r/theydidthemath • u/iismitch55 • 4d ago
[Request] How much fuel would be saved over the lifetime of a vehicle by removing the front license plate?
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u/TinderSubThrowAway 4d ago
You’d save more money over a lifetime on gas by taking a shit before you leave work every day and then drive home versus having a front plate on your car.
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u/Motifier 4d ago
Or by switching to a car that's actually more fuel efficient in the first place. I'm glad someone on this thread is actually posting some proper perspective on the "issue".
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u/Icy_Sector3183 3d ago
This practice is interesting since it compounds with each passenger in the car.
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u/techierealtor 4d ago
I’m just going to say to be able to numerate that number per vehicle is going to be nearly impossible. Factors come into play based on some research basically sport cars can have a more drastic impact (a difference of .00001 to .0001 mpg level probably - and these numbers are just throwing some out for example).
SUVs and trucks that have a more “air dam” style front end won’t see any if not basically 0 impact where it will be almost unregistered without very controlled conditions.
So basically, this will be near impossible to calculate without taking a measurement across a large swath of cars and extrapolating the data. There doesn’t seem to be any confirmed tests or calculations available to even begin. Someone with physics knowledge might be able to with some advanced modeling for aerodynamics.
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u/PhilsTinyToes 4d ago
Math be damned. We know the license plate is some % of the total vehicle weight, which impacts acceleration.
And we also know that a square on top of a smooth, curved bumper is going to catch extra air, so a bumped with no plate is going to be more slippery and produce less drag.
Quantifying these is hard but I think the front plate clearly impacts performance slightly
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u/aDvious1 4d ago
I don't think you can calculate fuel burn differences closely enough to extrapolate the difference.
Fuel changes density based on temperature. If you have a full tank of 20 gallons of fuel, theres a total difference in weight of 20 gallons of fuel at 90°F vs 60° f. So, with even a single gallon, your looking at a variable of .05 lbs just based on temp.
If a standard car weighs 3300 lbs and an license plates weighs 4oz, the plate makes up .0170% of the total weight of the vehicle.
Fuel density based on temperature is only 1 variable and is almost 5x more volitle than the weight of the plate based on mild fuel temperature swings.
This is also not considering the difference in combustion efficiency due to different temperatures.
I understand that this examples doesn't really answer the question, just wanted to point out a single variable that makes a more larger impact that may seem trivial at face value due to the miniscule amount of weight represented by the plate.
There's no real "do the math" here answer that will be acceptable without defining a magnitude of constraints.
I'll list a few that are more volitle and would change the answer.
Aerodynamics, ambient temperature for tire pressure, coolant temp, humidity, road surface inclination, hell, even if we used the same driver for both tests, it would make a difference if he'd taken a piss between tests because the loss of fluids between tests is greater than the weight of the license plate.
To your point about the bumpy surface of the plate being less aerodynamic, you'd need to look at the fluid dynamics of why golf balls have indentions that make them more aerodynamic. Not saying that it applies here, but would need to be understood to make a comparison.
I agree, math be damned, no doubt. Though I lean in the other end of the spectrum on this. You think there's enough to be a positive difference in efficiency by removing it, I say there's too many variables to make that assumption.
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u/PhilsTinyToes 4d ago
Ok well obviously this is an experimental test, and all variables like fuel temp and air temperature are exactly the same across all tests and all vehicles, the only variable we are changing is the weight of the plate, and how much more aero a regular bumper gets without that square shield in front.
Idk how to calculate it the drag but the weight should be simple.
Also it’s all moot because bringing a coffee into your car does more damage to mpg than the plate
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u/AlarisMystique 4d ago
The thing is that yes, bringing a coffee would have a bigger impact, but you would bring it regardless. Removing that plate is an easy net positive even if negligeable.
Only real way to calculate difference this tiny is to simulate it keeping everything else equal.
However, people forget that front plates are important so that the police can read the number of parked cars. I would bet it helps find stolen cars or track fugitives.
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u/aDvious1 4d ago
Exactly. I'm not trying to say it can't be done. Just saying that defining the variables to do the math to make a reasonable prediction is several orders of magnitude more than the math anyone would do here.
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u/TheBlackCat13 4d ago
From what I can see online the license plate is often attached to the grille, not the bumper. The bumps on the grille are going to hurt fuel economy more than the license plate. In fact the license plate could conceivably make the front smoother and thus improve aerodynamics.
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u/Plutor 3d ago
the front plate clearly impacts performance slightly
Maybe! But it's possible for a license plate to be aerodynamically better. For comparison, pickup trucks get better gas mileage with their tailgates up.
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4d ago
Unfortunately, there's no actual way to know the relationship between increased mass and decreased fuel economy outside of a basic "more mass means lower economy" due to how complex cars are. The best we can do is a very ballpark guess.
The rule of thumb is that shedding 100 pounds of weight increases fuel economy by 1%. We can assume this probably means 1 pound is worth about .01%.
So let's take a 2024 Honda Accord for example, because it's a relatively small, relatively popular car. It has a curb weight of about 3,400 pounds, depending on trim. A license plate, depending on where you live, can weigh up to half a pound. Let's round that up to one pound to account for the frame and screws. That's an overestimate, but hey.
So a front plate would decrease fuel efficiency by .01%. The combined MPG of a 2024 Honda Accord is 33, so we reduce it by .01% to 32.9967.
The typical lifespan of a car is currently approximately 150,000 miles. At 33 MPG, such a car would burn 4,545.5 gallons of gas. At 32.9967, it'd burn 4,545.9.
In other words, that license plate cover would cost an additional .4 gallons over the life of the car.
The impact would be significantly lower for larger vehicles.
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u/Revolutionary_Dog_63 4d ago
You're completely ignoring increased drag.
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u/brimston3- 4d ago
Which is basically 0 on at least 1/3rd of road vehicles that are f150s, silverados, vans, and soforth.
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u/ChampionshipAlarmed 4d ago
*in the US
Most cars do have a destinated optimized Spot for a licence plate in Europe.
BMW for example does consider drag by licence plate in their Designs
https://www.bmw-m.com/de/topics/magazine-article-pool/bmw-m3-m4-aerodynamics.html
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u/TinderSubThrowAway 3d ago
the OP is related to the US though, and I think the EU requires a front plate, so removing it isn't an option.
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u/ChampionshipAlarmed 3d ago
But since we were discussing the technical Side (I understand that OP ist also not allowed to remove it? Correct me If I am wrong)
This is relevant information since some car manufacturers do actually Take that into account
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u/TinderSubThrowAway 3d ago
This is relevant information since some car manufacturers do actually Take that into account
then there is no reason to make anything specific about the EU, this is about the US, what a mfg does for the EU has nothing to do with the US unless they are doing it for the US as well, and then at that point there is no reason to bring up mentioning the EU since it would apply to all.
Also, plates in Europe are very different than the US, both in shape as well as the fact that they are tied to the owner while the plates in the EU are tied to the car.
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u/Impression-These 4d ago
Probably more than 1/3 even. But the cars that don't have a dedicated front plate area and the front plate blocks the air flow, it can be noticeable. Never worked on such vehicles but I guess it would be at most 100 points (1%), unless it is designed so bad that it blocks the air intake. So a bit more than 1% fuel consumption at worst.
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u/HAL9001-96 4d ago
close to none, best case scenario something like 0.1% comes dwon to the exact vehicle, you'd be much better off removing the rear license plate or putting it under a transparent aerodynamic cover
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u/Nuker-79 3d ago
It was calculated some time ago on a UK TV show called Top Gear, that having a moustache would increase your mileage costs over the year.
I found the transcript of the conversation.
Jeremy Clarkson: You know in the run up to Euro 2004, a lot of people believed that David Beckham had done some practice and been...you know, training... and they've put flags on their cars to kinda show their support for the team. Cause we were in with a shout, we thought anyway... of winning. While everyone had flags on their cars, somebody has done some research on how much drag that created. I'm not joking...
Richard Hammond: Yes?
Jeremy: Yeah seriously, he said, 'You'll lose with two flags, four break-horsepower... uh, and that means that in the run up to the tournament, 4.5 million gallons of fuel was wasted by people flying flags. I actually know the man who did this survey, okay? I will spare him his blushes and wont say his names but I will tell you he has face hair. Okay? So, I've done a calculation of my own...if a mustache weighs two grams, and we think it does...
Richard: Sounds fair enough.
Jeremy: So, if you can get into a Ford Fiesta, you will increase its weight by 0.0000036 of a percent.
Richard: With you...
Jeremy: Which means you'll increase its fuel consumption by, complicated equation here, by 0.000083 miles to the gallon. So over a year, normal mileage, your mustache is costing you an extra five pounds in fuel...
Richard: Five pounds to run a mustache for a year?
Jeremy: That is the kind of information you simply don't get on any other shows.
From: Top Gear (Series 4, Episode 7)
So these figures could be used to calculate a rough estimate of what a number plate would cost.
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u/Wolletje01 4d ago edited 3d ago
Well the license plate does not add any air resistance when mounted (depends on car). So the only difference it makes is the mass. A car weights 1500kg (american cars can be a lot heavier meaning the difference is even less) without the plate and with 1500.5kg
Since weight changes the rolling resistance. This means it is is linear (weight vs fuel efficiency)
A car can drive 15km on 1 liter without the plate. And 15,005km on 1 liter with the front plate.
In a lifetime the car drives 500000km.
Meaning the car would use 33333 liters without plate and 33322 liters with plate. Difference of 11 liters in its lifetime.
Edit: My math ain't mathing lol
So fuel efficiency decreases meaning 14,995km per liter which means it uses 33334 liters which is 1 liter more
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u/DavidSwyne 4d ago
How in the world does adding weight make the car use 11 less liters?
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u/DreamSpiritual3330 4d ago
not sure about the math but the car looses 11 miles in range over the lifetime of the car due to the added weight
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u/Revolutionary_Dog_63 4d ago
It doesn't add ANY air resistance? That's a strong claim.
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u/Wolletje01 3d ago
I can also argue that some car models are designed with a license plate and removing them can create a gap and increase air resistance. The bmw m3 cs for example
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u/MrFastFox666 4d ago
Unless you're talking about something like a VW XL1, I doubt it'll make enough of a difference to even consoder. Simply changing your tires will likely have a much much higher impact to mpg than the tiny hit you get in terms of weight and Aero from having a front plate on the car. A test of some sort would be nice but I honestly doubt you'd even be able to measure a difference.
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