38 lbs pressure? Really?

[SuperFudd]

My 5 day old Sonic came with 30 lbs of air in the tires, according to On Star. I see that 38 lbs is required according to GM.
What tire pressure would you recommend?

 

[River_Rat]

I recommend that you run 38 psi. Personally, I usually run 40 or 42. I like the increased sidewall stiffness, and I usually drive on pretty good roads so harshness is not an issue. There is nothing wrong with 38 psi, though. It is a perfectly happy medium--probably the reason it is the recommended pressure.

 

[rdss]

If you have the stock wheels and tires I would run what is on the sticker on your door frame.

 

[ahtoxa]

Factory recommendations for tire pressure are usually a compromise between ride comfort and responsiveness. You can run a couple pounds above that for minor fuel economy improvement but I wouldnt go more than a few pounds and definitely not above the tire's actual rating. This is because of the reduced contact patch once you start to expand the margins.

That said, for street driving in the rain, you really want to be at 38-40 lbs on the Sonic. Under inflated tire tends to fold inward under water pressure when driving in the rain, resulting in drastic contact patch reduction. Even being overinflated by more than 2-4 lbs is better than under inflated when it comes to rain. Treaddesign needs to be aple to perform to specs.

Edit. What I said mainly applies to stock tires. Once you replace tires, the factory recommendation becomes a mere reference as each tire has different desigb features that include side wall stiffness and compound. The only way to determine optimum contact patch on nin-factory rubber is to do a chalk test.

 

[Blue hedgehog]

38psi? According to the onstar app my car is supposed to be 35, but I tend to run 38-40.

 

[sx sonic]

Well you've got 2 good explanations so far, I concur with those statements.

I'm running the max (44psi) in mine, save for snow/ice because I like the stiffer sidewall stiffness, and minimal mpg gain. I've also found that tires inflated over 34 psi last much longer than those inflated below 32 psi, especially the front tires on FWD cars (for typical 44 max psi car/light truck tires).

I'm guessing you were expecting 32 psi?

 

[radsonic08]

Always go for the oem recommendation like the door sticker. That's what the manufacture put there pressures at for all there testing. Imo 38 is high for such a small car. I'm a mechanic and I always fill tires to oem pressures on the door sill if they have oem wheels. 38 psi is one way to achieve the high gas mileage. Once again I put the air to oem to cover my ass you can't be sued if you put it back to oem. I'm in socal so weather is not an issue but if it's snowing go down to 30-32 psi so there's more contact area with the road. This is my opinion please add to it but don't bash me

 

[SuperFudd]

OK then.
I will try 38.
Yeah, I was expecting ~32.
Hmmm... The local gas station compressor has trouble getting up to 32. I may have to go elsewhere.

 

[Swordsmith]

For the (quarter mile strip...edit, I mis-said track... I meant when nothing matters but accelerating in a straight line) 28. For long highway trips in good weather, 42. Normal driving around, 40. Winter, 38. Helps I have my own compressor so changing tire pressure is just a couple minutes work, no bother.

The higher the pressure, the stiffer the ride but the better the gas mileage. However, the lower the pressure, the more contact with the ground, so the better the traction, both for acceleration (thus, the extreme low pressure at the track) and for braking (thus the relatively low pressure for winter).

Since you picked this car in part based on the ride feel, I'm gratified to find that your tire pressure was crazy low, that explains the difference in feel between it and the 1.4T you test drove. This also means you'll probably want to keep your pressure a little lower than the "best mpg" setting... tight tires mean a harsher ride. 30 is still well below spec, though, and shouldn't be used for normal driving.

Try 38, see if your butt can stand that, if not, maybe go as low as 36.

I still can't get around them all being 30, I can't imagine a dealership, or the factory, deliberately doing that, but I also can't imagine the same accidentally low pressure happening four times in a row.

 

[theenico]

For the track, 28.

That's a fairly generic statement. I will assume "track" in your post means drag strip. (My best 60' time was a 2.25 with 42psi BTW)

If you ran 28psi at an autocross, the sidewalls and shoulder tread will get destroyed. For autocross I recommend at least 42psi up front. Even then, with the stock camber settings, you will get noticeable shoulder wear on the front tires.

For a track day event on a road course, I would start around 38psi cold with the idea of the tires rising to ~42-44psi hot.

Again, these recommendations are for the stock tires. Once you move into tires dedicated to a specific use, I would go with the tire manufacturers suggestions.

Edit:

To answer the OPs question, I run 42psi in my Sonic's tires for daily driving on the street.

 

[$ub$onic]

I ran 39psi up front for autocross on the stock tires. On the 195/15 tires, when I ran 42 I had very little grip. Lowered it to 38/39 range and that was the sweet spot.

After a run they would always be 42 psi. They are pretty consistent with heat up

 

[whitnith]

As shown, drag strip and auto cross and track days all have very different needs.

You also need to note if people are talking about cold or hot pressure. Most people are going to measure hot pressure at the gas station where they drove to an air compressor. The sticker on the door sill is for cold pressure.

 

[Luv2xlr8]

I use around 28-30psi on my drag radials for the civics. The more it rotates or faster you go, they tend to stretch a bit so you don't want to put that much air in them. On summer tires, I usually put 32-36 psi at the drag.

Currently I have 38psi on my Goodyear Nordic winter tires and when I had the stock hankooks I was using 40psi.