I'm confused

[jamesqf]

If your drive is anything but level, then the cruise control could be contributing to poor fuel economy. It tries to hold a steady speed, up hill and down, which means it could be using extra gas to climb up, then braking on the downhill side. See various posts on "Driving With Load" or DWL.

[MobilOne]

Thermostat OK?

[Xusi]

But are all of you 100% sure that tire pressure doesn't affect grip? Anyways, I've read that tires with high pressure tend to wear down faster from the centre than from the sides. Do you strongly recommend me inflating my tires way further than those recommended by the manufacturer? (I think maximum PSI for my tires is 50. Must check).

It's quite strange that I don't lose any grip with a higher tire pressure.

So, what pressure would you recommend me, if my car weights a total of 1370 kg + 55 kg (me)?
Keep in mind that sometimes I'll carry up to 5 people + charge in the trunk (+350 kg)

[Xusi]

Yes, thermostat is ok. Maybe Cruise control is what affected my mileage, as I noticed that it was braking rather than letting the car go downhill with an increasing speed

[digital rules]

Originally Posted by Xusi

Anyways, I've read that tires with high pressure tend to wear down faster from the centre than from the sides.

There is ZERO truth to that assertion with modern tire construction. The main drawback with higher PSI is reduced ride quality which can vary tremendously depending on the car.

Those that think tires wear in the center faster most likely are the same that think a car needs to be warmed up before driving. They are still living in the past.

[RedDevil]

Originally Posted by Xusi

But are all of you 100% sure that tire pressure doesn't affect grip? Anyways, I've read that tires with high pressure tend to wear down faster from the centre than from the sides. Do you strongly recommend me inflating my tires way further than those recommended by the manufacturer? (I think maximum PSI for my tires is 50. Must check).

It's quite strange that I don't lose any grip with a higher tire pressure.

So, what pressure would you recommend me, if my car weights a total of 1370 kg + 55 kg (me)?
Keep in mind that sometimes I'll carry up to 5 people + charge in the trunk (+350 kg)

I'm sure it does affect grip, in a positive way.

Wear should be even with modern radial tires, where the wires in the carcass are evenly distributed over the track width.
It would just wear slower as the thread bends and scrapes less when it hits the road.
My two sets of tires (summer and winter) have worn evenly at 40+ PSI, with lots of thread depth left after 45.000 miles combined.

When you distribute the same weight over a smaller contact patch, that patch gets pressed into the road deeper, making it harder to slide.

Best pressure is up to you. The further you go the better it gets BUT the improvement recedes quickly.
Going from say 30 to 40 PSI can give you a 5% gain in overall efficiency.
Going to 50 PSI would only add 1% to that, and another 10 PSI would only add 0.1 % or so. Comfort and road noise may increase at those pressures, so that would be a clear sign to take it no further.
Max sidewall is another logical boundary. While most tires can handle way more than that you'd take it outside its intended use.

Whatever you do take small steps and check the tires after airing up, and again some time later. If a tire deforms it has been damaged and needs to be replaced asap regardless of pressure.

[CapriRacer]

Originally Posted by Xusi

But are all of you 100% sure that tire pressure doesn't affect grip? .......

There is a grip loss, but the drop off in grip isn't a straight line.

Originally Posted by Xusi

.....Anyways, I've read that tires with high pressure tend to wear down faster from the centre than from the sides. .....

You will see lots of disagreement on this point, but there is a tendency towards center wear with elevated inflation pressure, but there are other factors that contribute more, so it is not always easy to see.

Originally Posted by Xusi

........ Do you strongly recommend me inflating my tires way further than those recommended by the manufacturer? (I think maximum PSI for my tires is 50. Must check). ........

I'm kind of the odd man out here, but I don't think the increased inflation pressure is such a good idea. It also causes groove wander, harsh ride, and increased impact and puncture damage.

Originally Posted by Xusi

........ It's quite strange that I don't lose any grip with a higher tire pressure. ......

You will find many people for whom the increased fuel economy out weighs any other factor - and some will even deny that there are any negative issues.

Originally Posted by Xusi

....... So, what pressure would you recommend me, if my car weights a total of 1370 kg + 55 kg (me)?
Keep in mind that sometimes I'll carry up to 5 people + charge in the trunk (+350 kg)

Personally, I recommend no more than 5 psi (0.3 bar) above the pressure listed on the vehicle tire placard.

[RedDevil]

As you see, opinions differ.
You need to test and find out what works best for you.

[Fat Charlie]

My opinion is that if you live at the edge of grip, you shouldn't be asking for advice on teh interwebs.

If your tires never squeal while cornering, pressure won't change your life. If they do, you need to explore things a bit more on your own.

[star_deceiver]

Originally Posted by RedDevil

When you distribute the same weight over a smaller contact patch, that patch gets pressed into the road deeper, making it harder to slide.

yeah.... noooooo....

Having aired up my Winterforce to the max of 44psi and going for a drive in the snow, I can tell you that there is a LOT of grip lost running that high of pressure compared with the recommended 32psi.



During the winter I had them at 36psi for the most part but the second the snow came back it was back to 32.

You may want to read up a little more on how sipes, studs, compound and pressure work to grip the snow.

Mind you, how often would you see this: