Guess which Tire had 36 PSI and which had 42 PSI ?

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knightmb

Well-known member
Joined
Jan 12, 2015
Messages
2,212
Location
Franklin, TN
As the subject says, my wife and I conducted a long term experiment. She had identical tires that I had on my Leaf, but she didn't think running higher air pressure made a difference on the tire life because the door says 36 PSI and why not trust the manufacture? We got an identical tire set at the same time and after only 28K miles, this is what the difference was between running 36 PSI (in her Leaf) and 42 PSI (in mine). These tires are Michelin Energy Saver A/S X Green (the cheap ones). Both of these are front tire pictures. When I did tire rotations I did both at the same tire mileage (10K miles) each time to even out the wear. I put the answer at the bottom of the post under the pictures.

AzrW4eJ.jpg


RR0gEFl.jpg

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Top picture was mine, bottom picture was hers. :mrgreen:
 
I find that it's a rare person who changes his or her mind on the basis of evidence, sadly. I can still remember my (ex) GF screaming at me that I was going to blow her tires up when I put 38psi in her Corolla, because she'd inflate them to the 32psi on the door, then drive until they were visibly soft...Thanks for doing that, though!
 
LeftieBiker said:
I find that it's a rare person who changes his or her mind on the basis of evidence, sadly. I can still remember my (ex) GF screaming at me that I was going to blow her tires up when I put 38psi in her Corolla, because she'd inflate them to the 32psi on the door, then drive until they were visibly soft...Thanks for doing that, though!

To be fair, my wife and I don't drive to the same places, just around the same city. I know someone will chime in that conditions are not identical and I agree, maybe some roads cause more wear than others, maybe someone is a more aggressive driver than the other (my wife calls me a lead foot), maybe the tires have some manufacturing differences even though they are the same exact model/size/brand of tire. I really think though, the 36 PSI might be better for ride comfort and stopping distance, but going more (at least 40 PSI or higher is what a lot us are doing here) does have a tangible benefit in the long run, both in tire life and probably range. It might be a small benefit, but little things add up over time and while I can do another tire rotation and probably squeeze some more miles out of mine (back tires are in better condition on both of ours actually), my wife is going to need some new tires very soon. :lol:
 
Your photos reinforce what I learned shortly after getting my 2011. I noticed vague handling and drifting due to side winds almost immediately and soon noticed premature inside and outside tire edge wear. After reading recommendations for higher pressures on the forum, I tried 44 psi (maximum cold inflation pressure molded into the sidewalls of the OEM Bridgestone Ecopias); handling improved immediately and the car was much less susceptible to side winds. Also, tire wear became more even across the width of the tread. I also noticed that wet stopping distance was significantly reduced (probably because the higher pressures help maintain front tire contact patch area under heavy braking loads).
 
GerryAZ said:
I also noticed that wet stopping distance was significantly reduced (probably because the higher pressures help maintain front tire contact patch area under heavy braking loads).
That's interesting, I know I've read that over-inflating tires can cause stopping issues in the rain, but maybe the Leaf is so heavy that even at the max tire pressure, it still works within the margin of error for rain stopping distance given the extra weight. I'm sure it has some effect, as mentioned in some other topics by increasing stopping distance by X amount of feet, but I think hydroplaning is probably more dangerous than increased stopping distance provided you aren't riding the rear end of someone in a rain storm, so I don't worry running my tires at a higher PSI either. I would rather have more control in a rain storm if to sacrifice a little stopping distance since I have control over that by not following behind someone so close.

I thought it would also be helpful to have some actual "before and after" pictures for the forum since we talk about tire pressure and wear but it helps to have something to show for it as well. :)
 
That's pretty convincing evidence. 42psi definitely wears more evenly. Based on your signature, I'm guessing on car is 40kWh and the other is 62kWh. But the difference in weight amounts to the equivalent of a passenger or 2.

I may try 40 psi again and see what I think. I felt my car was excessively blown around by wind and passing SUVs at speeds above 60 mph when my tires were at 46 psi (set by dealer) and 44 psi. That issue reduced at lower pressures. I think the root problem is the ridiculously overboosted steering that gives no feedback.
 
The difference in curb weight is close to 300# per the specs I've seen. So yes, a couple of passengers. Not a trivial difference actually.

Since the tire sizes are the same, I would expect the recommended pressures to be slightly higher on the 62 kwh, but they're not to my knowledge. If the 40 is spec'd on the "comfort" side of the tire load calculation (as I suspect and is often the case), it would be enough to matter.

Pics definitely tell a compelling story.
 
I'm not a tire expert, but the difference between the two pictures would suggest to me that my wife was running her tires with "not enough air" enough though I made sure her tires were at the 36 PSI properly, checking often, especially when the weather gets colder. On a warm day, her tires would easily go from 36 PSI to 40 PSI while driving, but as the temperature goes down, even adding air to make up for the cold weather difference, they stay around the 36 PSI when driving in colder weather and maybe gain only 1 or 2 PSI while driving around.
She never complained about the ride comfort, so maybe it's worth the extra tire wear for her. :?
 
Do you have photos showing the full width of the tread?

If the tires are worn near both sidewalls, then they may be underinflated. If they are only worn on one sidewall, it could be the wheel alignment is incorrect and/or the driver has been hooning it around the corners at high speed a lot.
 
philso said:
Do you have photos showing the full width of the tread?

If the tires are worn near both sidewalls, then they may be underinflated. If they are only worn on one sidewall, it could be the wheel alignment is incorrect and/or the driver has been hooning it around the corners at high speed a lot.

I'll look through my photos and see if I have a better angle. I've since replaced those worn ones in the picture with some new Ecopia, but I do remember when I have the wheels turned sharp (left or right) where you can see the whole tire, both sides looked the same, but photo proof would be better. :)

[edit]
I didn't take any pictures with the front wheels turned sharp so you can see the whole tire, but both sides where like that and it did include the inner part. It's possible her Leaf had a mis-alignment on both front wheels, but if she did, it doesn't appear to be doing anything to the tires now and was never reported by the tire shop about an alignment issue.

Enough though the pictures have a stark contrast, the better "looking" tire doesn't have much thread left either, so it wasn't far behind the other tires, but it certainly had less wear on the edges with more PSI.
 
driving style can make a big difference...example hard braking in the turn vs. doing most of the heavy braking then turning with light braking only.

Also taking turns at a faster average speed could make a difference in wear.

Not trying to discourage that running higher tire pressure is better for Leaf tire wear...I run mine at 40 psi and they seem to be wearing normally.
 
By luck, I found an old image of the front tire with both sides visible. Not the best picture because it wasn't really a focus on the front tires, but at least one can see what both sides of the tired that was running 36 PSI looked like in the end. :D

9k9KuCC.jpg
 
Yes on my Leafs I run maximum sidewall pressure after my OEMs wore out in less than 20k miles using 38psi. Due to the weight of the Leaf I've wondered if one could get a load range "C" tire in the Leaf size. Besides having a higher maximum sidewall pressure I feel the stiffer sises would probably wear quite a bit better on the Leaf. I know on things like cargo vans that can carry heavy weight if you don't run at least load range C tires, they wear out quite quickly on the sides.......
 
running 40 psi...just rotated my stock Michelins at 20,000 miles and they look great. At this rate I should be able to go to 40,000.


C5ahBhUl.jpg
 
My experience is similar: 40-42 psi on our Leaf+, managed pretty closely when weather changes (you lose about 1 psi / 10 degree decrease in ambient temperature). Tire wear is dead even on all 4 tires. Rotate 2x/yr with swap to/from snow tires. I run my snows a tad higher on warm days so they don't run lower on cold ones, call it 40-44 (they're rated to max 51).

The even wear profile suggests that the door sticker is indeed too low for whatever reason. Aside from the advantages to range, running 36 will wear the shoulders prematurely, and lead to handling "mushiness".

Proof is in the pudding as they say.
 
Manufacturers post the door sill pressure so low because they want people to experience a nice, soft, cushy ride. That goes back to the days when American cars floated around on the road like giant steel marshmallows. I don't understand why they never raised the number to give better fuel economy instead, because that's a better way to make people happy these days.
 
LeftieBiker said:
Manufacturers post the door sill pressure so low because they want people to experience a nice, soft, cushy ride. That goes back to the days when American cars floated around on the road like giant steel marshmallows. I don't understand why they never raised the number to give better fuel economy instead, because that's a better way to make people happy these days.

I agree, thought in a technical sense, 36 PSI seems to be ok for hot weather (provided the tire is 36 PSI in the morning when it's cooler) and the 4 PSI it gains during the day from the heat and driving friction easily bring it up to 40 PSI which is where we all like to start from when doing a PSI upgrade. But during the winter time, colder days, I've only seen the tire gain 1 or 2 PSI. Unless you are checking your tire pressure daily to make sure it is always at least 36 PSI starting out, cold and winter months are basically rolling around on flat tires (for a heavy EV anyway) and even though I disagreed with my wife's logic, she did a have a good point of trusting what the manufacture recommends. To get around that argument (she now runs 44 PSI on all 4 *new* tires she has), I told her it was the "minimum recommended" tire pressure by the manufacture, not a hard limit. That seemed to a be a good compromise for her not to admit defeat. :lol: :twisted:
 
Learjet said:
running 40 psi...just rotated my stock Michelins at 20,000 miles and they look great. At this rate I should be able to go to 40,000.

They look to be in great shape, especially for stock tires. Yeah, if you can stretch them out to 40k before upgrading to better tires, it was well worth running the higher PSI to sacrifice a few feet in stopping distance. ;)
 
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