Your tire pressure

Would you be unhappy if I put up your question as a poll?

Bob Wilson

 

I was just going to post a question about this myself. I'm now confused!

My door and manual say to use 35 front 33 rear. But I've read numerous times on this board that people are using 44, 42, 40psi. I'm about to return home from the holidays and wanted to see if I get a difference in mileage after inflating the tires some more.

I had read a thread that had something about where someone was looking at the "bead seal" pressure, whatever that is and I cannot find it again. Also, a search for "tire pressure" didn't even bring up this thread and didn't find any threads that looked like the ones I had read before about this.

My tires are the Yokohama Avids, P195/65R15. I can barely read what it says on the tire, and of course now I can't remember, but I think it said something like max 40psi with a full load?

Can anyone help me determine what is a safe pressure for me to fill to before I take off on my 350 mile drive home?

Thanks.

EDIT: Found the thread I was looking for, this may help:
http://priuschat.com/forums/gen-iii.../63266-2010-tire-pressures-yokohama-15-a.html

 

Bit the bullet and went with 42/40 for my drive back. Interested to see how it affects my mileage. Will report back.

UPDATE: According to the car I got about 2.5 more mpg on the trip home (380 mi) but there were other variables as well so it was not a controlled experiment.

 

I have Toyo tires delivered with 30-32psi. Inflated to 45psi today.

 

You guys (girls?) are NUTS to be over-inflating your tires past the posted limits. You should do some research on high speed tire explosions .... many are DEADLY. My Yoko's are 35fnt & 33rear - I would consider a couple of pounds higher, but no way at or near the 40psi max on the tire. Each to their own. Bart in CA

 

The one thing we agree on is "to each their own". It'll be interesting to see how long our tires last.

 

Examples? How often does this happen compared to underflated tires that overheat and fail, too often with deadly results?

I don't go over 'posted limits', but did find that my Honda's placard pressure was dangerously low for the Pacific Northwet, where having wet roads half the year causes a significant risk of hydroplaning.

 

*edit* duplicate posts

 

I've researched it and I think you are over-reacting unless you are talking about sustained high speed of 100mph+.

Under-inflation has proven to be much more deadly than over-inflation within limits. I've had no problems with tire wear or excessive heat running as high as 60psi at times. Do some searches on the subject in this forum. We've gone over it many times and you may find some of the results interesting.

 

I'd take what this guy says very seriously. A tyre blow out is not a nice experience - if you're lucky enough to survive it!

I hear some Hyper-milers pump their tyres right up and they probably get away with it for a little while, but you certainly do not want to pump your tyres right up to near their max and then drive at 80mph with a loaded car.

It's asking for trouble

 

I've been running 38/36 to 40/38 F/R. I don't have enough data to conclusively say what the mileage improvement is--as others have said, too many other variables (T, speed, roads, wind, etc). I think you'd seriously have to go waaaay above the placard suggestion to approach 'dangerous' limits. I personally don't want to go higher than I do because the city roads where I live are so cr*ppy they'll jar the teeth out of my mouth.

FWIW, where I work we have a motor pool, and I've gotten into the habit of checking the TP before I take a fleet car out. They usually are 5-10 psi below recommended, and I either inflate them to spec or take my own car. I'd bet the vast majority of tires out there on public roads are similarly *under*inflated and pose a far greater hazard from flexing/overheating/kablooey than does going a few psi over the little sign on the door. Just my thoughts.
T

 

Perhaps a few observations about tire pressure might help.

ROLLING DRAG

Over the years, I've collected these two graphs from various sources:

Also,


The non-linear reduction in drag indicates that at the highest pressures, there is a smaller rate of drag increase per unit of lost pressure. So I top off my tires to maximum sidewall pressure and don't worry about it for a couple of months.

SPEED



There is a non-linear increase in tire rolling drag that happens at higher speeds. Now tires can be designed to minimize this effect so it really needs to be measured on a case-by-case basis. Still this adds to the aerodynamic drag ... speed kills mileage.

TREAD TEMPERATURE



Lower tire pressure causes the tires to flex more and this leads to heat. These series of charts were done using an IR temperature reader as part of a study to look at wheel alignment versus tire wear and temperature. Obviously a lower tire pressure leads to more heat. For our metric friends, the normal tire pressure on the door jam is 32-35 psi. These Sumitomos are rated at 51 psi, maximum sidewall.

BTW, tire load capacity increases with pressure. It is one of the reasons why trucks run such high pressures.

WHEEL ALIGNMENT


The last bit comes from tire wear, the tread depth, on tires that had significant service. In this case, approaching 50,000 miles. I knew the camber needed correcting as well as rear wheel camber and toe. That led to this solution for rear wheel alignment:

The front wheel required a different camber bolt.

Bob Wilson

 

I sure do agree. The new installation procedure for seating the bead of the tire is to inflate @ 30psi. We use to bring the pressure up to 50 psi and it would make a big pop. NOW MORE OF THAT>
One should never over inflate the the recommended MFG tire inflation stamped on the side wall.

Under inflation is very bad aslo. I have seen many a tire ruined. Then one complains about the replacement price?

If you keep the tire inflation, rotations and rebalance in check, you will get long tire life.

Most important is one does not take any short cut in replacing the tires. Size and Speed Rating is paramount. The speed rating like S, T. H, V etc. is related to tire construction. It has a direct effect on braking distance, handeling. Lower your speed rating and is asking for touble. Don't try to save a few $ and risk an accident.

My V came with Michelins Pilot P 215/45/17 MXM V4 93V

They are great performing tires. Replacement cost $1060. ($260.00 each)

 

One can choose replacement tires with higher maximum sidewall pressure. Sumitomo is not the only option:


Bob Wilson