15 more PSI = 7% better MPG
 

I filled up last night and this tank was the first tank with the tires pumped up to 45 PSI. I originally had them at 30 PSI. This is my 4th fillup this month, and the others have been around 41-42 MPG. For the tank the only thing that changed was the tire pressure, and I managed 45 MPG. Thats about 3 MPG, or 7%.

I think I can do a little better on the next tank, as 50 miles of this tank were still on 30 PSI. No driving techniques or modifications on this tank. I have one rule, speed limit is 60 mph. I'm going to do a couple more tanks at 44 PSI, then a few at 60 PSI to see what effect it has. By that time I should be ready for my alternator delete (almost done, just need the battery) and power steering delete. With those mods I hope to be around 50 MPG without any advanced driving techniques or aero mods.

Update 8/20/2013
3 tank average at 30 PSI = 41.4 MPG
5 tank average at 45 PSi = 45.4 MPG

(4 / 41.4) x 100 = 9.6 % gain

https://lh5.googleusercontent.com/-r.../graph5944.PNG

That's a good increase, But I think you should change the topic title from 15 to 45 PSI.

Nice. Definitely ask MetroMPG to change the subject line for you to "45" instead of "15". What was the previous pressure? What is max sidewall?

Sorry guys, meant to say "15 more PSI", it is changed.

Original was 30 PSI front and rear. Now it's 45 PSI front and rear. Max sidewall is 44 PSI.

Suggests confirmation of what MetroMPG showed in his test: big gains from maintaining max sidewall. He also saw further gains from going as much as 6 psi above sidewall. I go all the way up to 16 over sidewall after warming the tires and at peak daily ambient temps, partly so that cold tires and cold mornings will not likely see psi below maybe 10 psi over sidewall.

I plan on going to 55 or 60 after this current tank. I want to see the difference in fuel economy compared to how harsh the ride gets. I'm perfectly satisfied with the ride at 45 PSI. I can feel more bumps, but I am the type of person that likes to feel the road when I drive so it doesn't bother me a bit. And the girlfriend didn't notice, so that is always a good thing!

One more thing I should mention, lean burn is not working on my car, so there is further potential when I get that working again.

So don't tell her (ever). It might start to bother her. Leave well enough alone.

Yah. LB would be a big bonus. It tends to replace P&G, I think. Someone with experience behind the wheel of one with working LB will chime-in I hope.

Congrats on the improvement!

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Agreed: lean burn, used properly, is a good replacement for high/medium speed P&G, and far less troublesome.

You'll want to investigate aero mods though (at least the stealth ones), to "widen" your lean burn envelope by reducing engine load at your 60 mph target speed.

The alternator delete will help there too, provided the computer stays happy with the reduced voltage.

Here's the link to the PSI testing I did:

http://ecomodder.com/forum/showthrea...tire-2721.html

That thread contains results for a 1999 Camry, 1998 Firefly (Metro), and my 1992 Metro EV.



http://metrompg.com/posts/photos/met...scale-1200.jpg

http://forkenswift.com/album/8-chart...arious-psi.gif

Thanks and it's alright. I've made mistakes too.

As illustrated above tire pressure can make or break you!! I noted a great improvement in our Toyota minivan when I pumped up the tires to 45 PSI from 20~30 PSI... it was good for roughly 3 more highway MPG.