Tires and improving fuel economy

[kaisen]

Originally Posted by speeder

so what you're saying is that i need to run bald, over-inflated tires, right?

Yes

[9dreizig]

hey that is exactly what I AM running!! cool
So I don't have to buy new ones?

[peppy]

I saw a formula in another bbs, 50% reduction in PSI = 10% reduction in MPG.

I ran it on my jetta reversed and it is about right.

[masraum]

Originally Posted by peppy

I saw a formula in another bbs, 50% reduction in PSI = 10% reduction in MPG.

I ran it on my jetta reversed and it is about right.

I if I run my tires from 30psi to 45, I'd get 10% improvement in mileage.

[masraum]

Originally Posted by kaisen

The actual tires make a big difference too. Not just the PSI they run.
I bought low rolling resistance Kumho 'Eco Solus' KR22 tires for my wife's Camry and picked up 2-3 mpg over the Michelins that were on there, running at the same PSI. And the KR22s have a 100,000 mile warranty. And they're half the price of the Michelins.

Some tires take more energy to push along.

I haven't yet had the opportunity to read your three long posts. I suspect that in most tires designed for fuel economy and with high mileage warranties, they will be running a VERY hard compound rubber.

It's been my experience that hard compound rubber gives up a lot in grip.

So, you've got eco tires, you hit the brakes and the brakes lock up and you slide forever, or, you've got ABS and they keep the brakes from locking up but it takes much, much longer to stop the car than it would have with softer grippier tires.

Even worse if you try to swerve around something with the eco tires.

If I have to sacrifice safety for eco, I'm going to go with safety every time.

Even if this is a wife that drives like a little old lady, other people don't drive like that. When the circumstances are under her control, it may be fine, but when things go bad, that's when you really need to rely on tires for grip. Fuel economy and tire life be damned.

I would think that it would be possible to build a tire with a hard carcass and small footprint but grippy rubber that would still provide decent grip.

[kaisen]

Originally Posted by masraum

I haven't yet had the opportunity to read your three long posts. I suspect that in most tires designed for fuel economy and with high mileage warranties, they will be running a VERY hard compound rubber.

It's been my experience that hard compound rubber gives up a lot in grip.

So, you've got eco tires, you hit the brakes and the brakes lock up and you slide forever, or, you've got ABS and they keep the brakes from locking up but it takes much, much longer to stop the car than it would have with softer grippier tires.

Even worse if you try to swerve around something with the eco tires.

If I have to sacrifice safety for eco, I'm going to go with safety every time.

Even if this is a wife that drives like a little old lady, other people don't drive like that. When the circumstances are under her control, it may be fine, but when things go bad, that's when you really need to rely on tires for grip. Fuel economy and tire life be damned.

I would think that it would be possible to build a tire with a hard carcass and small footprint but grippy rubber that would still provide decent grip.

Partially true. It is all about compromise. Still, it's not all or nothing, it's picking the best blends of attributes for your needs.

[kaisen]

BTW, the Kumho KR22 turned in 0.88G lateral and 50-0 in 97.2ft (dry) vs Goodyear Assurance at 0.90G and 101.3ft. So it's not like it's a dramatic difference.

[BRPORSCHE]

Since I have a long commute, one hundred miles a day, I wanted to try this out. Gas saving is money saving, right? Well, I was averaging 24 mpg. On 3-26-11 I had a mpg of 27.49 and then today I filled up and had a mpg of 29.42. By just increasing my fuel pressure up to 42 psi.

Can't say I am any more happy.

BTW this is a 2005 Mazda 6i.

Edit: My gas light used to come on right around 400 miles. Now I can get up to 470 miles. Quite the improvement.

[Porsche-O-Phile]

Max. rated pressure = 44 psi. Filled to 45 psi. Hard ride but dramatic increase in mileage (previously around 28-32).

[BRPORSCHE]

Think I should increase the psi a little but more?

[VincentVega]

By just increasing my fuel pressure up to 42 psi.

Next you'll need bigger injectors

[BRPORSCHE]

Originally Posted by VincentVega

Next you'll need bigger injectors

Confused?

[island911]

Originally Posted by speeder

So what you're saying is that I need to run bald, over-inflated tires, right?

Add "skinny" to the list.

As any cyclist knows, fat tires suck energy. (lots of aero drag)

[RWebb]

add with old, hard rubber to the list