rear bump stops

[tom4bren]

Aww cmon tom, like my dad always says, 'if im not razzin ya, that probably means i dont like you anymore'

I think I told you once that you strike a disturbing resemblance to my nephew. If'n we're in fact fambly then ... GAME ON Peanut Butter!!!

[Ldub]

I DO have a response to that ... actually 2.

1. PV=eRT

2. Watcha gonna do when the recommended pressure on the door jam is higher than the max pressure listed stamped on the tire???

In response to:

1. . ...P-vert?

2. . When that happens, lemme know, we'll talk...

[tom4bren]

Mt Dew tru da nose on dat 1 Mr. Dub

[SlowPro48]

I'm not say'n that high psi is bad or dangerous, as long as you are satisfied with the wear etc, go for it.
It's the misconception of the max press on the sidewall being mistaken for a recommendation that I disagree with...

Well I'll say it then. It's dangerous!

Example: max recommended pressure on my TerraGrapplers is 50psi. At that pressure there would be about 42% less rubber in contact with the road than what Isuzu intended, which will significantly increase stopping distance - and reduce lateral grip as well. Unless you're hauling a lot of weight, for safety's sake you might want to air down a little! Who knows - it might keep you from rear-ending somebody on the freeway someday. And BTW, 29psi is specified as cold - so pressure increase according to the Ideal Gas Law is already accounted for.

[RickOKC]

How much sidewall do you have compared to before? By ride, are you referring to handling or cushy-ness.

I went with a tire that was 3" taller overall so there was a bit of growth. I'm talking strictly about ride comfort quality - I really haven't seen any noticible difference in handling except for when I had them aired down super low (15-20psi) for off-road. Some of the streets around here are in extremely poor condition!

[pbkid]

Well I'll say it then. It's dangerous!

Example: max recommended pressure on my TerraGrapplers is 50psi. At that pressure there would be about 42% less rubber in contact with the road than what Isuzu intended, which will significantly increase stopping distance - and reduce lateral grip as well. Unless you're hauling a lot of weight, for safety's sake you might want to air down a little! Who knows - it might keep you from rear-ending somebody on the freeway someday. And BTW, 29psi is specified as cold - so pressure increase according to the Ideal Gas Law is already accounted for.

I'm gonna agree to disagree with this statement. sure at rolling speed, you lose an amount of rubber contact with the road as the tires expand in the middle of the tread, but what happens when you press those brakes hard and the weight of the vehicle is thrown onto the front tires? you then have 100% contact and have regular tire grip.
Lets see if i can word this to make sense as it does in my head
As well, if we are talking safety, which is my point for inflating my tires so high; if you have your tires at lower pressure, say 29 psi as your door jam suggests, how is your vehicle supposed to handle in a panic skid or quick swerve? My reasoning is, as your sidewall gives, it causes body roll, increasing chance of a rollover. I personally would rather skid a little (key word little), than have the tires grab hard and roll me over.
Now, this also supports my thought behind hard straight line braking, if you swerve and put the weight of the vehicle on 2 tires, you now are operating at optimal traction levels (enough to skid but also handle). Rather, at low tire pressure you increase your traction to a level of rollover or poor handling (low tire pressure proves to make for sloppy handling).

Let the bashing and arguments begin

[PK]

Wheres RiffRaff when ya need him??

He will sort you guys out.

PK

[tom4bren]

Well I'll say it then. It's dangerous!

Example: max recommended pressure on my TerraGrapplers is 50psi. At that pressure there would be about 42% less rubber in contact with the road than what Isuzu intended, which will significantly increase stopping distance - and reduce lateral grip as well. Unless you're hauling a lot of weight, for safety's sake you might want to air down a little! Who knows - it might keep you from rear-ending somebody on the freeway someday. And BTW, 29psi is specified as cold - so pressure increase according to the Ideal Gas Law is already accounted for.

I'm gonna agree to disagree with this statement. sure at rolling speed, you lose an amount of rubber contact with the road as the tires expand in the middle of the tread, but what happens when you press those brakes hard and the weight of the vehicle is thrown onto the front tires? you then have 100% contact and have regular tire grip.
Lets see if i can word this to make sense as it does in my head
As well, if we are talking safety, which is my point for inflating my tires so high; if you have your tires at lower pressure, say 29 psi as your door jam suggests, how is your vehicle supposed to handle in a panic skid or quick swerve? My reasoning is, as your sidewall gives, it causes body roll, increasing chance of a rollover. I personally would rather skid a little (key word little), than have the tires grab hard and roll me over.
Now, this also supports my thought behind hard straight line braking, if you swerve and put the weight of the vehicle on 2 tires, you now are operating at optimal traction levels (enough to skid but also handle). Rather, at low tire pressure you increase your traction to a level of rollover or poor handling (low tire pressure proves to make for sloppy handling).

Let the bashing and arguments begin

I'm going to agree to disagree with both Y'all.

Traction is more a factor of tire design than it is air pressure. I know that my old Wrangler MTs had a stiff sidewall so tire pressure made very little difference on any of the factors you're talking about. The Firestone ATs I'm running now have a softer sidewall so I've got to keep a closer eye on the pressure - but only in terms of wear, handling seems unaffected. IIRC Marlin is running tires with Kevlar in the sidewalls. He can prolly run at 0 psi & not notice (yes, I'm exagerating).

[Cobrajet]

Let's compromise...

Tire pressure is a compromise. Optimum tire pressure is based on a multitude of factors. Tire design, tire size, temperature, vehicle weight, road conditions, etc. Take NASCAR for instance. During the course of a race the crew chief is constantly adjusting tire pressures to compensate for track conditions, weather/air temp, chassis adjustments, etc. Do they look at the pressure stamped on the side of the tire? Do they use a set pressure from the chassis maker? No. My tire pressures are based on my own experience and have little to do with whatever Tom or PK or SlowPro run their tires at. They don't have the same tires and wheels, so they run a different tire pressure. I personally don't think either the car mfg tire pressure on the door OR the max pressure on the tire sidewall is optimum. It's going to be somewhere in between. At least for me!

[evillecutter]

my tires say 55 psi my vx says 29 psi so i go 40psi and they both seem happy - the ride feels exactly the same as if they were 29 psi

[PK]

Let's compromise...

Tire pressure is a compromise. Optimum tire pressure is based on a multitude of factors. Tire design, tire size, temperature, vehicle weight, road conditions, etc. Take NASCAR for instance. During the course of a race the crew chief is constantly adjusting tire pressures to compensate for track conditions, weather/air temp, chassis adjustments, etc. Do they look at the pressure stamped on the side of the tire? Do they use a set pressure from the chassis maker? No. My tire pressures are based on my own experience and have little to do with whatever Tom or PK or SlowPro run their tires at. They don't have the same tires and wheels, so they run a different tire pressure. I personally don't think either the car mfg tire pressure on the door OR the max pressure on the tire sidewall is optimum. It's going to be somewhere in between. At least for me!

I fully agree with Cobrajet on this..
The optimum tyre pressure is very much a seat of the pants selection.
Just do not exceed the maximum stated on the tyre, as that is a safety requirement.
I run mine at 32PSI unloaded, and bump the rears to 36 if I have a heavy load in the back.
If you really want to get the optimum balance of good fuel consumption, and maximum tyre life, then use the chalk mark across the tyre method to match your tyre pressures to the load of the VX.

PK

[Triathlete]

I run my tires at 110psi on my daily driver

[89Vette]

Couple things:

Contact patch varies from tire to tire...And that can be with the same pressure. Changing pressure to stay in line with tire manufacturer's intended contact patch really is the correct solution. Thought there are other considerations... Bounce of the tire is matched with suspension travel, rebound rates, springs, etc... The suspension is geared up as a "unit" with the tires mounted from the factory. SUVs have a much bigger variance in tire selection/type than sedan (cars), so more has to be judged by the driver and performance. In general, though, I agree that starting with recommended manufacturer (VX suggested) pressure is your best option. My 285-50's will take way more pressure than 29psi. Even the stock, original tires would take more than 29psi. That should be your clue!

I think there's a ride trade-off vs. MPG. More air is gonna give better mileage by reducing the contact patch (that may or may not be starting at the same area as stock.) Here, it's only a matter of less patch=less friction. That will provide better MPG. But you'll have to judge issues with tire bounce and handling if you stray more than say....10-20%. No one can determine YOUR preference. Softer (until dangerously soft -- less than 20psi for example) should always make the ride softer -- as it will absorb more bumps.

I can't see how 20, or even 29psi, can feel the same as 40psi. There's gonna be some difference. The harder you drive, the more obvious it'll be.

Softer will "roll" more in turns and degrade handling. Harder may degrade traction -- especially in rain/snow.

Pick what's best for your taste, climate, and mpg/longevity concern. Really, there IS a correct pressure that determined by viewing tire wear and contact patch. So, you could/should let those decide for you. If you'be strayed too far from stock configuration, you may just have to compensate and adjust your suspension.

[Maddawg]

I run my tires at 110psi on my daily driver

What the hell is it a big rig 18 wheeler?????????

[TheGanzman]

I run my tires at 110psi on my daily driver

Is that ALL?! I'm running a buck-twenty! Looks like you and I are the only ones "in on" this one...