mythbusters tests tyre / tire pressure

[lightblaze]

Not just air pressure but size effects fuel efficiency.

[kanaloa]

Thanks for the great post!

[Vekke]

I did also pressure testing in my electric ID3 at 100km/h speed with 195/55r20 Nokian Hakkapeliitta R2 winter tires. There optimal pressure was not higher than recommended. I found optimal pressure is around 2,5 bar.

[bwilson4web]

Originally Posted by Vekke

I did also pressure testing in my electric ID3 at 100km/h speed with 195/55r20 Nokian Hakkapeliitta R2 winter tires. There optimal pressure was not higher than recommended. I found optimal pressure is around 2,5 bar.
. . .

Just curious about the methodology:

1. What are the units of the measured values?
2. How long (time or distance) was each measurement taken?
3. Were bi-directional runs averaged together?
4. Have you loaded the data into a spreadsheet to generate graphs?

In my Prius days, I typically tested at ~65 mph (104 kph.) My interest was in tire tread temperature measured using a hand held IR thermometer. I would typically drive ~8-16 km; stop the car on an exit ramp shoulder, and; measure tread temperatures recorded with cell phone video.

The reason I ask is the prospect of replicating your methodology with my Std Rng Plus Model 3. Only my interest is in using the tire pressure and temperature sensors in each tire (requires an independent sensor receiver.)

My uncalibrated fingers and increases in pressure reported by the car suggest the tires are running warmer than I want. Heat is the signature of energy loss.

Thanks,
Bob Wilson

[Vekke]

A runs are north direction and B runs south direction. So you need to calculate ((a+b) /2)*0,96 to correct tire size error= result.

Units are kwh

Wind ruins the measurement accuracy fast so try to choose day when its calm. On that video it was too windy on that morning when I did those measurements on the video.

That best pressure is valid only for this car and those tires. With summer tires best pressure migth be differend.

Route is about 5.5km hilly route.

Here you can see the route.

https://www.youtube.com/watch?v=BqGumJCHb-8

[Vekke]

I have been doing more calculations on the results I posted here. If you want to find out the optimal pressure for lowest rolling resistance then you should try to use slower test speeds. I used 100km/h as thats the figure I am trying to get lower consumption, but it causes problems for measuring RR as the wind has bigger impact to results. If you have little wind at 60 km/h its not so critical to get good results as most energy is used on Rolling resistance anyhow.

48km/h = 5725W
56 km/h = 6612W
64 km/h = 7650W
72 km/h = 8888W

On my ID3 at the moment air resistance becomes higher than rolling is at 70 km/h speed. If you keep test speed under that wind should not play so big role. I recommend that 60 km/h speed for RR measurements.

At 100km/h +10 km/h headwind means 2500W more resistance from wind.

When you have found your optimal pressure for lowest rolling resistance then you need to test which start pressure with cold tire gives you that in real world driving as when tires warm the pressures get 0,1 to 0,2 bar higher in general.

[Snax]

One thing that I discovered with my i3 is that my EP-500s really don't offer much reduction in rolling resistance above 42 psi. I saw marked reduction in low speed roll-out below that (using recommended pressures), but even up to 50 psi I could not confidently say it wasn't just noise in my data over 45 psi.

So I usually just fill them to 50 psi until they eventually drop below 45 since that also significantly reduces road hazard damage risk to the wheels as well.

[CapriRacer]

Just a word of caution from a tire engineer.

Increasing the inflation pressure above the vehicle tire placard can have negative affects on other properties, some of which affect safety. You'll get better fuel economy and the steering response will be quicker, but dry traction, non-hydroplaning wet traction, snow traction, and, obviously, the ride will be worse. You may also get more tire wear in the center of the tread, but there are other things that have a stronger effect on wear, so this isn't a 100% thing.

[Snax]

Originally Posted by CapriRacer

Just a word of caution from a tire engineer.

Increasing the inflation pressure above the vehicle tire placard can have negative affects on other properties, some of which affect safety.

*Can* being the operative word. But as the Ford Explorer debacle has shown, placards are not always focused on these issues the same. Tread (pardon the pun) with caution.

[Drifter]

Originally Posted by Vekke

I did also pressure testing in my electric ID3 at 100km/h speed with 195/55r20 Nokian Hakkapeliitta R2 winter tires. There optimal pressure was not higher than recommended. I found optimal pressure is around 2,5 bar.

There are diminishing returns above a certain point, but I've never seen a tire have worse rolling resistance at a higher pressure *on a smooth surface.*

One thing to keep in mind is that pumping tires to higher pressure makes them larger. This is quite obvious to see when you go from 5psi to 15psi to 25 psi, but it is much harder to spot going from 40psi to 50psi.

In my testing, I observed no mpg gain going from 40psi to 50psi in my Prius. It wasn't worse, but it wasn't better. But when I marked the tires and measured how far they rolled, I discovered that at 50psi the tires rolled about 1% farther than at 40psi. So my 0mpg gain was actually a hidden 1% gain...


Not mine, but this shows the diminishing returns I've seen from higher psi: