How to get free beer with compass - Jeep Compass Forum
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post #1 of 16 Old 01-20-2019, 02:55 PM Thread Starter
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How to get free beer with compass

Hey Guys,

I put this in a different thread, but I think it didn't really match the title, so here it is:


I increased the tire pressure in my 19 Compass TH to 42.5 PSI and have some measurable data that may be of interest.

First, with this tire pressure, I did the "highly technical" test where you wet the tires and drive on the driveway to make sure they are not overly inflated/ tire surface contact. It is good to go. The tires are rated to 45 PSI max.

Second, When the tires heat up, meaning after multiple 60+ mile trips, the max they have expanded to is 44 PSI, within the tolerances.

Numbers: I have increased an average of .4 MPG over the measured 3 tanks of fuel. Being as the TH has a 13.5 gallon tank, that adds up to 5.4 gallons. At $2.25 dollars a gallon, 5.4 gallons of fuel EVERY TANK adds up to $12.15.

Impact: An 18 Pack of Coors Light at Walmart is $14.49. The difference in the price per tank and an 18 pack of the worlds finest beer is $2.34. That means every time you fill up you get a 18 rack for $2.34.

This is science people. SCIENCE!
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post #2 of 16 Old 01-20-2019, 03:09 PM
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Actually being that you've over inflated them, you've also increased the diameter of the wheel which makes your speedometer less than accurate and you're calculation is flawed.



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post #3 of 16 Old 01-20-2019, 03:14 PM Thread Starter
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Actually being that you've over inflated them, you've also increased the diameter of the wheel which makes your speedometer less than accurate and you're calculation is flawed.



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how so? its below the max......
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post #4 of 16 Old 01-20-2019, 06:58 PM
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I don't have any issue with the microscopic tire diameter differences caused by raising or lowering the air pressure, but three tanks of fuel is not much data to go on. The weather change over the course of presumably three weeks it took to burn that fuel could have more to do with the measured difference than anything.

FWIW I was just at the dealer having a frozen door latch de-iced and it had just started complaining about tire pressure being too low (hit 27 PSI when the temps here dropped to -20 yesterday), so without saying anything to me they pumped all four tires up to 40 PSI before they rolled it back out of the garage. That is obviously meant to combat the issue we have up here of cold temps lowering the pressure but still interesting they felt comfortable with setting them so high, because at some point I will drive long enough to warm up the tires AND eventually the weather will get warmer and the pressure will presumably increase.

I wonder if these TPMS systems will call for the pressure to be lowered at some point? Or if they are only watching for the low pressure condition? I bet my book says something about that but too lazy to look right now. Might also depend on which TPMS system you have, ours has the fancier version that shows each tire's pressure and position individually but I understand not all of them have them.
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post #5 of 16 Old 01-20-2019, 07:36 PM Thread Starter
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Yea, the idea of the tire diameter changing measurably is dumb.

You are correct that 3 tanks isnt a lot, but when justifying beer I will absolutely make it work in my favor!
post #6 of 16 Old 01-20-2019, 10:32 PM
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Have fun ruining the tread from over infaltion


Quote:
Originally Posted by [email protected] View Post
Hey Guys,

I put this in a different thread, but I think it didn't really match the title, so here it is:


I increased the tire pressure in my 19 Compass TH to 42.5 PSI and have some measurable data that may be of interest.

First, with this tire pressure, I did the "highly technical" test where you wet the tires and drive on the driveway to make sure they are not overly inflated/ tire surface contact. It is good to go. The tires are rated to 45 PSI max.

Second, When the tires heat up, meaning after multiple 60+ mile trips, the max they have expanded to is 44 PSI, within the tolerances.

Numbers: I have increased an average of .4 MPG over the measured 3 tanks of fuel. Being as the TH has a 13.5 gallon tank, that adds up to 5.4 gallons. At $2.25 dollars a gallon, 5.4 gallons of fuel EVERY TANK adds up to $12.15.

Impact: An 18 Pack of Coors Light at Walmart is $14.49. The difference in the price per tank and an 18 pack of the worlds finest beer is $2.34. That means every time you fill up you get a 18 rack for $2.34.

This is science people. SCIENCE!
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post #7 of 16 Old 01-21-2019, 04:13 PM Thread Starter
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Originally Posted by 84z28 View Post
Have fun ruining the tread from over infaltion

Have fun trying to make cheap tires last for no good reason!

Check this out....... Big picture concept..... Math is hard....

These are relatively inexpensive cars with inexpensive tires. You can purchase and have mounted Falken Wildpeak HP 215/65r17's for $550.00 all day. According to the manufacturer they are good for 60k miles. Going back to original post "TH has a 13.5 gallon tank, that adds up to 5.4 gallons. At $2.25 dollars a gallon, 5.4 gallons of fuel EVERY TANK adds up to $12.15."

Step 2 for big picture: Assuming 25 mpg @ 13.5 gallons that's 337.5 miles per tank. What this means is it would take 177.7 tanks to reach 60K miles. 177.7 (tanks) X $12.15 (savings per tank) = $2,247.90. $2,247.90 (total savings) - $550.00 (new tires) = $1,697.90 (total saved after tires).

Lets say the tires only last "half life" though this is a VERY CONSERVATIVE speculation, at 30k miles. This eliminates the argument that I will ruin my tires (though under the max PSI.) This means it takes 88.8 tanks of gas to reach 30k miles. 88.8 (tanks) X $12.15 (savings per tank) = $1,080.00. $1,080.00 (total savings) - $550.00 (new tires) = $530.00 (total saved after tires.) This even factors in getting new threads twice as often as those who try to make cheap parts last.

In both scenarios (standard and worst case) this is absolutely the correct answer. Roasted.

Last edited by [email protected]; 01-21-2019 at 04:18 PM.
post #8 of 16 Old 01-21-2019, 07:40 PM
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Theirs no argument that you'll ruin the tread life of tires over inflating them and now also that you're a moron. You assume and speculate alot, it speaks volumes. Manufacturer set tire psi for a reason snowflake

Quote:
Originally Posted by [email protected] View Post
Have fun trying to make cheap tires last for no good reason!

Check this out....... Big picture concept..... Math is hard....

These are relatively inexpensive cars with inexpensive tires. You can purchase and have mounted Falken Wildpeak HP 215/65r17's for $550.00 all day. According to the manufacturer they are good for 60k miles. Going back to original post "TH has a 13.5 gallon tank, that adds up to 5.4 gallons. At $2.25 dollars a gallon, 5.4 gallons of fuel EVERY TANK adds up to $12.15."

Step 2 for big picture: Assuming 25 mpg @ 13.5 gallons that's 337.5 miles per tank. What this means is it would take 177.7 tanks to reach 60K miles. 177.7 (tanks) X $12.15 (savings per tank) = $2,247.90. $2,247.90 (total savings) - $550.00 (new tires) = $1,697.90 (total saved after tires).

Lets say the tires only last "half life" though this is a VERY CONSERVATIVE speculation, at 30k miles. This eliminates the argument that I will ruin my tires (though under the max PSI.) This means it takes 88.8 tanks of gas to reach 30k miles. 88.8 (tanks) X $12.15 (savings per tank) = $1,080.00. $1,080.00 (total savings) - $550.00 (new tires) = $530.00 (total saved after tires.) This even factors in getting new threads twice as often as those who try to make cheap parts last.

In both scenarios (standard and worst case) this is absolutely the correct answer. Roasted.
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post #9 of 16 Old 01-21-2019, 08:14 PM
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I'll just leave these here also since i wouldn't want anyone to assume or speculate

https://www.popularmechanics.com/cars/a940/4199963/

https://axleaddict.com/misc/tire-pre...-really-matter
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post #10 of 16 Old 01-21-2019, 10:33 PM
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Quote:
Originally Posted by [email protected] View Post

Numbers: I have increased an average of .4 MPG over the measured 3 tanks of fuel. Being as the TH has a 13.5 gallon tank, that adds up to 5.4 gallons. At $2.25 dollars a gallon, 5.4 gallons of fuel EVERY TANK adds up to $12.15.
You've made a fundamental error in your calculation. If your fuel economy is improved by 0.4 mpg, then you gain 5.4 miles of driving range per tank, not 5.4 gallons of fuel per fill-up. And that's assuming you burn all 13.5 gallons in your tank each fill-up.
That has a trivial, but measurable, improvement in your range and driving cost. It has a value of, very roughly, $0.50. That might buy you something like half a Coors Light.
Drink responsibly. And don't drink while doing math.
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post #11 of 16 Old 01-22-2019, 01:18 AM
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Lmfao

Quote:
Originally Posted by mr leroy View Post
you've made a fundamental error in your calculation. If your fuel economy is improved by 0.4 mpg, then you gain 5.4 miles of driving range per tank, not 5.4 gallons of fuel per fill-up. And that's assuming you burn all 13.5 gallons in your tank each fill-up.
That has a trivial, but measurable, improvement in your range and driving cost. It has a value of, very roughly, $0.50. That might buy you something like half a coors light.
Drink responsibly. And don't drink while doing math.
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post #12 of 16 Old 01-22-2019, 05:02 AM
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On top of all what has been pointed out, you are one good bump or pothole away from catastrophically blowing the tire and ,at best destroying the rim, or at worse losing control and causing a crash.

There is a reason why manufacturers suggest 32psi when max rating is ~45psi. When the tire hits a bump or pothole, it is compressed and pressure increases. If you are all the way at ~45psi, it will explode like a balloon and you will essentially be traveling on your rim in 3 secs or so. So, at best that rim will be ruined or at worse you will crash.
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post #13 of 16 Old 01-22-2019, 05:10 AM
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so without saying anything to me they pumped all four tires up to 40 PSI before they rolled it back out of the garage. That is obviously meant to combat the issue we have up here of cold temps lowering the pressure but still interesting they felt comfortable with setting them so high, because at some point I will drive long enough to warm up the tires AND eventually the weather will get warmer and the pressure will presumably increase.
Based on the ideal gas law (link below), with the given pressure of 40psi and -20F, right now you have about 1.36 moles of gas in you tires (I assumed tire volume is 10 liter, which is the average value for car tires). So when if tire temperature hits 80F, the pressure inside the tires would be around 49 PSI, assuming tire volume doesn't significantly increase with tire expanding (which it should not).

I would lower the tire pressure to ~35psi, just to be safe, as tire temp would be way above 80f in summer during driving.

https://www.chemicool.com/idealgas.html

Last edited by Tripod; 01-22-2019 at 05:19 AM.
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post #14 of 16 Old 01-22-2019, 05:11 AM
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Quote:
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On top of all what has been pointed out, you are one good bump or pothole away from catastrophically blowing the tire and ,at best destroying the rim, or at worse losing control and causing a crash.



There is a reason why manufacturers suggest 32psi when max rating is ~45psi. When the tire hits a bump or pothole, it is compressed and pressure increases. If you are all the way at ~45psi, it will explode like a balloon and you will essentially be traveling on your rim in 3 secs or so. So, at best that rim will be ruined or at worse you will crash.
Handling is also compromised due to a reduce tread contact patch ie less traction.

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post #15 of 16 Old 01-22-2019, 09:32 PM Thread Starter
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You've made a fundamental error in your calculation. If your fuel economy is improved by 0.4 mpg, then you gain 5.4 miles of driving range per tank, not 5.4 gallons of fuel per fill-up. And that's assuming you burn all 13.5 gallons in your tank each fill-up.




Damn! This is exactly right.... yea, that's a case of beer annually if that... while tempting, probably not worth the stress on components like you all have stated...

Damn!
post #16 of 16 Old 01-30-2019, 03:41 AM
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I enjoyed this post until people felt the need to dig too deep in their calculators and "correct" the original post (I don't have the patience to "run the numbers"). But the post was funny...just laugh. All those who commented unnecessarily to prove how smart they are NEED a beer; if you play your cards right (and inflate your tires perhaps) you may be able to afford one next time you fill up!

P.S. - Beer is good
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