Well, it's been long enough since I last posted or even dipped into the forum, that it had forgotten / expired my cookies and logged me out. But I hopped back in to relate a somewhat hairy story from last month, involving a somewhat "interesting" tire puncture and the ability to get out of a dangerous situation quickly because of having a spare wheel on board. http://techno-fandom.org/~hobbit/cars/ev/fl22saga/ The Modern Spare paid for itself that day. 1500+ miles each way, camping/boondocking in the car on overnights, mostly EA charging but the occasional EVGo or Chargepoint. I've got a bunch of CCS locations mapped as waypoints in my Open Streetmap app on the tablet, so I don't have to be on the net as I navigate my way in to where they are. Planning legs of about 150 miles straight-line works out well, leaving enough safety margin for an 80% charge to get there. If anything the trip logistics are more relaxing than when I used to do it in the Prius, where I'd be at a given fuel stop for almost as long! Now I arrive, plug in, and *then* do all the other stuff needed. _H*
Good read. What tire pressure were/are you running on the stock tires, 51psi? (and i will admit to a certain amount of curiosity about your feet)
I generally run substantially over sidewall, like I did in the Prius, so they were probably up around 60. That wouldn't have made any difference in this case, though. The replacement now-oddball tire is a 44psi sidewall, somewhat annoyingly, but it'll be fine above 50, so all 4 will still show maxed out on the TPMS display. And, I don't do shoes... _H*
One question here, why do you put your tires above max pressure prescribed by the tire manufacturer? What is your rationale here? I know that tires can be put in high range of pressure for example for cars in long term storage, to avoid them becoming square-ish. But for every day driving, I would like to understand why.
Better energy efficiency (Miles/KWH) in this case. Radial tires do not become as much roundish resulting in excess wear in the middle when overinflated like older non radials did. So those overinflating while keeping it under maximum pressure specified on tire is OK. Ride does get harder a bit with higher pressure.
I tend to do mild over inflation - going approx 10% above pressure marked on the car sticker. But to go above the max load max pressure which is marked on the tire is something completely different.
As the hypermiler community is always fond of pointing out, the bursting strength of a modern car tire is somewhere around 200 - 300 psi. Going mildly over sidewall leads to better tracking, significantly less squirming and rolling resistance, and dead-*even* wear across the width of the tread as opposed to the edge wear more commonly seen. Consider: I put my tires at 36, 44, whatever PSI on a cold winter morning in the Northeast, and then drive to Florida and arrive into 90-degree weather a couple of days later. With my base pressure now higher, I go over a bunch of nasty bumps on a backroad. The tires are probably experiencing pressure peaks close to triple digits, never mind where and when I started.. They're fine with it. Punctures from sharp objects are completely orthogonal to this. 4.1 average miles/kWh for the trip, at interstate speeds, also speaks volumes. _H*
I understand that there are safety margins built into tires regarding burst pressure, but other performance components of the tire might suck at elevated pressure. One of the worst is longer braking distance. And when you add that EVs are much heavier than fossil counterparts and all-ready have longer braking distances due to weight factors, bad things tend to compound. Having a Kona EV on stock Nexens dramatically over-inflated is not a best combination for emergency braking situations. Getting killed due to few kWh of electricity is not worth it. Interesting academic article with tests, under-inflation and over-inflation compared for braking distance, it the article "only" -20% and +20% was tested: http://article.sapub.org/10.5923.j.ijtte.20130202.01.html
