Increased air in tires to sidewall max -> +10% mpg

[RGUN]

That's not an article.... that's a message board discussing this issue. Also they never use the words "braking distance" anywhere so I know you didn't read anything on that page.

Not to belabour the point but I did address that. "According to your article, wider tires can offer more grip - presumably with a commensurate reduction in braking distance."

Of course I am assuming that with more grip, braking distance will generally be reduced - but I think that is a valid assumption.

 

[exar333]

fleabag?

HAHAHAHAHA!

'Inflate to sidwall?'

Epic thread...

http://forums.anandtech.com/showthread.php?t=323036

 

[tortillasoup]

Not to belabour the point but I did address that. "According to your article, wider tires can offer more grip - presumably with a commensurate reduction in braking distance."

Of course I am assuming that with more grip, braking distance will generally be reduced - but I think that is a valid assumption.

Embedded in the thread were discussions about how in a drag race, narrow tires would probably be better because of the shape of the tread footprint. That they use wide and tall tires because of heat dissipation. Wide tires are definitely beneficial for handling purposes but can only be useful so much before suspension geometry or road geometry have a negative effect.

 

[ElFenix]

You can also do "Extreme MPG" by not going anywhere to begin with.

0/0 = null

 

[996GT2]

Braking distance isn't going to be shorter with wider tires...

Wrong.

Wider tires = larger contact patch = more grip = shorter braking distance.

 

[tortillasoup]

Wrong.

Wider tires = larger contact patch = more grip = shorter braking distance.

Not true. Wider tires do not change the size of the contact patch, just the shape.

 

[JEDI]

Not true. Wider tires do not change the size of the contact patch, just the shape.

what?
so a tire from a tricycle that a 5yr kid would ride has the same contact patch as a nascar racing tire?!

 

[Yuriman]

what?
so a tire from a tricycle that a 5yr kid would ride has the same contact patch as a nascar racing tire?!

What he meant was, in an ideal situation, if the weight, pressure and materials were the same on two different tires of different widths, the contact patch would be the same because the narrower tire would flatten out more compared with the wider one. This isn't what we see in practice though.

 

[tortillasoup]

What he meant was, in an ideal situation, if the weight, pressure and materials were the same on two different tires of different widths, the contact patch would be the same because the narrower tire would flatten out more compared with the wider one. This isn't what we see in practice though.

We do see it in practice because proper tire pressure means even contact with the road. Even with radial tires, it IS possible to have uneven tire wear with more happening in the middle if there is too much pressure for the given load. As for the tricycle analogy, a tricycle isn't capable of holding the same amount of weight as a car wheel so physics be damned! Larger, wider, PASSENGER tires tend to have a higher load carrying capacity except when otherwise notated such as low profile tires.

 

[desy]

K instead of all the opinion with nothing to shore it up I used the google
Cause A I believed larger contact patch = shorter stopping
Turns out its complicated and it seems that isn't the case
For me I used to increase 10% over door for better fuel economy however I found I didn't like the rougher ride in spite of the minor fuel economy increase


"Inflation doesn’t affect contact patch size?
Yes, pressure has an extremely minor effect on contact patch size, but remember: Contact patch size doesn’t affect traction. Back in our tabletop experiment, we found that the friction was unchanged whether we tried to slide the block on its large side, its smaller side, or its smallest end.

Yes, that does mean that you’d get the same traction from a skinny bicycle tire as from your 180- or 190-section rear tire, provided the same rubber was on the outside. We don’t use bicycle tires for other reasons: With less rubber, that skinny tire would wear very rapidly; it wouldn’t support the side loads in cornering or the acceleration and deceleration stresses as well as the larger tire; it would overheat easily. There are probably other reasons known to tire engineers. But the traction would be the same.

I know, you don’t believe it. I don’t care. I invite you to do the experiments which will prove the scientists and engineers have been wrong ever since 1699, when Guillaume Amontons introduced F = μW to the world. After you’ve proved them wrong, you can laugh all the way to Stockholm to receive your Nobel Prize. Tell em I sent ya. "
http://www.stevemunden.com/frictiontopics.html

 

[Pulsar]

K instead of all the opinion with nothing to shore it up I used the google
Cause A I believed larger contact patch = shorter stopping
Turns out its complicated and it seems that isn't the case
For me I used to increase 10% over door for better fuel economy however I found I didn't like the rougher ride in spite of the minor fuel economy increase


"Inflation doesn’t affect contact patch size?
Yes, pressure has an extremely minor effect on contact patch size, but remember: Contact patch size doesn’t affect traction. Back in our tabletop experiment, we found that the friction was unchanged whether we tried to slide the block on its large side, its smaller side, or its smallest end.

Yes, that does mean that you’d get the same traction from a skinny bicycle tire as from your 180- or 190-section rear tire, provided the same rubber was on the outside. We don’t use bicycle tires for other reasons: With less rubber, that skinny tire would wear very rapidly; it wouldn’t support the side loads in cornering or the acceleration and deceleration stresses as well as the larger tire; it would overheat easily. There are probably other reasons known to tire engineers. But the traction would be the same.

I know, you don’t believe it. I don’t care. I invite you to do the experiments which will prove the scientists and engineers have been wrong ever since 1699, when Guillaume Amontons introduced F = μW to the world. After you’ve proved them wrong, you can laugh all the way to Stockholm to receive your Nobel Prize. Tell em I sent ya. "
http://www.stevemunden.com/frictiontopics.html

Sigh. In an ideal world, with non-interacting surfaces (read HARD) that holds true. However, in the real world a tire is not flat nor is a road flat. There is an interaction between the surfaces where they interlock - the high points (we're talking on an incredibly small scale) push into the rubber of the tire.

If you'd like to take this effect to an extreme, I suggest you try using velcro. Try sliding velcro against eachother. You can't, because of interactions.

That's why a larger contact patch has more traction. It yields more surface interactions between the two media.

Tortilla soup is trying to argue an ideal world. But the reality is that drag tires are wide for several reasons, one of which is increasing the contact patch size.

 

[desy]

Yes absurdly large compared to a regular car they also use a lot different rubber compound too.
We are talking about contact patch decrease size with an increase in pressure is the debate here
Its a negligible change

 

[WackyDan]

lol.

Next up "Why is the center of my tire going bald so fast?"

Along with these winners:

Why is my car handling different in wet conditions?
Why is my car taking longer to stop in emergency conditions?
Why is my tire pressure reading 55 PSI on a hot day after a long drive? * What was that popping sound and why and why am I losing control of my vehicle?

I only air up the tires to over door jam spec when I've got my trailer hooked up to the truck - Because load.

 

[tortillasoup]

Along with these winners:

Why is my car handling different in wet conditions?
Why is my car taking longer to stop in emergency conditions?
Why is my tire pressure reading 55 PSI on a hot day after a long drive? * What was that popping sound and why and why am I losing control of my vehicle?

I only air up the tires to over door jam spec when I've got my trailer hooked up to the truck - Because load.

Except all of those things you listed aren't true. Just because a tire wears faster down the center, doesn't mean it's magically going to brake significantly worse, that it will "pop" because of higher pressure, or handle poorly in wet conditions. In fact, on hot days, tires with higher pressures heat up a lot less if at all compared with tires that have significantly less inflation. I've seen tires inflated to 32psi heat up and get to 40psi but a tire inflated to 40psi may only increase about 2 psi. That means, quite a lot of heat is being generated in the tires, therefore wasted fuel, etc. Most tires blow out due to excess heat not excess pressure.

It's ideal to have an even contact patch with the road but an "overinflated" (not even contact patch) isn't going to be so significantly adversely affected. The overinflated tires even have the benefit of less likely to hydroplane and will cut through the snow down to the road surface better.

 

[WackyDan]

Except all of those things you listed aren't true. Just because a tire wears faster down the center, doesn't mean it's magically going to brake significantly worse, that it will "pop" because of higher pressure, or handle poorly in wet conditions. In fact, on hot days, tires with higher pressures heat up a lot less if at all compared with tires that have significantly less inflation. I've seen tires inflated to 32psi heat up and get to 40psi but a tire inflated to 40psi may only increase about 2 psi. That means, quite a lot of heat is being generated in the tires, therefore wasted fuel, etc. Most tires blow out due to excess heat not excess pressure.

It's ideal to have an even contact patch with the road but an "overinflated" (not even contact patch) isn't going to be so significantly adversely affected. The overinflated tires even have the benefit of less likely to hydroplane and will cut through the snow down to the road surface better.

When I'm paying $150 per tire and they are prematurely wearing due to over inflating to save some $ on gas... Well, that kinda defeats the purpose doesn't it?

 

[Yuriman]

When I'm paying $150 per tire and they are prematurely wearing due to over inflating to save some $ on gas... Well, that kinda defeats the purpose doesn't it?

The charts I've seen have actually shown decreasing overall wear with higher inflation pressures. See page 1 of this thread.

 

[tortillasoup]

When I'm paying $150 per tire and they are prematurely wearing due to over inflating to save some $ on gas... Well, that kinda defeats the purpose doesn't it?

I don't even know why you're quoting me. I've never suggested that it's ideal to have a tire wear down the center. Ideal is to have it wear evenly. On my Camry, that means putting 44psi in the front tires and 40psi on the rear. If I had followed the doorjamb recommendations, the sides would have been bald with the center having plenty of tread. All I was pointing out was that his specific complaints about too much inflation weren't founded in any reality.

 

[WackyDan]

I don't even know why you're quoting me. I've never suggested that it's ideal to have a tire wear down the center. Ideal is to have it wear evenly. On my Camry, that means putting 44psi in the front tires and 40psi on the rear. If I had followed the doorjamb recommendations, the sides would have been bald with the center having plenty of tread. All I was pointing out was that his specific complaints about too much inflation weren't founded in any reality.

Fair enough.

It can affect handling. Every time I forget to air down my rears after towing my trailer, I get far more wheel spin dry or wet then when I'm inflated per the manufacturers spec on the door jam.

If you want to figure out exactly how much pressure you need in the fronts vs the rears, good on you... I've done exactly that on my bikes as it does make a difference in the ride and handling against what the bike manufacturer specs. I just don't have the time to give a shit about it on my other two vehicles. WE don't drive them all that much so the price/use of gas doesn't bother me as much I guess.

*Plus towing I get 9-10 MPG and tire pressure isn't going to help me there.

 

[Subyman]

I don't get the battery thing. The alternator has to charge it one way or another. Unless the guy charges the deep cycle through his garage socket and doesn't use the alternator at all.

 

[Tsavo]

Not true. Wider tires do not change the size of the contact patch, just the shape.

Uh. What.

So all that extra rubber on the ground isn't actually touching the ground.

Right.

 

[Yuriman]

Fair enough.

It can affect handling. Every time I forget to air down my rears after towing my trailer, I get far more wheel spin dry or wet then when I'm inflated per the manufacturers spec on the door jam.

If you want to figure out exactly how much pressure you need in the fronts vs the rears, good on you... I've done exactly that on my bikes as it does make a difference in the ride and handling against what the bike manufacturer specs. I just don't have the time to give a shit about it on my other two vehicles. WE don't drive them all that much so the price/use of gas doesn't bother me as much I guess.

*Plus towing I get 9-10 MPG and tire pressure isn't going to help me there.

I'd like to point out that the actual dollar value difference between 9.0pmg and 9.5mpg is larger than 40mpg vs 50mpg. If you can get an extra 0.5mpg towing, you're saving as much money as if I got an extra 40-50mpg out of my car.

 

[Tsavo]

I'd like to point out that the actual dollar value difference between 9.0pmg and 9.5mpg is larger than 40mpg vs 50mpg. If you can get an extra 0.5mpg towing, you're saving as much money as if I got an extra 40-50mpg out of my car.

Assuming 15k miles/year, current cost of gas:
9-9.5 MPG is $21.93/mo savings
40-50 MPG is $18.75/mo savings

Over the life of the note, assuming 15k miles/year, 60 month note:
9-9.5 MPG is $1,315.79 total savings.
40-50 MPG is $1,125.00 total savings.

but...

Life of note cost of gas:
9 MPG: $25,000
9.5 MPG: $23,684.21
40 MPG: $5,625
50 MPG: $4500

 

[Tsavo]

Here's yet another reason why dumb people have no money.

I once knew a guy who commuted 30k miles a year in his truck. I told him to get a used Buick...the ones that get 32MPG all day without breaking a sweat.

I did some quick napkin math for him, but to no avail. He continued driving that truck for another two years, and whining about the cost of gas. He could have easily bagged $9700 in savings not including selling the car when he decided to quit the long commute. So...pretty close to $12k lost to the stupidity tax.

This is on top of the $5k the dealership soaked him for a stripper truck in the first place....he paid full sticker. And then he ran transmission fluid in the engine "to clean out the carbon soot". He did this on the advice of his last rate mechanic BIL. Utterly predictable results. The engine sounded like a metal can full of ball bearings.

 

[Subyman]

Here's yet another reason why dumb people have no money.

I once knew a guy who commuted 30k miles a year in his truck. I told him to get a used Buick...the ones that get 32MPG all day without breaking a sweat.

I did some quick napkin math for him, but to no avail. He continued driving that truck for another two years, and whining about the cost of gas. He could have easily bagged $9700 in savings not including selling the car when he decided to quit the long commute. So...pretty close to $12k lost to the stupidity tax.

This is on top of the $5k the dealership soaked him for a stripper truck in the first place....he paid full sticker. And then he ran transmission fluid in the engine "to clean out the carbon soot". He did this on the advice of his last rate mechanic BIL. Utterly predictable results. The engine sounded like a metal can full of ball bearings.

I don't understand why people use full size trucks to commute. I own a truck, but only take it out when my equipment or load will not fit in my car.

 

[Yuriman]

I don't understand why people use full size trucks to commute. I own a truck, but only take it out when my equipment or load will not fit in my car.

The Wrong Tool for the Job: this is what you are doing, if you use a full-sized pickup truck for anything smaller than hauling multi-ton loads. And I’m not even going to mention the folly of using a pickup truck to commute to an office job. Fuck.

Source

Quoted for hilarity.

I also have an F150, but I can count on my hands how many times I use it in a year. Its resale value is practically zero at this point, or I'd probably move over to using a rental when I couldn't pull whatever I needed in a trailer behind my car.