Tire pressure is suppose to be 35psi. What psi is too high and should I keep it below 35psi?
If the placard on the door jam or your owners manual states 35 PSI the car will perform best at 35 PSI, one or two PSI above or below should be okay. Going outside of manufacturers guidelines can affect handling, tire wear, and fuel economy.
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Set the pressure when the vehicle is ācoldā meaning not just driven. You donāt have to worry about a few added PSI. The Tires can add a few PSI normally from changes in temperature and from the heat added by driving. If you are asking how high you can set the PSI above the vehicleās door stamp, I wonāt comment. I will say, āa fewā more than 35 wonāt change anything for the worse.
If you set the tire pressure correctly when cold, it will go higher when hot, after driving. Do NOT let any air out of the tire. The recommended pressure applies to the ācoldā measurement.
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I agree with everything that has been said. I like to keep mine a pound or two above the spec: it gives me some leeway if a leak develops.
Note it is fall now. Temperatures will be falling. This will cause your tire pressure to drop.
You will need to add more as the weather coolsājust set it wherever you decide, at the
ambient low temperature going on wherever you live.
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The pressure gauge is probably accurate only to +/- 1 o 2 psi, so within that range of the spec seems like you should be ok.
To answer the question: How much pressure is too much? As a tire engineer, the practical answer is you can use as high as 5 psi more than the placard states (assuming the tire size is the same as the placard.)
In theory, the max cold pressure is what is written on the sidewall, but anything above or below what is written on the vehicle tire placard results in issues. Needless to say, the further away you are, the more severe the issues.
What issues?
Anything over the placard is directionally towards worse ride, better handling, worse impact resistance, better wear, worse dry traction, better hydroplane resistance, but worse wet traction below the point of hydroplaning, and better traction in snowing conditions up to the point where you no longer are in contact with the road surface (in my opinion, you want to get the tire through the snow to get to pavement where the better traction is.).
Iāve added up some air into my hybrid Accord over this weekend, it was 31.5psi with 33.0psi recommended.
Somehow my commute MPG went from 42 to 44 right away.
Even a little bit low on air can affect MPG in a noticeable way.
Iāve noticed that on my MKZ hybrid, sure sign of a low tire. Of course, the mpg numbers at the 42 mpg level are VERY sensitive to any change in tires, roads, driving, etc. I go from 42 mpg driving to work to 36 mpg driving home. Itās a VERY gentle downhill to work.
My commute is 11 miles and only after 3-4 miles the MPG settles to reasonable, first miles it is under 25.
I happened to drive around 60 mile to the national park next to me and back the other week, 65-75 MPH and my MPG was in 51-52 MPG range, even with low tires 
Also, I noticed that MPG difference is not much between āvery gentleā and āa little bit inspiredā.
As long as it is not ājack rabbit styleā, it is pretty close.
So, the main MPG killer for me is the initial warmup sequence.
No wonder carcomplaints.com is full of āI can not get even close to the EPA numbersā stories for this car.
Short-commuters I assume.