The inflated debate

[ParknVibe]

I placed this copy of my reply to (New member here with questions) from the lounge here as well......

Kincaid wrote:
I do not know about towing. I second the addition of the SRI. I'd like to get one myself. The only other thing for mpg that I can think of is the old trick of pumping up the air pressure in the tires to about 40 psi. Believe it or not this also takes some of the harshness out of the ride, I think because you are getting a bit more space between the ground and your rims. You could maybe add a better flowing exhaust system but 1) it isn't needed for sound if you have the SRI and 2) it is expensive and I doubt you'd ever recover on the investment

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Since I now have my own air compresser to put air in my tires, I just went ahead to have all of the tires inflated to 40 PSI. A bit of history....When I had the 2009 Vibe new for a about three months, I found that the tires were inflated to 40 PSI and I wasn't really complaining about the harshness over rough roads and potholes. After my "shock" of the high tire pressure, I reduced it to the 32/32 psi as per the card. It was after doing that that I started to feel all the road harshness (using Goodyear RA OEM 17") tires. I since also adjusted the pressure to different rates and felt that 35f 33 rear was ok, still getting a harsh ride.

After taking a short ride around town, with 40 PSI pressure, I felt that the car floats over the rough road surfaces or road patches and cracks in the road. I feel that it is more smoother and even quieter then before.

While adding the air to one of the tires, I found that a circle crack is starting to form on the sidewall face. Now I'm thinking that with correct or lower pressure, the sidewalls are flexing to much over bumps and potholes and that flexing is causing the harshness. Now with a higher pressure and making a stiffer sidewall, the tire will not flex but bouce over the bump.

I'll let you know about how the car feels after a longer run of driving.

[Chiadog]

When I had the 2009 Vibe new for a about three months, I found that the tires were inflated to 40 PSI and I wasn't really complaining about the harshness over rough roads and potholes. After my "shock" of the high tire pressure, I reduced it to the 32/32 psi as per the card. It was after doing that that I started to feel all the road harshness (using Goodyear RA OEM 17") tires.

While adding the air to one of the tires, I found that a circle crack is starting to form on the sidewall face. Now I'm thinking that with correct or lower pressure, the sidewalls are flexing to much over bumps and potholes and that flexing is causing the harshness. Now with a higher pressure and making a stiffer sidewall, the tire will not flex but bounce over the bump.
I'll let you know about how the car feels after a longer run of driving.

Sounds counter-intuitive on the tire pressure vs harsh ride correlation. I will post my results, if/when I decide to test different tire pressures: 40 vs 32. It is snowing today
On the sidewall cracking, I would attribute this to over-pressurizing and expanding an old and un-flexable tire. Just my opinion.
chiadog

[Zimm]

i know it sounds counter intuitive, but i'll second the notion that my '10 base rides better when inflated to around 38-39 PSI than it does at 32. at 32, steering is sluggish, braking is longer, MPG is terrible and the ride is generally less comfortable.

this is on the stock goodyear RSA's, now with around 44k miles on them.

[thebornotaku]

FWIW vehicle manufacturers figure tire pressures based on vehicle weight, in order to keep the tread completely in contact with the road.

When you overinflate, the outside edges of the tire don't carry as much load, and you effectively reduce your overall traction and increase tread wear in the center.

I see it almost every day at work -- somebody with their tires pumped up to some ungodly pressure, bald in the center and plenty of depth on the edges.

Though it makes sense that it would *feel* more responsive. Less sidewall flex means turning and braking will feel more responsive, because you don't have to wait for the tires to "settle" in to position before the suspension starts working and everything will generally react more quickly.

As far as ride quality, that seems really counter-intuitive but again: eliminating tire movement means the suspension components can do their job better.

Like I said though, just be warned that ultimately you will have less grip and increased tread wear. Though the grip argument could go both ways -- it's not uncommon for guys running autocross or race events to up the pressure on their tires, to keep them from rolling on to the sidewalls. In my daily driver (1985 Volvo) with some suspension mods, I run 36psi daily and around 42psi while racing (yes, you read that right) to keep the tires off of the sidewall and on the tread blocks.

[vibenvy]

FWIW vehicle manufacturers figure tire pressures based on vehicle weight, in order to keep the tread completely in contact with the road.

When you overinflate, the outside edges of the tire don't carry as much load, and you effectively reduce your overall traction and increase tread wear in the center.

I see it almost every day at work -- somebody with their tires pumped up to some ungodly pressure, bald in the center and plenty of depth on the edges.

Though it makes sense that it would *feel* more responsive. Less sidewall flex means turning and braking will feel more responsive, because you don't have to wait for the tires to "settle" in to position before the suspension starts working and everything will generally react more quickly.

As far as ride quality, that seems really counter-intuitive but again: eliminating tire movement means the suspension components can do their job better.

Like I said though, just be warned that ultimately you will have less grip and increased tread wear. Though the grip argument could go both ways -- it's not uncommon for guys running autocross or race events to up the pressure on their tires, to keep them from rolling on to the sidewalls. In my daily driver (1985 Volvo) with some suspension mods, I run 36psi daily and around 42psi while racing (yes, you read that right) to keep the tires off of the sidewall and on the tread blocks.

I recently upped the tire pressure on both our 2009 Vibe GTs from 32 PSI (factory) to 34 PSI. The front tires always looked low, so I figured I'd up all 4 tires by 2 PSI. Will this effect the tires at all or is 2 PSI nothing major to worry about? Thanks in advance!

[ParknVibe]

I have been driving the '09 Vibe with all the tires inflated to 40 psi for two months now. These are the 17 inch low profile OEM Goodyear tires.

The ride really does feel better. However, I did not recheck the tire pressure during this time. But, with the outdoor temperature rising for the summer, I'm sure the tires have about the same pressure if not higher. My MPG is better as well. It went from less then 20 mpg to 24 mpg with mixed driving.

I am thinking that with tire pressure down at 32 psi., and with low profile sidewalls, the road harshness is transfered to the wheels faster by the flexing then it would if there was more vertical space between the road and the wheel.

Now during the winter months, the rubber will become stiffer and so the ride will become hard.

[Kincaid]

FWIW vehicle manufacturers figure tire pressures based on vehicle weight, in order to keep the tread completely in contact with the road.

When you overinflate, the outside edges of the tire don't carry as much load, and you effectively reduce your overall traction and increase tread wear in the center.

I see it almost every day at work -- somebody with their tires pumped up to some ungodly pressure, bald in the center and plenty of depth on the edges.

Though it makes sense that it would *feel* more responsive. Less sidewall flex means turning and braking will feel more responsive, because you don't have to wait for the tires to "settle" in to position before the suspension starts working and everything will generally react more quickly.

As far as ride quality, that seems really counter-intuitive but again: eliminating tire movement means the suspension components can do their job better.

Like I said though, just be warned that ultimately you will have less grip and increased tread wear. Though the grip argument could go both ways -- it's not uncommon for guys running autocross or race events to up the pressure on their tires, to keep them from rolling on to the sidewalls. In my daily driver (1985 Volvo) with some suspension mods, I run 36psi daily and around 42psi while racing (yes, you read that right) to keep the tires off of the sidewall and on the tread blocks.

I agree with everything above. I do stand behind my original statement that higher pressure removes some harshness over bumps and potholes, etc. Turning takes less effort because the contact patch is less. I think treadwear will be worse in the center - except that I tend to fling my car around on curves quite a bit so with more aggressive driving it is working the outside/inside of the tread more anyway, so it seems to work out about even anyway. My RS-As only lasted to 41,000, through a combination of aggressive driving and higher air pressure, but the wear was even across the tread face as far as I could tell. However, I wasn't sorry to see those RS-A's go bye bye!