Does running higher (40+ psi) really help MPG that much. Testing this weekend

If there is a elevation / grade difference coming to and from, your results will be completely invalid.

 

Hi k...d...,

It does help mileage. But initially Prius people started running 42/40 PSI (F/R) to avoid tires wearing out on the outer edges in about 1/2 th mileage they were rated to last...

 

Also wind velocity and direction, where the gas pump clicks off during fill and/or MFD consistancy, traffic, driver inconsistencies. On a two tank test those variations easily add up to a bigger difference than you will get from a change in tire pressure.

 

How much gain in mpg for how many psi extra air is very hard to determine in any short mileage testing. Unless you can conduct closed circuit test runs in a climate controlled environment there are just too many uncontrolled variables. Anyone who has ridden a bike with soft vs hard tires can attest to the fact that hard tires require less energy to ride. This will directly translate into better mileage with harder tires, its the quantities that are involved that create the controversy.

 

I have seen some good test work done on hypermiler, ecogreenie, forums that give a generic idea what quantitative difference tire pressure makes. That would be more meaningful than what an individual could accomplish by driving one car under real world condition. There are too many other uncontrolled variables.

 

Depends.

Different cars, road conditions, weather conditions and drivers work the tires differently.

I have the OEM Yokohamas and the highest I've run is at 43/41. That was during summer and found that on warm days the car was a bit skittish on lower-grip surfaces. So I've reduced my tire pressures to 41/39 and I find it comfortable.

Now it's winter and I'm using the same tire pressures. I drive almost exclusively on busier roads so I don't have to deal much with bad conditions. But I also feel comfortable with an occasional bit of slip in poorer conditions. I just adapt to the conditions by making gentler maneuvers.

 

How about 20f-18r and compare with 35f/32r?? Just kidding!!!

 

This has been covered in a million threads. Yes it makes a huge differnce. I run 47/49.

 

I say go ahead with your test. It would be best if you could do it both ways with each tire pressure . . . Only kidding, unless you do this trip frequently, in which case I bet you could, with something like similar temperatures and maybe even winds.

 

Mythbusters did that. They got 6% better MPG with 40PSI and 7% better MPG with 60PSI over 35PSI control. However, i'm afraid their measurements were not precise as they got only 2% MPG hit at 10PSI!

 

Wow.

10 psi = expected mpg - 2%
Control (35) = expected mpg
40 psi = expected mpg + 6%
60 psi = expected mpg + 7%


So .... a 14% increase in tire pressure over control nets you 6% bump in mpg.

70% increase in tire pressure over control nets you only 1% more mpg.

I wonder how much less all these cars would rattle if they weren't riding on the rock hard 42/40s that are often recommended here. I'm running 38/36 - maybe that's why they don't bother me so much? And maybe that's why my mileage isn't that far off of what others are seeing at that psi.

Just thinking out loud here folks. I like myth busters.

 

The bogus number for 10 psi is one example of why I consider Mythbusters to be entertainment that frequenly but not always has some factual basis.

 

I should have clarified my previous comment by saying - "I like Myth Busters because they make me think".

I can't really get on board with the 10 psi either, but if there is truth in the rest of it, it does give one reason to pause and consider the pressure more.

 

Firmer shocks and struts. Has anyone tried this approach for increased fuel efficiency and more power? I did this on a Camry and instantly the car ran more effortlessly, all around. (there was NOT a "Whole lotta shakin' going on" from then on)

ARE there "sports suspension" aftermarket shocks and struts out there for the Prius?

 

There would be some small secondary effects. The car would spend more time at nominal ride height where the wheel alignment is correct (assuming the alignment was done correctly).

There would also be some effect from the car body maintaining it's nominal design ride height/attitude more of the time. The time the car sits lower (less aero drag) might offset the time the car sits higher (more aero drag) and make that a wash though.

I doubt that you could measure the difference by checking your mileage at the gas pump but it would be an interesting experiment if controlled properly.

 

Just remember that higher tire pressures will contribute to a more bumpy ride. I also take into consideration just how much a tire will bounce or skip on the pavement in a sudden stop. ABS brake systems will not work well if the tire does not maintain contact with the road surface. I have also posted long ago that any insurance expert who is sharp will check the tire pressure of the vehicle in question if the driver blames the brakes. Maybe most insurance folks would not think of checking this, but I would if I was doing a report on such an an investigation. I have tried the higher pressures and did notice an increase in overall mileage on the freeway, but it was not worth the bumpy ride to save a few percent at the pump. When you consider the fact that some parts of the car may just rattle apart from the higher tire pressures, its not worth it to me. I am happy running 38Front and 36Rear to have a smooth ride and maintain the braking system that was designed for the vehicle. Slowing down overall and not having a lead foot on take off are the objectives for me. Your mileage may vary. I average between 45-50 MPG day in and day out. For a vehicle that is over 5 years old and has 142 thousand miles, I'll just stick to safety first and fuel efficiency second, in that order.

 

Nice to see somebody w/ that many miles !!! I drive about 76 a day round trip so I'll be piling the miles on pretty quickly.

Also, I am running 38f/36r. Figured it was a good compromise between getting higher mpgs and not ruining the ride any.