How tire pressure impacts range - insight into impact of 245/50 R19 tires on stock 19 wheels?

mkhuffman

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I found this article that tested the impact of tire pressure on BEV range.

https://www.sae.org/news/2020/10/tire-pressure-impact-on-ev-driving-range

I am trying to determine if I want to change out the tires with 245/50 R19 tires to give the car a more aggressive look, and to improve handling. But I do not want to significantly impact highway range. It seems to me that adding width may be similar to low tie pressure, and maybe increasing tire pressure before a highway trip could offset the impact of getting wider tires.

According to the article, proper (and high) air pressure in the tires can improve range:
"Over the vehicle’s life, a variable tire RRC could account for up to 4% battery-charge difference. Reducing IPLR and “in-use” RRC creates the potential for Tier-1 suppliers and OEMs to consider a lighter and/or less-expensive battery. And ExxonMobil Chemical road testing has demonstrated that EV range can be improved from 3-7% with optimized tire IPLR. "

It seems a 5% hit to range is possible due to the wider and stickier tires. However, I bet if you crank up the air pressure in the tires, that can be mitigated significantly. My guess is with 32 psi, you probably will see close to a 5% range hit with the wider tires. I guess that raising the pressure to 40 will reduce that impact, so a good guestimate is 2-3%. I will go with 3% for a worst case analysis. 210 miles of highway range (on a full charge) will become 204 miles. So I guess you will loose 6 miles of range with 245 tires. If that is true, it is worth it to me to replace the tires. I hope someone will test this. Or maybe I will...

On a side note, it is interesting how significantly tire pressure impacts range. I bet a lot of EV owners do not monitor tire pressure and are getting less range just because their tire pressure is low.
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jeffdawgfan

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I can verify that air pressure plays a big part of the efficiency of the vehicle. Our Nissan Leaf is supposed to have 38# in tires. I keep them at 42# cold pressure and get around 7-8 mores miles of range per charge. The ride is not as comfortable so you have to make the choice on ride and range. On our soon to arrive MME I will change out the tires on the stock rims to 235's when it is time for new tires. I will probably keep my tires 2-4 pis above recommended also.
 
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mkhuffman

mkhuffman

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So I know the following article is for a bike tire, but I think this analysis is applicable to car tires as well. I am not ready to jump to the conclusion that there is no range impact with wider tires, but I think this suggests maybe the impact is even less than 3%.

https://www.bicyclerollingresistance.com/specials/grand-prix-5000-comparison

You can find other articles that test wider bike tires and rolling resistance, and the results are similar. And if you look at the tires, the width difference is very significant. A 245 tire is 9% wider than a 225 tire. For the article that tested bike tires, the difference between the narrowest and widest is 30%.

30%! So with a 30% increase in width, they measured barely any difference in rolling resistance at the same tire pressure comfort level (see article for explanation). That means tire pressure impacts range much more than tire width.

"We feel the ultimate test is adjusting all tires to the same comfort level. When all tires are adjusted to the same comfort level, rolling resistance is nearly the same (0.2 watts max) for all sizes of the GP 5000. "

Conclusion: I think a 3% hit to range is really worst case, and if you keep the tire pressure at the proper level, there might not be any range hit. We need to test this!
 

dml105

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Whenever I think about whether I can optimize something better than the $50B car company, I ask myself if I'm a $50B car company, THEN I ask myself if I'm an engineer. (No to the former, yes to the latter.) Point is, I'm absolutely certain that Ford chose the narrow 225s on the Mach-e for a reason.

With that said, the GT will come on 245s. Same battery, bigger motors, 250 mile range. That's a fair number of variables changing, but only an 8% hit on range. So, that 8% is probably the ceiling on the hit you would take by switching to 245s.
 

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I'm already running low 40's because I like the handling of fully inflated tires better. And it does help the range and also gas mpg. It can make the car a bit jumpy, but I'm used to that. I would get the next width up, all season, with as high an efficiency rating as possible.

What tires are on the GT in comparison?
 


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mkhuffman

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Whenever I think about whether I can optimize something better than the $50B car company, I ask myself if I'm a $50B car company, THEN I ask myself if I'm an engineer. (No to the former, yes to the latter.) Point is, I'm absolutely certain that Ford chose the narrow 225s on the Mach-e for a reason.

With that said, the GT will come on 245s. Same battery, bigger motors, 250 mile range. That's a fair number of variables changing, but only an 8% hit on range. So, that 8% is probably the ceiling on the hit you would take by switching to 245s.
I am only worried about highway range, but Ford is worried about EPA range (and real world range also, I am sure). 245/50 tires are heavier, maybe significantly so. Once you are in motion, weight has a minor impact on range. But if you are slowing down and speeding up, weight can have a significant impact on range, especially in the wheels. So I think a 5-8% hit to EPA range is reasonable, although I am sure the 8% hit on the GT is more than the wheels and tires. So a 5% hit is reasonable with just putting heavier, wider tires on the car.

Rolling resistance has a significant impact on highway range, as does air resistance. I think the 8% increase in tire width will have a very, very minor impact on air resistance. The variable to be concerned about is rolling resistance, and I think the data shows that is significantly mitigated by tire pressure.

All guesses, I know. I certainly don't have the data and resources of a $50B company. Sure, it makes sense to use 8% as a worst case estimate, but I think in reality it is much less than that, especially with proper tire pressure. Again, just referring to highway range here...
 
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mkhuffman

mkhuffman

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How about 255/50 R19s? These appear to fit the rims. Note the huge increase in weight. That will definitely impact city range. Probably steady state highway range not so much, with proper tire pressure. (Specs from Tire Rack.)

Ford Mustang Mach-E How tire pressure impacts range - insight into impact of 245/50 R19 tires on stock 19 wheels? 1615904449481

Ford Mustang Mach-E How tire pressure impacts range - insight into impact of 245/50 R19 tires on stock 19 wheels? 1615904465218
 

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I'm already running low 40's because I like the handling of fully inflated tires better. And it does help the range and also gas mpg. It can make the car a bit jumpy, but I'm used to that. I would get the next width up, all season, with as high an efficiency rating as possible.

What tires are on the GT in comparison?
Based on the current specs the ranges for the GT are 250 & 235 for the performance edition, in steady state driving I can't imagine much difference in power usage apart from tires with the performance edition being in summer tires as the tire compound is going to make a difference to the rolling resistance and range.

Compared to its competitors that are a similar size (i-pace, model Y, polestar 2 & id.4) the mach-e is running on the smallest section width tires @ 225. So you could probably split the difference between the base and the GT and run a 235 section width without that much impact in range if sticking to a EV friendly tire
 

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Whenever I think about whether I can optimize something better than the $50B car company, I ask myself if I'm a $50B car company, THEN I ask myself if I'm an engineer. (No to the former, yes to the latter.) Point is, I'm absolutely certain that Ford chose the narrow 225s on the Mach-e for a reason.

With that said, the GT will come on 245s. Same battery, bigger motors, 250 mile range. That's a fair number of variables changing, but only an 8% hit on range. So, that 8% is probably the ceiling on the hit you would take by switching to 245s.
Ford optimized them for a specific purpose - maximizing range. If you're ok with taking a hit, change out the tires to something wider and fatter to trade range for performance or ride quality.
 

Trede

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Just so you're aware - more pressure in the tire can reduce the surface area of tire on the road (REALLY overinflated tires end up with contact patches closer to bicycle tires...I'm exaggerating, but hopefully you get the point). Your tires will take a hit in longevity (same weight distributed over smaller area, the middle of the tires will wear and the edges won't).
Conversely, less pressure can give more surface area on the "road". (too little, the edges will wear and the middle actually kinda tacos in so it doesn't wear/as much) Some military vehicles have built in air compressors so you can actually change tire pressure while driving...drop pressure for better grip in sand etc.
Things to factor in. :)
 

dml105

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Ford optimized them for a specific purpose - maximizing range. If you're ok with taking a hit, change out the tires to something wider and fatter to trade range for performance or ride quality.
I'm definitely not opposed to changing out the tires. I may do a seasonal split with wheels wearing 245s in the summer and stock wheels in the winter, but I want to see how the stock wheels perform on snow first. I'm assuming the typical advice holds that the narrower tires work better in winter.
 

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Ford optimized them for a specific purpose - maximizing range. If you're ok with taking a hit, change out the tires to something wider and fatter to trade range for performance or ride quality.
I get in theory why people say that, but this is a Mustang, and recent Mustangs never cared one bit about range, hence the teensy fuel tanks and big V8s.

People who want efficiency will buy a different EV.

Ride and performance are what define a Mustang, I seriously think they missed the mark hard with these Prius-esque tires.

Even the GT at 245? Come on. The Mustang GT has 255 square options, optional 255 front, 275 rear, or up to 305 (!) rear on the Performance Pack Level 2.
 

sockmeister

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I get in theory why people say that, but this is a Mustang, and recent Mustangs never cared one bit about range, hence the teensy fuel tanks and big V8s.

People who want efficiency will buy a different EV.

Ride and performance are what define a Mustang, I seriously think they missed the mark hard with these Prius-esque tires.

Even the GT at 245? Come on. The Mustang GT has 255 square options, optional 255 front, 275 rear, or up to 305 (!) rear on the Performance Pack Level 2.
Agreed, but although this is a Mustang, it's also an EV, and I think for their target market, range was, first and foremost, the priority. Especially if they wanted to compete with Tesla on paper.

So for the tests, reviews, and everything else, the car will ship with these tires to get every last mile out of its targeted range on the books.
It's up to us to revive the Mustang "soul" by putting on the performance upgrades :)
 

dml105

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Helpfull video about wheels-tires-range

Cool video, but unless I missed it, I don't think it explains WHY the higher diameter rims reduce range. Is it just the air resistance of the higher diameters? Could that be fixed by having fins in the rims?
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