Is 42/40 trading tire life for MPG?

After 6k miles this is not visible on my OEM tires (Integras).

 

I tried 42F/40R last October to see if it made such a big difference. As far as city commuting at speeds 70 km/h and under, no difference in fuel consumption.

On the Trans Canada at cruise controlled speeds of 100 km/h up to 110 km/h, the higher pressure resulted in 5.1 litres per 100km. With factory spec pressure, 5.3 litres per 100km. Around a 2 MPG difference. This was under similar conditions of road surface, ambient temperature, and wind.

The much higher pressure resulted in a *much* harsher ride. If you ever get a chance to drive on Winnipeg city streets, especially the Perimeter and Bishop Grandin, you'll immediately know what I'm talking about. I've had folks from NYC comment on our streets "Oh just like back home ..." so *that* can't be good!

 

My experience is with the Classic Prius that weighs a few hundred pounds less and comes with 175/65R14 tires. Yours would be 185/65R15.

For both the original tires and a replacement set I bought, I repeatedly measured tread depth across the tire at different inflation pressures. My goal was to find inflation pressures that gave even wear across the tread. Pressures very close to the often-quoted 42/40 do in fact provide this.

The disclaimers are to never inflate above the max. cold value printed on the tire sidewall, and never below the manufacturer's spec. Between those values, you are free to select a best compromise, as far as I'm concerned.

My original Bridgestone Potenzas were not yet fully worn when I removed them after 33k miles, and this was good service life for those tires. Now I have about 40k on Goodyear Allegras and they are not done yet.

Theoretically, the belt design of radial tires is supposed to prevent high center wear even under max inflation. In any case, edge wear at lower pressures is FAR more common, as you might see at any gathering of Prius cars.

 

DAS:

I've noticed edge wear on many front drive cars. Just the fact of life if you accelerate, corner, and stop on the same tires, especially in city traffic.

 

The ride is much harsher with a higher pressure. Vehicle manufacturers usually err on the side of lower pressure in their tires so that the ride is soft and comfortable. Consider that factory recommended tire pressures are usually just on the very bottom end of what keeps the surface of the tire flat against the road. Increasing your pressure to 40/38 or 42/40 shouldn't cause any meaningful misshapening of the tire, and should actually offer better tread life because the footprint against the road will be more positive. I found 42/40 to be very harsh. 40/38 is about all I can stand, however it gave me instant fuel economy gains regardless of the type of driving I was doing.

 

Short answer: NO

In fact, on my Classic Prius I was able to prove the opposite. Tire life was actually extended.

On my HSD Prius using premium grade tires, it's a pretty safe bet that they are built so well shape is retained all the way up to the max PSI... which is actually what I'm using. 14,000 miles into them at 44/42 PSI, the wear is even all the way across the surface of the tire.

 

John's right. (Of course.)

Manufacturers often give tire inflation pressures that result in a slightly underinflated tire. This results in a more comfortable ride, but (depending on the degree of underinflation) can result in premature edge wear.

Anyone remember the Ford Exploder (erm, Explorer) fiasco? Tires in a high percentage of vehicles were blowing out at speed. It wasn't the tire, per se, but the grossly underinflated pressure that Ford felt compelled to push in order to make the ride in that vehicle bearable. This is an extreme example.

The Integrity tires are rated at 44 PSI. They really shouldn't balloon at 42.

 

Can you point me to the thread saying you could trade your OEM tires for other Goodyear tires within 500 miles, or am I misinterpeting your post?
A search came up with nothing. Thanks!

 

my brother did tires for a living and recommended unofficially that 5-10 psi above recommended would extend tire life without uneven wear and no safety issues. in fact, most tires will inflate up 20% beyond their max pressure without issues under most conditions that do not involve max loading.

 

The OEM tires on my '04 say max press is 44 psi. I always run them at 44, but sometimes 46, (I always go 2 lbs lighter in the back tires due to less vehicle weight on the back axle). My tread wear is almost perfectly flat after 33,000 miles, with a little more edge wear (underinflation) than center wear. I generally rotate at 5,000, but I missed 2 rotations during the winter due to not enjoying handling metal tools in the cold.

After many years of driving (over 400,000 miles), I have found that following tire manufacturer max pressure ratings always results in too much edge wear and short tire life due to underinflation.

As far as safety, the manufacturer is NOT going to tell you to use the highest safe pressure. They have to have a safety factor. Though I personally would not feel safe going more than 2 or 3 pounds over since I don't know what the factor is. It also seems to reason that if the tread is flat on the pavement, you get better grip and better water channeling in wet weather than if the tire was under or over inflated.

The ride does get a little harsh, but not as bad as low profile tires.

Time for conspiracy theory - Tire companies wants to sell more tires. So they recommend low pressures for nice ride and short life so you can buy them again sooner.

 

CP Waites...I had my tires at 32/32(upon recommendation from a service manager), then upon a recommendation from one of the Prius owners on priuschat, I inflated them to 42/40. When I brought my vehicle to Discount Tire to inquire about changing out the Integritys to the Triple Tread Assurance or Michelin HydroEdge, they checked my pressure in the tires and told me that the PSI was extremely high and should be back down to 35/33. I do prefer the 32/32 setting because of the softer ride but you have to remember that typically down south(Houston area), you do not want to inflate too much because summer is coming and this will increase your PSI setting. I'm not sure what setting I will stick to but I know it will not be 42/40. I may just average 35/35. Regarding the size of the tire, the Goodyear Triple Tread line starts at size 195/65/15. As long as the height is the same as the original, the 195 should be ok. Any ideas?

 

Craig0812----- I put on triple treads at 1300 mi after slipping around in 2 snow storms. the oem tires had 40/30 from the dealer. I ran 42/40 on the TT's until the frost heaves and pot holes of the past 2 weeks jarred my teeth too much! Just lowering them to 40/38 made a big difference in the jolts to the car, and milage seems not to be affected. TT's are great tires in snow and rain from my experience, and they cut down on the high speed jittery steering also ( tracks more steady) hope this helps

 

Its not so much tire life you trade, it's traction and mileage. Lower tire pressure increases traction and reduces mileage. In the snow, I think I might lower mine to 32/34. The rest of the year, I want the milage, so I've got it at 42/40. If this reduces tire life by 5 or 10%, who cares. According everyone here, my factory tires are crap anyways! Though I've had no complaints with them, I suppose I might find them to be bad next winter when they aren't brand new.

 

Actually I think 42/40 is a win win situation, better mileage(tire life) and better mpg. I notice improved wear since I got new tires and keep them at 42/40. Also my Prius tech said the reason my original tires wore out prematurly was because the tire press. I was running was too low. He said to keep them at 42/40

 

To each his own, I guess. 42/40 was too harsh for me. With the prevalence of expansion joints in streets and freeways. I started to notice rattles and it was just damn annoying.

 

Tell me about it. On the roads in and around Winnipeg, you would shake the car to pieces.

However, I think the "efficiency" gains are really overblown. With both the OEM Goodyear Integrity and Michelin Harmony inflated to 44F/42R, I gained around 2 MPG Imperial gallon. Not worth the much harsher ride.

My 1990 4Runner came with 31 x 10.5R 15 tires. If I recall, the recommended inflation was around 26 lbs. Never had any unusual wear.

 

There seems to be some difference in factory fitted tyres.

We don't have any options on wheel size here, so my car was delivered with 195/60 R15 88V - Michelin Energy.

I am not really a tyre kind of guy and in light of some of the posted comments, I am not sure if these are good, average or bad.