Tire pressure question

In my carrer I performed hundreds of mpg tests against various tires and pressures. Don't remember a single incident where greater pressure up to the point of too little trasction to be safe did not result in greater mpg's on level ground. These were caefuklly measure with calibrated fuel supplies. So increasing tire pressure up to a point ius better foir mpg's no matter whether in low speed, many stops city conditions or high spoeed interstates.
OEM rfecommendedc pressures are mainly for comfort, not performance. We find here about 40m psig frot and 36 rear yield good economy and long wear and reasonable comfot. We did try 50 psig and thouigh I woud us that for an economy run its a bit rough riding normally and a bit less cornering power as well.
If you're 37 psig is a bit rough drop back to 34 or 35 psig and see. There is no 'magic' pressure; only each driver can find the magic pressure fior himself.

 

NOOO, the Goodyear tires states 51 psig MAXIMUM, not the pressure to use on the sreet, just the maximum pressure to meet tire engineered specs. And yes my Vette runs pessures from35 to 40 psig depending on the street or track I'm on. And I'm pretty sure the maximum pressure in those tires are 45 psig or more

 

The tire company knows tires, Car company's want smooth rides and good handling. Going above 40 psi will decrease ride quality and handling. But you will see a great increase in MPG. I am running 40psi and saving the Gas Money. I bought the car to save gas money. If I wanted a good riding car I would have bought a Cadillac. Just make sure you allow for temp heat up and don't get crazy, Hard tires don't stop for crap. DRIVE SAFE !

 

I disagree that higher psig deters handling; the truth based on tens of thousands of race track miles with showroom stock vehicles is increasing pressure up to 10 psig over the OEM recommendationwill improve handling and mpg because the tire contact is slightly decreased on stright ahead but because with higher pressure the sidewall is stiffened there is an increase as the tire tread contact area and the crcumference is stiffened as well. As the tead 'rolls under on side loads the tire contact area increases and thus the contacxt patch is better.That help both cornering and mpg. Less pressure lets the insided edge lift from the road, thus decreasing tread contact area and cornering power.
Of course if you overdo it in the quest for better mpg when crnering ability is decidededly reduced there is a penalty in cornering ability. Its called drifting.
cheers.

 

Wow, I hadn't thought of that aspect of high tire pressure vs. contact area before. I like unlearning wrong ideas like that.

When I had my SUV, my tires stated 33 psi recommended, 44 max, and I usually aimed for 37 all around. If I pushed 39, I got 27-30 mpg on the highway, and on those real cold icy mornings, the tires would flatten out to the sweet spot between friction and minimal drag.

With my c, front/rear recommended of 35/33, same max, I've definitely noticed rolling resistance when I used the recommended value. I just increased the tire pressures to 40/38, and the resistance has gone down enough for me to have longer EV glides. I have no idea how much higher my fuel economy will actually be, but with the summer heat finally coming to the northeast I bet it'll improve.

 

Very useful information. There is one thing that bugs me with this pressure business. I have been using three different air pressure gauges, the dial type (analog) at the end of the compressor hose, a plunger type (analog) with a graduated stick that goes up with the pressure and finally, a digital gauge. To my surprise they all give me a different reading, as much as 4 PSI difference. Is there a reference I can use to verify which one is the most accurate ? Or maybe I should take an average of the three readings and stick to average ?

 

The digital will be the best and most accurate choice. Stop using 3 different gauges and stick with the digital.

 

I've got a digital and a stick, and they read about the same. I like the stick, it's simpler to use, doesn't get me fretting over tenths of a pound.

 

How do you get your PSI in that front 40/rear 38 range? I had that done with my old Prius at the dealership during my servicing, but then they said they were told not to do that anymore, and would only set it to 35 PSI all around.

 

Do it yourself?

 

Huh, weird. Well I go to a local service station and use their air hose (it's free), and I recheck every 2 weeks. To check the values, I just use an ol' fashioned tire pressure gauge stick, they're like $4 at Walmart:
Slime Low Pressure Tire Gauge: Automotive : Walmart.com

 

Looks like I'll have to get a new gauge and go back to doing that once in a while.

 

Get a digital gauge and check them every month

 

just bought my C2 and the bridgestone tires were at 35 all the way around. i looked at the tire and it says 44 max so I filled them to 40, it is a rougher ride BUT i gained about 2 MPG on the tank. (obviously other factors play a part in my differing MPG but one can dream right)

How come I am seeing everyone with different tires on there C's? I understand the C's that come with 16" tires will be different manufacturer maybe BUT shouldn't all C's 1 thru 3 have the same rubber manufacturer?

Would alloy wheels (15") gain me any MPG?

 

Manufacturer's often use different tires. What will be common is they'll be decent RR and relatively cheap.

I don't think alloys will gain you any mpg. Maybe a bit, if they're very light, and aerodynamic.

 

The Prius Liftback comes equipped with Bridgestone, Goodyear or Yokohama tires. It's not uncommon to see this on higher volume vehicles.

 

The rating on the sidewall is the maximum rated tire pressure, not the recommended pressure, Goodyear makes no such recommended pressures except on track.Being a Vette racer we run 40-45 psi on track except when on Hoosiers where we do run 35 to 40 psi.

 

The recommended tire pressure (from my past Prius history) has the front tires 2 PSI higher than the rear (like front 37/rear 35). Does it make a difference if all the tires have the same pressure?

 

Only to ride comfort and MPGs. The weight is in the front of the car, so the specs are higher to compensate.

 

OK, spent the week at the track and evaluated the difference between 30 psig and 40 psig. Handling is much improved based on lap times some 3% better and more comfortable while mpg improved by 8% just increasing psig from 30 to 40. Top speed increased from 96 to 100 mph.