Tire Pressure Gauges

oops you are right... its to control oversteer. guess i should read what i type. its to help the rear end from swinging around in a panic stop.

 

Actually, not quite. The reading accuracy for a device is one half of the smallest increment indicated on the device. In this case, the gauge has an increment of 0.5 psi, therefor, its reading accuracy is +/- 0.25 psi. That, though, is only one of the potential sources of error, but is the easist to determine.

(Cavet: this is not exactly always true. Some gauges, especially analog can be considered more accurate then this rule. An example would be a very large thermometer marked by the degree. The expected error would be +/- 0.5 degree. The user, though, could reasonably determine when the mercury was above or below the halfway point between the degree marks. The error might be considered closer to +/- 0.25 degrees. This is very dependent on the situation, and does not typically apply to digital gauges.)

 

actually on my cheap gauge, the error is listed as +/- ½ psi and yes i realize that this is counterintuitive to a device with ½ psi increments

 

I have an AccuGauge analog tire gauge that works great. Holds the reading until you push a button, no batteries to replace, big enough you won't lose it but small enough you'll actually use it.

 

That also assumes the rounding algorithm is actually a rounding algorithm and not one that truncates. I don't want to get too technical, but... In the case where a device has the *capability* to show the range between zero and nine tenths on its display yet is implemented to only to show in 0.5 increments, I'd seriously doubt it's doing the math internally in the most accurate manner. This isn't a graduated cylinder where the limit is physical space in the markings.

If the internal sensor knew the pressure was 38.27 PSI, tell me why it should bother rounding up to 38.5 instead of 38.3 -- both numbers could be displayed with equal ease. Instead it shows 38.27 PSI as 38.5 or 38.0 -- my bet is on 38.0. In computer programming, the integer math result of 2/3 is 0 even though rounding would suggest 1. I think a similar thing is going on here.

Short story: on these consumer devices that measure in 0.5 PSI increments, I don't hold them to anything more exact than +/- 0.5 PSI. And that was much more technical than I intended; sorry.

 

A little more info on my AccuTire experience:

I bought this AccuTire gauge at Target because I needed one and remembered while I was in the store. I used it once, was satisfied, then put it away in the tote I keep in the back of the car. A few weeks later, I decided to check my tires and when I tried to use it the display showed "00.L" and wouldn't give me a reading. So not even two successful uses.

I replaced it with this item from Amazon.com and it's much higher quality, gets a better seal on the valve stem, comes in a protective sleeve, and has already lived up to the task on more than one occasion.

 

I also have the Brookstone tire gauge.

Brookstone Tire Gauge Link

I like its features and accuracy.

Stores PSI settings for two vehicles or differing PSI for front and rear tires. Big-digit, easy-to-read display with colored screen prompts show GREEN for FILL, RED for BLEED and BLUE for TARGET REACHED. Bleeder valve for manually reducing PSI if you overfill.

Endorsed by the Automobile Club of New York and AAA New Jersey.

[Broken External Image]:http://www.brookstone.com/bs_assets/images/shop/thumbnail/412858_t.jpg

 

The major problem with many of the digital gauges is that they have difficulty sealing against the valve.. This is really surprising considering that in general, even the cheapest analog stick gauge tends to work perfectly every time..

The second issue is that none of the digital gauges use a direct sensor for pressure but have a mechanical movement inside similar to an analog gauge. The digital portion just translates the mechanical position into a digital display.. In other words, none of the "digital" gauges are 100% electronic, they are all still basically an analog gauge, but with an electronic digital readout..

 

I too prefer an analog gage. Mine is many years old but it's still accurate to within a pound or so and consistant to within a quarter pound, and that's what's important to me. Plus, as you said, it's easy to use and doesn't need batteries.

 

I don't claim to be an expert, but I think the problem is when you're going around a corner, if you're going to lose traction; you want to lose it in your front tires first, so you can steer out of it. If your back tires go first, you're screwed. Also, more weight towards the front of the car gives them more traction.

I think it's good to keep in mind that you get your best left-right traction when in neutral. You learn in motorcycle class (where traction is critical) that it is a balance between ac/deceleration traction and turning traction.

I remember skidding towards another car on the ice thinking for sure I was going to hit it. I was turned away but headed right for it. At the last second I took my foot off the brake and the car immediatly started going the way I was steering and dodged the car. It was sure unintuitive to release the brake when I thought I was going to ram that other car.

Also, my dad was going down a snowy mountain road, and thought he could put it in a lower gear to slow himself down. Well, as he rounded a corner, the transmission slowed the rear tires slower more than the vehicle and it started spinning. He would have been much better off using the brake that he could more immediatly release and would be using the front tires as well. 75% of your braking power comes from your front tires (at least on a motorcycle ).

Let's see, for all my stories, I also was following a car that suddenly started fishtailing, I thought it was just some kids screwing around, but then it spun around backwards and flipped over into the ditch. Turns out it was a lady who said she started losing traction and remembered that she heard she should pump her brakes. She probably had anti-lock brakes anyway, but that's beside the point.

Didn't mean to go so long, but sounds like Prius owners should be thinking about traction as they're overinflating their tires and all.

Looks like a pretty good definition of oversteer here. From there: Understeer is when the front tires are turned but the car travels in a straight line. Oversteer is when the rear tires lose grip going around a corner. (when the car seems to turn 'more' than it should.) And they link to pictures.

 

<_< Here's another recommendation...

I had bought a digital gauge at a handy auto parts store and found it hard to use, didn't seal against the valve stem well. On recommendation by another PriusChat forum member, I ordered a large dial analog gauge from Racer Parts Wholesale - easy to read, can even interpolate to ¼ pound pressure. Cost $24.99 plus $9.34 shipping but worth it to me. About a 3" dia. rubber-padded gauge with ~6" high pressure hose with a heavy cast end which mates to the valve stem well. This gauge also has a small bleed valve in the hose to allow accurate pressure setting. This gauge and the 12v mini-compressor enable me to maintain optimum tire pressure - 40/38 is my choice.

Part #21588 0-60 Tire Gauge. Be sure to specify the 0-60 range (Prius spare requires 60#).

www.racerpartswholesale.com

 

I don't think 2 psi will make any appreciable impact on oversteer/understeer. My position still is it is weight. 2psi higher in front due to 60/40 weight ratio.

 

You may well be right. This car, due to its weight distribution, should have plenty of understeer which most manufacturers would see as the desired condition. Reducing rear tire pressure should reduce understeer a little. But I think a couple of pounds difference in tire pressure in a race car might be a very large change, in a street car it is not noticeable. At least not by me.

I tried my Prius in a deserted, large, parking lot on dry pavement with the OEM tires at 42 psi. What I discovered was that the VSC would not allow the car to break loose at either end. Although it did leave tire marks on the asphalt neither end would slip enough to call it oversteer or understeer, I would say that due to the VSC the handling was neutral.

Some people may think such tests are unsafe. I consider they make me safer because if I do need to take serious evasive action I have some idea what to expect. I also find a deserted stretch of highway and test my ABS at lower speeds, then at highway speeds.

 

I agree, I heartily recommend people get a feel for what their car can do in an emergency BEFORE the emergency

 

I see that this forum is a bit old but I will add my 2c worth anyway.
Most posters who refer to an accuracy of 0.5 psi do not quite understand what that means. You will find that this measurement is the display accuracy not the accuracy of the actual psi in the tires.
A quote from one of the sellers of a gauge:

"Pressure read in .5 PSI increments for accurate readings"

Yes, that is correct - accurate reading not accurate tire pressure. For example, let say the gauge under reads by 4 psi. The gauge is inaccurate but the reading would be accurate because it would always under read by 4 psi +- 0.5.

 

Hi !


Put on simmilar to theese after having the correct pressure in the tires. works like a dream , and You can buy them for different Pressure ,, those i have are actually very accurate



simmilar to theese


http://chaiyi1024.trustpass.alibaba.com/pr...Valve_Caps.html


cheers
Andreas