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Old 06-01-2006, 08:55 AM   #1
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Tires, my secret sauce formula.

My tires were at 55psi and i went back down to 30psi for a couple of days. I have never seen my gas gauge move so fast. So even with the screwed up right side of the car I pumped them back up to 50psi. My gas gauge started to move slow again. I think the pumped up tires increased 5 out of the 6mpg that I have increased before I pumped up them up. Let's discuss a pumped up tire.

-A pumped up tire gets harder
-A pumped up tire weighs more
-A pumped up tire has less rolling resistence(still don't get this one)

I personally think tire stuff is voo doo magic like the automatic transmission.

Let's discuss tires, especially rolling resistence and what it is and how it changes with higher psi.
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Old 06-01-2006, 09:02 AM   #2
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Quote:
Originally Posted by Compaq888
-A pumped up tire has less rolling resistence(still don't get this one)
http://en.wikipedia.org/wiki/Rolling_resistance
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Old 06-01-2006, 09:36 AM   #3
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i think you must get about a mile to the gallon to be able to see your gas gauge, move. i only ever notice it after a hard turn.
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Old 06-01-2006, 09:58 AM   #4
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Quote:
Originally Posted by SVOboy
i think you must get about a mile to the gallon to be able to see your gas gauge, move. i only ever notice it after a hard turn.
30mpg and 24mpg is a huge difference. With tires at 30psi I get 20mpg on the street. With tires at 55psi I get about 24-25mpg on the street. Tires at 30psi on freeway is 29mpg. Tires at 55psi on freeway 39-40mpg.

My gas gauge moves too on sharp turns but once I'm driving straight it's very accurate. After it gets to E I don't know how much fuel I got till the lamp goes on. As soon as the lamp goes on I know I have 50-60 miles of fuel left.
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Old 06-01-2006, 12:38 PM   #5
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the gas gauge will never be as accuate as a scangauge. It dips and moves too much, under a FAS sometimes it will have a mind of its own! I find just tracking mileage with your odometer usually is always the accuate solution.

The needle is evil
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Old 06-01-2006, 01:55 PM   #6
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Originally Posted by philmcneal
The needle is evil
The Metro's needle is useless. It is roughly accurate at 1/2 tank (20 liters), but for my last fill up I put in 23 liters and the needle had been hovering at 1/4 tank.

I basically know absolutely for certain that my car will go 570 km on a tank (40 liter tank - 2 liter safety margin = 38 liters * 15 km/liter worst-cast mileage = 570 km). Anything under 570 km and I'm safe to keep going.

But, this thread was about tires and now we're chatting about gas gauges. Compaq, I had my tires at 40-43 psi for my last tank compared to my usual of 33 psi. Unfortunately I can't definitively say how much they contributed to my 13% mileage increase due to major environmental changes and some slight driving style changes, but they must have contributed some.

However I don't know how you would measure the rolling resistance of the tires at any given psi.

sq. in. tire footprint x road friction? I don't know.

EDIT: Oh, that wikipedia link has formulas. Note to self: Read first then answer next time.
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Old 06-01-2006, 03:36 PM   #7
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I have done extensive testing under controlled conditions with the Prius and the difference between 35 PSI and 60 PSI was only 2.5%. In your case that would be 1 MPG. I have noticed a 3-5 MPG increase due to switching to smaller, lighter wheels with smaller, lighter LRR tires,

Compaq, I am dumbfounded by your results. A 33% increase in FE, IMHO, cannot be explained by a change in tire pressure alone, unless your tires were at 10PSI to begin with.
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Old 06-01-2006, 03:47 PM   #8
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I agree with Krausdb.

At 29 or 30 psi, yes, you are going to have high rolling resistance, which will cost a couple mpg, but the only difference you will find between 43 psi and 50 psi is that your teeth don't rattle on every pavement joint. I tested and lost no mpg going from 50 down to 43. That's what I'm running now. I bought some larger diameter LRR tires, which just arrived, and we'll see if they help any.
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Old 06-01-2006, 09:33 PM   #9
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Quote:
Originally Posted by Compaq888
-A pumped up tire gets harder
-A pumped up tire weighs more
-A pumped up tire has less rolling resistence(still don't get this one)

I personally think tire stuff is voo doo magic like the automatic transmission.
the weight difference in relation to the psi is COMPLETELY marginal. it doesnt effect anything.

voodoo magic? its proven that higher psi saves gas. its also proven that slush boxes suck.
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Old 06-01-2006, 09:41 PM   #10
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Quote:
Originally Posted by thisisntjared
the weight difference in relation to the psi is COMPLETELY marginal. it doesnt effect anything.

voodoo magic? its proven that higher psi saves gas. its also proven that slush boxes suck.
It's also proven that coke is preferred to pepsi 2:1
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