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Discussion Starter #1
Hi everyone, hope you're all staying safe and healthy and far from COVID-19.

I have been trying to figure out what's the correct tire pressure for my 2016 CLA250 4Matic. The tires I have are <225/45 R17 91 H> (front and rear). They are all season run flat tires.

Here are the numbers I see:
  • The B pillar label says "Cold Tire Pressure" of 41 PSI (both front and rear). Is this the maximum tire pressure?
  • The gas filler cover label says Normal Load (38 PSI and 33 PSI, front and rear respectively) and Maximum Load (41 PSI and 41 PSI, front and rear respectively).
  • On the tire itself, the max. pressure is indicated as 51 PSI (for the max load).
Can someone please tell me what should be the correct tire pressure? Thanks in advance.
 

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If your normal driving is just yourself and maybe i passenger, then use the gas filler cover as your standard.
On those occasions when you are transporting a full load & maybe some cargo, increase the tire pressures to 41.
 

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Yeah it is confusing. I've always used the PSIs listed on the filler cap.
 

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The pro-s and cons are: If you go with a higher pressure, you get less rolling resistance and better gas mileage.
OTOH you also get a less pleasant ride, and the center strip will wear faster than the shoulder strips.
I tend to go with 38-39 cold and 2 psi less in the rears. This is a nod to the extra wgth the engine, and the tranny represent. Results in a moderate amount of extra
center strip wear. What is printed on the sidewall, is the maximum safe pressure the particular brand and model tire can take without blowing up. It should not be used as an inflation target. It is far from ideal for tire wear and ride. So the 38/35 sounds pretty rational actually. It sound like that was based on aiming for the ideal, even tire contact and wear.
 

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Depending on how warm ambient is, for the fwd model, 36/32 (cold at about 70F) has worked extremely well over 5 yrs with totally even wear
And the ride is definitely more compliant
 

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Discussion Starter #8
Depending on how warm ambient is, for the fwd model, 36/32 (cold at about 70F) has worked extremely well over 5 yrs with totally even wear
And the ride is definitely more compliant
Thanks @jmc Another good point which I forgot to mention in my original message. I used to have ~40/41 PSI in my car (wasn't paying attention to the gas filler cover and the different normal/max load recommendations) and as you all may know, Tucson gets insanely hot. Driving late mornings or afternoons, it feels like the heat is just going to blow up anything on the road. Even after ~10-15 min drive, the tire pressure goes up to ~46-47. That's when I noticed the very bumpy ride too and started looking at the ideal tire pressures to set/use.

I have been using 38/34 (cold) for the last few days and it definitely feels much better.
 

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Give 36/32 a try since your ambient right now is normal to warm
Can raise to 37/33 when ambient is cooler
For our typical weight distribution i try to get hot tires to read 40/35
 

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Discussion Starter #10
Give 36/32 a try since your ambient right now is normal to warm
Can raise to 37/33 when ambient is cooler
For our typical weight distribution i try to get hot tires to read 40/35
Thanks. That's a good reference point, for what the 'hot' tire pressures should be. Will definitely try 36/32 and let you know.
 

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I run mine at 38 Front and 33 rear, as per factory recommended setting (found on the fuel filler flap inside). Sometimes, I run them at 40 front and 35 rear, just to get a bit of a sporty feel to the ride.
 

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Discussion Starter #13
Really wish they would stop messing with us yanks and monties with all these variants of the tire pressure sticker
Consistency went out the window!
Haha! Totally agree... and for someone like me who is not an engineering/auto expert and who just wants to enjoy the pleasure of driving a wonderful car, such differing numbers all around really ends up confusing! 😁😝 Thanks to this forum and the people here, its been very good to get lot of valuable information.
 

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Discussion Starter #14 (Edited)
Give 36/32 a try since your ambient right now is normal to warm
Can raise to 37/33 when ambient is cooler
For our typical weight distribution i try to get hot tires to read 40/35
Just reporting back: So, I've been using 36/32 and after ~20 min of driving around 8-8:30 a.m. (Tucson; it was ~80-90F if I remember well), the hot tire pressures were ~40-41 front and ~35-37 rear. I'll be driving bit more during the week and in peak heat (+ have a long drive, ~2000 miles, coming up soon). Curious to see what the pressures will be like.
 

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Your hot tire data is about right
For the long drive ... how loaded will the car be? If super loaded with full cabin and luggage so say +750lb you may want to consider +1.5~+2psi all round
 

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Discussion Starter #16
Your hot tire data is about right
For the long drive ... how loaded will the car be? If super loaded with full cabin and luggage so say +750lb you may want to consider +1.5~+2psi all round
Thanks.

The long drive won't be loaded. It's just me and very light packing - nothing heavy. So I was thinking of keeping it as it is now 36/32.
 

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Discussion Starter #18 (Edited)
Worked well for me over 5 yrs
Hope it works for you too
2k is one long trip but your mpg is gonna be pretty good
Yep! During previous long trips, (including a few with ~1K and one with ~2K), I've consistently seen 36-38 mpg. With a very heavy load in one of those trips, got ~34-35 mpg. Saw another thread in the forum where people report similar mpg. So I guess I'm on par... :)
 

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I have one more observation: Ever noticed that as you drive on the highway for a while, your individual tire pressure reading on the right and left side tend to balance out?
I believe this is because a softer tire flexes more as you drive, and the moxe flexing generates more heat. This probably woudl be pretty easy to quantify using one of those
infra thermometers.

Hence I always tried to keep the rear and front cold pressure difference under 4 psi, I figured if I leave the rears at lower pressure than that, they just heat up more.

The different pressure in the front and rear just aims to achives aprox. the same size road contact patch for the front and rear. If you maintained the
same cold tire pressure front and rear, the front contact patch woulds be larger because there is more weight on the front tires.
 

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Yup ... delta = 4psi works well
The fronts usually get +4~5psi and rears +3~4psi even on hot days
A little less heat capacity for the rears no doubt though the fronts do absorb more heat with the drivetrain and brakes dumping heat
After a long drive cant touch the fronts but the rears much cooler
 
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