE OF IT AND DRIVE LIKE YOU WANT IT.

    Otherwise just stick with the basics, I'm sure your prius is saving more gas than your previous car.

    As a percentage for over the psi limit I like to stick with 15% or 20% if i'm really greedy, as for tireblow outs NONE in the 2 years I've experimented with high tire pressure. There has been holes and leaks, but with the crazy amount of air I had in the tires, I managed to get home and change to the spare instead of doing it in the middle of the road :D happened twice too!

    or like the chevy commerical says... "LIKE A ROCK!" some of my passengers don't even realize the ride is firm until I tell them what my psi is... then they go , "What no way!"


    Once again just personal info, don't take it too seriously and start flaming me about safety and such... I can gareentee that I'm much safer than anyone who drives in my city.


    edit: also i understand for some since summer is coming, high psi equals boom? well think of it this way... a soft tire (low psi) warms up much quicker than a hard tire with high psi. I once drove 50% city and 50% highway for around 15 or so miles and then checked my pressure. To my amazement all four tires were the same when I left for my trip.

    So in theory... your tires never warm up!
     
  16. tochatihu

    tochatihu Senior Member

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    <div class='quotetop'>QUOTE(philmcneal @ May 3 2007, 03:36 PM) [snapback]435096[/snapback]</div>
    A very significant observation in this context. Softer tires experience sidewall flex while rotating, and this heats them and raises the internal pressure. To a simple approximation, this is where the extra energy goes when you drive on softer tires and obtain lower mpg.

    If your tire pressures increase by more than 10% during driving, it is a pretty good indication that your pressure is too low, your driving speed too high, your driving style is too 'strenuous', or the tires are simply overloaded. Some combination of those factors.

    I have never seen 0% 'hot tire pressure increase' as Phil has, but then again I don't run em quite as hard as he does.
     
  17. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    <div class='quotetop'>QUOTE(daniel @ May 2 2007, 04:45 PM) [snapback]434277[/snapback]</div>
    Sorry, haven't looked at this thread in a while.

    Yeah, I checked them last night in fact because I didn't feel that I was getting the gliding roll I expected. With the warming temps, they are reading 53f/51b.

    I pumped them up in the middle of last summer. I was carpooling up to a Milwaukee Hybrid Group meeting with Wayne Gerdes (xcel). Wayne asked what my tires were at and I told him I overinflated to 42/40. He laughed and said that I should go up to 60, where he keeps his Honda Accord. We argued back and forth and in the end I pulled the "it's my car" trump card and compromised at 52/50.

    Immediately, I could tell a difference. The rolling was easier, stealthing was easier, and gliding was easier. It wasn't until a few tanks later that I noticed a trend (see chart below). I've suffered two flat tires since I've started keeping my tires at that level - both caused by injected construction debri. Sears Auto always checks all four tires for wear when they do tire work so I receive updates on wear patterns. So far the tires are showing no adverse wear patterns.

    Now, time for that chart. It was July when I drove to Milwaukee with Wayne. That's the time when my mileage numbers took a noticable seperation from the temperature line. (your results may vary)

    [​IMG]
     
  18. philmcneal

    philmcneal Taxi!

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    <div class='quotetop'>QUOTE(TonyPSchaefer @ May 4 2007, 10:00 AM) [snapback]435491[/snapback]</div>
    hahaha i would laugh too :D

    no but seriously... depending on your route if you have many bumps and such high tire pressure like mine should be used with CAUTION... but I take it with a grain of salt... for example... if the milk carton says your going to get sick if you drink it after the expirey date. But in theory it varies from human to human, some may get sick, others will get away with drinking 1 day after, but in the end its UP TO YOU on how you want to dictate what the results will be. So if one does want to try high tire pressure, be advised to CHANGE YOUR DRIVING HABITS to suit the conditions. Which I do faithfully, I coast like a madman, I use the engine when I need it (pulse and hard ev glide) and I rarely use my brakes unless I have no choice left.

    Also I avoid bumps and pothoes to the best of my ability, but if I do have to touch it, drive it STRAIGHT on, never swerve or take the bump at an angle... its just nasty sounding... but drive it straight on and the bump should feel like normal... in my case anyway.

    but yeah there has been a few times where my father took my prius and he's an extreme agressive driver (lets just say when i got the car back, my mileage jumped from high 50's to low 50's mpgus and my battery meter was almost full hense he was braking like a madman), he has made it back safety in 3 times he used my car and he travels quite a bit! But yeah... I try my best to not let him use my car :p

    Although when I look at my tires, my tires pick up a lot of tiny rocks that gets seated in the tread... i think that's a characteristic with high tire pressure.... but i check them daily to ensure the PSI is consistant and doesn't over expand as the temps rise for this summer weather.

    Good luck all, and use that digital gauge like a religious person!

    hm I've tried that test twice, once on this car, and once on the civic i use to hypermile on. The theory is harder tires take much longer to warm up, and with the way I drive I don't think they'll ever get a chance to warm up. Hard tires for the endurance run!
     
  19. ystasino

    ystasino Active Member

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    So I drove the integrity tires 3/4 of a mile to the gas station and filled to 50/48.

    Is that considered "hot pressure"?
     
  20. philmcneal

    philmcneal Taxi!

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    <div class='quotetop'>QUOTE(ystasino @ May 5 2007, 11:53 AM) [snapback]436095[/snapback]</div>

    try this ystasino

    i recommend a digital gauge (keep an eye on your stores for sales, they have HUGE markups!!!) so that you can record by the decimal point, also analog gauges wear out over time and inaccuracy's is a huge no no for psi tires.

    3/4 mile i highly doubt it, I drove just over 30 miles today and my tires gasp! was still the same! (yes i checked today, I wanted to prove myself wrong)

    but most people recommending checking it before you drive, (i recommend a flat road, hills put too much pressure on the back tires, throwing off readings) but if you feel that in that 3/4 mile the way you drove was not aggressive then I'd consider it cold pressure still.

    You really have to push your tires to the limit to get it hot, that means burnouts, fast speeds, lots of hard braking, anything to throw the weight of the tires all over the place. But if you barely touch the brakes (and remember you have regen ;) which doesn't enforce as much weight to the front tires as you would with normal brakes) and you can get to the gas station then cold it is :)

    Here's a small guide of what pressures are related to different compounds in tires, if anyone played racing games you'll know what I'm talking about:

    "soft" 30-40 psi (excellent grip (more rolling resistance), low tread life, cushy bouncy ride)

    "medium" 40-50 psi (medium grip, less rolling resistance, medium tread life, firm ride)

    50+ "hard" (adequete grip, barely any rolling resistance, longest tread life, hard ride)


    but this is a BASIC guideline, it gets much more complicated in terms of accelerating wear on the outside edges of the tires, hydroplanning, and blowouts.

    then there are some that claim that high tire pressures get rids of these problems... or so they say... I yet have a lot to learn.


    But ya 3/4 mile .... cold :p
     
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