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What is tyre drag
- Thread starter Lddex
- Start date
Tyre drag = rolling resistance.
Unavoidable, as all tyres will have a rolling resistance - it's where their grip comes from. Some are better than others (EV-specific tyres are generally low resistance, but provide less grip for cornering, etc), but apart from choosing tyres with a lower rolling resistance when you swap there is bugger-all you can do about it!
Unavoidable, as all tyres will have a rolling resistance - it's where their grip comes from. Some are better than others (EV-specific tyres are generally low resistance, but provide less grip for cornering, etc), but apart from choosing tyres with a lower rolling resistance when you swap there is bugger-all you can do about it!
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It is also called roll resistance. When a tyre rolls, its shape changes, and there is friction between the tyre surface and the road surface. This means that energy is lost. (And, by the way, particles are rubbed off the tyre surface.)
The roll resistance force is in a first approximation independent of speed. This means that the related energy lost per mile is the same, regardless of speed. At low speeds this is the biggest energy consumption of a rolling car.
The other big energy consumer is aerodynamic drag. As opposed to roll resistance, this force increases with the third power of speed, translating into the energy loss per mile growing with the second power of speed. At higher speeds the air drag becomes bigger than the rolling drag.
There are some other energy losses, for example, decreasing electric efficiency at low speeds and some constant energy consumption (electronics, climate) present at any speed, so the speed at which a Tesla Model 3 has the lowest energy consumption per mile turns out to be between 20 and 30 mph.
Tyres differ a bit in their rolling resistance. There are energy-saving tyres on the market. But it is a tradeoff between energy and grip (and noise, and longevity, etc.).
Addendum:
While we are at it, my recommendation is to keep the tyre pressure at the value recommended by the manufacturer. This means that in spring, when the temperature rises, you have to let some air out of your tyres to prevent excessive pressure. Conversely, in fall you have to pump up your tyres again whenever the temperature falls, to keep the pressure high enough. I find that I have to pump up at least three times, as winter approaches. Be careful not to do that after some of your tyres sat in direct sunlight. And consider that the tyres warm up when driving long distances, particularly at higher speed. This is normal. The recommended pressure is meant for tyres that have sat still, out of sunlight, for some hours.
If you have a good opportunity to pump up during or after a fast drive, pump up two or three percent, like 3 PSI or 0.1 bar, above the recommended pressure. As the tyres later cool, their pressure will come down.
The roll resistance force is in a first approximation independent of speed. This means that the related energy lost per mile is the same, regardless of speed. At low speeds this is the biggest energy consumption of a rolling car.
The other big energy consumer is aerodynamic drag. As opposed to roll resistance, this force increases with the third power of speed, translating into the energy loss per mile growing with the second power of speed. At higher speeds the air drag becomes bigger than the rolling drag.
There are some other energy losses, for example, decreasing electric efficiency at low speeds and some constant energy consumption (electronics, climate) present at any speed, so the speed at which a Tesla Model 3 has the lowest energy consumption per mile turns out to be between 20 and 30 mph.
Tyres differ a bit in their rolling resistance. There are energy-saving tyres on the market. But it is a tradeoff between energy and grip (and noise, and longevity, etc.).
Addendum:
While we are at it, my recommendation is to keep the tyre pressure at the value recommended by the manufacturer. This means that in spring, when the temperature rises, you have to let some air out of your tyres to prevent excessive pressure. Conversely, in fall you have to pump up your tyres again whenever the temperature falls, to keep the pressure high enough. I find that I have to pump up at least three times, as winter approaches. Be careful not to do that after some of your tyres sat in direct sunlight. And consider that the tyres warm up when driving long distances, particularly at higher speed. This is normal. The recommended pressure is meant for tyres that have sat still, out of sunlight, for some hours.
If you have a good opportunity to pump up during or after a fast drive, pump up two or three percent, like 3 PSI or 0.1 bar, above the recommended pressure. As the tyres later cool, their pressure will come down.
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Thanks. As long as it's a avoidable that is fine. Thought it might be something I could control or doing wrong. But it will put it down along with "going up hill" and "air drag" just something the car is telling me is affecting my drive. It's only 0.1% so not massive.
Like I say. Tyres are inflated to PSI recommendation. Apart from that I'm guessing it's just the tesla computer trying to be helpful.
Like I say. Tyres are inflated to PSI recommendation. Apart from that I'm guessing it's just the tesla computer trying to be helpful.
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To stop last weeks ‘low tyre pressure’ nags in the cold (they were down to 38PSI), I topped them up to 42psi.
Now that the ambient temperature has risen by about 20’C, they’re up to 45-46! The ride is noticeably ‘jiggly’. I’ll have to let the air out again.
Bloomin’ physics - what’s it ever done for us
Now that the ambient temperature has risen by about 20’C, they’re up to 45-46! The ride is noticeably ‘jiggly’. I’ll have to let the air out again.
Bloomin’ physics - what’s it ever done for us
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Nick77
Deep Blue Model 3 LR (2021 MIC)
Same here. Topped them up to 42 again as it was constantly at 38/39 and nagging me. Was 44 yesterday when I went out.To stop last weeks ‘low tyre pressure’ nags in the cold (they were down to 38PSI), I topped them up to 42psi.
Now that the ambient temperature has risen by about 20’C, they’re up to 45-46! The ride is noticeably ‘jiggly’. I’ll have to let the air out again.
Bloomin’ physics - what’s it ever done for us
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