Tire pressure when changing to 18's

[BoostedDreams]

I've recently come across some info stating that when changing tire sizes from OEM, you should adjust your tire pressure accordingly. I have been running the oem door jam pressures of 35psi front, 33psi rear. But now I am gathering that I should be running 26psi front, 24psi rear.
Just looking for some insight before I go lowering my tire pressure.
Thanks!

 

[ManEatingPenguin]

I am running 28 front and 26 rear for my 245/40r18 all season set of wheels

 

[BoostedDreams]

I am running 28 front and 26 rear for my 245/40r18 all season set of wheels

Any noticeable change in driving characteristics ?

 

[dwag0588]

That sounds low to me. The taller sidewall is already going to reduce turn in sharpness. I would imagine lowering the pressures to that point would further worsen the turn in.

 

[ManEatingPenguin]

Any noticeable change in driving characteristics ?

just makes the ride more comfortable. I'm on Michelin A/S 3+ and the sidewalls are plenty stiff for the 28/26 psi I am on. depending on what tires you are on, you can try lowing it a bit to like 32/30 and work from there

 

[seed3540]

Where did you find that calculator?

 

[ehCobra]

Where did you find that calculator?

https://tiresize.com/pressure-calculator/

 

[FK8CW2019]

I stick to same pressure as OEM and rides good. 35 FR 33R on 255/40/18 PS4's

 

[tinyman392]

I’ve stuck to the stock pressure (35/33 F/R) on my 18’s. It’s been consistent on giving me pretty even tire wear across the tire. If it were over-inflated I’d expect more wear from the middle of the tire (vs the edges for under-inflated). Then again, this is sort of anecdotal. What’s Honda’s recommendation for the spare? If it’s higher or the same as the recommendation in the OP, I might be dubious to whether or not its true.

 

[BoostedDreams]

I

I’ve stuck to the stock pressure (35/33 F/R) on my 18’s. It’s been consistent on giving me pretty even tire wear across the tire. If it were over-inflated I’d expect more wear from the middle of the tire (vs the edges for under-inflated). Then again, this is sort of anecdotal. What’s Honda’s recommendation for the spare? If it’s higher or the same as the recommendation in the OP, I might be dubious to whether or not its true.

Agree. I feel like it ls wearing out even and provides good maneuverability and road manners. I’ll leave it to OEM spec

 

[gtman]

Generally speaking, car companies chose tire pressures that work best with the car's suspension and offer decent ride quality. Stick with stock psi numbers.

OP, 28/26 is way too low for any 10th gen civic, let alone an R. It's also crap on gas mileage (if that matters at all to you).

 

[ManEatingPenguin]

Generally speaking, car companies chose tire pressures that work best with the car's suspension and offer decent ride quality. Stick with stock psi numbers.

OP, 28/26 is way too low for any 10th gen civic, let alone an R. It's also crap on gas mileage (if that matters at all to you).

The stock psi is meant for the stock wheels and tire setup based on the weight of the car. When you go to a different wheel and tire setup, the weight of car doesn't change but the load rating (how much the tire deforms under load) changes. This is also why the OEM spare is rated at 60 PSI due to the tire that is being used and the weight of car

note: not my photo, taking from here

 

[gtman]

The spare is a 125/70. Why are we comparing that?

I've driven cars for 40+ years. When I've changed wheels or tire size I keep it similar to stock with some slight deviation here and there. Just a bit of trial and error. Never had a problem.

What you don't want to do is run super low pressure like the 26/24 the OP is talking about. Of course I dont think you want drastically higher pressure than what you see on the door jam either.

 

[ManEatingPenguin]

just a reference of how wheel and tire sizes changing may require different PSI. Also I'm not arguing that keeping it the stock psi is wrong. I am just giving my explaining of why that calculator exists. There are also 100 different variables in play like stiffness of the side wall (varies from tire to tire) and if this is for track duty vs daily during cold months.

I'm sure that keeping it 35/33 is perfectly fine and I also said to OP that if he does want to try dropping it, start off small like I did and go with something like 32/30, feel it out and proceed accordingly

 

[tinyman392]

The spare is a 125/70. Why are we comparing that?

I've driven cars for 40+ years. When I've changed wheels or tire size I keep it similar to stock with some slight deviation here and there. Never had a problem.

I think his point is different size = different pressure. Which isn’t an entirely wrong thought. His example may be extreme, but it gets the point across. The recommended tire pressure is normally set so that you get the optimal contact patch with the road (IE the entire tread is making equal contact with the road or some other criterion). This can change if you change tire size. Sometimes the change is small sometimes it’s huge.

One other idea to see if you’re near the ideal is to draw a straight line on your tires using chalk and drive around for a little while. The chalk line should disappear uniformly and evenly across the entire tread. If it doesn’t, then you could have other issues:

• Outer treads wear, center doesn’t: underinflated
• Center treads wear, outer doesn’t: overinflated
• One side of tire wears, other side doesn’t: alignment issue

Edit: also keep in mind that you’re asking why compare a 125/70 to a 245/30... But don’t bring up the question about comparing a 265/35 to a 245/30... Or to put it in more rectangular numbers: 125x86 vs 245x73 vs 265x92.

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