Tire Pressure and Range - One Mans Test Results

Objective:
I wondered just how significant air pressure really is to EV range and decided to test it.


Background:
Car, (MYLR) left a 60f heated garage to 40f ambient and was driven 25 miles to warm up. Air pressures were validated between 2 digital gauges (which match to within ¼ psi, and tire TPMS. 11 mile interstate runs with speed matched, trip odo reset @ identical start and stop points, autopilot and self-driving managing the car, and all climate/HVAC off. Runs are back to back, at night, same direction, with traffic a non-factor. Tire pressures were checked via TPMS before and after each run. The 35 psi run did show a ½ PSI increase from start to, so there was some heat increase.

I used large gaps in speed and pressure so we’d get obvious results.

As the 50mph (lower wind resistance) was repeatable it suggested the process didn’t require two passes @ 35 psi. (I was also low on battery. Got home at 2%.)


Results:

Thoughts:

• The 45 psi runs showed no tire pressure changes. 35 psi run did show a ½ PSI increase from start to finish so there was some heat increase.
• I don’t get these lowish power demand number in real life. Climate control has a big impact!
• I expected tire rolling resistance to play a reduced role at higher speeds, but I wasn’t so sure we’d see it, nor that it would be this significant.
• I’m a little bummed the two 75mph runs don’t match more, but at higher speeds it doesn’t take much for even minor wind changes to affect things.
• Ride difference was significant and immediately noticeable.
• I was surprised at the how significant air pressure changes are at lower speeds
• Although that usually means I’m local and care not at all.
• On a real-life trip where I’m expecting something like 250 miles of range at most? I’m not likely to worry about what is likely to be less than 5 miles of range difference.
• Range/pressure is not linear. Delta drops as pressure increases. Meaning the increase in 35-40 is larger than the increase from 40-45.
• I don’t run 35 PSI either. I normally inflate to 37-38 and add when I hit the 35 PSI warning light.

YMMV.

Note: This will be added to the "Air Pressure" document I've shared/linked to elsewhere.

 

[240vPlug]

Tire pressure affects rolling resistance. Higher pressure = lower RR and vv. This is well established. As your test shows the degree to which it is affected varies by a number of different factors. The only way to accurately gauge this is to perform the tests in a controlled environment.

It all has to do with how much tire is making contact with the road. There is a safety element here as well. Too much pressure can compromise safety because not much of the tread is contacting the road surface. Too low a pressure will produce more heat and accelerate tire wear. Driving on low pressure in the right conditions can also cause the tire to suffer catastrophic failure.

There's a lot riding on your tires.

 

[jcanoe]

At ~50 MPH, lowering tire pressure by ~2.5 PSI decreases efficiency by 1%. Raising tire pressure by ~2.5 PSI should increase efficiency by about the same 1%.

 

[thefisch]

Is there a rule of thumb for those who are trying to balance comfort and efficiency? My MYP came set at 45psi and I'm waiting to see if that's not too uncomfortable for us before lowering.

 

[jcanoe]

Is there a rule of thumb for those who are trying to balance comfort and efficiency? My MYP came set at 45psi and I'm waiting to see if that's not too uncomfortable for us before lowering.

The rule of thumb is whatever works for you. The vehicle manufacturer is required to provide a sticker, located on the B pillar by the driver's seat, that provides the maximum vehicle load and the recommended tire pressure. The Tesla Model Y has this sticker; 42 PSI for front and rear tires. The fact that Tesla Service set 45 PSI may mean they assume the vehicle owner won't regularly check the tire pressure, a few extra pounds of air to account for slow loss of air from the tire.

You can vary from the recommended tire pressure by 2 to 4 PSI with no issue. Setting the tire pressure too low can be unsafe as the tire will not be able to carry its rated load and may heat up while driving leading to tire blowouts (this is why every new vehicle is required to have a TPMS.) Too low tire pressure will cause cupping where the outer edges of the tire will wear faster with the center part of the tread.

Setting the tire pressure too high may cause the ride may become too harsh. Too much pressure will limit the tread area contact patch with the road and reduce grip. The center part of the tread will wear faster than the outer tread.

The maximum tire pressure for tire inflation is molded into the side of the tire. Note: All tire pressures are when measured cold before being driven more than 1 mile.

After trying different tire pressure setting I have set the OE Continental ProContact RX 19" tires to 44 PSI.

 

[kelpcar]

Results:
View attachment 922926

love the effort, but the fact that run 1 and 2 at 45psi show nearly the same delta as 45 vs 35 means no conclusion can be drawn here, and potentially challenges the trust we can place on the short term data coming from the Energy display. It could just demonstrate the number of uncontrollable variables for a short run, which then means none of the comparisons can be trusted too far.

i walk away thinking the impact of tire pressure is likely to be very minor, but the book is still open for contradictory evidence. Also wondering if the results would be the same for the 21" tires.

 

[240vPlug]

Is there a rule of thumb for those who are trying to balance comfort and efficiency? My MYP came set at 45psi and I'm waiting to see if that's not too uncomfortable for us before lowering.

Jcanoe did a good job of explaining...generally a couple psi variance is fine. Remember though, depending where you live, summer temps and driving can increase PSI above the cold set point. Cold weather will have the opposite effect. So if in summer you set it at 44 cold it's very likely you will be at 46 psi easily after some driving. Wet traction can become an issue at higher psi.

Service set mine at 44 psi. I believe years ago the standard pressure for model 3 was 44. I was told Tesla reduced it.

I know some folks want to get every last little bit of efficiency so they bump it up a little. Anything above 44 is extremely rough IMO.

 

[dafish]

Is there a rule of thumb for those who are trying to balance comfort and efficiency? My MYP came set at 45psi and I'm waiting to see if that's not too uncomfortable for us before lowering.

There are load vs air pressure tables, professional tests on rolling resistance vs air pressure, even some modeling of model y loads possible in the below link. I didn't want to write it all over and over so put in a PDF and loaded it on google drive, but I can't see the mods caring about the link. LOTS of reference links too, so...

EV Tires - Sizing & Air Pressure vs Comfort, & Replacement.pdf

drive.google.com

 

[CyberGus]

 

[dafish]

View attachment 923204

Now that's funny right thar!

 

[tivoboy]

View attachment 923204

As silly as this post might sound, it’s probably true!. I once did a management rotation stint in a domestic OEM call center. One day, customer called in to the call center, had recently bought a ”brand new“ car. First car she’d ever bought. husband “used to do that”. (elderly woman most likely over 70) Drove it fine for nearly two weeks and then, it just stopped working.. wouldn’t start, nothing. Wanted someone to come and fix it for her or get all her money back.

Anyone have an idea what the problem was?

 

[kavyboy]

As silly as this post might sound, it’s probably true!. I once did a management rotation stint in a domestic OEM call center. One day, customer called in to the call center, had recently bought a ”brand new“ car. First car she’d ever bought. husband “used to do that”. (elderly woman most likely over 70) Drove it fine for nearly two weeks and then, it just stopped working.. wouldn’t start, nothing. Wanted someone to come and fix it for her or get all her money back.

Anyone have an idea what the problem was?

 

[RichAZ/CapeCod]

As silly as this post might sound, it’s probably true!. I once did a management rotation stint in a domestic OEM call center. One day, customer called in to the call center, had recently bought a ”brand new“ car. First car she’d ever bought. husband “used to do that”. (elderly woman most likely over 70) Drove it fine for nearly two weeks and then, it just stopped working.. wouldn’t start, nothing. Wanted someone to come and fix it for her or get all her money back.

Anyone have an idea what the problem was?

Out of gas...?

 

[tivoboy]

Out of gas...?

Yes, out of Gas.. this was actually one of the more mundane while nonsensical things people would call in about.

 

[dafish]

While I will date myself and take us even further off topic, I was in IT when this first made the rounds.

http://wise-obs.tau.ac.il/~friedel/computer_fun/jokes/help-desk.html

 

[CMPT PAD]

All Tesla Pros out there
Any recommendation for a digital tire pressure?
Thx and enjoy your ride

 

[240vPlug]

All Tesla Pros out there
Any recommendation for a digital tire pressure?
Thx and enjoy your ride

I have the JACO high accuracy type. Mine is a tire inflator as well but they sell just the gauge. I have been happy with it. Measures PSI in .1 increments.

 

[TomB985]

Very interesting data! This must have taken at least a couple hours to run, and I appreciate the effort. It would be great if the runs covered more distance, but that would increase the variation with weather.

I run at 36 PSI because I like a smooth ride, and it makes sense to see a small range penalty. Not as much as I took switching from the stock 19’s to a set of takeoff Überturbines, though. I was extremely concerned about efficiency when I had my SR+ Model 3, which sometimes needed a Supercharge to get me home in the winter. The LR Y has always been more than enough, so I don’t worry as much about getting every last mile out of the “tank.”

 

[CMPT PAD]

I have the JACO high accuracy type. Mine is a tire inflator as well but they sell just the gauge. I have been happy with it. Measures PSI in .1 increments.

Thanks ... JACO has a few designs. Which is better for Tesla tires, especially the ease of measurement?

 

[TomB985]

Thinking further about this, a better way to measure this over the long-term would be with a logging service like TeslaFi.

They generate efficiency reports in a variety of context, and their system logs tire pressure as reported by the Tesla API.

You can run speed efficiency comparisons between dates. This is comparing my 18" winter wheels run from 12/20-3/21 with stock Überturbines from 3/21-3/29. Obviously a different comparison than with tire pressures alone, but it shows how the site can compare datasets over long periods of time.

The dates running Überturbines are the green line, and the 18" winters the blue line. Obviously, temps were very different between these date sets, but it shows how easily you can compare different setups over days, weeks, or months.

Just an idea for next time. Maybe I'll do a tire pressure comparison over week-long periods later this year when temperatures stabilize.