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Best Tire Air Pressure

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I have a quick question. My car manual lists different tire pressures based on how many people are in the car at a time. See the attached picture. 98% of the time it’s just me. I have been using the recommended pressures for 2 people, 29 psi in the front and 33 psi in the back. Is there an advantage to using a different pressure like an intermediate level? My dad whose car this was did 33 and 38.5. Obviously relevant would be tire wear, bumpiness of ride, and MPG. What’s the best option considering these factors?

If it were my car, and most of the time it’s only me in it, I’d do 31/35. Slight increase in MPG, and it gives me a little wiggle room if I forget to check the pressures once a week or every 2 weeks

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In this case, I think it’s simple. I’d use the two-person pressures.

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My solution to the problem was to buy a manual tire pump. I set the air pressure for just the driver. If Mrs. Triedaq wants to go along, she has to pump up the tires for two passengers and reduce the pressure when we return home.

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I would bet Mrs. Triedag has a different storey about that.

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Wow, and I thought I was anal about tire pressure. The only reason I could see changing the tire pressure based on the number of people in the vehicle would be if they are riding with you during a racing competition and you need to optimize traction for the track.

BMW’s come with ultra high performance summer tires and they are very sensitive about pressure when pushed to the limit. If you are driving in traffic like a normal person, you don’t need to be that picky.

Constantly changing the pressure in your tires is NOT good for them. This is true if you are using a small 12v compressor or manual pump because you are adding more moisture to your tire. In the end, that could shorten the life of the tire. It is not as much of a problem if you go to a garage and use their compressor tha thas an air/water separator in the line or are using nitrogen. Note: the only real advantage of N2 is that it is dry, but then so is air that has gone through an air/water separator.

I check mine about every three months. Since the tires will lose about a pound a month, I add about two pounds over the recommended so the tires don’t get too low. Slightly higher is a lot better than slightly lower. I make sure that the pressure in both tires on each end are as close as possible. I use a calibrated meter that measures in 0.1 psi increments. I also watch the wear patterns closely for problems.

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Leave it to BMW to over complicate.

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I cannot imagine having to change my tire pressure to pick up my folks and 2 suitcases at the airport. What a pain!

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Then why not set the tire pressure at the full load setting? Most of use do.

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Yup, many German vehicle manufacturers over complicate the tire pressure thing on older cars. But more recent model years have been simplified because the government told them to.

So to answer the question, as you increase inflation pressure, the tires get better steering crispness, worse ride, better fuel economy, better wear, better wet grip, better snow penetration, and worse dry grip, worse snow grip. So what is best depends on what you want.

Just be aware that the pressure specified by the vehicle manufacturer has been thoroughly tested.

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Can you imagine if the vehicle was in use by a taxi company?

Driver: “How many are in your party? Four? I thought it was three.
Sorry, but I’ll have to re-adjust my tire pressures. It should only take 15 minutes”

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It surprises me that there is an up to 11 psi spread in pressures.
Is this to cover cruising at 120+ mph on the autobahn?

Yes. Most German cars used to be that way. Stopped about 2008.

Wow I struck up quite the conversation :slight_smile:

I remember that on American cars In the 60s with bias ply tires, having different PSI specs for different load and driving conditions.

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This is supposed to be from an early 60s Chevy, though I don’t recall such a wide front-to-rear difference.

And then for an early Corvette:
image

A Corvair in the first photo. Its very unusual inflations specs were one reason it became a poster child for Unsafe at Any Speed, Ralph Nader’s first book. Too many owners and mechanics and gas station attendants did not follow the inflation specs.

It was the first car I drove to any extent on the roads, the summer I turned 16.

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Same here. The summer I turned 16, I got to drive our old family 63 Corvair convertible. Brings back great memories.

I only drove a Corvair once, I liked it alright.
As far as the tire pressure—Guilty, I was 16, we inflated ALL car tires to 30 PSI, I know a lot better now. Back then people would install all different sizes. Tom McCaHill in one of his guides from the late 50s recommended going up one tire size and higher viscosity than manufacturer specified.

We’re living up to your screen name. :blush: