I'm used to inflating tyres to the recommended pressure when cold. On my M3 L3 I find that when doing this the ride quality feels pretty poised when starting to drive. Once on the road for a few minutes and the tyres have warmed up and the TPMS shows the pressures as up about 5% from cold (44 from 42psi) the ride then feels jittery and unsettled on the poor quality roads we have where I live. Is there a case for setting the cold tyre pressures so that they reach recommended pressure when warmed up? Presumably the temperature difference between cold and warm is pretty large, probably bigger than the seasonal differences in the temperate UK climate.
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Ride quality seems good when tyres at cold pressure, too firm when tyres warm up
- Thread starter Nujec
- Start date
Kimmi
Member
Set pressure when cold to pressure shown on drivers door. Don’t worry about hot tire temperatures.
jackmott
Member
Tesla specs a pretty high pressure for improved range. If you don't need the range then by all means drop the psi to 40 or 38 when cold for better comfyness.
I have a 2021 LR and with the 19 inch sport wheels and the inflation spec from Tesla calls for 41psi. I routinely run them 10% lower at 36-37psi as Elon had tweeted once when people complained about the jarring ride. There is a very notable difference and the suspension noises from uneven roads are quieter as well. The car seems to be OK with the lower tire pressures and won't throw a warning unless you are way low.
What a world we live in. Auto engineers design and test a car around some very specific settings which are legally required to be on the door sill as part of the vehicle design and compliance. These are the settings the EPA uses for mileage, engineers use to tune stability control, ABS, and shock valving. So much is based on this.
Then Elon tweets "eh, try a lower tire pressure if you don't like it" and people react as if that is some great insight and an official position from Tesla engineering.
Can you imagine if people complained about the ride in a different brand and the CEO tweeted "well, try a lower tire pressure"?
Realistically, tire air pressures vary over time of day due to temperature variation. Seasonal changes in temperature also cause changes if not adjusted. Tuning of stability control, ABS, etc. needs to account for that.
Vehicle companies these days probably prefer to specify pressures near the higher end of the range that is possible for a given vehicle, because of (a) better economy, (b) higher load capacity, and (c) greater margin of safety against neglectful underinflation. The last of these gained awareness when Ford Explorers had failures of Firestone Wilderness AT tires, leading to some crashes. The recommended pressure of 26psi at the time left little margin of safety against dangerous underinflation if drivers were not vigilant about checking pressures over time. Combine underinflation with a relatively low quality tire to begin with (C for UTQG temperature rating), with some questions about manufacturing quality control at one of its factories. Ford Rangers used the same tires, but did not have as high a rate of failures; Rangers weighed less and specified a higher tire pressure.
You can't design a car to make 100% of people happy. Changing tire pressure allows users a degree of customization. There is nothing wrong with that.
jackmott
Member
The engineering isn't anything near as sensitive to this as you are implying. The difference in vertical spring rate between various tire models that Tesla ships on model s3s is as large or larger as the difference 2 or 3 psi will make.
Hence proving my point that Elon's response was not engineering driven and is just marketing blabber, and that it does not make a "Very noticeable difference"
The idea that springs stiffness completely compensates tire pressure difference is weird.
Tesla marks target pressure to get declared range. If you want better ride, better traction, but lose some range and and some pothole protection - set slightly lower pressure. He just told the truth.
If setting the tire pressure to the full spec was that important, then the TPMD would warn users much sooner. I've set the pressure several pounds below spec for 10,000 miles now, and never had any warning; the tire tread is even across the tire and not worn more on the outsides as you would get with under-inflated tires. Perhaps if I were racing the car, or even driving fast on curvy roads, I'd worry more because traction decreases faster with underinflated tires than over.
My son's BMW X3 didn't warn him until the tires were something like 10 lbs low. They also specify a high pressure.
My son's BMW X3 didn't warn him until the tires were something like 10 lbs low. They also specify a high pressure.
The law defines how TPMS must work. It must warn at 25% below the door label. It's not up to the OEM.
This is highly dependent on tire structure. Lots of track focused tires gain grip at lower pressures.
Yeah, but what about TPMD?
oops, glad you knew what I meant. I wasn't saying who decided when to warn, though. If it was that critical, the law would be tighter, perhaps. Or, perhaps the reason the pressure is specified so high is so that it will still be safe when it's 25% low. I don't know any stats, but i'm pretty sure the average driver only fills the tires when warned, or when they take it in for service.
DIY-Trev
Member
I'm finding the ride too firm on recommended pressures. Did you try lowering them & if so how did you find it?
I lowered the pressures slightly and I'm not convinced it was better. Will have another try now the weather's changed. Still find the ride quality is best at the beginning of the journey, assume it's because the tyres change behaviour as they warm up. Still on factory Michelin 4S sport summer tyres. Will try all season tyres at some point.I'm finding the ride too firm on recommended pressures. Did you try lowering them & if so how did you find it?
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@Nujec Factory PS4S means you have an M3P with 235/35R20 tires right? You can get a pretty useful improvement in ride quality without sacrificing any handling by downsizing your wheels to fit more tire sidewall. It won't transform the car into a magic carpet ride or anything like that, but it sure takes the edge off in a nice way.
I switched my M3P to 245/45R18 on 18x8.5" wheels and everything is better. No loss of performance at all, in fact it grips better now thanks to better tires, while riding better at the same time. (My car came with Pirelli PZ4 and I switched to Bridgestone Potenza Sport on the 18s.)
On my 18s I've been using 42psi at gentle daytime cold. Which means a little lower in colder situations before they warm up on the drive.
I've actually got a M3 LR with 18 inch aero wheels. I opted to avoid larger wheels to improve ride quality.
Good tip about calibrating the tires in the warmer part of the day. I'll try that in future.
I suspect that at 15K miles my original tyres will need replacing soon which will be all season tyres so it'll probably depend which tyres I go far. Leaning towards Vredstein Quatrac Pro so far from what I've read.
Try 39 cold, per one of Elon's earlier tweets. But just know that every 10 degrees increase in air temp results in about 1 lb increase in tire pressure. So if its 50 degrees in the morning and your tires are at 39, they will be ~41 at noon when its 70 degrees outside even if you haven't driven the car. And if you drive the car in 70+ degrees, they'll warm even further to say, 43/44 when hot.
The reverse is true: 50 degrees dropping to 30 means the tires would drop to ~37.
The reverse is true: 50 degrees dropping to 30 means the tires would drop to ~37.
