anyone got a tire pressure vs fuel economy graph?

MetroMPG · 02-05-2006, 09:14 PM

seeing the number of people running 45, 50, and even 55 psi lately, i'm wondering about tire pressure again.

has anyone got a plot of mpg over a range of pressures for a given speed(s)? just curious.

the figure from the fueleconomy.gov is a 0.4% fuel economy drop for every 1 psi drop (in all 4 tires): http://www.fueleconomy.gov/feg/maintain.shtml

but it doesn't say anything about what kind of car, what speed driving, abmient temps, what size tires, etc., etc. maybe someone has some more detailed info out there.

as i've said before, i'm reluctant to use very high pressures in the cold since the suspension seems to take such a brutal pounding. it's far too harsh - there's just no give when the tires/bushings are frozen and the shock oil is thick as glue. frozen suspension is a bad situation when it coincides with frost-heaved roads and the arrival of the annual late-winter pot-hole pandemic.

still, i'm curious to know what new efficiency heights i could expect if i pump things up further as spring rolls in and the suspenders are a bit more forgiving.

Matt Timion · 02-05-2006, 09:21 PM

I'm interested as well. 0.4% per psi is a lot, but that is a negative drop. There is nothing that says that there is a .4% increase for every PSI OVER the stock limit.

Something tells me that the difference is probably within the margin of error, but I'd be glad if someone proved me wrong.

krousdb · 02-06-2006, 03:09 AM

Quote:

Originally Posted by MetroMPG

seeing the number of people running 45, 50, and even 55 psi lately, i'm wondering about tire pressure again.

has anyone got a plot of mpg over a range of pressures for a given speed(s)? just curious.

the figure from the fueleconomy.gov is a 0.4% fuel economy drop for every 1 psi drop (in all 4 tires): http://www.fueleconomy.gov/feg/maintain.shtml

but it doesn't say anything about what kind of car, what speed driving, abmient temps, what size tires, etc., etc. maybe someone has some more detailed info out there.

as i've said before, i'm reluctant to use very high pressures in the cold since the suspension seems to take such a brutal pounding. it's far too harsh - there's just no give when the tires/bushings are frozen and the shock oil is thick as glue. frozen suspension is a bad situation when it coincides with frost-heaved roads and the arrival of the annual late-winter pot-hole pandemic.

still, i'm curious to know what new efficiency heights i could expect if i pump things up further as spring rolls in and the suspenders are a bit more forgiving.

I just found this excellent report on LRR tires that actually
quantifies the benefits in terms of fuel economy.

westcarb.org/reports/2003-01-31_600-03-001CRVOL2.PDF

To summarize, for every 10% of rolling resistance reduction, you could
expect a 1% increase in urban FE and 2% in highway FE. See section 3.2.
Another study showed that with a 30% RR reduction a 2% - 6% reduction
in fuel useage was measured. Also, see figure 3 which shows the effect
of tire pressure on FE. It appears that there is on average a 0.5%
increase in FE between 35PSI and 45PSI. This is consistant with my
findings when I did some testing prior to the Prius marathon.

Cool report! Good read

GasSavers_DaX · 02-06-2006, 05:56 AM

Quote:

Originally Posted by Matt Timion

I'm interested as well. 0.4% per psi is a lot, but that is a negative drop. There is nothing that says that there is a .4% increase for every PSI OVER the stock limit.

Something tells me that the difference is probably within the margin of error, but I'd be glad if someone proved me wrong.

Agreed. That phenomenon is known as hysteresis.