air COMPRESSOR QUESTION - help

Submitted: Friday, May 17, 2013 at 12:15
ThreadID: 102256 Views:1790 Replies:6 FollowUps:5
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Hi everyone
when putting back air into our tyres we get different readings depending what we are looking at:
Ironman air compressor (while operating) - 40
Ironman air compressor (when switched off after inflating tyre) - 35
Pirahna hand held tyre pressure gauge - 37

Which one would you go with? When reading the Ironman should we look at it when the air is going in or after it's switched off?
Thanks
Carolyn
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Reply By: Mick O - Friday, May 17, 2013 at 12:22

Friday, May 17, 2013 at 12:22
You will only get an accurate reading on a compressor gauge when you have stopped inflating the tyre. The most reliable tyre pressure reading will be gotten on a good quality hand held unit. The 2psi discrepancy could simply be caused by heat in the tyre or the heated air generated by the compressor.

I usually use the compressor gauge as a guide, turning off the compressor for the reading. If you are worried about a 2psi discrepancy, then it would pay to go round the tyres with the hand held tyre gauge after inflation.

Cheers

Mick
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Follow Up By: Bazooka - Friday, May 17, 2013 at 13:57

Friday, May 17, 2013 at 13:57
Yep, same thing happens with service station air guns. Almost always read a couple of psi higher during inflation than when you detach and measure with the same gun. The second reading is more accurate.
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Reply By: Member - Fab72 (Paradise SA) - Friday, May 17, 2013 at 12:26

Friday, May 17, 2013 at 12:26
Hi Carolyn,
You're not alone. The same thing happens to me. I use a hand held and go by that one. At the end of the day, it's the pressure that best works for you in the situation you're in that counts.

Different tyres, sizes and vehicle weights will determine what pressure best suits your immediate need, be it sand, mud, highway, whatever.

Focus more on getting your tyre pressures consistant from side to side rather than trying to match what others recommend. Use their recommendations as a guide only.

Fab.
AnswerID: 511235

Follow Up By: landseka - Friday, May 17, 2013 at 13:40

Friday, May 17, 2013 at 13:40
"Focus more on getting your tyre pressures consistant from side to side rather than trying to match what others recommend. Use their recommendations as a guide only."

Precisely, a pound or two away from reccomended setting is nothing, much more important to be consistent all round.
For this reason I always check & adjust my tyre using the same gauge (mine).

Cheers Neil
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Reply By: Robin Miller - Friday, May 17, 2013 at 12:31

Friday, May 17, 2013 at 12:31
All those readings are wrong why ? because the air is heated by the compressor and all will read high by a couple of psi. From your listing I would go with Pirahna.

If you want an accurate reading , first don't take a reading until 10 mins or so after putting in air. Air tyre directly exposed to sunlight will also read high than others.

All those guages have a limited accuracy and could be +_ 3 psi out.

The right approach is to verify the accuracy of any tool you use as well as having the right measurement approach.

You can buy products with stated accuracy - maybe your Pirhana guage has an accuracy - I don't know, but the rule is always verify any measurement device.

Surprizingly the most accurate "off the shelf" type of product are those ones shaped like a pencil which push out a rod with marks on it - usually come free with most cars.
Robin Miller

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AnswerID: 511236

Follow Up By: Bonz (Vic) - Friday, May 17, 2013 at 18:06

Friday, May 17, 2013 at 18:06
My digital gauge is exactly accurate Robin, cause it reads to one decimal point. Like if it says 34.5, then its 34.5
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Follow Up By: Robin Miller - Friday, May 17, 2013 at 19:05

Friday, May 17, 2013 at 19:05
Your a special person Bonz so they gave you a good guage but for the rest of us I have to tell on the manufacturers about there pressure / voltage conversion sensor - they simply don't make one with 3 digit (1 part in a thousand) accuracy.
Robin Miller

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Follow Up By: Member - Andrew & Jen - Friday, May 17, 2013 at 19:10

Friday, May 17, 2013 at 19:10
Bonz, your tongue in cheek one liners often make my day :-) Thanks
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Reply By: Member - John and Val - Friday, May 17, 2013 at 13:59

Friday, May 17, 2013 at 13:59
The difference between compressor operating and not operating can easily arise from resistance to air flowing into the tyre. I wouldn't trust any gauge measuring around 35 psi to be accurate to within 2 psi.

I've carried up to 6 pressure gauges at the one time! Finally paid lots of good money for a digital one of reputable brand - didn't take long before it started reading about double the actual pressure and doing so quite consistently. Recently bought 2 very cheap identical ones (2 for $9) and they seem to read what I'd expect them to quite consistently. They are in broad agreement with my collection of stick types and with the gauge at my local servo. I don't trust any of them to be absolutely correct, or even close, but I think this is less important than consistency.

With no opportunity to check against a pressure standard, we just have to accept that most gauges are ok if within a few psi of actual pressure. Equalising pressures from side to side seems to me far more important than being absolutely correct.

Cheers

John
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AnswerID: 511238

Reply By: passionfruit - Friday, May 17, 2013 at 16:26

Friday, May 17, 2013 at 16:26
Best Tyre gauge I found to be a Michelin motor bike tyre gauge .We used them at Aussie Post for the reading on the CT110 Honda's .They are very accurate.
AnswerID: 511248

Reply By: olcoolone - Friday, May 17, 2013 at 18:00

Friday, May 17, 2013 at 18:00
You're talking 5psi difference over all three..... is it REALLY that important.

Sooner the Uni's offer a doctorate in 4wdology the better.

Maybe you should look at a true scientific calibrated temp gauge...... should be able to get one for under $1000 for a basic one.

Being serious you will not notice the difference.
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