215/50R18 Tire?

[MacO512]

Has anybody tried a 215/50R18 tire size for additional range?

I recall hearing an out of spec youtube trip in a M3P where they said 225 18's with cargo roof box was same efficiency as 20's without. If 225 was that huge improvement; you'd think 215 would be even better. I'm interested in having a "max range" wheel/tire setup for any trips where range/efficiency is most important. Most of the time I'll probably have higher performance tires on the vehicle.

Two main potential issues I'm researching for 215's;
Issue 1; Need a wheel width of 8.0 or smaller. Martian MW03 barely fits, but stock Aero or FastEV EV01 that are 8.5 inches don't.
Issue 2; Need tire that has good range. MXM4 appears to be best range tire but is in stock 235/45r18 size and not 215.

Martian MW03 is expensive, and I'm not sure how aerodynamic it is. Secondly I'm not sure of best 215 tire option and how that efficiency compares.

 

[The Other Dan]

The diameter won't matter as much as the overall aero of the wheel.
How do the Aero wheel covers attach? Can you find some other 18x7.5 wheel that the covers would attach to?
For tires, what do other EVs run? Whay are they spec'ed with? Is there some Prius tire that works?

 

[MacO512]

215 is width not diameter, its narrower tire but similar diameter to stock. People report range decrease going up from 235 to 255 so I'd think the reverse that there should be a range increase going from stock 235 down to 215.

I have never heard of the Tesla Aero cover attaching to any wheel outside the stock Tesla 18. It would seem like a good idea as a wheel manufacturer to allow this, kind of surprised we haven't heard of it.

I have heard Prius runs MXM4 just as some model 3's; its one of the if not the best tires for range, although it has other shortcomings.

That's a good idea to look at other EV stock tires; perhaps one is available in 215/50R18.

 

[pdx_m3s]

Martian at one point made an 18x7.5" wheel. You may be able to find a used set.

You'll get a range increase, for sure, but is it worth it to have a car that handles like an i3?

 

[Mash]

I would be concerned about load rating of such tire.

 

[dfwatt]

Has anybody tried a 215/50R18 tire size for additional range?

I recall hearing an out of spec youtube trip in a M3P where they said 225 18's with cargo roof box was same efficiency as 20's without. If 225 was that huge improvement; you'd think 215 would be even better. I'm interested in having a "max range" wheel/tire setup for any trips where range/efficiency is most important. Most of the time I'll probably have higher performance tires on the vehicle.

Two main potential issues I'm researching for 215's;
Issue 1; Need a wheel width of 8.0 or smaller. Martian MW03 barely fits, but stock Aero or FastEV EV01 that are 8.5 inches don't.
Issue 2; Need tire that has good range. MXM4 appears to be best range tire but is in stock 235/45r18 size and not 215.

Martian MW03 is expensive, and I'm not sure how aerodynamic it is. Secondly I'm not sure of best 215 tire option and how that efficiency compares.

if you get into an accident and somebody does any kind of forensic deep dive (in other words in a serious accident,) and they discover you have down-sized your tires, you could have a denial of coverage. You talking about a 4000 pound car on a 215 tire section. Not sure that range trumps safety. Also, the amount of money you would save in this is trivial compared even to your insurance deductible. If you are denied coverage on the other hand and you are at fault, and someone is injured, your bill could run into six figures easily. So even from an economics standpoint this is a bad idea.

 

[ay221]

Martian has an 18x8 in the mw05 version.

 

[gearchruncher]

if you get into an accident and somebody does any kind of forensic deep dive (in other words in a serious accident,) and they discover you have down-sized your tires, you could have a denial of coverage.

I'd love to see the insurance contract that covers this and what it says.
If it does, it would also cover any changes, even if they "improved" performance. Like wider tires. That are more likely to hydroplane.

Does anyone actually know of a case where this happened, where an insurance company denied coverage on the whole accident because of a mod to the car?

 

[android04]

I believe you can still order the 18x7.5 wheel from Martian Wheels, but you have to put in a custom order because it's not an available option on their website. Whatever tire you get, make sure that it's XL rated or at least rated correctly for the load of the vehicle (minimum of 92 load rating, but recommend 94 or higher).

 

[MacO512]

if you get into an accident and somebody does any kind of forensic deep dive (in other words in a serious accident,) and they discover you have down-sized your tires, you could have a denial of coverage. You talking about a 4000 pound car on a 215 tire section. Not sure that range trumps safety. Also, the amount of money you would save in this is trivial compared even to your insurance deductible. If you are denied coverage on the other hand and you are at fault, and someone is injured, your bill could run into six figures easily. So even from an economics standpoint this is a bad idea.

Its a decent argument you make, and something I should consider. However I believe if the tire load rating still met the vehicle weight requirements I'd be fine.

If there is a legit safety risk I wouldn't want to drive it. However there are plenty of vehicles on 215 tires; and I would suspect some could handle the weight. Yes the M3 is heavier than many tiny ICE sedans, but its not a 9000lb hummer.

 

[tm1v2]

@MacO512 Are you doing drives where the little bit of extra range would actually save you charging stops? Or where you're already pushing the car's range limit between chargers with 235-245 tires on stock-size 18x8.5" aero wheels?

As long as you find tires with an appropriate load rating you should be fine, but to me this doesn't seem worthwhile.

Now for snow tires on dedicated winter wheels...I'd consider 215/50R18 for that. Not sure I'd actually choose it, but certainly I would consider it. (I say that without having checked tire availability and load ratings in that size, which is obviously rather important.)

 

[dfwatt]

Its a decent argument you make, and something I should consider. However I believe if the tire load rating still met the vehicle weight requirements I'd be fine.

If there is a legit safety risk I wouldn't want to drive it. However there are plenty of vehicles on 215 tires; and I would suspect some could handle the weight. Yes the M3 is heavier than many tiny ICE sedans, but its not a 9000lb hummer.

The difference between that car and my car which will stop from 60 mph under 100 ft is about 35 ft stopping distance. But I have a tire compliment of 265 and 275/30 tires. My range isn't that great but I don't have to worry about that because we have solar and unlimited free supercharging. That extra 35 ft isn't trivial in a potential accident situation. You have no idea what you're trading off for a little extra range. No idea. And I truly hope you never have to find out.

 

[MacO512]

@MacO512 Are you doing drives where the little bit of extra range would actually save you charging stops? Or where you're already pushing the car's range limit between chargers with 235-245 tires on stock-size 18x8.5" aero wheels?

As long as you find tires with an appropriate load rating you should be fine, but to me this doesn't seem worthwhile.

Now for snow tires on dedicated winter wheels...I'd consider 215/50R18 for that. Not sure I'd actually choose it, but certainly I would consider it. (I say that without having checked tire availability and load ratings in that size, which is obviously rather important.)

Yeah I'm not sure I would actually go through with 215, just trying to research it and as you say consider it. Yes winter tires might be an ideal case, as narrower helps anyways for those to cut through snow, and winter range is EV's worst season. The improved range wouldn't be significant if I'm only doing a one or two day trip. But I plan to do some over a large portion of the US, ~2000 miles each way. So then range as well as time at the charger start to be much more significant.

I also just like the idea of pushing an EV's range to the limit; maybe someone could set a M3 record putting around 45mph on skinny tires.

 

[MacO512]

The difference between that car and my car which will stop from 60 mph under 100 ft is about 35 ft stopping distance. But I have a tire compliment of 265 and 275/30 tires. My range isn't that great but I don't have to worry about that because we have solar and unlimited free supercharging. That extra 35 ft isn't trivial in a potential accident situation. You have no idea what you're trading off for a little extra range. No idea. And I truly hope you never have to find out.

Yes a M3 on 215 would likely need more feet to stop. Would it stop much quicker than an F250? I sure would think so, and plenty of people drive those big trucks around. Yes a M3 driver would have to leave a lot more distance with 215 efficient tires than a M3P on sticky performance tires.

If you really want to be as safe as possible its probably best to never drive at all. I'm fine with some tiny one in a million risk. Now if 215 tires would take double the distance to stop as an F250 there is a major problem and no I wouldn't use such a vehicle.

 

[The Other Dan]

215 is width not diameter, its narrower tire but similar diameter to stock. People report range decrease going up from 235 to 255 so I'd think the reverse that there should be a range increase going from stock 235 down to 215.

I have never heard of the Tesla Aero cover attaching to any wheel outside the stock Tesla 18. It would seem like a good idea as a wheel manufacturer to allow this, kind of surprised we haven't heard of it.

I have heard Prius runs MXM4 just as some model 3's; its one of the if not the best tires for range, although it has other shortcomings.

That's a good idea to look at other EV stock tires; perhaps one is available in 215/50R18.

Re Dia. Vs Width... yep, my indirect point was you could go 19s as well rather than stick solely with 18s. May open up rim options.

I would be concerned about load rating of such tire.

They make LT tires that size with plenty of load capacity. Actually that may help the efficiency if you can find a "Highway" style tire. Usually they have tread patterns closer to the PS4S, but a harder rubber. Might be less rolling resistance.

 

[tm1v2]

@MacO512 I just noticed your profile pic is an M3P on the 20" wheels. You'll get a nice efficiency bump just from going 18" wheels even with stock-like width and summer performance tires.

I swapped my 2021 M3P to 18x8.5" forged wheels with 245/45R18 300TW "max performance" category tires (same category as stock). I wasn't even expecting an efficiency benefit since I was staying with performance tires and non-aero wheels, but turned out my efficiency went up in all driving, both highway and rural roads (lots of slowdowns + speedups for the turns).

My driving isn't very consistent so I can't give exact numbers but it became easier and more frequent to match the car's EPA rating (when not putting the hammer down ). I'm sure I didn't get the full efficiency of a base Model 3 with aero wheels and MXM4 eco efficiency tires, but that's okay, I like tires that grip and give confident road feel. My wife and I tried the MXM4 once on our Model S and neither of us liked them...they really didn't grip well or give much confidence in the turns, especially in the wet. Obviously summer performance tires are in a different league, but even many regular allseasons handily outperform the MXM4 aside from efficiency.

(The M3P is currently on 500TW UHP allseasons for the winter, and the S P85 is on some random Conti allseasons that a local shop had in stock when we were desperate...and they way outperform the MXM4 that they replaced.)

 

[MacO512]

Re Dia. Vs Width... yep, my indirect point was you could go 19s as well rather than stick solely with 18s. May open up rim options.

They make LT tires that size with plenty of load capacity. Actually that may help the efficiency if you can find a "Highway" style tire. Usually they have tread patterns closer to the PS4S, but a harder rubber. Might be less rolling resistance.

My understanding is 18" are much more efficient than 19" even with identical widths/tire compound/etc as explained in this video;

 

[tm1v2]

My understanding is 18" are much more efficient than 19" even with identical widths/tire compound/etc as explained in this video;

I think that's true. My guess is it's a combo of two things (in no particular order here):

• Smaller wheel / taller sidewall always results in an overall lighter wheel+tire setup, for every wheel and tire I've ever checked weight specs on.
• Tire sidewall is probably more aerodynamic than wheel spokes.

If you're after efficiency in this car 18" is the way to go. It's also cheaper (wheels and tires both) and more practical (more sidewall for wheel protection).

19" has several very real benefits on this car, but for maximum efficiency 18" is the ticket.

 

[dfwatt]

Yes a M3 on 215 would likely need more feet to stop. Would it stop much quicker than an F250? I sure would think so, and plenty of people drive those big trucks around. Yes a M3 driver would have to leave a lot more distance with 215 efficient tires than a M3P on sticky performance tires.

If you really want to be as safe as possible its probably best to never drive at all. I'm fine with some tiny one in a million risk. Now if 215 tires would take double the distance to stop as an F250 there is a major problem and no I wouldn't use such a vehicle.

Course it's an empirical question and perhaps if you do this you should test your Panic stop distance if you have one of those specialist timing devices like draggy or vbox. Of course you can always find a vehicle that stops more poorly. Semi trucks are incredibly bad at emergency braking, but their drivers know this and drive accordingly for the most part. If it turns out that your stopping distance is roughly about the same as an F250 you'd have to change your driving habits to accommodate the poor emergency braking. Once again, not sure it's worth it. But it is up to you to decide, but I would check for sure with my insurance company first.

 

[gearchruncher]

What a yarn @dfwatt is slinging. Look at all the poorly maintained vehicles on the road. Now go look for stories of insurance companies denying coverage because your braking distance was longer than the factory one.

I mean, while we're at it, insurance companies deny your coverage if you're even 1MPH over the speed limit too, right? Insurance is only for accidents when everyone was driving a perfectly maintained vehicle fully within the laws?

(dfwatt has me blocked so he doesn't have to answer pushback like this though)