Optimal tire PSI for max range?

[GerryAZ]

Denwood,

Feel free to run your tires soft, but you will wear the outside/inside edges prematurely. I had 215/50 R17 Bridgestone Ecopias as my last set on the 2015 and tire wear was even with at least 44 psi (usually 46 to 48). I have 215/50 R17 DriveGuard run flats on the 2019 and generally run them at 46 to 48 psi to keep them from building up too much heat. Tire wear after almost 15,000 miles is even across the tread.

 

[denwood]

I'll check tire temps across the face and report back on what the preferred pressure is. The Ecopia 422 Plus is very much a different tire from the OEM Michelin A/S that were on there.

 

[knightmb]

Anyone remember fiasco of when Ford set the recommended pressures on first generation Explorers at 26 psi? Those tire pressures are set by the Tire and Rim Association (TRA), which in of itself is just of the big tire manufactures working together. So because a tire can be used in so many different ways, they are purposely recommending low(ish) PSI for both safety and to avoid lawsuits I'm sure. So while all the Nissan Leaf have a door sticker recommending 36 PSI, a lot of us here that drive them everyday know that after a while of driving, the tire pressure heats up to 40 PSI and then the ride and handling feel better, better mileage, etc. The problem is while waiting for the warm up, you suffer on the range and handling, the colder it is outside. So why wait and burn extra tire when you can set it in the +40 PSI range to begin with? A lot of manufacturers have the door sticker to max out the tire PSI (Volkswagen for example recommends 44 PSI), so why would one car manufacturer have low tire pressure and the other with a similar vehicle have max tire pressure for the same tire? Did the laws of physics change for the two vehicles or is it simply some manufacturers also see the benefit of using higher PSI to increase range and handling?

 

[knightmb]

Welcome to the forum! So before an overload of people chime in, this is why a lot (and I mean a lot) of us run the higher PSI despite all the specs from both Nissan and any tire manufacturer we purchase from.

1) The range increase/decrease can be tested. Unlike a gas car where it is very difficult to detect if your gas mileage is increasing or decreasing with small changes in tire pressure, it is very easy to see this in an EV because of the precision of the power usage (I use precision loosely as we know it's not like it has high precision scientific equipment measuring power but good enough for us to test with) So we can drive the same routes over and over and get data readings that nudge us to either we are getting better mileage or worse mileage.

2) We know the EV is lot heavier than the gas counter-part, so we suspect a lot of the reason the recommended tire PSI for EV seems low is because it has its history and roots in gas vehicles which were lighter riding on the same tire. I know the manufacturer does some testing on the tires as well, but I'm sure the two probably work together to arrive at a (legally) safe number since it would be impossible to test *every possible tire in the world* that can fit on your vehicle to arrive at averaged PSI number. So for the Nissan Leaf, 36 PSI might be the safest number for the crappiest tire you can buy that will fit on the rim.

3) Given #2, we exchange data with the tires we do buy and how they perform. For example, some people buy brand X tire and others brand Y tire and compare if the ride and mileage seem better once the PSI goes up/down/etc. That is why the consensus here seems to like the 40 to 42 PSI range, others use the max 44 PSI because the tire does well with it, others may not.

Given that, me personally, having gone through many brands of tires over the years, some tires I ran 42, others I did 40 because I see the difference in the numbers and feel it in the handling, visual inspection of tire wear, etc. My current tires, appear to run fine on 44 PSI so far, so unless something changes, for me, I feel safe and comfortable with it. That is why the question "What is the Optimal tire PSI" depends on the tire that you have, but all tend to be higher than the 36 PSI recommended.

My first post here..go figure

The tire fellow at Schwab was doing his job exactly.

Tire inflation pressure is a function of the specific tire's load rating and max pressure, vs the GVW rated max load it will see. For my new Ecopia Plus tires (215/50R17 XL) we can see the max pressure is 50psi, at 1512 lbs (from the sidewall). It also has a higher load rating (1512lbs) than the Michelin Energy Savers. It's an XL (extra load) tire with a load index of 95.

The 2018 Leaf SL has a curb weight around 3500 lbs, and GVW of 4453lbs. We know weight distribution is pretty close to 50/50 so each tire needs to support a max of 1113 lbs or so (4453/4)

You can find the Bridgestone inflation pressure /load charts here: http://octopup.org/img/car/tires/Bridgestone-Firestone--2006--Replacement-Tire-Selection-Manual.pdf

On page B12 of the tables, you can look up the 215/50 17 XL spec: 215/50R17 (XL) Load Index 95. and read across to the 1134 lbs column. The pressure there is 29psi. So for this tire, and the Leaf's GVW, 29 psi is what the pressure "should" be, to maintain the correct contact patch across the tire. I'll likely run them at 36psi, which is the correct pressure for 1356 lbs of load per tire.

One of the ways we test tire pressures on the autocross track is to check temps across the tread area after each race. Too hot in the middle, you are overinflated. Higher temps at the shoulder means under inflation. You want consistent temps across the tread face.

If you run an OEM tire at max pressure, you'll likely find elevated temps mid tread, and your contact area will drop. You don't want this if you need to stop in a hurry...and it may have zero effect on range.

 

[SageBrush]

I run a little under sidewall maximum, but if your roads are littered with dangerous potholes I recommend ~ 3-5 psi lower.

 

[denwood]

Knight, thanks for the welcome I have read quite a few threads on this forum specifically with respect to tire pressure, wear etc. which actually led me to the Ecopia 433 Plus tires I always find owner opinions the best by folks actually putting miles on the tires and reporting back.

Manufacturers are well aware that folks often exceed GVW. Four "healthy eatin" boys in a LEAF is pretty much GVW..ha. They also know that tires heat up with highway use, and factor that in.

Here is the relevant snip from page B12 of the Bridgestone load tables: http://octopup.org/img/car/tires/Bridgestone-Firestone--2006--Replacement-Tire-Selection-Manual.pdf

Note that the highlighted row is for an Extra Load (XL) tire with a load rating of 95. The OEM Ecopia and Michelin Energy saver have lower load ratings, have a weaker sidewall, and have lower max pressure ratings vs the Ecopia 422 plus in 215/50 17" flavour. If you look at the chart, 40 psi on an XL tire with 95 load rating is the suggested inflation pressure for a tire supporting 1444lbs. That would be the 2018 Leaf with about 2275 extra weight onboard. Keep in mind that if you see different door placard pressures front/rear, this is a good indication of the weight distrtibution fore/aft in a car. The fact that the Leaf pressures are the same, reinforces the 50/50 weight split.

When you get into racing and deep dive into tire handling and performance, tire pressure becomes a handling tool to control understeer and oversteer, just like swaybar rates, springs etc. It always takes a few autocross races to dial in front/rear pressures to balance handling on the race tires. The Leaf is not a light car, and has a pretty stiff suspension, combined with low COG. This is predicatably pretty hard on tires with softer sidewalls, they will literaly roll over on a turn.

My whole point here is just to illustrate that when you put a non OEM tire on the car, it's worth educating yourself on why you might want to change inflation pressure from the door column sticker, and how to do this safely. Our roads here are pretty bad, so running the lowest pressure possible, while keeping temps/wear etc. balanced is the sweet spot. The load chart is a start. Temps using a tire pyrometer and chalking the tire (white band across the tread face) is a good way to play with pressures. On the track you can very much see oversteer/understeer changes as you play with pressures, but I would not try that with a 3500 lb Leaf..ha.

If you do go right to max (say 50 psi) the end result will be a scare if you're braking on the highway in wet conditions...as the overinflated contact patch will be centric biased, and you'll take a lot longer to stop. Cuz I'm a geek, I'll do some experiments with my brand new set of tires and let you know.

 

[DaveinOlyWA]

My first post here..go figure ...



If you run an OEM tire at max pressure, you'll likely find elevated temps mid tread, and your contact area will drop. You don't want this if you need to stop in a hurry...and it may have zero effect on range.

 

[denwood]

Dave, the information was provided in an attempt to add intelligent conversation to a very important topic. Sorry that this has offended you. If you had to choose between 20 ft less stopping distance in a panic, or an extra 0.5 % range, which would you pick?

Sage, yep our roads are pretty awful at this time of year particularly as we see -16 C to +10 C in a day. Wreaks havoc on the pavement.

 

[DaveinOlyWA]

Dave, the information was provided in an attempt to add intelligent conversation to a very important topic. Sorry that this has offended you. If you had to choose between 20 ft less stopping distance in a panic, or an extra 0.5 % range, which would you pick?

Sage, yep our roads are pretty awful at this time of year particularly as we see -16 C to +10 C in a day. Wreaks havoc on the pavement.

Your comments ignore basic physics AND the topic of discussion.

 

[denwood]

Dave, thanks for your insight and guidance. I defer to your superior intellect

Btw, from your blog, which is quite extensive and does have some good information, based on data gathering.

Others choose the maximum tire pressure listed on the sidewall; typically 44 PSI and this gives you the best tire life, the best range, and the least traction.

What I've posted is exactly consistent, with the caveat that running lower pressures will increase traction (safer) and that at some point, the range difference will not be material. I won't get into my credentials, cuz no one cares.

 

[frontrangeleaf]

Wow, Dave. Really?

Denwood, thanks for the thoughtful posts. I think your point that there is a pressure for a given tire under a given load that is optimal is well taken - more is not necessarily better, and there certainly IS a point of decreasing returns. No argument with any of that.

If all you're optimizing for is better range, then yes, more pressure is better. But yes there are trade-offs at some point, related to the shape of the tire patch and the impact of that on handling and braking. Plenty of physics there to reference, for those who care to geek out. Clearly running too low is not a good idea either, for lots of reasons.

As a practical matter, I can feel the already ridiculously light steering of our Leaf+ get even more squirrelly when I jack the pressures up above about 42# on the stock Energy Savers (not my favorite tire for lots of reasons, but they _are_ efficient...). I put this to the tire patch cross-section "rounding" due to excessive pressure for actual load. I've seen the same type of thing on our camper - I upgraded to higher load rated tires, but run them a bit below the actual spec in order to keep the camper from dancing around.

In my experience, I have seen a tendency across many manufacturers - just about all of them in fact - to lean toward softer pressures in the US market. I think that has to do with perceptions regarding market preferences - Americans have a reputation for better or for worse for preferring comfort over handling. Our road conditions are also pretty crappy in a lot of places. Having lived and worked in Germany for many years and seen how their cars are set up and spoken at length with them, there's definitely differences in the common notions around driving.

Question for Denwood: it's my understanding, notwithstanding the info on every tire made, that SL tires are load rated for 35psi, and XL tires are load rated for 42psi. I don't see that in your chart above though. I have that from a guy who worked in the tire industry, once upon a time. This would imply that the load rating does not rise above spec on an SL rated tire at pressures above 35psi. And also that you don't need to run max pressures to get there, despite what's molded into the sidewalls.

Thoughts?

Edit: Actually. nevermind, I do see it in the right most columns for each tire, you see the load given for 42-51psi for the XL tires and 35-51 psi for the SL tires. Confirmed.

 

[DaveinOlyWA]

Dave, thanks for your insight and guidance. I defer to your superior intellect

Btw, from your blog, which is quite extensive and does have some good information, based on data gathering.

Others choose the maximum tire pressure listed on the sidewall; typically 44 PSI and this gives you the best tire life, the best range, and the least traction.

What I've posted is exactly consistent, with the caveat that running lower pressures will increase traction (safer) and that at some point, the range difference will not be material. I won't get into my credentials, cuz no one cares.

I am not disputing your facts; only your contention that is what we are looking for in this thread. Everyone knows lower pressures increases traction as well as everyone knows lower pressures decreases range. Its basic physics. The more the tire flexes, the more energy is put to the air within the tire and not in maintaining forward momentum.

So yeah, your facts are accurate but not pertinent to the discussion. As far as safety? Any reduction in stopping distance can easily be overcome by simply obeying safe following distances which are waaay overboard erring on the safe side.

But we now have less time, more to do, and farther to go to get there so we don't follow the guidelines. We also have ABS (something not considered when guidelines were set) on our side so we take the risks and guess what? Still have thousands of accidents anyway because taking a little risk encourages us to take bigger risks.

Another drawback on the above our overreliance on the "Greg Abbott" rules of logic to prioritize our day ignoring the low tire pressures for days, weeks or even months thinking in 15 minutes, the tires will have heated up enough to put me back into the safe range then 6 months later we cry because our tires didn't reach 50% of their rated mileage or while sitting on the side of the road cause our tire had a blowout on a pothole successfully navigated by 400 people before us.

 

[denwood]

Front, thanks for your thoughful reply

Every manufacturer will have different (but similar) load charts for their passenger, commercial, trailer etc. tires.

This is the one I quoted for Bridgestone: http://octopup.org/img/car/tires/Bridgestone-Firestone--2006--Replacement-Tire-Selection-Manual.pdf

You can see in Bridgestone's passenger charts that many of their XL tires are rated to 50 psi...but note D at the bottom of each page adds some detail.

What's the downside of overinflation with respect to pressure? If you look at this test: http://article.sapub.org/10.5923.j.ijtte.20130202.01.html
we can see that the stopping distance went up 17% when they increased tire pressure 20% beyond the OEM listed recommendation. If you look at C/D stopping distance for the 2018 Leaf, you get 191 feet from 70-0. The French test was only testing a stop from 30mph. If you extrapolate, taking a Leaf's tire pressures from 36psi to 43psi, you end up with an extra 33 feet in a stop from 70mph..and it's likely more than that. 33 feet more (224 ft) in a panic stop under dry conditions is something to think about.

The whole point of my comments are this: Max'ing the sidewall pressure in your leaf (particularly with a 50psi XL rated tire) is not the best combination of safety and range. I should say that I nearly always exceed placard pressures myself, (on all of our vehicles) but never to the max, and always with an eye to the best compromise between safety, wear etc. I support several tire shops here locally, and I'm honestly not sure how many of the tire guys are aware of load tables..ha. The commercial guys, different story as they are working on semi trucks.

Given the Leaf's combination of weight and low COG, (and based on what I saw on the outgoing Michelins) you definitely want a stiff sidewall and some elevated pressure. I'd even say add .5 degree of negative camber, but of course you need aftermarket strut bolts for that...

 

[frontrangeleaf]

Denwood, I've referenced tire load charts before, specifically when choosing uprated tires for the camper. It came with tires rated just 20# (not percent!) over the load limit of the axle, which I wasn't happy about.... so if I have the load a little high on one side, I could overload that tire, especially if pressures fall even a pound or two under spec. Not my idea of safe, but it's legal, so that's what the RV industry does.

I needed a higher rated tire so I could gain some load capacity at a slightly higher pressure, even if I didn't need to go all the way to spec. I run about 58 psi on a load C tire rated at 65 psi. Still gets me 200# of cushion, instead of 20.

And yeah, I care about braking distance. (Duh. Doesn't mean I tailgate anyone either.)

Priorities on this board tend to be a bit different though. Understandably. Especially for all those driving older Leafs with really short range relative to what they're trying to do.

 

[denwood]

Front, sounds like you know your stuff I'm all about efficiency with the the Leaf. I've been itching for an EV for a decade now and finally bit the bullet a few months ago.

I'll be throwing it up on the hoist, pulling panels/liners and doing some corrosion control application during the snow tire/rim to summer changeover. I'll post pics

I always try to post back in areas where I've harvesting information This forum is the goto for Leaf owners for sure.

 

[frontrangeleaf]

I've learned a lot on this board, among others. Lots of really knowledgable people here.

Good crowd in general. Some discussions get a bit more lively than necessary. Comes with the territory I guess.

 

[LeftieBiker]

If you extrapolate...

That isn't sufficient, weighed against the collective experience here. I agree that exceeding the max load pressure isn't wise, but if you are going to argue that Nissan's terrible 36psi recommendation (now a slightly better 38psi on Gen II Leafs) should be followed, you need to provide more real world data. FWIW, I recommend 40-42psi in Summer and a bit less in Winter, as long as it will be checked regularly. I'm considered a bit conservative in that regard.

 

[denwood]

Lefty, I'm not suggesting you stick with 36psi. I'm just highlighting the point that going to max rated pressure is not necessarily a good idea either. There will be a pressure beyond which you won't see much rolling resistance improvement, but you will see less traction. Every tire will have a different sweet spot.

It's also obvious that a tire with a 95 load rating is a better fit for the Leaf. Low COG combined with high mass is a pretty good recipe for shoulder roll on a tire with weaker sidewall construction. I'm on studded 16" winters right now so rolling resistance is pretty much a non-issue..ha. I'm running those at about 39 psi knowing that at -30 C they are dropping a few psi.

 

[GerryAZ]

Personally, I disagree with the general statement that stopping distance is increased with higher tire pressures. My experience with 3 different LEAFs (all heavy cars) is that wet stopping distance (at least with better quality tires) is improved with higher pressures than the 36 psi recommended by Nissan. I believe this is due to tire distortion (contact patch distortion and tread grooves closing) under braking loads. In my climate, with all of the tires I have used on the LEAFs except the OEM 17-inch Michelins, the stopping distance is significantly reduced on wet pavement with 44 psi compared to 36 psi. It is true that braking traction is generally reduced with higher tire pressures on a lighter weight car. Both wet and dry braking distance with the OEM Michelins were so bad that pressure changes did not help so I replaced them with much better tires.

Note, the door placard on my 2019 SL Plus recommends 36 psi which is the same as recommended for my 2015 SL. They both came from the factory with 215/50 R17 Michelin Energy Saver A/S tires and the 2019 is considerably heavier because it has a larger battery pack. This indicates to me that Nissan did not really consider the weight in determining the recommended inflation pressure.

 

[denwood]

Gerry, my guess is that very few folks have done track testing with panic stops in the wet from 70 mph. I have, but certainly not in a Leaf.

Your 2019 Plus is about 300lbs heavier than a 2015, so about 75lbs per tire more. If you look at the load table for that tire, you'll see that weight range is within the same window..hence the same PSI. Check page B12 on that table I linked to. 36 PSI is the suggestion for a 91 load index 215/50 17" tire, carrying ~1350 lbs ... keeping in mind that the table is from Bridgestone.

Four x 1350 is 5400lbs. Your Leaf GVW is around 4800lbs, so based on the load table and a "fully loaded" Leaf, you're safe at 36 psi, and I'm pretty sure Nissan's OEM placard is not leading you into danger.

To illustrate how much tire pressure affects grip, I'd offer that I would normally tune on the autocross track to 2 psi. Need some trailing throttle oversteer? Add a few psi pressure to rear. Understeer in corners? Reduce front pressure. Grip and pressure are very much related so that once you go over the "recommended" pressure for an application, you're almost always losing grip. The reason some cars have different front/rear inflation pressures is precisely to maintain the correct contact patch given the weight on each axle on a car that does not have 50/50 weight distribution. So you can mess with under/over steer by tweaking on those for the track when fine adjustments are needed.

If you take a close look at the load table charts you'll see notes:

NOTE B: Some European Metric tires may be branded with a maximum inflation pressure of 32, 36, 44 or 51 psi for high speed and handling optimization. However, there is no load increase above 36 psi.
NOTE C: Some P-Metric Extra Load tires may be branded with a maximum inflation pressure of 41 or 50 psi for high speed and handling optimization. However, there is no load increase above 41 psi.
NOTE D: Some European Metric Extra Load tires may be branded with a maximum inflation pressure of 42 or 51 psi for high speed and handling optimization. However, there is no load increase above 42 psi.

In Note B (specific to your tire size and load rating) Bridgestone is basically saying that the tire pressure on a 91 Load Index tire is at max load at 36 psi. You can also see that there is some room there for OEM engineers to go higher for the same reason folks here like bumping pressures...ride/handling etc. To my mind, the Michelin is good choice for rolling resistance but has a pretty weak side wall..hence the accelerated shoulder wear on cornering.