12

I always thought that even if you go the large wheel + low profile tire route one should keep the pressure to what's recommended by the manufacturer. However I noticed that some people swear by increasing the pressure significantly when they switch to low profiles.

For example if the manufacturer recommended pressure shown in the owner's manual or on the car body is 2 bar - they'll pump up 3 or even 4 bar for every day driving. The reasoning behind is that in poor road conditions there is a lesser chance of damaging the wheel upon hitting a pothole. Which makes sense, as the wheel is closer to the ground with low profile tires. Higher pressure will make the tires compress less and give the wheels a bit more clearance. I've also heard claims that that the recommended pressure values are for maximum comfort, and higher pressure will improve steering response and cornering stability.

And to be fair, for many cars large wheels and low profile tires aren't among recommended dimensions anyways. It might not make sense to cling to their pressure recommendation when the largest wheel the manufacturer recommends is R16 with 215/45 tires and the owner fit some R18s with 215/30s.

So, should one keep the pressure to what's recommended by the manufacturer regardless of the tire dimensions? Is it beneficial in any situation to increase the pressure of low profile tires? How much is alright without wearing down the tread unevenly?

  • Why? A more thorough explanation would be nice. Usually there are no recommendations for low profile tires specifically, just universal ones. – I have no idea what I'm doing Jun 1 '16 at 13:58
  • 1
    Not a chance. My huge 75 profile 10-ply tires on my truck, Load Range E, are currently at 75psi with a sidewall cold max of 100psi if I remember. Usually higher pressure means higher load capacity, right up to the maximum load capacity, which occurs at the highest rated pressure. – SteveRacer Jun 1 '16 at 19:59
  • 1
    ok, up to this day I was pretty sure that it works like that as I wrote in deleted comment, but I was wrong... – krzyski Jun 2 '16 at 9:43
8

tl;dr: it depends. Usually bigger wheels + thinner tires = higher pressure.

So, should one keep the pressure to what's recommended by the manufacturer regardless of the tire dimensions?

Sort of. If the manufacturer has a recommendation for your wheel and tire dimensions, you should definitely start with those.

If your new wheels are bigger (and the tires are even thinner) than the manufacturer's recommended sizes, you're going to have to start tuning them be feel, research and some math.

Remember, the pneumatic tires are one of the primary undamped springs in the whole suspension system. The air volume in the tire is the first place that feels and absorbs the impact of transients like rocks, bumps and potholes. The air pressure in the tire is the only defense your expensive new wheels have in this case. Too low and that pothole could bend your new rim.

If pressures are too high, though, you begin to lose the whole benefit of pneumatic tires. The wheel + tire subsystem begins approaching the behavior of a solid wheel. This is, of course, the standard noise, vibration and harshness trade off.

Is it beneficial in any situation to increase the pressure of low profile tires?

Of course. Lower pressures will have a larger contact area on each tire. This means that they feel more sluggish on steering input. However, they will also have more grip (higher contact patch area = more grip). Higher pressures will also stiffen the sidewalls. You'll be less likely to roll over the sidewall in a steady state turn. Rolling the sidewall feels terrible, isn't great for the tire and can, in severe cases, pull the tire bead right out of the wheel. However, your wear pattern will begin to accentuate the center of the tire.

How much is alright without wearing down the tread unevenly?

It depends. What trade offs are you willing to make? Do you have two driven wheels or four? AWD cars often need the front and rear tires to maintain an expected rolling circumference.

My car, for example, fusses at me when coasting down from speed in second gear if my rear pressures are too high relative to the fronts. My 16 inch wheel pressure recommendations have the fronts about three psi higher than the rears. The 17 inch wheel pressure recommendations are higher for both and are actually equal. I suspect that that is a consequence of the fact that the higher front end weight causes a more significant impact on the rolling circumference on the smaller wheels.

As always, this is your car. You have to make appropriate choices.

13

In almost all circumstances you should use the manufacturer's numbers as your guide. They are aware of the requirements of their wheels, and they do understand that a low profile requires a certain pressure to resist damage. This doesn't necessarily need to be a higher pressure (although it sometimes is) because the wheel construction also needs to be factored in.

The reasons you should adjust from the manufacturer's guidance include:

  • Vehicle weight requirements - a heavy vehicle requires more tyre pressure
  • Handling characteristics - all cars are different, and some require different pressures. Usually this info can be found from enthusiast forums
  • Driving style - I like my Subaru a couple of psi over recommendations, with the fronts a little higher than the rears, as this fits my cornering style
  • Road conditions - going more off road is safer with more air in, and wet roads may be safer with higher pressure

If you do plan on changing the pressure, try only a few psi at a time. In my example, I run my fronts at 36psi, and my rears at 34 - against a manufacturer recommendation of 32psi all round - with my 18" low profile tyres, against the stock 16" or 17" tyres.

2

To answer the original question, there is no value in an Original Equipment Manufacturer (OEM) tire pressure recommendation, if you are not using OEM recommended wheels and tire sizes.

It's that simple.

The ONE really important "recommendation" is that you should never exceed the maximum rated sidewall pressure cold.

1

I've been driving for over 50 years and have owned more cars than I can remember. I usually inflate my tires to the recommended PSI listed inside the door jam. However, my newest car is equipped with low profile tires and inflating them to the recommended PSI makes the car feel like the rim is hitting the edge of ruts and large cracks in the road. This makes for a very uncomfortable ride, not to mention the possible damage that could be done to the wheels. I inflate my tires to 35 PSI instead of the 31 PSI listed in the door jam. Result? Much better handling and a smoother ride. Not saying it's good for everyone, but this is what works for me.

0

The manufacturer almost certainly has specified the recommended air pressures for all recommended tire sizes.

In my case, a 2016 Toyota RAV4 hybrid, there are normal-profile 225/65R17 tires and low-profile 235/55R18 tires. The low-profile ones are wider.

The recommended pressures? For 225/65R17, it's 2.3 bar and for 235/55R18 it's only 2.2 bar. I suspect the pressure difference is due to the width of the low-profile tire.

Usually, low-profile tires are wider, and therefore, you could use a bit lower pressure than for normal-profile tires. But this may not be always the case. Check the manufacturer's recommended tire pressures to be certain.

Also, for extremely low profile tires, there may be so much rim and so little tire that increased pressures could help.

0

Because in a lower profile, wider tire/wheel combo, the tire is more spread out, laterally, it needs higher PSI to ensure even tread contact with the street.

Higher profile, narrower tire/wheel combo, can go with lower PSI, since more of tire, and contact patch, are already concentrated directly beneath the wheel.

I prefer the latter setup, since it self-centers more readily, and cuts through snow and slush better. Why would one want wider tires? Does the car travel sideways? lol!

0

Yes, lower profile tires should be inflated to a higher pressure since there is less distance from the tread to the rim. Hitting any large pothole or obstacle can damage your rim. Normally, lower profile tires gives you better lateral support (inflated properly) because there is less sidewall in which to roll over. The negative aspect will be a harsher ride. The positive aspect is better handling.

New contributor
user49155 is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct.
  • Given the answer by juhist provides the evidence for the opposite case ie lower profile and lower pressure... What evidence do you have to support your answer? – Solar Mike May 21 at 10:54
  • you should always follow manufacturer's recommendations. Sure, your information of potholes is correct, but if you overinflate the tire, you will balloon it out in the middle, causing uneven tread wear and cut thousands of miles off of the life of the tire. – John Lord May 21 at 13:32

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.