Busting the non believers

[cfg83]

trikkonceptz -

Well done. What I really like is that you drove like a "regular" person *with* AC. He had nothing left to hide behind. If you only had to deal with the car (not him), it would have been interesting to do the same drive before/after filling the air in the tires. But, they also sounded like they were almost dangerously low.

CarloSW2

[vtec-e]

Originally Posted by trikkonceptz

What really surprises me is how entrenched some of the mechanics are with information that may not be accurate and their unwillingness to accept change.

Congratulations Trikk. Inch by inch!
I had tears from a service shop manager a while back re: tire pressure. I guess he never researched the subject! My brother in law is a mechanic and i bounce ideas and theories off him and he just gives me the blank stare. I reckon his job is to plug in a laptop and find out what part needs replacing. I checked his tires today and they were at 25 psi. Nuff said.....

ollie

[Daox]

Awesome story Trik! 2.5 times the other guys mileage has gotta shock him somewhat, even if he won't admit it.

[TrikeKid]

Originally Posted by Clev

This is the kind of self-competition that I'm really enjoying. I can spend thousands of dollars to get my Accord into the 12's, and what do I achieve? Nothing; thousands of other Accords are modded in the same way, and some yokel with a warmed-over Camaro can achieve the same thing.

Getting an Accord to 45 mpg, on the other hand, not only is an accomplishment among Accords, but an accomplishment among all cars--just as 70 mpg is an accomplishment in a Metro (yeah, I'm talking about you, MetroMPG.) :-)

Last fillup is 35.70... with no mods so far except tire pressure. Working my way there!

I agree completely. My truck is far from the best rock crawler out there, but the best rock crawler out there isn't going to be pulling within half a gallon of EPA with only mods to the driver.

[MetroMPG]

Great story, Trik.

FYI, your anecdote was also picked up by TreeHugger: Real-World Anecdote: How You Drive is Very Important for Fuel Economy : TreeHugger

[jazzie604]

Originally Posted by trikkonceptz

He keep telling me I'll get better traction by lowering the PSI and I keep telling him I'll do it as soon as I go driving on the frozen lake here in South Florida.

He's correct about the traction issue. What he may not understand is that you are trying to get the best traction out of your tires. And if you ever get into a situation where you need the most traction from your tires, you will suffer. But those situations are called accidents, and you'll do what you have to....

[vtec-e]

Originally Posted by jazzie604

He's correct about the traction issue. What he may not understand is that you are trying to get the best traction out of your tires. And if you ever get into a situation where you need the most traction from your tires, you will suffer. But those situations are called accidents, and you'll do what you have to....

So you're saying traction is compromised at higher pressures/smaller contact patch? I've been looking for data on this for a long time. Did you find some?

ollie

[TrikeKid]

Originally Posted by vtec-e

So you're saying traction is compromised at higher pressures/smaller contact patch? I've been looking for data on this for a long time. Did you find some?

ollie

Yes, you can safely push your pressures slightly beyond the sidewall rating, but you will lose traction with too much air. Lower pressures allow the tires to flex and grab, where a harder tire wont, and in turn has less rubber on the ground. There is a reason you don't see people at the drag strip running 35 pounds of air in their drive tires. Same in off road situations, or snow.

[jazzie604]

Anecdotal data from the last 5 years of autoxing that I have done. there is always a sweet spot of traction where the tire holds the best. run it too high, and you can feel the car not gripping the same. same thing with too low of pressure. Especially on street tires, you have a certain range of pressure that is ideal for the tire carcass to maintain its shape during straight line and turning conditions. Too low, and the tire rolls all the way onto the sidewall. Too high, and you can actually see the edges of the tire not get used.
For hypermiling purposes, I cant see this making any difference in your MPG pursuits. the decreased rolling resistance during driving and turning should help, and obviously does make a difference. Only in the most extreme cases of handling needs (accidence avoidance, bad weather conditions, racing) will you approach the limits of adhesion, and it's only during those circumstances that you will need the maximum available grip. Its a game of chance and percentages at that point anyways, so an argument could effectively be made that the difference in tire pressure may not make any difference to the overall out come. Like ABS systems though, sometimes a little more grip and 5 less feet of travel is the difference. its all trade offs really.

[jazzie604]

Originally Posted by TrikeKid

There is a reason you don't see people at the drag strip running 35 pounds of air in their drive tires. Same in off road situations, or snow.

Keep in mind the difference between specialty tires and real "street" tires. you run 12 psi in a rock crawler, 15 psi in a drag slick, 20psi in a drag radial, but 28-35 in a street tire to keep the sidewalls from flexing and effecting the contact patch.