Higher tire pressure -> lower MPG??

[nemo]

Originally Posted by Old Mechanic

Sorry to the OP for overinflating his tires, he observed it and the gauge read 40psi, versus his requested 38. Having a pressure gauge in my glove box, I figured he could reduce the pressure any time, like myself. In the meantime he could drive the car with (what I thought based on the gauge reading) was 40 psi.


regards
mech

This bring up an interesting point, which pressure reading is correct. No two of my gauges read the same.

[Hersbird]

Originally Posted by Old Mechanic

Being the one who changed the OP's tires, a job I think I will never do again, I refrained from posting any response.

Marks post hits the nail on the head, my 2015 Mirage is one of the best coasting cars I have ever driven, including a 1st gen Insight on RE 92s.

I can not remember a single instance where it was confirmed that increasing pressure reduces mpg.

Sorry to the OP for overinflating his tires, he observed it and the gauge read 40psi, versus his requested 38. Having a pressure gauge in my glove box, I figured he could reduce the pressure any time, like myself. In the meantime he could drive the car with (what I thought based on the gauge reading) was 40 psi.

he (cyclopathic) even advised me on placement of the tire in relation to the valve stem while I was changing his tires and the last two (after taking his advice) needed no weight and, as far as I know, were riding fine when we drove back to my house.

We made a deal on his Ensaves, which measure exactly as new 8/32nds in all treads at 3300 miles. I have them for when mine wear out, waiting in the garage. 7300 miles on my Mirage since 5/9/15.

regards
mech

I bet they were 40 psi cold and then the PO measured 49 psi after driving. The 40 psi cold is correct and measuring the tires after driving is a worthless/meaningless number. So many people make the mistake of measuring pressure some other time then first thing in the morning before even the sun has a chance to heat up the black sidewalls and before driving the car which also heat them up and raises the pressure.
This is why I also believe under inflation is the only real possible point for pressure related tire failure. The tires can be inflated to max sidewall in sub-freezing Montana and then driven across the country to 110 death Valley in the sun where I bet the pressure reading would be almost off the charts and yet still correct as being set cold.

[roosterk0031]

I see 3-4 degree swing in my car with TPMS that indicates real pressure. My Cambell Hausfield chuck indicates 28 when real pressure is 40 yesterday(stick gauge and car).

[Hersbird]

Originally Posted by roosterk0031

I see 3-4 degree swing in my car with TPMS that indicates real pressure. My Cambell Hausfield chuck indicates 28 when real pressure is 40 yesterday(stick gauge and car).

Throw it in the trash.

[CapriRacer]

Originally Posted by Old Mechanic

.... Sorry to the OP for overinflating his tires, he observed it and the gauge read 40psi, versus his requested 38. Having a pressure gauge in my glove box, I figured he could reduce the pressure any time, like myself. In the meantime he could drive the car with (what I thought based on the gauge reading) was 40 psi.....

Actually, you did the right thing. Tires grow a lot in the first 24 hours. Our test garage used to over inflate new tires by 2 to 3 psi, which came out really close a couple of days later.

[user removed]

Makes me wonder if there is a correlation between the pressure rise and rolling resistance of the tires. Makes sense that there would be one.

regards
mech

[deejaaa]

Originally Posted by Old Mechanic

Makes me wonder if there is a correlation between the pressure rise and rolling resistance of the tires. Makes sense that there would be one.

regards
mech

lol!!!

[euromodder]

Originally Posted by CapriRacer

I am of the opinion that tire pressure needs to be referenced to the vehicle spec pressure, not what it says on the sidewall and I think anything over 5 psi is excessive.

Having just gotten my VW up! back from servicing, they also "adjusted" the tyre pressure.

Down to the manufacturer recommended 2.2 bar / 32 psi, coming from 2.8 bar / 41 psi
(3 bar / 43.5 psi is excessive, as the rear gets bouncy and tail-happy)

They need not have stated the fact - it was noticeable right away.
The ride was sluggish, wallowing (65% profile is rather high these days), understeering, but comfy-soft .
FC was up compared to what I'm used to seeing @ the speeds driven.

Car manufacturers clearly use low-ish tyre pressure to hide flaws in their suspensions, at their customer's expense.

My tyre wear has been lower since I started using higher pressures.
Wear evened out on Hagär the Volvo.
No uneven wear issues on the up! which has been using higher than recommended pressure since day 1.

Increasing inflation pressure changes the shape of the footprint regardless of who makes the tire and what technology they employ.

Sure does.
I've used "excessive" pressure to correct uneven thread wear caused by
using "correct" - manufacturer prescribed - pressure.

[cyclopathic]

Originally Posted by roosterk0031

Too many varibles, old bald smooth tires are roll easier than new tires.

Old tires had 3,000mi, brand new.

Originally Posted by ksa8907

Double check your brakes for drag

Brand new car brakes are fine

Originally Posted by Hersbird

I bet they were 40 psi cold and then the PO measured 49 psi after driving. The 40 psi cold is correct and measuring the tires after driving is a worthless/meaningless number. So many people make the mistake of measuring pressure some other time then first thing in the morning before even the sun has a chance to heat up the black sidewalls and before driving the car which also heat them up and raises the pressure.

They were measured early in the morning, and the difference btw tires on sunny and shady side was less then .5psi; below gauge accuracy.

Originally Posted by CapriRacer

Actually, you did the right thing. Tires grow a lot in the first 24 hours. Our test garage used to over inflate new tires by 2 to 3 psi, which came out really close a couple of days later.

On m/c tires I used to pump them to 60psi while sitting in garage (operating pressure 42psi for rear) then drop pressure to 28psi and go for short 1/2hr sub-50mph ride. It would take several cycles to completely break in tires this way.

M/C racing tires are said to grow so much that by the end of the race people would need different gear ratio. So the trick was to get it on lower side so it would be more or less ideal in the middle of the race.

[cyclopathic]

Originally Posted by Old Mechanic

Sorry to the OP for overinflating his tires, he observed it and the gauge read 40psi, versus his requested 38. Having a pressure gauge in my glove box, I figured he could reduce the pressure any time, like myself. In the meantime he could drive the car with (what I thought based on the gauge reading) was 40 psi.

don't worry it is expected for gauges to differ. I've gone through dozen of them, and there are only 2 which seem to agree on the pressure. One of them is attachment for inflation and another one is a premium pencil type which I think I had as long as I remember.. 25 years? And it is not that any loss of MPG is a big deal, I'd like to understand what is going on.

As others mentioned there are too many variables, for example starting Sept 16 they started switching to winter blend, cooler temperatures, getting gas from no-brand gas station (not that station may have been cheating, but different pumps have different shut off sensitivity). Not to say that some gas station pumps may have issues, I've put 5.3gal in 4.8gal m/c tank in the past. Bike was still running fine w/o switching to reserve, so there should have been at least .5gal.

RT43 are non-LRR tire, and Enasaves are LRR, so some loss is expected.

Now, what I am interested in the actual physics of rolling resistance. This is what Continental is saying about "Low surface abrasion technology":

“Low Surface Abrasion technology is an actual construction change that shows a substantial double-digit gain in wear,” he said. “The original RT tended to wear on the inside and outside shoulders; the RT43 shows even wear because of LSA technology, even though siping is increased. The increase in siping while offering reduced wear is the paradigm shift.”

From what I've read there are several venues tire makers explore to make LRR tires. For example on LRR tires Bridgestone or Michelin use special more flexible rubber compound in sidewalls, and probably best LRR tires in US market Michelin Energy Savers have the thinnest sidewalls I've seen. Other makers (Enasaves would be a good example) make sidewalls stiffer, to reduce flexing and flex-related heating.

For this very reason (sidewall heating/flexing) higher profile tires of the same make tend to be more fuel efficient. Taller sidewalls = less flex = less heating = less losses.

The question becomes that if the tire was optimized for specific contact patch shape, could over-inflating and changing shape be detrimental to wear/rolling resistance?

On a side note alignment is a big variable of the rolling resistance, and some tire designs seem to be more sensitive to small misalignment than others. Then again, less inflation = softer tire, which in theory should help to negate less than ideal alignment.

If anyone came across any articles on tire rolling resistance, could you please post a link? thnx