New 2023 GLC 300 with 18" Procontact GX tires. Coming home the tire pressure warning was on. The pressure was 41psi in each tire. Label in gas filler door says 37psi. Tires I believe are max 51? What pressure does anyone suggest?

Thanks

 

gas labelor door jamb label..

Tire max is max andnot what you should fill to .
It is helpful in calculating tire load capacity at lower air pressures since it is pretty much linear wrt pressure.

 

You use what the label on the fuel door says. It will list two pressures, normal load and max load. Normal load is when you only have yourself and a couple of passengers in the car and barely any cargo. Max load is if you load the car up to its gross weight. Trunk full of cargo and car full of passengers. There's probably also a note to increase pressure further if driving faster than 100 mph. That's for prolonged fast driving.

Basically tire pressure needs to be high enough to cope with the load. The more you load up the car, the higher the pressure needs to be and same the faster you drive due to the higher forces on the tire at those higher speeds.

As far as the max tire pressure on the sidewall goes, each tire has a load rating that indicates how much load the tire can carry, but it can only carry that load at the pressure indicated on the sidewall. At lower pressure the load it can carry is lower. That's why if you load up your car with additional weight, you need to increase the tire pressure, so that the tires can safely carry the additional load.

Also, remember those are cold pressures. If you check your pressure right after driving, they will be higher. Let the tires cool down in the shade for at least 3 hours, then check the pressures, adjust if necessary and then reset TPMS to store the new reference pressures. Your TPMS probably didn't have the correct reference pressures stored, so you got a false alert.

 

After inflating tires to the pressure you want, you need to navigate into the car's settings and set the current pressure as the new reference point. See your OM for more info.

 

I have a 2017 GLC300, base model. My door well label has 35 psi for front and 42 for the back tires. Both the front and back tires are the same size tires, 235/55 R19 Perilli Scorpion Verde AS Run flats H101.

The rear tires always wear out faster. They get bald way before the fronts. I rarely carry a heavy load. Its usually only me and my wife. I have a short freeway commute (10 miles) to work. The rest is to my local home depot!

Can I run with the same "lower pressure" front and back? Or what do you recommend?

 

As explained above, the door sticker only lists max load pressure in the USA. That pressure is only really suitable if the car is fully loaded up to its gross weight and you plan to drive it near the top speed. The sticker inside of the fuel door lists alternate pressures depending on load, tires and speed. That's what you go with. For most driving, you wanna use what's known as the normal load pressure. It's the lower pressure listed on the fuel door sticker. FWIW, below is the sticker from my AMG. As you can see, the recommended pressures vary widely based on tires, load and driven speed. This all has to do with the amount of deflection in the tires. As the tire rolls, the part that touches the pavement deforms. That deformation creates heat. The lower the tire pressure the more deformation and the more heat is generated, potentially causing the tires to overheat, so you always need to match the tire pressure to the load of the car and the speed. The faster you drive the more deformation per second, so again more heat produced. Tire pressure compensates for that. Increasing it with load and speed will reduce the amount of deformation that the compound experiences and therefore prevents the tire from overheating.

The other aspect is tire wear. If the tire pressure is too high, then the surface of the tire kinda balloons and you will see more wear in the center of the tire. Conversely if the pressure is too low, you'll see more wear at the edges. The other aspect of that is you compromise the tire's contact patch. You want the entire surface of the tire to make contact with the pavement for optimal grip. Not inflating the tires properly will essentially leave potential of the tire on the table. The best way to dial in the exact tire pressure is to drive the car, then use an infrared thermometer and measure the temperature of the compound across the entire tire. You want it to be even, which means the tire is making optimal contact with the road. If the temperature in the center is lower, then the pressure is too low, and if it's higher then the pressure is too high. This is overkill for the road, but at the track, this is what people do in order to dial in the perfect tire pressure.

 

Does lower or higher tire pressures affect fuel economy and ride in a positive way? Higher pressure is rougher ride but better fuel economy and vice versa right?

 

It does that, too. Reducing the contact patch by overinflating the tires reduces rolling resistance and therefore improves mpg at the cost of tire wear and ride comfort. Lower tire pressure will improve comfort. Basically using the normal load pressure when the car is mostly empty makes the suspension work as it's supposed to, and increasing the tire pressure will stiffen the ride.

 

Fact / Reality is today's autos ever increasing speed of new car assembly lines Front Camber and Caster along with Rear Camber has been deleted. Now only one fixed setting at “showroom height”.

Often quoted reassuring “Full ‘4’ Wheel Alignment” is now only basic Toe (directional) adjustment !

NO LONGER CAN YOU ADJUST TIRE CONTACT ANGLES - to spread load more evenly to prevent costly premature tire replacement.

Allowing to cater for high cambered roads with excess passenger side edge wear. Varying road and load conditions encountered in day to day commuting.

SEE SPOILER





AUDI to VOLVO - Experience Of Resolving OEM Suspension Shortcomings (and Costs) Since 1964 !

 

I see, thank you.

 

Long-haul truckers use to over-inflate their tires to improve their fuel economy -- maybe some still do. Some weigh stations check truckers' tire pressure. When you drive the interstate highways that are badly rutted, this is the result of carrying 50,000 lbs of cargo on reduced tire contact surface area on roads that were constructed marginally to begin with.

 

I see.

 

I'll go with the fuel door label which shows normal load @ 35 psi for both front and rear. Thanks!