TOPIC: Tire pressure and MPG's

Hello all- I wanted to share a "free trick" I recently implemented on my '85 Subaru wagon, the one in my avatar.

Last winter I bought new tires for Subie. Now I'm lucky since it wears 175-70 /13 tires, they are relatively cheap compared to most other vehicles around today. I originally bought this car for a courier route job I had 9 years ago, I needed something good on gas, with lots of cargo room, also good in bad weather & snow. This little Subie is all those things.

My last tire set was rated for 44 lbs. max inflation, so I simply assumed these were the same. I learned years ago to look for higher inflation press. ratings, as this of course reduces rolling resistance, a source of parasitic losses to MPG. I noticed that ratings for max. pressure had increased from 35 to 44 lbs, in some makes/models of tires. A couple weeks ago I finally got down and checked the sidewalls to see the press. rating- and saw it is 51 lbs. I inflated up to 51, using a good press. guage. It drove noticeably better. So-using an old "cheap trick" I tried adding just 3 more lbs. press.,checking cold, of course. Tires should be cold to check pressure, I try to check in early morning before driving and long sun exposure. Heat of course boosts the pressure.

Now this car will roll for blocks in Neutral gear (5 speed trans. I only do this if conditions allow). Ride is only a bit harder, not objectionable. This combined w/ the MPG Remedy, has added better acceleration, and allows some enhanced "hyper-miling" driving styles, though I don't really do so much of that. My local traffic doesn't allow too much of that, though I might put in Neutral and roll down a long off-ramp going to work. Traffic reg's prohibit driving in Neutral gear, and should be avoided w/ automatic transmissions...

So that's my recent experience. IF you're shopping for tires, pay attention and ask about pressure ratings- I was favorably surprised by these tires' rating!!

This free trick of checking the tire press. can make a real difference! Common sense must prevail- tires need to be checked periodically, check and maintain the pressures. The gubmint has been telling us for decades to check the tire pressure, AND condition for safety's sake. Don't go overboard w/this, DON'T try adding 20 lbs. press. to tires rated for 35 lbs, or tires in poor condition! Use your noggin here, there might be "free" gains available! If tires and all else are in good shape you might try adding a few extra lbs.of preesure over the sidewall rating, checked cold. Compressed air is cheap or free, tire guages are cheap, and the MPG Remedy isnt too expensive to try. another useful "trick" for Gadgetmen to try!

Tracy G

yes good trick, on my 1997 chey truck tires call for 32 psi-- I put 40 psi in them for 22 years drove 100 miles to work, use this truck and other trucks same psi in tire, pulling 7k pound trailer with 6006 Duetz tractor on it, tire lasted longer
geraldc

Tracy,

Just wanted to say I checked my tire pressure and it was low, supposed to be 41 and all tires were in the high 30's. I filled them to 43 and it rolled down the highway with ease. Great tip!

I'll get braver and try a little higher. It was so hot today I didn't wanna blow out my new tires.

Isaiah

1995 GMC Jimmy 177,000 miles and still rolling.

well Isaiah, there ya go! I try to check tires dead cold if poss. IF in good cond., and all else (suspension, front end, brakes, etc.) is OK, and they are rated to 41 lbs., maybe try 45?? Drive 'er and see how it does. IF you go too high it'll get squirrelly and watch out for any signs of traction loss, we gotta use good sense on this one. Nice to feel less rolling resistance isn't it! This helps set the stage to enable gains...

Good for you buddy, keep us Posted!

BTW, I think your GMC will have the TBI injection that looks kinda like a carburetor, the air cleaner looks just like the carb. type. Those are a fav. of Ron's to Groove. I've done one, but the owner could'nt document anything for me. Look in the Index section of forum the blue box says index. click that and you go into the back room where tons of good data is! Look in the Service bulletins area of Index, you will see a couple writeups and pics of how to do these TBI's. The Idle Air Pathway (IAC)re-do is critical for good gains on these, it's all in there Isaiah!



Tracy G