Fuel Economy Myths vs. Facts - Page 3 - Ford Mustang Forum
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Originally Posted by Buck268 View Post
I also find the claims about Nitrogen inflation hard to swallow, but lets save that for another day.
Since its another day now, I agree Nitrogen is of little value on the street. Even with a Nitrogen tank in the garage, I always used air in my street tires.

Nitrogen is useful for racing (not track days). The lack of water compared to most air means less expansion and pressure change as the tires heat up. That is useful in racing because you don't have to compromise as much between the first laps and the last laps. But the water is only a factor at temperatures higher than you will get on the street plus you are not cornering on the street within a percent or two of what the tires are capable of. Even on track days where the temperature may get high enough to matter, you don't care if you are 1 or 2% slower for the first few laps until the temperature stabilizes.


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But the water is only a factor at temperatures higher than you will get on the street plus you are not cornering on the street within a percent or two of what the tires are capable of.
Depends on your driving style. Obviously you won't be doing it 100%, all the time all day long the way you would at the track, but I know that every time I'm on a circular onramp getting on a highway, I push it to the absolute limit of adhesion, to the point where I actually let it slip a bit, as I'm merging onto the highway. Isn't that the point in having a sporty car?


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Depends on your driving style. Obviously you won't be doing it 100%, all the time all day long the way you would at the track, but I know that every time I'm on a circular onramp getting on a highway, I push it to the absolute limit of adhesion, to the point where I actually let it slip a bit, as I'm merging onto the highway. Isn't that the point in having a sporty car?
And just how do you think Nitrogen helps in that situation? Nitrogen helps in racing so you can have very slightly higher pressures when your tires are cold without them being slightly too high in later laps when they are hot. What you described is about as far from racing as you can get. I assure you your tires are never at their optimum temperature on an on ramp so its totally irrelevant.

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That's a common misconception, but it's just that, a misconception. It's an idealized freshman physics problem, that holds up well if the item in question is extremely deformable, like a balloon. Tires are not that deformable, especially low profile high performance tires, so it really doesn't quite work that way.

You're not going to triple your contact patch by going to a tire that's three times as wide, but it's not going to stay the same either.

OK, I'm willing to conceed that sidewall strength does play a role, but I would like to see PROOF that tire pressure isn't the primary factor in contact patch size.

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All else being equal and for any given tire, internal pressure will be the major factor in contact patch size. But you can't compare a narrow tire (say a 195/75-14) with a wide tire (say a 315/35-20) at the same pressure and think they will have the same (or even similar) contact patch size. The 195 is less than 7" wide while the 315 is more than 12" wide. The tire shape doesn't deform enough to account for that difference. If you want proof, go out in the parking lot and look at any tire on any car - the tire contacts the road across the entire width of the tread. That means the 315 contact patch is at least 5" wider than the 195.

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Yes, 5" wider and X" shorter. The narrower tire will have a longer patch fore-to-aft.

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You really think that the contact patch of the narrower tire would be 5" longer to make up for the difference in width (in order to match your theory of same contact sizes at the same pressure)? I'm afraid not.

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How much weight do you think the tire carcass itself supports such that you feel it necessary to minimize the effects of PSI?

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I have an entire weekend to kill, I have two sets of wheels, 1 set of stock bullitts with 255 50 17s and a set of split spokes with the stock size (235 55 17?).

You guys agree on a method to measure contact patch and I will do it. And I will do whatever air pressure you guys want. But my money is on the contact patch increasing with tire size.
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Interesting idea. Maybe lowering the tire onto some kind of colored powder might work - kind of like making a fingerprint with the tire tread. Perhaps some of that powdered chalk that carpenters use on marking string?

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Interesting idea. Maybe lowering the tire onto some kind of colored powder might work - kind of like making a fingerprint with the tire tread. Perhaps some of that powdered chalk that carpenters use on marking string?
Flour.

(f**ing 15 character min. limit)

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Ok. I will put one of my split spokes on the rear axle. I will dust the tires, drop the on the pavement (gently as to not let flex taint results) then jack it back up and post pics of the footprints with a tape. Same pressure both tires? 32? Or 51?
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Quote:
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Flour.

(f**ing 15 character min. limit)
My concrete is too white...
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