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Diesel Dave

Tire pressure

What tire pressure do you run at?   29 members have voted

  1. 1.

    • Below 29 psi
      0
    • 29 psi
      10
    • 32 psi
      9
    • 35 psi
      2
    • 36-40 psi
      2
    • 41-44 psi
      2
    • Don't know
      2
    • Don't know, don't care
      0
    • Service center looks after mine
      1

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19 posts in this topic

I was wondering what tire pressure many of us operate at. The manual says 29 psi. Some people say that 29 is for maximum comfort and you should run a higher pressure for better fuel economy and handling. I tried 35 psi and found the handling improved but the ride was a bit harsh. I am now running at 32 psi. A couple of owners suggested running at the maximum listed on the tire sidewall 44 psi. Yikes! No thanks. Please vote for the closest correct answer.

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Running the tire presure at the tire manufactures recomendation is the best way to go. running over 10 pound lower is over a 25% differance and will wear out the inner and outter edges of the tire. The patch of tire that contact the road will be arched, sort of like this but laying down to the right. ---> ( It also decreases traction in the rain as water will not displace and you can get hydroplaining. You will get used to the 44pis quickly, just as you got used to the lower pressure. The car wont feel as mushy in turns anymore. I actually go to 50, if the tire says 44. Never had a tire malfunction yet, though it is a little tricky in the rain...

:slybump:

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Running the tire presure at the tire manufactures recomendation is the best way to go.

Why? The tire manufacturer doesn't know what load your particular car, passengers, and cargo place on them. They could set some ranges and criteria at best.

Whereas, smart designed the car, did all the tests and is in the best position to recommend tire pressures to complement the car's handling abilities. 29 psi is in the manual, and guidelines are on a sticker in one of the door jambs.

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(Vehicle Weight in lb/100) + 2 psi at heavier end + 2 psi all around if suspension and alignment are stock.

Example: Stock 911, 3,000 lb.

(3000/100) = 30 psi

Add 2 psi all around = 32 psi

Add 2 psi to heavy end = 34 psi at rear

With modified suspension, the result is 30 psi front, 32 psi rear.

Source

Your right! I always thought, how does the manufacture know what tires you put on the car? So the :smart: weighs about 1730lbs? That would be 19 in front and 21 in the back? :?

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Today I think I will switch my air pressure from 32psi back to 29psi. I still think the ride is too harsh and not worth the slight gains in other areas. Another concern I have is that squeaks and rattles can appear in a car as it ages. I tend to think that hard tires could bring these problems on sooner.

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I currently run my front tires at 27 PSI and my rear tires at 35. This has the effect of reducing the oversteer characteristics of the car. I find the car now exhibits neutral handling, that is - I can coax oversteer out of it depending on where I am in the gearing and torque curve.I noticed even before I got the remap and sport suspension that running my front tires at 4 or 5 PSI below manufacturer's recommendation helped with high speed stability.The tires do gain about 4 or 5 PSI on sustained highway driving.

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mine are al wonky right now.... between 27 and 29, but usually i have them all at 29 or 30

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I run 41...I'll nitrogen fill em to maintain the pressure hot or cold...Except they charge $20 for that... OUCH!I wonder if I could get them helium filled... And reduce the unsprung weight!Eddie

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Just wondering, does it actually list the pressure in psi? I'm kinda ticked if it does. Should be kPa or bar...

-Iain

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Whereas, smart designed the car, did all the tests and is in the best position to recommend tire pressures to complement the car's handling abilities. 29 psi is in the manual, and guidelines are on a sticker in one of the door jambs.

I agree that is the best way for a default. Having said that, I have added 3 lbs all around to stiffen the sidewalls slightly, due to the number of tires that have been damaged, as reported on the forums, due to road hazards. :dunno:

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I run 41...

I'll nitrogen fill em to maintain the pressure hot or cold...

Except they charge $20 for that... OUCH!

I wonder if I could get them helium filled... And reduce the unsprung weight!

Eddie

Don't forget that air is mostly nitrogen and less than 20% is oxygen and others. Check them monthly, and save your money.

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I took my other car (a Saturn) into the dealer for a winter special which included wheel/tire rotation and pressure adjustment. When I got it home, I was looking at the right front wheel, thinking that I'd have to keep an eye on that one now, since the right rear wheel had had a small leak because of corrosion of the alloy rim at the valve stem. Something looked odd, and I was surprised when I found that the rears had been moved left-to-right and right-to-left. The front Michelin Hydroedge unidirectional tires were mounted to rotate the wrong way! I returned it immediately, and an embarrassed technician quickly reversed them. The method he used is valid, but only for non-unidirectional tires. This morning, I checked the tire pressures all around. The pressures that are recommended and which have served me well are 26psi rear and 30psi front. Guess what ... the tire pressures were not adjusted; the rears were high and the front (drive wheels) were low. I adjusted the pressures myself. I hope the brake job they talked me into was done better than this aspect of their service. This was my experience at a dealership of a brand that prides itself on its high level of service.

The bottom line is that you cannot rely on service centres; check everything that you can easily check yourself.

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I took my other car (a Saturn) into the dealer for a winter special which included wheel/tire rotation and pressure adjustment. When I got it home, I was looking at the right front wheel, thinking that I'd have to keep an eye on that one now, since the right rear wheel had had a small leak because of corrosion of the alloy rim at the valve stem. Something looked odd, and I was surprised when I found that the rears had been moved left-to-right and right-to-left. The front Michelin Hydroedge unidirectional tires were mounted to rotate the wrong way! I returned it immediately, and an embarrassed technician quickly reversed them. The method he used is valid, but only for non-unidirectional tires. This morning, I checked the tire pressures all around. The pressures that are recommended and which have served me well are 26psi rear and 30psi front. Guess what ... the tire pressures were not adjusted; the rears were high and the front (drive wheels) were low. I adjusted the pressures myself. I hope the brake job they talked me into was done better than this aspect of their service. This was my experience at a dealership of a brand that prides itself on its high level of service.

The bottom line is that you cannot rely on service centres; check everything that you can easily check yourself.

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Did you have them put the winter air in the tires? Or did they use up the last of their summer air before it expires? :goodbad:

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Did you have them put the winter air in the tires? Or did they use up the last of their summer air before it expires? :goodbad:

Seriously tho, don't forget to check your pressures once it gets cold! I think the pressure drop is something like 1lb for each -5C it drops since you last filled them. :BlahBlah:

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29 psi is in the manual, and guidelines are on a sticker in one of the door jambs.

I had another look at the manual, and 29 psi is a minimum cold tire pressure, and you're urged to not leave the tires under-inflated. And check it every 14 days. I should be cranking it up a bit for my load, and keeping an eye on things as the temperature here swings. Also, tire pressure varies by 1.5 psi per 10 degrees Celcius change in ambient temperature.

The ride on Summer tires was definitely harsher when I took delivery a year ago, but when I had them reinstalled last Spring, I specified 29 psi and the ride was softer, more like the Winter tires.

Using the supplied smart air compressor, I added about 2-3 psi per tire, which took about 10 seconds each. For that amount of time, the device didn't even get warm.

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I currently run my front tires at 27 PSI and my rear tires at 35. This has the effect of reducing the oversteer characteristics of the car. I find the car now exhibits neutral handling, that is - I can coax oversteer out of it depending on where I am in the gearing and torque curve.

I run 35psi all around, but find this comment very interesting. I had noticed a slightly harsher ride using 35 compared to 29, but also thought I detected poorer fuel economy at 29. (lots of varibles in both, so add appropriate salt....)

Using tire pressure to affect the handling hadn't occured to me, but of course makes sense. I'll have to try this as well. It will be interesting to see as we go into winter if this has any effect on slippery road conditions.

Later!

Dang

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I meant to say that it had the effect of reducing the UNDERsteer characteristics of the car. I was making adjustments to give me more oversteer (which I like).

What I notice (especially on wet roads) is that the application of power in lower gears allows me to push out the rear on a corner just a bit. The unfortunate thing is that the damned on board computer then decides that I'm having too much fun, and robs me of power just as I am ready to accelerate out of the corner. It does this to me for just a second with no warning indicators, but it is enough to take the grin off my face. I have referred to it as "getting spanked by the computer" in the past.

I am thinking I might grab the traction control disabler module just to see if it helps with this 'feature'; however, it does disable the ABS as well, so that makes me cautious.

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