What is the correct tire pressure????

[OtterBob]

So i got 245-35-20 tires on my M45.. When I take it to an Infiniti dealer they will put the PSI to 32. However, when I take my car to the tire shop to get a leak patched they fill the tire to 45 PSI claiming that because the max PSI on the tire is 50 you put 45 in and let 5 for the air to move around. They also said that its better for fuel efficiency because the less air in the tire would cause the tires to drag.. this did make sense to me though.. Im in a dilemma right about now. What is the correct tire pressure?

[speedeast]

Load index rating is based on 35-36 psi... maybe that's a good starting point.

On the other hand, I'm pretty sure it's stamped on that tag in the driver's side door jamb.

[EniGmA1987]

I generally keep my tires 10-15psi below the max load rating, depending on time of year. 15 below max psi when cold in summer, because sometimes it gets to over 100 degrees and with normal tire heatup plus ambient temp, the tire pressure can easily go up 10 psi. Plus then there are a lot of pot holes in certain areas and if you happen to hit one on accident that will raise the tire pressure when the tire is compressed from the impact. I prefer to be on the safe side of things than have it pretty close to max as the starting point. Even if a tire has a max of 50, it can still be plenty fine to use it between 30-35. Under 30 would be a problem though.

[szh]

Load index rating is based on 35-36 psi... maybe that's a good starting point.

Yes! Definitely a good starting point.

(BTW, 32 is a tad too low, and 45 is definitely too high for most tires for the M.)

Lots of threads on this topic. Please do a search for "tire pressure" in this forum.

Z

[debiniarthug]

The stamp on the Car says 33 PSI but your not exactly riding on a stock set up. My tires live at 35-37. The tires wake up at around that PSI.

[M45Caliber]

ignoring toe-in/out and camber settings here, UNDER inflating will cause excessive wear on the outsides of the tires and "squealing" when cornering; OVER inflation will cause excessive wear on the center of the tire treads, but improve cornering/handling at the expense of a rock-hard ride. In my Y34 with 245-45-18's, I find that 34 to 36 PSI cold is the best compromise for wear and handling/ride.

I can't believe HOW MANY tire dealers think that the MAX PSI stamped on the sides is the inflation point for tires.

[tkeskic]

I run mine at 36 PSI also in the summer, and lower the winter... as the Drag of lower tire pressure also lets them settle into the snow/ice and grab a litter better for going/stopping on the snow...

I run about 32 in the winter (cold) - but whent he car gets going it gets to 33 or 34 based on outside air temp;

I also run 18 in the winters, and 19 in the summer..

since your on 20 that may change the pressure requirements;

But 32 seems really low to me... I found the car felt best on dry pavement when I was driving with 35/36 - more than that felt way too hard, and lower than that was way too soft for me..

I'm sure there is a better way to calculate the optimal pressure... I stuck with 36 for the summer as thats what the performance shop who installed them recommended them. The dealers recommendation was a 34 so I figure that 2 PSI was all about how I wanted the car to feel, so I went to 36

tk

[MZH]

I keep mine at 36 or 37 in CA all year @ 36K they still look good I dont do interstate trips on my car.

[The00Dustin]

I can't believe HOW MANY tire dealers think that the MAX PSI stamped on the sides is the inflation point for tires.

I think the rest of them just go with 35 regardless of door jamb and tire max. It may not be intentional, could just be poor training, but I once had a tire place inflate my tires to 35 where the sidewall read max psi 32. I have asked managers at other places, and they say they do 35 becaues it's enough and even if it is more than the door jamb, it's better safe than sorry for the drivers who never check their pressure (sad but true, probably most).

[RYCH]

Whatsup maan. I got a 03 m45 n i'm lookin to get a spoiler for the trunk, like what the msport has. Where can i get that?

[geomap55]

Underinflation can cause the tires to heat to the point of failure, which is why tires with slow leaks eventually blow at extended highway speeds. Couple that with sloppy handling and excessive wear, intentionally running 10-15 psi under the manfacturer's recommendation is both silly and potentially dangerous. Excessive tire pressure causes excess wear and a very stiff ride. Why do either?

[The00Dustin]

Underinflation can cause the tires to heat to the point of failure, which is why tires with slow leaks eventually blow at extended highway speeds. Couple that with sloppy handling and excessive wear, intentionally running 10-15 psi under the manfacturer's recommendation is both silly and potentially dangerous. Excessive tire pressure causes excess wear and a very stiff ride. Why do either?

You should mention which manufacturer you are referring to. M45Caliber was talking about the MAX cold rating on the tire, not the recommended PSI from the vehicle manufacturer on the door jam. The max rating on the tire should only be used as a target when it is lower than the vehicle manufacturer's recommended pressure, and I have never seen that scenario.

[szh]

Underinflation can cause the tires to heat to the point of failure, which is why tires with slow leaks eventually blow at extended highway speeds. Couple that with sloppy handling and excessive wear, intentionally running 10-15 psi under the manfacturer's recommendation is both silly and potentially dangerous. Excessive tire pressure causes excess wear and a very stiff ride. Why do either?

Hmmm ... no one is recommending running at 10-15 psi below mftr recommendation as far as I can see (did I misread any post?).

Car tires have a MAXIMUM pressure rating from the tire manufacturer, which has been either 44 (older Z rating tires may still have these) or 51 psi (almost all current gen tires have these) for more than a decade for almost all tire manufacturers. This is not the setting they want you to run at - it is the maximum the tire can be set at cold without blowing up, or popping off the wheel, etc.

OTOH, Infiniti is recommending 33 psi or so, as a standard for the OEM tire. For a variety of reasons the actual setting by the owner needs to be adjusted - usually upwards only - from this standard recommendation.

Most car owners do not check their tire pressure often enough. This means that setting a few psi higher is safer since pressures will drop 1 to 2 psi naturally over a period of 2 to 4 weeks. Plus, weather changes will also cause similar drops over time. Setting a few psi higher prevents going too low - which is dangerous (as you noted also).

Note that tire manufacturers use either 35 or 36 (more common value) psi as the value where the tire load index is measured. Setting the tire pressure around that point gets you the most effective load rating.

Higher than 40 psi will make most tires feel rock-hard and give a very harsh ride.

Side-bar: increasing by 3 to 7 psi above your normal setting is required for very high-speed driving - all European car and tire manufacturers state this for auto-bahn speeds. For the same reason as the Ford-Firestone problems with too low a pressure at US highway speeds (due to owners not checking) causing increased sidewall flex and heating and tire failure, driving at auto-bahn speeds (i.e., > 100 to 125 mph) requires stiffer sidewalls . Hence, the increased pressure.

My recommendation is to start any new tire at about 36 psi and then go up or down from there based on the actual tread wear as measured with a tread depth gauge across the width. Tread gauges cost next to nothing at auto parts stores - I keep one in both our cars in the glove compartment and measure periodically - about every 3 to 6 weeks. Remember to do measurements across the width of the tire to get a sense of whether the tire is over or under-inflated.

Then, when adjusting the pressure, increasing above 36 psi you can go as high as the MAX rating of the tire, but it is unlikely that this is going to be your actual setting. If you need to drop below 36 psi to compensate for the wear, then never go below the 33 psi recommended by Infiniti. If you do end up selecting 33 or 34 psi as your standard setting, then you must also change your schedule to do weekly checks (never more than 2 weeks) of the pressure to avoid being too low.

And, as always, measure your tire pressure when the tires are cold. Ideally inside the garage in the morning, before driving even a few miles. Or letting the sun warm it up, etc. Good tire gauges are not expensive, and a tire pump (particularly a 110 V one) is not too much cost either. This allows checking and setting at home pretty easily!

Z

[szh]

The max rating on the tire should only be used as a target when it is lower than the vehicle manufacturer's recommended pressure, and I have never seen that scenario.

Agreed. No car manufacturer is going to recommend a tire pressure higher than the MAX rating of the tire.

Z

[EcstaSPT]

Are the TPMS pressures displayed usually off a few PSI from the actual or are they pretty much spot on?

[M45Caliber]

My Y34 TPMS is spot on, and I'm using a very decent digital gauge and also double-checking with the standard "stick" gauge. What's cool is that I can check the tire pressures every few days, while driving. I can't find a way to do that on the EX35 - it's just a light that triggers when one tire falls below about 28 psi.

Be sure to use a gauge that is calibrated from 1 to 50 or 60 psi -- stay away from the ones that read to 120 PSI as it's impossible to get an accurate reading of +/- 1 or 2 pounds. Those gauges are meant for bicycle tires where if you are within 5 psi you are fine.

Also, if you've dropped your gauge on the concrete, it's probably now inaccurate.

[ear60008]

I run tires at 35psi.

[Slyfox16]

We are picking up a 2010 M35x with the Goodyear tires. After reading the posts, what should the correct pressure be?

[szh]

We are picking up a 2010 M35x with the Goodyear tires. After reading the posts, what should the correct pressure be?

My first recommendation:

1. Change the Goodyear RSA tire as soon as you can afford to do so. Ideally, have the dealer do it before you pick up the car - for free.

My second, more typical , set of recommendations:

1. Start by setting at 36 psi. Measure it cold, in the garage in the morning, regularly (every other week or so). Use a good gauge - not a pencil type - and a home pump to keep it at 36 psi. This may not be an absolute accurate reading based on the quality of the gauge, but it will be accurate from a relative perspective from measurement to measurement.

2. Buy a tire depth gauge from a local auto parts store, and measure tread depth a number of points across the tread periodically - between 1000 to 2000 miles of driving or so (certainly no more than at the tire rotation mileages I recommend below).

4. If the center of the tread is wearing faster than the edges, reduce pressure by 1 or 2 psi steps, but do not go below 33psi regardless of wear - measure/set pressure more often if you keep it at 33psi. Continue measuring and adjusting downwards till you reach a good balance between center tread wear and a minimum pressure of 33psi.

5. If the center of the tread is wearing slower than the edges, increase pressure by 1 or 2 psi steps, but do not go above the MAX rated pressure of the tire (which is 50 or 51 psi for most modern car tires). Continue measuring and adjusting upwards till you find the right balance of the road harshness you are willing to accept, when making the tread wear even across the read.

I suspect that your final value will be somewhere between 34 and 38 psi ... maybe 40 psi.

A simpler approach: keep it as constant near 35 psi as you can, with regular measure/set times. This will probably give you the right balance between wear, road harshness and safety.

Some of my other general tire recommendations:

1. Replace the tires when the tread depth gets down to the legal limit of 2/32" - but keep in mind that 4/32" is likely to be a safer minimum if you drive in wet weather. For the Goodyear RSA tires, this could be a long time, since they do last well, unfortunately .

2. Never use a tire once 5 or 6 years have elapsed from the date of manufacture (stamped on the sidewall - learn to read the tire code). No matter what tread is left. At that length of time, the rubber material has vulcanized and hardened to the point where it could crack unexpectedly - if you are at significant speed at that point, it could be fatal.

3. Measure and set tire pressure at least once a month - sooner is preferred, particularly if the weather has changed.

4. Rotate tires using a four-tire scheme (or five-tire if your spare is a full-size replacement) every 3750 miles or so. Do it every oil change and you will not forget. As I recall, the RSA can be done side-to-side too - not just front-to-back - since it is not a directional tire. The specific scheme will be described in your Users Manual.

Hope this helps,

Z