So with ICE cars there is the concern that if you have AWD and get a flat that cannot be repaired, now you have one tire with different diameter and that is bad for your differentials. Whether that is true or not, it is another question.

How about AWD EVs? I know Teslas for example have dual motors, one for the front and one for the back. Do they still have differentials like in ICE, I mean differentials where you need to replace the fluid after some miles? or did they find a different solution? also does unmatched tire thread matter in those cases since the Front and Rear are driven by different electric motors and there is no mechanical coupling between the 2 axels?

Some Teslas have a single motor in the rear, most have dual motors front and rear, and the Plaid version has a single motor in front with dual motors in the back.
To further complicate it, many have a “square“ set up where the front and the back tires are the same size, and others have a staggered, set up with different size tires in front and the rear.
Yes, other than the rear of the Plaid, they still have differentials, so the same rules apply regarding tires.
The Plaid gets around the differential by using what is called “torque vectoring“ which lets the computer, and the electronics determine traction and the "differential“ that the wheels need for turns.



Edited 1 time(s). Last edit at 05/25/2023 06:31PM by Ken Sp..

I'd think for vehicles like the Rivian R1T/S, Lordstown Endurance, Lucid Air...any vehicle with 1 motor per wheel, it shouldn't matter. But if 1 motor is powering 2 wheels, there's a differential involved.

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OK thanks. I guess in the worst case, if you are really concerned, you replace that pair not all 4 tires. I mean if one is damaged beyond repair, you buy 2 new tires instead of 4 new tires, just make sure you keep them matched.

Ioniq 5 manual for our new AWD EV does not show concern for that...but I am guessing anyone that sells tires will certainly bring it up.

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‘New EV tire for Teslas, Mustang Mach-E promises better durability’


[arstechnica.com]

On gas fueled AWD vehicles, the “suggested maximum” actual diameter (not nominal tire size) difference on each axle and front to back should not exceed 1/2”.

I imagine (but haven’t researched) that the 1/2” difference would apply to each axle in an EV.



Edited 1 time(s). Last edit at 05/25/2023 05:17PM by Cary.

I've never in my whole life replaced less than a pair of tires. Plus, I feel like it wouldn't be good for an automatic tranny for the tires on the drive wheels to be different sized either.

I hope those new Bridgestones are good tires. I like the Continentals, but they don't seem to last very long.

Note that there is another option. If you wreck a tire and the other one is on a driven wheel and on the same end of the car (i.e. front or back), then if the remaining tire still has most of its tread you can buy a single new tire and have the tread shaved down to the same diameter as the remaining tire. Usually way cheaper than buying two new tires.

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Edited 1 time(s). Last edit at 05/25/2023 07:00PM by davester.

That said, taking a great risk of saying anything here...

In 30+ years of AWD car ownership, I have yet to have a need to replace one tire. Yes, I have had an occasional flat that needed a repair. But never a blowout or sidewall problem that required replacing just one tire. Never.

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Quote
Markintosh
That said, taking a great risk of saying anything here...

In 30+ years of AWD car ownership, I have yet to have a need to replace one tire. Yes, I have had an occasional flat that needed a repair. But never a blowout or sidewall problem that required replacing just one tire. Never.

Wish I could say the same. We just had a flat on one of our '03 Forester's winter tires that are one season old. The hole is in the sidewall, so the tire is toast. Luckily, it's a Blizzak, a popular tire in this part of the world, as are 0X Foresters. I suspect that before next winter, I'll find a replacement that will work for us. I've already seen numerous ads on CL for Blizzaks in the last week—not in our size, yet— so I'm hopeful.

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Quote
btfc
‘New EV tire for Teslas, Mustang Mach-E promises better durability’


[arstechnica.com]

Great! I rarely speed away from a stop but still my Bridgestone’s low rolling resistance tires wear quickly on my PHEV. I’m also conscious of how fast I go around curves, cloverleafs, etc.

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Quote
gadje
So with ICE cars there is the concern that if you have AWD and get a flat that cannot be repaired, now you have one tire with different diameter and that is bad for your differentials. Whether that is true or not, it is another question.

How about AWD EVs? I know Teslas for example have dual motors, one for the front and one for the back. Do they still have differentials like in ICE, I mean differentials where you need to replace the fluid after some miles? or did they find a different solution? also does unmatched tire thread matter in those cases since the Front and Rear are driven by different electric motors and there is no mechanical coupling between the 2 axels?

One problem with your example: The tire rep[lacing the damaged tire is not always a different size. If it is a different size, it should be installed on the opposite end of the car from the differential. Most non-matching sizes differ very little in diameter, and even matching sizes will differ by the lack of wear on the new tire.

There has to be significant difference in tire sizes to have a real effect on the differential.

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Ed (modelamac)

I think I will just put an OUT OF ORDER
sticker on my head and call it a day.

Quote
modelamac

Quote
gadje
So with ICE cars there is the concern that if you have AWD and get a flat that cannot be repaired, now you have one tire with different diameter and that is bad for your differentials. Whether that is true or not, it is another question.

How about AWD EVs? I know Teslas for example have dual motors, one for the front and one for the back. Do they still have differentials like in ICE, I mean differentials where you need to replace the fluid after some miles? or did they find a different solution? also does unmatched tire thread matter in those cases since the Front and Rear are driven by different electric motors and there is no mechanical coupling between the 2 axels?

One problem with your example: The tire replacing the damaged tire is not always a different size. If it is a different size, it should be installed on the opposite end of the car from the differential. Most non-matching sizes differ very little in diameter, and even matching sizes will differ by the lack of wear on the new tire.

How to decode tire sizes: Example P225/60R16-
(There are also the weight and performance ratings which can make a slight difference in the rolling diameter of the tire once it has been installed and is under load, but below are the basics)

"P" = P-Metric, a standard for sizing.

"225" = The tire's width at its widest point in millimeters.

"60" = Aspect ratio, the tire's height from the bead to the road as a percentage of its width.

"R" = Radial.

"16" = The diameter of the rim the tire goes on in inches.

225 (width) x 60% (aspect ratio) = 135mm (sidewall height), divided by 25.4 = 5.31 inches, x 2 + 16 (wheel size) = 26.62 inches (overall diameter).

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modelamac
There has to be significant difference in tire sizes to have a real effect on the differential.

On conventional differentials, yes. The problem with using different sized tires on AWD vehicles is that the center differential, which splits torque between the front and rear axles and compensates for different rotation speeds when turning, is usually a fluid coupling and the constant difference in rotational speed can cause the fluid in it to overheat and damage the center differential, and those puppies are NOT easy or cheap to replace.

Electric AWD vehicles are a whole different ball of wax since on a lot of them there's no mechanical connection at all between the front and rear axles, and instead EV manufacturers tend to use one or two motors on each end, which as stated up-thread varies from make to make and even model to model. I'm not recommending it as a practice but you might be alright using one slightly different sized tire, however I'm willing to bet the ABS and/or traction control systems, which depend on very accurate wheel speed sensors at each wheel and constantly compare the reading from all 4 wheels, will notice the difference and illuminate a warning light or two about it at the very minimum.

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Edited 1 time(s). Last edit at 05/26/2023 08:03PM by Thrift Store Scott.

<<I've never in my whole life replaced less than a pair of tires. Plus, I feel like it wouldn't be good for an automatic tranny for the tires on the drive wheels to be different sized either. >>

In my whole life I bet I have worked on 300 cars, 260 of them at a place that sold tires.

They *loved* customers like you.

One problem with your example: The tire replacing the damaged tire is not always a different size. If it is a different size, ...

I didn't mean a different nominal size. I mean the same nominal size, but different thread depth, thus effectively a different diameter. In fact I didn't use the word Size in my original post, I used Diameter and Thread.

Quote
chopper
<<I've never in my whole life replaced less than a pair of tires. Plus, I feel like it wouldn't be good for an automatic tranny for the tires on the drive wheels to be different sized either. >>

In my whole life I bet I have worked on 300 cars, 260 of them at a place that sold tires.

They *loved* customers like you.

I think he's saying two tires wore out at a time. That's how mine have always been. As he said, I've never NEEDED to replace just one tire.

I’ve always replaced tires in pairs, when there was tire damage that could not be repaired. Call it safety insurance.

I once saw the aftermath of an accident when a drivers side front tire blew out of a Smartcar and hit a guardrail on the Interstate. I think the driver was OK, but the car was totaled.



Edited 1 time(s). Last edit at 05/27/2023 07:15PM by Forrest.

When I've run into this issue, I just buy one used tire that has about the same tread depth as the others. I've done this multiple times with ebay and it's been great. For example, I got a new car last year and six months later had a nail in the sidewall. It couldn't be repaired. I could have spent $450 on one new tire, or bought them as a pair like some of you do for $900. Instead I spent about $120 and got a tire with 9/32nds on it. No patches, plugs or repairs on that tire.

Quote
Cary
On gas fueled AWD vehicles, the “suggested maximum” actual diameter (not nominal tire size) difference on each axle and front to back should not exceed 1/2”.

I imagine (but haven’t researched) that the 1/2” difference would apply to each axle in an EV.

Some manufacturers (eg Audi) say 4/32nds max. That would be 1/4" diameter.

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