SL/R231: Front tire over inflation warning?
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Member
Joined: Jan 2023
Posts: 90
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From: SE Florida
2025 GLC 300, (formerly) 2018 SL550
Front tire over inflation warning?
Took the car for its first out of town cruise last night, and got a front tire over inflation warning. I corrected the cold inflation (twice to be perfect), after the tire installer set all of them to 45psi! What do you all think is causing this? Could it be an alignment problem (camber/caster), since they seem to be well balance, ie no vibration coming through the steering wheel. Was somewhat disconcerting, since I've never seen this warning on any other car before, only the underinflation warning. I believe they were reading 44 "hot" last night. Was driving very sensibly, btw.
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From: NorCal
2015 ML350+2025 E350
Took the car for its first out of town cruise last night, and got a front tire over inflation warning. I corrected the cold inflation (twice to be perfect), after the tire installer set all of them to 45psi! What do you all think is causing this? Could it be an alignment problem (camber/caster), since they seem to be well balance, ie no vibration coming through the steering wheel. Was somewhat disconcerting, since I've never seen this warning on any other car before, only the underinflation warning. I believe they were reading 44 "hot" last night. Was driving very sensibly, btw.
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Joined: Jan 2023
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From: SE Florida
2025 GLC 300, (formerly) 2018 SL550
Yes, these were new non-runflats installed Fri. I did set them to 36F/42R after driving it home and next morning discovering they were wrongly set to 45 all around. Even did it a 2nd time this morning, using my analog dial gauge, as the fronts were 1 PSI too high. I was looking at the readout on the dash today, and it asked it I wanted to accept this as new value, or something like that, and I chose yes. Just got the car last Fri. Didn't know there was recommended PSI values on the fuel door, since I haven't needed to add fuel yet. My PSI values are on a placard on the door jab. If this comes up again, I'm going to pull over and take a reading to see if it matches what the TPMS sensors are reading out. Strange.
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From: Land of 10,000 lakes
AMG GTC Roadster, E63s Ed.1, M8 Comp. Coupe
I don't remember the tire pressure I was using except that I would use the base tire pressure on the fuel filler door (not the driver door jamb) but inflate the rear by 3-5psi cold. This is to offset the natural inner tire wear on SL's.
Either way, your tire pressures sound too high. Check the label on the fuel filler door.
Either way, your tire pressures sound too high. Check the label on the fuel filler door.
Super Member
Joined: Nov 2013
Posts: 743
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From: NorCal
2015 ML350+2025 E350
Yes, these were new non-runflats installed Fri. I did set them to 36F/42R after driving it home and next morning discovering they were wrongly set to 45 all around. Even did it a 2nd time this morning, using my analog dial gauge, as the fronts were 1 PSI too high. I was looking at the readout on the dash today, and it asked it I wanted to accept this as new value, or something like that, and I chose yes. Just got the car last Fri. Didn't know there was recommended PSI values on the fuel door, since I haven't needed to add fuel yet. My PSI values are on a placard on the door jab. If this comes up again, I'm going to pull over and take a reading to see if it matches what the TPMS sensors are reading out. Strange.
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From: SE Florida
2025 GLC 300, (formerly) 2018 SL550
Good info. Interestingly, the recommended PSI on the fuel door is 35 all around, when the recommended PSI on the door jam is 36F/42R/ I reset all mine to 35. The fronts were already at around 35, but I lowered the rears by 7 to also be 35. I need to drive it a little, then as recommended in the video, reset the TPMS to these values. So, you like to run 38 rear to offset the inner wear?
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Joined: Nov 2013
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From: NorCal
2015 ML350+2025 E350
Good info. Interestingly, the recommended PSI on the fuel door is 35 all around, when the recommended PSI on the door jam is 36F/42R/ I reset all mine to 35. The fronts were already at around 35, but I lowered the rears by 7 to also be 35. I need to drive it a little, then as recommended in the video, reset the TPMS to these values. So, you like to run 38 rear to offset the inner wear?
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From: Land of 10,000 lakes
AMG GTC Roadster, E63s Ed.1, M8 Comp. Coupe
Good info. Interestingly, the recommended PSI on the fuel door is 35 all around, when the recommended PSI on the door jam is 36F/42R/ I reset all mine to 35. The fronts were already at around 35, but I lowered the rears by 7 to also be 35. I need to drive it a little, then as recommended in the video, reset the TPMS to these values. So, you like to run 38 rear to offset the inner wear?
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Thread Starter
Member
Joined: Jan 2023
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From: SE Florida
2025 GLC 300, (formerly) 2018 SL550
I have to wonder if my TPM sensors are going bad, given my 2018 was built in 2017. I went with the Bridgestone Potenza RE980AS+ Ultra High Performance All Season non-runflats this time. I believe they will suit my driving style best, plus wear longer than an all out ultra high performance tire. But, that said, I will bump up the rears to 38. Odd that this overinflation warning is only coming for the fronts. They start out fine, then seemingly overheat after moderate driving. Definitely going to have the alignment checked soon.
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From: Land of 10,000 lakes
AMG GTC Roadster, E63s Ed.1, M8 Comp. Coupe
These are cold tire pressures, so ideally set them in the garage or as close to the house as possible.
Use a manual gauge for the correct tire pressure then reset the TP in the car with current values.
After a couple of minutes the tire pressure on the display should be very close to the psi you set them at manually.
If all that is good you should see the pressure rising on all tires by a few psi when driving, depending on temperature.
If any of the tires exhibits unusual behavior it is likely that tpms sensor.
There should no message appearing on the display either.
Use a manual gauge for the correct tire pressure then reset the TP in the car with current values.
After a couple of minutes the tire pressure on the display should be very close to the psi you set them at manually.
If all that is good you should see the pressure rising on all tires by a few psi when driving, depending on temperature.
If any of the tires exhibits unusual behavior it is likely that tpms sensor.
There should no message appearing on the display either.
Thread Starter
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Joined: Jan 2023
Posts: 90
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From: SE Florida
2025 GLC 300, (formerly) 2018 SL550
Did a new psi value reset and took a drive. Seems to have fixed the problem. psi only rose about 2 lb on this somewhat cool FL morning. Could be fixed. Time will tell.
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From: Hagerstown MD
2015 SL400; 2019 X5M40i
I run 35 psi all around except on road trips when the trunk is loaded, then I add about 4-5 psi to the rear tires. If the ambient temp is say 60 degrees and you drive at interstate speeds you will see around a 5 psi increase after you have driven for 25 or so miles. At least this is my experience. Also if you set the psi at an ambient temp of 70 and then it gets down to 40 and you check the psi again you will see a drop in psi of 2-3 psi. Again, this is based on my experience. I am also running non runflat tires, Continental DWS06+ at OEM 19" sizes. Very pleased with the ride and performance.
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Joined: Jan 2023
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From: SE Florida
2025 GLC 300, (formerly) 2018 SL550
Right, I'm sticking to 35 all around. If I ever load the trunk, I'll increase the rears a bit. I've always told my kids groing up to check their tires every month.
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Joined: Jul 2017
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From: southeastern NC
'18 SL 550, '19 1500 Z71 Silverado LTZ, '19 Mustang convertible
[QUOTE=Goodwood;8720274]I have to wonder if my TPM sensors are going bad, given my 2018 was built in 2017. I went with the Bridgestone Potenza RE980AS+ Ultra High Performance All Season non-runflats this time. I believe they will suit my driving style best, plus wear longer than an all out ultra high performance tire. But, that said, I will bump up the rears to 38. Odd that this overinflation warning is only coming for the fronts. They start out fine, then seemingly overheat after moderate driving. Definitely going to have the alignment checked soon.
I would have the alignment checked ASAP. My '18 SL 550 came from the factory out of alignment!
I would have the alignment checked ASAP. My '18 SL 550 came from the factory out of alignment!
Thread Starter
Member
Joined: Jan 2023
Posts: 90
Likes: 22
From: SE Florida
2025 GLC 300, (formerly) 2018 SL550
[QUOTE=SLclass;8721459]
Agree, will get an alignment next shop appt, which is coming soon.
I have to wonder if my TPM sensors are going bad, given my 2018 was built in 2017. I went with the Bridgestone Potenza RE980AS+ Ultra High Performance All Season non-runflats this time. I believe they will suit my driving style best, plus wear longer than an all out ultra high performance tire. But, that said, I will bump up the rears to 38. Odd that this overinflation warning is only coming for the fronts. They start out fine, then seemingly overheat after moderate driving. Definitely going to have the alignment checked soon.
I would have the alignment checked ASAP. My '18 SL 550 came from the factory out of alignment!
I would have the alignment checked ASAP. My '18 SL 550 came from the factory out of alignment!
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From: In the minds of others rent free.
SL 400
I keep mine set at 35 all around, but as mentioned they will rise a bit after I get on the highway. (On it twice a day for an hour) They will also drop a bit in real winter times while sitting in the driveway, etc.
Funny I have not driven my car in a week, but drove it today. Both rear tires were at 33, so the light is on now. Will add some air before I get back on the highway in a few minutes....
Funny I have not driven my car in a week, but drove it today. Both rear tires were at 33, so the light is on now. Will add some air before I get back on the highway in a few minutes....
