# Tyre pressures - variations.



## KeithChesterfield (Mar 12, 2010)

I've just bought a Draper Tyre Pressure gauge and used it to test my tyres.

The gauge showed 48psi on my front wheel tyre - but my newish foot pump, make not known, shows 55psi.

Rear tyre shows 58psi on the Gauge and 65psi on my foot pump.

According to the manual supplied with the second hand MH my tyres should be 55psi (3.8bar) front and 63psi (4.4bar) rear.

How can I find which of the two, gauge and pump, is right?

Do I need to take the MH to a garage/petrol station to get a more accurate reading?

And how do I know if they are correct?


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## rayc (Jun 3, 2008)

Take your new gauge to your friendly local tyre depot and ask them to check your new gauge against theirs.


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## Remus (Feb 10, 2011)

You could just take the spare to a garage and see how it compares against readings on your gauge and pump.


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## Oscarmax (Mar 3, 2011)

Ideally you would have been better off buying a Longacre Digital Pressure Gauge a bit pricey @ £34.90, but very accurate and will last a lifetime.


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## VanFlair (Nov 21, 2009)

My guess would be that the draper is right as the foot pump has to overcome the valve resistance and that will spike the reading slightly.

Martin


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## Jubilado999 (May 27, 2011)

I would say the Draper is likely to be more accurate. They are a quality manufacturer. The gauges fitted to inflators are of dubious quality only meant for a rough indication, always check with a proper gauge afterwards.

KenE


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## KeithChesterfield (Mar 12, 2010)

Thanks for all the helpful replies.

I'm going to take the spare wheel, pump and gauge to my usually very friendly Tyre supplier and ask them for advice and to check both the gauge and pump - possibly neither may be correct.

:wav: :wav: :wav:


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## bigtwin (May 24, 2008)

A single device is good - no real doubt in your mind.

Two devices are bad - which is correct?

Three devices are better than one or two - two of the three are likely to be similar giving confidence in the result.

High integrity (safety critical) systems tend to use a 3oo4 (3 out of 4) voting system.

But, in your example, I'd always have gone for the Draper since 100% of the cost of the device is associated with providing an indication of pressure whereas in the case of the pump the majority of the cost of the device will have been associated with the generation of pressure and not with the measurement function. The measurement function is secondary.


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## mikebeaches (Oct 18, 2008)

KeithChesterfield said:


> Thanks for all the helpful replies.
> 
> I'm going to take the spare wheel, pump and gauge to my usually very friendly Tyre supplier and ask them for advice and to check both the gauge and pump - possibly neither may be correct.
> 
> :wav: :wav: :wav:


Please let us know how you get on. I've got the Draper pressure gauge, so hoping you discover yours is OK.

Thanks, Mike


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## Spannerman007 (Jun 8, 2010)

*Tyre Pressures*

Hi

Your Draper Tyre Pressure Gauge is actually made by AccuGage in America.
I used to sell and service them under a different Brand name.
If you have only just purchased it and it has not been dropped or damaged it should be within 1psi accurate.
When using a tyre pressure gauge the pressure you are measuring should be mid scale of the gauge, i.e. if you want to measure pressures in the region of 50psi. you will need to use a 0 - 100psi pressure gauge.

Regards

Spannerman007


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## KeithChesterfield (Mar 12, 2010)

I've just come back from my friendly helpful Tyre depot and they have checked both the Draper gauge and the foot pump.

The Draper gauge is no more than 1psi out from the correct pressure – which is very reassuring.

The foot pump varies about 7psi from the correct pressures - which means I've been running my car tyres well below what they should have been.

Well done Draper.

:wav: :wav: :wav:


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## Spannerman007 (Jun 8, 2010)

*TyrePressures*

Hi

I forgot to add that the pressure gauge on a foot pump is at best an indicator. It should NEVER be used to check a tyre pressure. You should always use a tyre pressure gauge.

Regards

Spannerman007


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## bigtwin (May 24, 2008)

KeithChesterfield said:


> The Draper gauge is no more than 1psi out from the correct pressure - which is very reassuring.


Don't be fooled into thinking that the depot gauge is 'correct'. 
Has it been calibrated against a 'sub-standard' pressure gauge? If so, when was it last tested?

As I indicated in an earlier post, and as you've discovered, three devices are good!

Two out of the three devices were within 1 psi of one another and you have been reassured that, of your two gauges, the Draper is the one to have confidence in!.


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## KeithChesterfield (Mar 12, 2010)

bigtwin - Don't be fooled into thinking that the depot gauge is 'correct'. 
Has it been calibrated against a 'sub-standard' pressure gauge? If so, when was it last tested? 

I'm prepared to give their gauge the benefit of the doubt.

Why don't you nip down to Wingerworth Tyres on Derby Road in Chesterfield the next time you're passing and give them the third degree if you think they might be an un-proffesional establishment?


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## bigtwin (May 24, 2008)

No offence intended Keith.

I was, clearly inadequately, trying to point out that there would also be uncertainty associated with the accuracy of any measuring device unless you knew it met a recognised standard.

I was also indicating that it didn't really matter in that you had found that two out of the three devices you had access to had led you to an acceptable conclusion on which of your own two devices was likely to be the more accurate.

Happy testing!


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## Spiritofherald (May 18, 2012)

I could be wrong but I don't think even tyre bays have to have their gauges calibrated so it may be unwise to take their readings as a yard stick.


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## bigtwin (May 24, 2008)

Spiritofherald said:


> I could be wrong but I don't think even tyre bays have to have their gauges calibrated so it may be unwise to take their readings as a yard stick.


Hush your mouth!!!! :wink: :wink:


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