Quote:
Originally Posted by krousdb
I have actually done a lot of testing with overinflated tires. The following is a report from last summer. I had just switched to a new set of OEM tires which ended up dropping my mileage by 6%:
July 2005:
Well I'm back and the results seem to make sense, although I am a bit
surprised.
My first test was with the new tires (approx 5000 miles on them) at
62/62 PSI. The MPG was as high as 99.9 (100+) and as low as 96.3.
The final MPG was 98.8 at 77F. The low of 96 seems to confirm my
previous 104+ reading because at no time did it drop below 99.9 on
the 104+ MPG test.
For the second test, I dropped the pressure to 44/42. For the trip,
97.4 MPG at 82F.
For the third test, I dropped the pressure to 35/33. For the trip,
96.0 MPG at 86F.
I did expect the 6 MPG drop by switching to the new tires (my guess
was 3-5). I guess they have more breaking in to do. The larger
circumference of the new tires (due to full tread depth) had no
effect on the trip length as indicated by the trip odometer, which
was 23.4 miles. Actual measurements of the tires showed 77 3/16" for
the new and 76 3/4" for the old. The difference is about 6 tenths of
one percent, negligable in my opinion.
I was surprised however that tire pressure made such a small
difference, although the MPG's may be skewed higher due to the higher
ambient temps during each sucessive test. I guess what this tells me
is that if you spend most of your drive below 42MPH, you might see a
benefit in raising your tire pressure. Otherwise, you will not
likely notice a difference. The other thing it tells me was that
yesterday's results were not a fluke. These MPG's are repeatable.
My old set of tires spend most of thier lives at 50PSI. The wear on
them is perfectly symmetrical. Anyone who tells you that high
pressure will cause uneven wear, IMHO, is misinformed. The even wear
is also a testament to a prefect wheel alignment. If your tires are
wearing unevenly, have your alignment checked.
Based on these results, I will keep the new set on and drop the
pressure to 44/42. My ride to work is partially on a very bumpy
stretch of I-79 (Andy can attest to this) and the 44/42 PSI yields a
noticably better ride. The 35/33 yields an even better ride, but I'm
not quite ready to give up all of my advantages. The new tires will
probably drop my summer mileage from the low 70's to the mid to upper
60's. I guess thats the price I will pay for new, safe tires.
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i've seen TONS of tire with uneven wear due to improper inflation. i used to write service, toyota included actually, so i've seen it on alot of toyotas
. mostly camry's and tundras, since the recd pressure is way too low, IMO (iirc 29 and 26 respectively) and those vehicles always came in with lots of outer wear around 20K miles or so.
in my own vehicles i have seen inner wear from overinflation; i used to run my tires fairly higher than rec'd pressure for instance in my 16v vw to stiffen the sidewalls up. ran them around 38lbls iirc and recd was maybe 32lbls.
your prius (assuming you have a prius from your avatar) came with a "special load rated tire" due to the extra weight of the hybrid system. first off i think your not losing tread due to higher tire pressure is a special case vs the rest of us, since your tires should probably be pumped up higher than toyota tells you to anyway (due to the higher load on them). next switching to a lighter tire might help your mileage but in your car there is always the chance of that tire not holding the load.
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