max oem tire pressure

I ran 44/42 with my Allegras on my Classic Prius. Then the same on the OEMs from the HSD Prius. And continued on with it when later switching to HydroEdges.

Max Cold PSI is no big deal. Tires nowadays hold there shape wonderfully at the highest stated pressure.

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I used 49/47psi for a 3000 mile roadtrip which resulted in 50MPG for 30 degree temps and 55MPG for 50+ degree temps. Total trip average was 52.7MPG. Speeds ranged from 65-80mph (71mph avg). After the trip I deflated to the usual 44/42. I am sure it helped with my fuel economy, but not by much. Most of the improvement comes from getting the psi out of the 30's.

 

My Sumitomo are rated at 51 psi and I run that pressure all the time without a problem. I'm getting excellent mileage and it corners like it is on rails.

Bob Wilson

 

I know of some that have run 60+.

 

Ah! The cult of the high tire pressures to get a couple more mpg and a stiff ride.

Lets see now, the Toyota engineers were smart enough to design a very complicated and efficient car. Remember, the main goal for them was to design a fuel efficient car, and that includes the tire pressures. But from what I read on this forum, they were totally stupid when, after running hundreds of hours of tests of tires at various pressures, they decided to "arbitrarily" recommend 35 and 33 psi for the Prius. Come on now, folks, there is a lot of wrongheaded thinking going around. Sure, you want the best gas mileage, but there are other things to consider that the Toyota engineers probably figured in. For example, the extra wear and detuning effects on the suspension components and the rest of the car. As a fellow engineer, I resent the second-quessing by many untrained people in this matter. If the tire pressures are so totally wrong, the rest of the car must also be quite poorly designed and therefore you should not have bought it.

 

This is a question, I suppose, but I put the tire pressure at 42/40after reading comments on this board. Since then I have had two flats in two months, which according to my "tire guy" were caused by rocks (I drive on lots of marginal dirt roads).

However, two other cars "in the family" driving much the same roads with Kumho tires at 30/30 and 28/28 have had no flats in the past couple of years.

So, is it possible that higher pressures make the tire more likely to have flats on gravel. Or is the Goodyear Integrity just a "less better tire?"

 

The tire pressures are usually specified by the tire manufacturer. The tires shipped with the car are usually chosen at "the last minute", to get the best price. So the pressure is usually specified from a table, tested quickly, and set in stone. Often incorrectly!

Do not run more than the max pressure on the sidewall. A tire engineer warned me (and anyone else who would listen) that with "too much" pressure in the tire, you could damage it internally if you hit at speed an abrupt road transition, such as a pothole. Being an engineer, he works on the safe side, so recommended pressures below the max rating on the sidewall.

If you go to a tire store and look at the max pressure ratings on the sidewalls of actual tires, you will note the better quality tires have higher numbers than the poor quality tires. The Goodyear Integrity is a low cost tire, so consider it a "poorer quality" one. For example, it is rated at 44 PSI max, while the same size Nokian WR is rated at 54 PSI max.

I run a nice conservative 40 PSI front, 38 PSI rear, with Nokian WR tires in the 15" stock size.

 

No, tire pressures are set by the auto manufacturer to achieve the desired sidewall spring rates and rebound rates.

This is the basis for the suits against Ford in the Bronco roll-overs of some years ago. They specified an unsafely low tire pressure to avoid re-engineering the suspension to gain desired ride qualities.

The tire manufacturer certifies maximum tire pressures and load ratings.

 

As another poster commented, it may not be wise to second guess the excellent engineers at the factory. Low pressure causes tires to fail of course, but to set the max sidewall pressure cold, then run on a hot road on a hot day may result in disaster. I run 35/33 exactly and have no mpg complaints. Usually right at 51-52 mixed driving lots of stop and go. I still don't like the rather harsh ride even at 35/33. 35 psi is not a low tire pressure IMO. I also believe extreme pressures cause more impact stress to the suspension parts. But to each his own.

 

Toyota designers, manufacturing staff and sales staff had to reach various standards and, as in any successful business venture, had to make numerous compromises. I have known no car owner who is completely happy with every feature of his purchase, regardless of the price paid. The end product has satisfied nearly all Prius buyers - Toyota has succeeded.

I drive very conservatively, on the original tires, and opt for the common 42, 40 balance, largely to avoid the faster wear at outside treads, but also to lessen drift during tight turns at aggressive speeds, and to gain about 1 m.p.g. When I measure tread depth at each 5,000 mile (self)service I find very uniform wear (average .003"/1,000 mi.), at 10,000 mi. intervals (to balance slight wear differences between fronts and rears after rotation).

Technical discussions on this site by owners who sound like knowledgeable engineers provide overwhelming opinions and statistics, often at variance with "common knowledge," and occasionally among themselves. The best advice probably comes from the posts that offer the least opinion and the greatest documentation.

 

Toyota Engineers are smart people... the only issue that you need to be aware of is that when car manufacturers set the tire pressure or other maintenance type specifications - it has to be conservative enough to accommodate essentially 100% of the car users. (Could they really afford to have say a 1% failure rate because they pushed the technical limit of any part of the car...?) So, the pressure recommended is a set of compromises that works essentially in all situations.

Now, in your personal case, you might be able to set tires at a higher level without negative effects. For example, the roads your on are in excellent condition and are smooth... In that case you can take advantage of the technical capabilities of the tires without any adverse consequences.

In summary, the engineers are not deficient, it is just that they have a different objective and are working under a different set of assumptions than you or I might be.

 

Ah, the usual can of worms. I'll merely point out that tire
bursting strength is in the neighborhood of 200.
.
_H*

 

While I agree the engineers at Toyota are Smart, there is no magical perfect pressure setting for the tires. It is alwas a compromise. I have tried up to 44psi per tire and the ride is much harsher than down at 35psi. It is just a personal preference as to what tire pressure you want to run at. 42/40 is not wrong, and no engineer will roll over in his grave if you dont run an the pressure printed on the door.

I have a friend with an Audi. On the door panel it has a variety of tire pressures for front and rear. It has one pair of pressures for 1-2 passengers, another for 4 passengers, and another pair of higher pressures for sporty driving. I think that highlights the fact that any single pair of tire pressures is a trade off.

 

Max tire pressures as listed on the tire relate to the tire being under maximum load, not just the max pressure you can run in the tire under any circumstances. I use the "dust" test. If you drive through some light dust, look at the tread and see if the entire tread is gripping the pavement. If it isn't, then more wear will happen on the center tread of the tire and less traction will be the result. The engineering goal is for all the tread to engage the pavement.

 

Amen, brother!!!!! :rockon: I would add that emergency handling would be degraded significantly, too.

 

I think it is going to depend on the tire and vehicle in questyion. A blanket statement like that does not apply in all cases.

Many autocross enthusiasts pump up tire pressure to the sidewall max or higher depending on how the tire is wearing on a particular day. I've yet to see one run significantly lower pressure. Low tire pressure generally harms handling.

Keep in mind that nearly all specs on a mass produced vehicle are going to be subject to comprimises. I highly doubt engineers have the final say.

 

Could you explain the disaster scenario?

 

Remember that the Toyota recommended pressure was for a specific brand of tire, the one that it is sold with, and not for other tires. The door pressure is specific to one make and model and really has application for warranty coverage. Once the tire brand and model is changed, Toyota warranty coverage is done. You are the owner of the car and should manage it based upon your best understanding of what works.

Before going with high pressure, I read a couple of reports:

• radial tires have less deformation at high pressure - one source pointed out that the steel belt does not deform in the center like the old cross belted tires. I have run my Sumitomo T4s at 50 psi for ~30k miles and there is no evidence of center wear.
• higher pressure tires have slightly better stopping characteristics - from a USA government study, this report indicated that tire stopping performance for over inflation was better or equal to placard pressure. But I'll have to hunt around to find it again.

Since then, I've been running hard tires and my car handles like it is on rails. I have no problem in wet weather and take turns very well. The earlier Mastercraft tires had evidence of edge wear and that isn't the case with my current tires. Other than the slightly harder ride, I can't find any negatives.

Using Google, here is what I've found:

"Over-inflation can be a problem too. An over-inflated tire rides on just the centre portion of the tread. The smaller contact area means reduced grip on the road, leading to a harsh ride, handling issues (such as steering and stopping problems) and increased wear on tires and suspension components. Seventeen per cent (17%) of vehicles in Canada have at least one tire that is over-inflated by 20%." Rubber Association - Proper Tire Inflation

". . . A tire also acts as a spring between the rim and the road. This spring characteristic is very important to the vehicle's ride. Too high an inflation pressure causes the tire to transmit shock loads to the suspension and reduces a tire's ability to withstand road impacts. . . ."
Dunlop Tires | Care & Maintenance | Proper Inflation

". . . So, what is overinflation? On "P-series" tires, we've experimented with cold pressures in the 40-to-45-psi range on law-enforcement Crown Vics and Caprices and haven't seen a huge downside in terms of handling or performance. At higher pressures, tire stability is improved, as is resistance to heat build up. The ride quality suffers a bit, with the stiffer sidewalls stiffening the ride noticeably. Will the tire wear faster overinflated? Perhaps, but only along the center ribs if at all.
We've even tried inflation pressures above 50 psi, and found that gross overinflation caused the tire to skip or chatter across the pavement during extreme cornering.
Our experiences during law-enforcement training confirmed that pressures in the 40-to-45-psi range worked quite well on these 4,500-plus pound squad cars.

. . .

So, as you can tell, we haven't found a safety issue with inflation pressures above the carmaker's recommendation. And that's confirmed by the tire inflation information found on every tire's sidewall. In a nutshell, this information indicates the pressure at which the tire will support its maximum load. For "P-series" tires, this is 35 psi, 44 psi or 51 psi for standard load tires.
Thus, to answer your specific question, I do not think passenger car tires are overinflated until pressures exceed 40 to 50 psi, depending on the tire and vehicle. I believe inflation pressures in the 32-to-35 psi range, which might be above the carmaker's recommendations for that vehicle, will improve braking and handling to some degree, provide a somewhat better margin of safety in terms of heat buildup, and will not significantly shorten tire life because of accelerated wear. . . .

"
Pumping up tire inflation has benefits
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I rotate my tires twice a year and get the tread depth. So far, there is no evidence of edge or center wear and last fall they were down to 7/32 from a starting 10/32. If there is ever any evidence of center wear, I'll reduce the pressure but the numbers indicate my Sumitomos are wearing equally, across all treads, and the handling is excellent.

If I were using the OEM tires, I would run what Toyota recommends until the warranty is over. After warranty, it is my car and I'll run it the way the numbers on the tread depth, and my handling indicates works best. I prefer to believe 'my lying eyes.'



Bob Wilson