Tire psi and advancing timing, worth it? - Fuel Economy, Hypermiling, EcoModding News and Forum

rick390 · 07-26-2008, 04:35 AM

I got 51mpg in my 97' Geo on my last tank. I'm wondering if it would be worthwhile to inflate my tires to 40 psi or more and to advance the timing 8 degrees or more. Does anyone have an estimate as to how much of an improvement in my mpg that will bring?

Will · 07-26-2008, 06:15 AM

The tire inflation I would do. If your tires are like mine they say 44 is max. The timing I am not so sure about. Some of the Metro guys will advance 10 degrees and back it off until it stops pinging. I have not done this.

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Daox · 07-26-2008, 08:12 AM

Rick390, its definitly worth it to do both. They are free mods after all. If you don't feel comfortable pumping your tires up that high, just start working your way up until you don't want to go any further. Then, back it down a few psi. The timing I'd get some advise on as I'm not familiar with Metro engines.

Johnny Mullet · 07-26-2008, 10:49 PM

It is worth it. Timing especially. These cars have the timing set too retarded from the factory and this may or may not be a contributor to the burnt exhaust valve issues these 3 cylinders have.

I would estimate that if you go 44PSI and then set the timing about 8 degrees advanced, you should get over 57MPH which would be a 6MPG increase respectively.

getnpsi · 07-27-2008, 12:26 AM

Metro tires are not $150 each like on my neon. Pump those babies up.

Will · 07-27-2008, 06:05 AM

Quote:

Originally Posted by getnpsi

Metro tires are not $150 each like on my neon. Pump those babies up.

Exactly

Hacksaw · 07-27-2008, 06:57 AM

I don't find 44psi to be excessive at all, that's what I run in mine. In fact, I've ran 40+ psi in every tire, of every car, truck, and van that I've ever owned. I've never had any wear issues or blowouts...(well, there was that time the wife ran over a muffler on the highway and blew out both passenger side tires after my son said, "Don't hit that muffler up ahead"...) The decreased rolling resistance makes for a cooler running tire, and will be safer as a result. Go ahead, rick390, puff 'em up!

Hacksaw.

Gregte · 07-27-2008, 07:47 AM

I also agree with pumping the tires up. Mine say 35 PSI max but I pump them to 40. Also, remember that the pressure rating stamped on the sidewall is always stated as the COLD pressure rating. It will go higher once the tire warms up. Don't let this concern you, it is supposed to be this way.

It is fun to find a small vacant stretch of road where you can start a coast at a given speed and see how far you can go till it stops. Try this with your tires pumped to various levels and see at what point further pressure increase does not show a further coasting distance.

99metro · 07-27-2008, 09:38 AM

My tires are also 35 rated, but I have them at 40 psi cold. I should have stayed with the 155/80/13 instead of these 175/70/13. Anyway, advancing the timing helps a lot. I go between 87 and 91 octane. I had been getting low 50's, but after advancing the timing and pumping the tires, I'm hitting 58 to 61 mpg average over my daily 110 mile round trip commute (as long as there is no headwind!).

rick390 · 07-27-2008, 10:49 AM

Sounds like a clear vote for airing up the tires and advancing the timing. I'm getting a new clutch put in it and should get it back this afternoon.

I think I'll go with air first for a tank and then the timing the next tank. Curious to find out which accounts for greater mileage. Thanks for the input.