Running tires at max sidewall pressure?

[Grog]

Yep, my truck tires max is 85. I run 80 in the front because the front axle has 5000 lbs on it. I laugh when people say trucks don't do good in snow because the back end is so light. My rear axle has 3100 lbs on it. I keep around 45 psi in the rear duals and they don't have full contact. When it's wet out you can see that the outside part of the tread doesn't make contact.

[legion]

Hmmmm....

On my Silverado, the factory recommends 35 psi all around, but I've been keeping them at 37 psi cold, as I notice a much better ride and handling. At 35 they feel too soft and the steering is mushy. At 37 the steering is crisp.

Anyway, my truck has an onboard tire pressure monitoring system, so I can see what pressures the tires are at all the time.

With the OEM American General tires, I kept them at 35 psi (that's where they felt the best cold). When they heated up, they would get to 39 psi. At that pressure, the handling was squirrelly at best. There was a noticeable loss of grip. Winding mountain roads were taken at 10- 20 mph below the posted speed limit.

After hydroplaning just south of Nashville coming back from Florida last year, I bought new Firestone tires. Like I said above, these seem to like 37 psi cold. When up to temperature, they will hit 40 or even 41 psi. (Max pressure on the sidewalls is 44 psi.) But the handling and grip IMPROVE dramatically at that pressure. I feel like I have racing slicks on, the grip is so good. They even do a better job in the wet or snow than my old tires.

[sammyg2]

Originally Posted by pwd72s

. Cheap tire pressure gauges are for entertainment purposes only...

LOL, you get what you pay for, right?

I have a bunch of tire pressure guages I've accumulated over the years.
Back when I was doing AX and TT I bought a couple of the more expensive gauges in an attempt to make sure I was making accurate pressure adjustments for optimum performance.

One is an top end dial gauge that I calibrated at work one time just for fun (we do that in our instrument shop all the time as we have tens of thousands of gauges here).
One of my gauges is a nice digital one, and the others are varying design and cost down to two small cheeeep stick types. the type you throw in the glove compartment for emergencies.

They all read within about 1 pound of each other.

The two 98 cent stick gauges are surprizingly accurate. They are more accurate than my $$$ digital gauge.


OOps, sorry for discussing technical stuff on the OT forum. Moderators, can you move this thread? j/k

[cashflyer]

Why would anyone think that a number on the door jamb is always proper??

While it's true that tire and car manufacturers spend a lot of time and money determining the correct tire pressure, there are a few things to consider:

A) That determination is made using a specific tire. A tire from a different manufacturer, or in a different size, or even in the same size and manufacturer but in a different model, can require different pressures.

B) That determination is made using a specific configuration. The car is loaded with a specific amount of weight, in a specific load arrangement. Changing loads can require changing pressure.

3) The determination is made to achieve a specific goal. In most cases, this goal is a compromise of ride comfort and handling. If you have a different goal, you may need different pressures.

Most people who drive on a track know that they have to frequently change their air pressures for optimum grip and handling; these changes can depend on track temps, track condition, and fuel loading, etc.

Door jamb tire pressure stickers are a guide - not some intergalactic law of physics.

[Pazuzu]

Originally Posted by sammyg2

The two 98 cent stick gauges are surprizingly accurate. They are more accurate than my $$$ digital gauge.

Even if they aren't always *accurate*, they are quite *precise*, as long as it's a dial type gauge. You can tell exactly what the reading is, and it doesn't change based on usage. I'm more concerned that my two drive wheels are within 1 pound of each other, than I am that they're exactly 32psi.

The "stick"style gauges are junk. neither accurate nor precise.

[pwd72s]

Originally Posted by Pazuzu

Even if they aren't always *accurate*, they are quite *precise*, as long as it's a dial type gauge. You can tell exactly what the reading is, and it doesn't change based on usage. I'm more concerned that my two drive wheels are within 1 pound of each other, than I am that they're exactly 32psi.

The "stick"style gauges are junk. neither accurate nor precise.

I bought a dial type at Shuck's auto parts here...$4.95. It read 25 pounds when the blue point read 34, so I tossed the cheapy...My Blue point was "made in usa"...buy one off a snap-on truck today? "Made in China"... So, took my blue point along when shopping for my next gauge...did some comparison of readings.

[kaisen]

Originally Posted by cashflyer

Why would anyone think that a number on the door jamb is always proper??

While it's true that tire and car manufacturers spend a lot of time and money determining the correct tire pressure, there are a few things to consider:

A) That determination is made using a specific tire. A tire from a different manufacturer, or in a different size, or even in the same size and manufacturer but in a different model, can require different pressures.

B) That determination is made using a specific configuration. The car is loaded with a specific amount of weight, in a specific load arrangement. Changing loads can require changing pressure.

3) The determination is made to achieve a specific goal. In most cases, this goal is a compromise of ride comfort and handling. If you have a different goal, you may need different pressures.

Most people who drive on a track know that they have to frequently change their air pressures for optimum grip and handling; these changes can depend on track temps, track condition, and fuel loading, etc.

Door jamb tire pressure stickers are a guide - not some intergalactic law of physics.

All true, but 99% of the time for 99% of the conditions encountered, the factory recommendations are best. Moving from 36 to 44 psi in a MUSTANG is a huge leap of logic. The tire Service Description (i.e. 91W) can't be very different for same-size tire fitments. It's not like going from a P tire to a LT tire, or a C load range to an E, where sidewall construction dictates tire pressure.

As you mentioned, a psi here and a psi there can really change the way a car handles on the track. Going from 36 to 44psi can make the break away lightning fast vs progressive, and make the front tires lose a lot of bite on turn-in.

Messing that much with tire pressures is a variable that can have big unintended consequences

[trekkor]

Yep, the free, 'over the counter' stick gauges they offer at the tires shops, read right there with the nice dial race gauges with the bleed-off relief valve.


KT

[legion]

Anyone know where I can get a dial tire gauge that reads in tenths of a psi?

[trekkor]

I would try a race shop or Summit.


KT

[cashflyer]

Originally Posted by legion

Anyone know where I can get a dial tire gauge that reads in tenths of a psi?

Longacre digital gauges read to tenths and are accurate to the tenth.
Their analogue is accurate to +/- 10%
Longacre Racing - Online Catalog: Electronic Wheel Scales, Gauges, Pyrometers, Chassis Setup and More!

They also have a temperature compensated gauge.
Longacre Racing - Online Catalog: Electronic Wheel Scales, Gauges, Pyrometers, Chassis Setup and More!

[legion]

Wow, that's a little more spendy than I want to get for a tire gauge!

[sammyg2]

Originally Posted by Pazuzu

Even if they aren't always *accurate*, they are quite *precise*, as long as it's a dial type gauge. You can tell exactly what the reading is, and it doesn't change based on usage. I'm more concerned that my two drive wheels are within 1 pound of each other, than I am that they're exactly 32psi.

The "stick"style gauges are junk. neither accurate nor precise.

Ahhh So you DO get what you pay for.

The two stick type gauges I have are as accurate and precise as my expensive gauges. That was the point of my post.

I checked them many times for not only accuracy but repeatability. The results showed that they were more accurate and had better repeatability than my expensive digital gauge which varied as much as a pound and a half over three or four consecutive readings.
One of mt stick gauges is round and the scale wraps around the gauge for very good seperation. the other has a straight rectangular shaped scale.
The round one could be read down to the 10th of a pound with interpretation, the other is basically good only down to the pound graduation.

Maybe it's just YOUR stick gauges that are junk.

[cashflyer]

Originally Posted by legion

Wow, that's a little more spendy than I want to get for a tire gauge!

Sorry... I thought you were looking for a gauge to equip your amateur Formula team with.

Accutire also has gauges that read in tenths, for much less money, but I am not sure how their quality is. (It may be great - I have never used one.)
ACCUTIRE GAUGE


I use one of these:

[Joe Ricard]

Thumbs up on the Longacre stuff.

Bought a good stick gauge for the truck goes to 140 PSI.

Most gauges are most accurate when used in the middle of the range.

Yea when your truck is 6800 pounds dry and empty. ya needs good tires. Load rating for each tire is 3454 pounds. Load range E Must be why they weight 52 pounds without the rim.

[pwd72s]

Here's the current snap on version of what I use...Now made in China, but looks the same as my old made in the USA gauge. Still under $20... When RoninLB was here, we compared with his digital gauge. Readings were identical...
YA243A, Gauge, Pressure, Dial Type, 0 to 100 PSI

My main objection to digitals? A pressure gauge that needs a battery just doesn't seem logical to me...

[teenerted1]

digitals need the battery for the display.