High air pressure vs lower air pressure in tires.

[CapriRacer]

Originally Posted By: XS650
Originally Posted By: CapriRacer

Regarding the +5 psi recommendation - even if it results in more than the max as specified on the sidewall, it's still OK. Dry traction differences are hardly noticeable and wet traction, especially hydroplaning, are generally improved.


CR do you have a source for that?

I don't doubt you at all. I also don't hesitate to do it myself when conditions all for it but would like to have another source for the Doubting Thomases.

I'm particularly interested in the P-metric 35 psi sidewall pressure not being an absolute max number.


P metric Standard load tires max out from a load carrying capacity at 35 psi, so you will find that with a very few exceptions, the pressure specified by the vehicle manufacturer is 35 psi or less. Most tires manufacturers put 44 psi max on the sidewall - with the major exception of the Michelin brands (Michelin, Uniroyal, and Goodrich) in S and T rated. For some reason that I can not make sense of, they put 35 psi max on their sidewalls, but it is within the design standards as published by The Tire and Rim Association to use up to 44 psi for these. Everyone else seems to think this is OK - and that's the basis of my comment.

The same is true for hard metric standard load tires (No "P" in front of the size).

 

[CapriRacer]

Originally Posted By: CrazyMike


......

Dry or wet, your threshold limit for traction is reduced if you're running excessive psi. If you've improved resistance to hydroplaning you've raised the outer edges, now you can maintain faster speeds before losing contact, but braking and cornering is compromised. How is this a good thing.

You can't tell me a Toyota Echo, an Avalon, or a Honda Accord or Civic has better handling qualities and traction with excessive psi, let alone it improving in the wet.

......



When I was racing on "street" tires, it was almost a given to use higher pressures - sometimes much higher. Some of this was because we couldn't put in as much camber as we would have liked - and some of it was to control the temperature build up - and some of it was because the tire's turn in was so much crisper.

Anyone who was new to the game was reluctant to do this at first, but as they boosted the pressure they all commented on how much faster the car cornered.

When it rained, we added a few more psi - again because we learned this works. I've used as high as 48 psi on a tire labeled with a max of 44 psi.

But I'm not suggesting that anyone go beyond 5 psi, but a radial tire's footprint is somewhat insensitive to pressure increases in this range. My own experience seems to bear this out. Listening to other's comments seems to reinforce this.

Again, don't get me wrong, but the car manufacturer's pressure seems to be geared more to ride than handling - and certainly the ride quality is diminished - but the steering crispness is greatly enhanced.

But there are some exceptions, and this should be approached with caution - and in steps.

 

[XS650]

Originally Posted By: CrazyMike



You can't tell me a Toyota Echo, an Avalon, or a Honda Accord or Civic has better handling qualities and traction with excessive psi, let alone it improving in the wet.

You can't tell me that a Toyota Echo, an Avalon, or a Honda Accord or Civic have factory recommended tire pressures that give optimum handling.

 

[CrazyMike]

Quote:
When I was racing on "street" tires, it was almost a given to use higher pressures - sometimes much higher. Some of this was because we couldn't put in as much camber as we would have liked - and some of it was to control the temperature build up - and some of it was because the tire's turn in was so much crisper.


NOW I get where you're coming from!!!

Quote:
Anyone who was new to the game was reluctant to do this at first, but as they boosted the pressure they all commented on how much faster the car cornered.


So the issue here wasn't traction, it was to improve lateral stability and steering response. Fine if you're running perfect road conditions, a tuned car and sticky tires.



Quote:
When it rained, we added a few more psi - again because we learned this works. I've used as high as 48 psi on a tire labeled with a max of 44 psi.


I've never raced, nor have I experimented with tires and sport cars in a racing application. I do know I've dropped pressure without changing footprint and gained traction on public roads.



Quote:
Again, don't get me wrong, but the car manufacturer's pressure seems to be geared more to ride than handling - and certainly the ride quality is diminished - but the steering crispness is greatly enhanced.


Car manufacturer's psi recommendations are geared towards protection from accident liability, not handling or ride. Those ratings are to carry the vehicle at it's maximum gross weight. If ride was the concern and not carrying capacity, most cars would show a lower psi reccomendation than the current one provided.


I don't see how this is applicable to public roads though. Race courses are maintained, spills are cleaned, a high traction, ridgid tire can find/maintain traction easily, it's in the best possible enviroment. On public roads we have frost heaves, spilled lubricants, rocks/pebbles, tar strips, let alone what rain does for available traction in these conditions.

If your public roads are extremly good quality, not neccessarily equal to a race course, I can definitely see working on this theory. If your roads plainly put, suck, your tires need all the help they can get, and a Windstar with Uniroyal Tiger Paws cranked up to 44psi is not the way to do it.

May be more regional than we think really. If these kind of roads exist down in the US, I want to take a road trip!!

 

[CrazyMike]

Quote:

You can't tell me that a Toyota Echo, an Avalon, or a Honda Accord or Civic have factory recommended tire pressures that give optimum handling.


Nor can you tell me it's improved.

 

[bluemax1]

Originally Posted By: CapriRacer
Originally Posted By: CrazyMike


......

Dry or wet, your threshold limit for traction is reduced if you're running excessive psi. If you've improved resistance to hydroplaning you've raised the outer edges, now you can maintain faster speeds before losing contact, but braking and cornering is compromised. How is this a good thing.

You can't tell me a Toyota Echo, an Avalon, or a Honda Accord or Civic has better handling qualities and traction with excessive psi, let alone it improving in the wet.

......



When I was racing on "street" tires, it was almost a given to use higher pressures - sometimes much higher. Some of this was because we couldn't put in as much camber as we would have liked - and some of it was to control the temperature build up - and some of it was because the tire's turn in was so much crisper.

Anyone who was new to the game was reluctant to do this at first, but as they boosted the pressure they all commented on how much faster the car cornered.

When it rained, we added a few more psi - again because we learned this works. I've used as high as 48 psi on a tire labeled with a max of 44 psi.

But I'm not suggesting that anyone go beyond 5 psi, but a radial tire's footprint is somewhat insensitive to pressure increases in this range. My own experience seems to bear this out. Listening to other's comments seems to reinforce this.

Again, don't get me wrong, but the car manufacturer's pressure seems to be geared more to ride than handling - and certainly the ride quality is diminished - but the steering crispness is greatly enhanced.

But there are some exceptions, and this should be approached with caution - and in steps.

What kind of racing were you doing? Something along the lines of autoX'ing?

To some extent, higher tire pressures work in autoXing. It reduces sidewall rollover and improves turn-in response due to the stiffer sidewalls although you can overdo it when the contact patch starts bowing (opposite of cupping, bowing is where the edges of the contact patch start lifting off, only way to tell if your alignment and tire pressures are properly setup for the car and driving style is to measure the tread temps across the width of the tire). Usually, a simple way is to use tire chalk on the shoulders and inflate the tires to the point you stop rubbing chalk off the shoulders.

On roadcourses though, it's a whole different story. In almost every case (using street and R-comps) folks discover that they need lower tire pressures to attain maximum traction. The abuse on roadcourses (and racing conditions that exceed the intermittent ~1-minute laps of an autoX) tends to generate much more heat in the tires and this increases the tire pressure negatively affecting the contact patch.

Just about every tire has an optimal hot tire pressure range for maximum traction. This pressure differs somewhat depending on the platform, weight and alignment (and driving style). The only way for racers to determine it properly is by actually testing it on-track by adjusting tire pressures no more than 2psi at a a time. Track telemetry is the best way to note the changes since seat-of-the-pants is not always right. Laptimes and cornering G's don't lie.

The occasional folks who drive to the track, run their cars and drive home all on the same tires (as opposed to trailering the track car or bringing a set of dedicated track wheels/tires that are mounted/dismounted at the track) usually end up dropping tire pressure at the track and then needing to reinflate them for the drive home.

Me and other usually help novices improve their handling by decreasing their tire pressures because most have them set at a relatively higher cold temp which becomes way too high once they heat up on-track.


Max

 

[ewetho]

Just run the door plackard and be done with it unless you want to chalk your tire and see how it is doing.

Other than that just monitor the tire wear. If it is even then your fine.

 

[grampi]

It depends upon the vehicle. On our family's smaller vehicles (Corolla, Civic, and Tercel) recommended +5 seems to work the best. I have roughly 40K on a set of 70K mile tires on my Corolla I've been running the entire time at +5 and it looks as though the actual treadwear will exceed the 70K mile rating. They appear to have more than 50% of their tread still left. Handling seems to be better as well at +5. My wife's MPV on the other hand rides too stiff at +5 and because of this, I keep them inflated to the recommended pressure.

 

[97tbird]

I have a 4.6L Tbird that weighs just a tad below 4000 lbs. and the rec. pressure is 32 PSI....I think that's kinda low...I run them at 35 PSI...

 

[youdontwannaknow]

I have experimented a lot with tire pressure too and have finally settled in to +3psi(35psi) for the GY Integritys on the MDX, and +2psi(32psi) for the GY Tripletreds on the Accord. Its a good compromise between ride comfort, handling and rolling resistance.

Contrary to the popular belief my experience is that lower tire pressure can also result into more road noise.
There is a sweet spot that you need to hit so they pick up the least amount of road noise and a good improvement in handling and rolling resitance.
Increase/decrease 1psi at a time and you will find it.

 

[wileyE]

Most of my cars (fwd) are heavier in the front than back and handle better with more air in front. The oem sticker shows the same all around. They probably have to take into account passengers in the back and stuff in the trunk, which would make equal inflation more logical?

If you got too much time on your hands there a little kids science experiment that is revealing on psi. Take pieces of stiff construction paper and slide into the contact patch from all 4 sides. Measure and calculate the square in of contact, then multiply it by the psi in the tire. result is pretty darn close to the actual weight on that wheel. You can add them up for total vehicle weight.

Whats revealing (for me anyway)is how much difference there is in contact patch front to back, and how much adjustment in psi it take to get them the same.

 

[youdontwannaknow]

to that effect I have always wondered how much the whole diameter of the tire affects other things. The front diameter would then be smaller than the rear i.e. the fronts would be rotating faster than the rears to cover the same distance.
Obviously it has implications in speed and odometer readings, not to mention traction control systems and abs that rely on individual wheel rpm as their input.

 

[buster]

For the Triple Treads I put on, I have them at 35 lbs for all 4. (80% of max psi). I noticed an improvement. I ran the OEM Bridgestone's at 37 psi for all 4 and they lasted 83,000 miles.