Tyre Pressures

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P-K
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Tyre Pressures

Postby P-K » Thu Apr 26, 2012 2:50 pm

I've noticed quite a few queries on some of the individual bike tech areas regarding tyre pressures.
So - I thought I'd share an article that appeared in MCN some years ago on this topic.
It was originally written by Leo Smith, who spent years as chief development tester at Avon tyres.
My original article is grubby and has thumb marks on it - so I've scanned it and OCR'd it, but I havn't altered the text or content in any way.
Hope you find it informative :smile:
Tyres-Pumped.doc
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Re: Tyre Pressures

Postby Galactic Greyhound » Thu Apr 26, 2012 5:50 pm

Thanks Phil - very informative!
Ced.

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Re: Tyre Pressures

Postby Agerbundsen » Sun May 13, 2012 6:52 am

Thanks from me too Phil, but it does bring up a question:

The bike is an R45 from 1980. The manual has a basic recommendation of 1.9 bar (28 psig) front and 1.8 bar (26 psig) rear for the basic setting, increasing the pressure on the rear with higher loads. Tyres are Metzeler 33 front and 77 rear. Both now old enough to warrant change, even though the thread depth is near new.

Both Metzeler and Bridgestone now recommend 2.5 bar (37 pisg) and 2.8 bar (41 psig) for the same tyres new today. This is very much in line with the quoted article.

Did the tyre construction change much from the original 1980 to the latest set 1998/2004 to today, or should I increase the pressures on the present tyres to the new recommendations for the last few miles before replacing them?

Incidentally, my leaning is towards Bridgestone BT-45's both front and rear.

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Re: Tyre Pressures

Postby goldenoldy » Sun May 13, 2012 8:17 am

Thanks, a question - I have three pressure guages, an old chrome pen type that pops up when used, a digital one and a footpump with one on. All differ by up to 5psi. I tend to go with the pen type. Can anyone recommend one that is true, if forcourt ones are unreliable how do you test what you use? Brian

BeemerRT

Re: Tyre Pressures

Postby BeemerRT » Sun May 13, 2012 8:30 am

Interesting read. Thanks for posting that, Phil.

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Re: Tyre Pressures

Postby george baker » Sun May 13, 2012 11:00 am

Hi
I have a range of gauges and dont know which to believe, ATM I am using a digital one which agreed with the garage one where I had a tyre replace.

If a garage charges for the supply of air the gauges are SUPPOSED to be calibrated. But, Do they? If it was calibrated yesterday is it still reading true? How do we know when the gauge was checked?

I am told the police (and VOSA) can check trye pressures, after an accident, to ensure that Construction and use regulations are being met etc. How are their gauges checked? If our tyre pressure is "wrong" when they check is it a defense to say "It must have changed in use" or "It was OK on my gauge"?

George
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BeemerRT

Re: Tyre Pressures

Postby BeemerRT » Sun May 13, 2012 12:37 pm

George, it's 6 years since I retired from Police and my Force supplied only standard gauges for checking the pressures on car/bike tyres and those on larger vehs. None were sent away for testing/recalibration but those were only the gauges used at the roadside or for vehicle examination. I was never an Accident Investigator so I don't know what kit they used. However, I used to be an approved Tachographer Fitter (for Police purposes) and the gauges used were those I've already referred to.
Never came up against any defence such as you suggest.

Perhaps there is someone out there who can give up to date info.

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Re: Tyre Pressures

Postby george baker » Sun May 13, 2012 6:06 pm

Hi
I was not suggesting that bike riders were careless of their pressures, I dont think any of us are that cheap about our lives but more honestly not knowing what the pressures are.

George
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Re: Tyre Pressures

Postby BeemerRT » Sun May 13, 2012 7:44 pm

George,
I wasn't thinking for a minute that you were suggesting anything like that. The problem is that as most of us know, forecourt gauges are notoriously inacurate. Are the types that we buy over the counter any better? I don't know but we put our trust in them, have confidence in the 'feel' of our bike/car according to what the gauges say and take it from there.
Anyone know if the gauges at tyre fitters are certified?
Ian

PS George, when is the East Fortune air show?

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Re: Tyre Pressures

Postby P-K » Sun May 13, 2012 8:14 pm

Thanks, a question - I have three pressure guages, an old chrome pen type that pops up when used, a digital one and a footpump with one on. All differ by up to 5psi.
I have also collected several tyre gauges over the years.
I used to check them all against a mercury manometer in the physics department at the University I worked at.
I found the most unreliable were the pencil type - you know, where a graduated stick pops out to tell the pressure.
I have 2 that have a proper pressure gauge on them, and 2 electronic digital ones. They all read to within 1.0 PSI of actual pressure.
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Re: Tyre Pressures

Postby BeemerRT » Sun May 13, 2012 8:54 pm

Phil, can you tell us the name of the manufacturers? I've got a digital one, cost me a tenner a couple of years ago, it bears the name Ring Automotive.

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Re: Tyre Pressures

Postby george baker » Sun May 13, 2012 9:30 pm

Hi Ian
28th July

http://www.nms.ac.uk/our_museums/museum ... rshow.aspx" onclick="window.open(this.href);return false;

I have been looking for a camp site/ hostel nearby. I thought I may come up and stay a day or two after, subject to midges, may even take in Ceds' Brigadoon

George
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Re: Tyre Pressures

Postby P-K » Mon May 14, 2012 9:36 am

Phil, can you tell us the name of the manufacturers? I've got a digital one, cost me a tenner a couple of years ago, it bears the name Ring Automotive.
Well, here they are :-
Pguages-small.jpg
The pencil type is rubbish.
If you get a bit of muck or grit on them they under read like mad.
You can see one of the digital ones is "Halfords" - the other one came from either Liddle or Aldi and is unbranded.
The 2 with pressure gauges on - I've had for years - and they came from small motorists discount shops.

I checked them all against a manometer at 20 psi & 30 psi (The Manometer only went up to 30)
As from before - all within 1 psi except the pencil one which was about 6 psi low.
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Re: Tyre Pressures

Postby Galactic Greyhound » Mon May 14, 2012 11:29 am

Hi Ian
28th July

http://www.nms.ac.uk/our_museums/museum ... rshow.aspx" onclick="window.open(this.href);return false;

I have been looking for a camp site/ hostel nearby. I thought I may come up and stay a day or two after, subject to midges, may even take in Ceds' Brigadoon

George
And maybe the local aviation museum? http://www.dumfriesaviationmuseum.com/" onclick="window.open(this.href);return false;

What I found interesting about this one is that the old Control Tower is stuffed full of WWII memorabilia including old aircraft engines.
Ced.

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http://www.researchgate.net/publication ... ing_bosons" - It works!

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Re: Tyre Pressures

Postby george baker » Mon May 14, 2012 2:07 pm

Hi
Geoff and I when there when we did the Longest day a couple of years ago when we stopped in the dog kennel. The museum and the camera obscura are both well worth a visit.

The campsite Gorsebank was a good place to stop but you had to remember not to try to take the bike to the timber tent, cos of the slope and gravel it took me 40 minutes to come back 40 yards to the carpark

George
Member 21, R100R, K75 and a Hyosung 250 FOR SALE

BeemerRT

Re: Tyre Pressures

Postby BeemerRT » Mon May 14, 2012 7:16 pm

Phil,
I've now made a note to pop into Halfords next time I get a chance. I'll invest in one of their digital ones. Thans very much for going to the trouble of posting a pic.

George,
If you like, let me now if you are definitely going to East Fortune. It would be nice to meet up with a club member. By the way, i never knew about the Dumfries & Galloway museum. It's a bit far from me but what the hell, that's what my bike is for :-)

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Re: Tyre Pressures

Postby george baker » Fri Jun 08, 2012 8:38 am

Hi
yep, air show paid for and campsite booked
George
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Re: Tyre Pressures

Postby P-K » Fri Jun 14, 2013 9:51 am

:smile:
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Re: Tyre Pressures

Postby mike pace » Tue Sep 22, 2015 8:40 pm

In answer to BeemerRT above.....
Running with the wrong pressures is what's called an 'absolute offence' under the Con and Use Regs.
The legal answer if prosecuted would be to plead a Special Reason for your licence not to be endorsed.

Something I do for Lorry drivers when VOSA now DVSA prosecute them for not knowing that one tyre is flat.

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Re: Tyre Pressures

Postby george baker » Wed Sep 23, 2015 6:56 pm

Hi
thanks for that Mike.


How do we know what the pressure should be? BMW give a different pressure from Bridgestone.

Even if we know what they should be there is the problem that our gauge may mis-read.

If you ask a garage where you have to pay for air when the gauge was last calibrated they never seem to know.

George
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Re: Tyre Pressures

Postby Tony the Skin » Wed Sep 23, 2015 7:46 pm

Go according to the tyre manufacturer. Tyre development moves on. Your handbook does not. The tyre you fit today maybe very different than that fitted 15 let alone 40 years ago.
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Re: Tyre Pressures

Postby george baker » Thu Sep 24, 2015 12:03 am

Hi Tony,
I am getting better so will be able to play out soon (I hope).

Even I dont keep tyres 40 years, although I might admit to 15

George
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Re: Tyre Pressures

Postby Tony the Skin » Thu Sep 24, 2015 11:49 am

Hi Tony,
I am getting better so will be able to play out soon (I hope).

Even I dont keep tyres 40 years, although I might admit to 15

George

Sorry to hear you have been unwell. Get well soon.
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Re: Tyre Pressures

Postby KHL100W » Thu Sep 24, 2015 5:25 pm

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Last edited by KHL100W on Tue Dec 12, 2017 1:50 pm, edited 1 time in total.

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Re: Tyre Pressures

Postby mike pace » Sun Sep 27, 2015 10:45 am

Let's start from the premise that the prosecution have to prove their case.
PC will say in his opinion the tyre was not. inflated correctly. He took a pressure reading with his tyre guage and....
The pressure reading was different to.. The BMW riders manual, Haynes manual, tyre manufacturers advise, local garage information plate.
So which is the correct one.
Well that's for them to prove. Obviously if a bike tyre was clearly under inflated you'd have a problem. If there was a nail in it and you'd been pulled up and had that pointed out you would go Special Reason.
If the arguement following an examination by a police examiner raised its head where it was being suggested that you were running at the wrong pressures, then that's a different arguement.
Remember, manufacturers 'recommend' tyre pressures, they are not set in stone.
In reply the rider (me) would say after a lot of research and riding out testing I have concluded that 36 front and 42 rear worked very well. I would back that up with my experience as a........t
So in order not to go on forever, they'd have a difficult job unless there was a real difference between what all the different info says and what the actual pressure is and that takes us back to the beginning, how accurate is their pressure guage?


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