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eran48
Member Since: 10 Dec 2007
Location: Sydney
Posts: 165
  
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| Interesting tyre pressure findings using new TPMS |
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G'day everybody,
Just got back from a 2 week holiday in Tassie - awesome place. Wouldn't mind retiring there 
Before I left, I installed a set of wireless TPMS (tyre pressure monitoring system) that I think is just a re-badged version of the Tyredog brand that is sold in Australia.
I had 4 adults, three kids and about 70 kgs of luggage on board the Tdv6 SE.
I was using the TPMS to aim for the ideal '4 psi rule' for my tyre pressures and were twiddling the pressures daily until I hit the 'sweet spot'
The way I understand it, the difference in pressure between a tyre's cold and running temperature should be around 4 psi. More than 4 psi means that the tyre walls are flexing too much - the tyre pressure is too low for the load. Vice versa for less than 4 psi change.
The sweet spot I got with the OEM Wranglers : 39 PSI front tyres and 45 psi rear tyres.
This is higher than the recommended 38 PSI front and 42 PSI rear for a fully loaded vehicle.
Prior to getting the TPMS, I had never dared go above 38 PSI. I do remember watching this 4WD Action video which had a segment on tyre pressures done by the managing director of Cooper tyres. He said that manufacturer's recommended pressures are almost always too low. I guess my findings above fits in with this.
The OEM Wranglers have a stated maximum pressure of 50 PSI. Does anyone know if this is cold temperature PSI or running temperature PSI? I was a bit concerned that the rear tyres were running at close to 50 PSI when I had it at the 'sweet spot' pressure of 45 PSI.
Please note that the above discussion is ONLY for highway / on road driving. You would be nuts to drive off-road at these pressures 
Regards.
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 4th May 2008 12:54 pm |
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catweasel
Member Since: 05 May 2006
Location: Bundaleer
Posts: 4805
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pressures are always done cold so 50 would be cold. the front is stated as 33psi regardless of load not 38. let us now in a few months as to how the tyre wears as that will be a better indication long term. I run mine at the recommended pressures and the tread wear after 30 odd thousand is even so I'll stick with the recommended pressures.
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| 4th May 2008 1:37 pm |
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Jamo
Member Since: 18 Jan 2006
Location: Esperance, Western Australia
Posts: 1170
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I run mine at 42psi front and 44psi rear (cooper 265/60R18 HP+). The fronts don't change by more than 2psi cold/hot and the rears 4psi.
It's better on the bitument.
I have found, however, that the recommended pressures are pretty well spot on when on the gravel for handling at speed. Have a nice day!
2010 Cayenne Diesel with PASM & Off Road Pkg
2005 HSE D3 (Sold)
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| 5th May 2008 12:50 pm |
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mick
Member Since: 21 Jan 2007
Location: Yorkshire
Posts: 2049
  
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I run mine at 33 front 36 rear,but if towing i go up to 40 on the backs seems more stable that way.
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| 5th May 2008 7:34 pm |
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TDV6
Member Since: 23 Apr 2006
Location: Queensland or there abouts
Posts: 96
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| Quick Chalk Tyre Pressure Check |
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G'day Eran48,
Here is a method of checking that I have tried as a quick check on future tyre wear that may save you $.
Mark a chalk line across each tyre, drive for approx 200 meters on smooth bitumen/concrete then look at the chalk line. If the line's worn the same for that tyre your pressure is ok in that tyre, uneven wear indicates a pressure or allignment problem for that tyre.
Regards
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| 5th May 2008 8:14 pm |
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eran48
Member Since: 10 Dec 2007
Location: Sydney
Posts: 165
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Thanks for your replies everybody,
I forgot to mention that my findings were ONLY for a fully loaded vehicle. Now that I am back home and mostly driving around with just myself in the car, the 39 front/ 45rear pressures are too high.
Unfortunately, I don't get to drive the car far AND frequently enough to properly twiddle the pressures for an unladen vehicle. I have also currently swapped back to the MTR's for some playtime 
Old age must be catching up with me eyes, catweasel. Is the front recommended pressure only 33PSI? I'll check when I get home tonight. That looks to be way too low for a fully laden vehicle.
The chalkline method is interesting - I'll certainly give that a go for both the Wranglers and the MTR's.
Jamo, do you run those pressures all the time or only when your vehicle is fully loaded? Or is your vehicle fully loaded all the time? 
Cheers.
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| 6th May 2008 12:09 am |
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pbhawkin
Member Since: 14 Dec 2006
Location: Mudgee
Posts: 377
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After having the TPMS on for a few weeks I wanted to bring to peoples attention a design flaw in the way the sensors are sealed on the tyre valve allowing a potential slow leak!
The small washer is threaded and needs to go FULLY onto the tyre valve and the O-ring placed up against it. Then when the sensor is screwed on it is supposed to squash the O-ring between the washer tand the sensor base causing a seal (there is another seal at the top end of the sensor also).
The problem is twofold. firstly if the sensor is not screwed on far enough the top seal inside the sensor does not engage the top of the tyre valve and therefore doesnt seal and secondly if the sensor is screwed too tightly against the O-ring it causes the O-ring to bulge or buckle allowing air to escape! There is no 'seat' for the O-ring to fit into in the end of the sensor and so overtightening will allow the O-ring to be pushed out.
So a very delicate positioning of the washer on the tyre stem needs to occur; far enough on to allow the top seal in the sensor to engage the end of the stem (and still cause the bottom of the sensor to engage the O-ring) and not so far that the sensor has to be too tightly screwed on to cause the O-ring to deform. regards
Peter
__________________________________________
Oct 2013 SDV6 3.0 HSE.
2007 TDV6 SE E-diff, adaptive lights sold 1/2014
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| 6th May 2008 12:12 am |
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DingMark
Member Since: 14 Sep 2007
Location: Perth Oz or Erbil, Iraq
Posts: 388
 
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I also found getting the o-ring to seal pretty fiddly. My plan will be to keep the locking nut in place whilst in the city but remove the locking nuts and o-rings when going bush (also makes it much easier to depressurise and repressure as needed by road conditions). Jim Dowell - D4 HSE TDi, 12,000 hydraulic winch & hidden winch mount, MTRs, TyreDog, Traxide 2 x aux battery system, fixed air compressor, Dolium roof rack, MitchHitch.
RIP 2005 D3 HSE V8 5 seater gold (stolen and torched)
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| 6th May 2008 1:52 am |
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eran48
Member Since: 10 Dec 2007
Location: Sydney
Posts: 165
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Good observation pbhawkin,
I had decided to ditch the threaded washer and O-ring. It is not a real security measure anyway. One can still unscrew the whole sensor off with the washer in place - it just delays the theft by about 5 seconds.
I found that the washer also prevented me from pumping up the tyres as I could not push the hose head fully into the valve stem.
Without the washer and O-ring, you can screw the sensors in tight and have no leakage. The sensors now functions exactly like a normal tyre cap - simply screw on and off to top up tyre pressures.
Here's hoping they won't get nicked by some low-life. 
Cheers.
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| 6th May 2008 1:56 am |
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Desert Traveller
Member Since: 06 Aug 2006
Location: The Gabba - QLD
Posts: 420
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I've ditched the locking components and screwed the transmitter/sensor directly on as a valve cap, I've noticed no leakage to date.
It is interesting to watch temperature fluctuations.
Are valve stems a standard length? 06 TDV6 SE with many LR and after-market extras. Used only on weekends and trips out west.
Audi TT Roadster (Daily and around town drive)
VW Eos TDI For Sale
Previously 01 TD5 and 94 TDI
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| 6th May 2008 2:47 am |
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WayneD
Member Since: 11 Sep 2007
Location: Sydney Darwin ,Singapore, USA, UK and now country NSW
Posts: 531
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Hi Guys
Just back from the Ocean Road in the wife's Audi  Sticks like glue to the road.
Desert Traveller the valve stems on my vehicle are different. I had problems fitting the TPMS to the front passenger tyre and had to use plumbers tape to seal it, also had the experience of having to take off the washer and O-ring to pump up the tyre. I think I might forget about the locking nuts (would not fot FL tyre anyway) and do what eran48 has done. Take the road less traveled. Dual battery system.ORS drawers,LR cargo Barrier.ARB Bull bar,side protection bars,Mickey Thompson ATR's 17" rims, Rear wheel carrier, radiator guard TPMS Mitchell Bros Tow Hitch LR RAI Steel Rims , GME UHF, Off Road GPS, Llams (yet to be fitted)
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| 8th May 2008 10:49 am |
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pbhawkin
Member Since: 14 Dec 2006
Location: Mudgee
Posts: 377
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Yes, I also have taken off the washers and O-rings and just screwed the sensor straight onto the valve with. I am thinking of using some 'Locktite' (just a little) to help prevent the sensor from coming off and ?seal it better. regards
Peter
__________________________________________
Oct 2013 SDV6 3.0 HSE.
2007 TDV6 SE E-diff, adaptive lights sold 1/2014
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| 8th May 2008 11:16 am |
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Jamo
Member Since: 18 Jan 2006
Location: Esperance, Western Australia
Posts: 1170
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I've found that mine seal really well.
I also found out that they can handle being submerged for at least two hours without harm! Have a nice day!
2010 Cayenne Diesel with PASM & Off Road Pkg
2005 HSE D3 (Sold)
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| 8th May 2008 1:06 pm |
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DingMark
Member Since: 14 Sep 2007
Location: Perth Oz or Erbil, Iraq
Posts: 388
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Was that saltwater? There might be a reluctant story somewhere here  Jim Dowell - D4 HSE TDi, 12,000 hydraulic winch & hidden winch mount, MTRs, TyreDog, Traxide 2 x aux battery system, fixed air compressor, Dolium roof rack, MitchHitch.
RIP 2005 D3 HSE V8 5 seater gold (stolen and torched)
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| 9th May 2008 2:32 am |
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lawrie50
Member Since: 26 Jul 2007
Location: On the road in Australia
Posts: 57
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Interesting, I just had first service on the D3 and they recommended 40psi front and rear. I had been inflating to the recommended 33/36psi and 33/42psi for towing. I haven't got a TPMS but have the poor mans Tyrecheckers valve caps so now I need to get a couple of 40psi versions for the fronts.  2007 TDV6 SE Towing 22' Boroma Primo Grandinata, Mitchell Bros. Tow Hitch, Bolle Tint, TomTom GoLive 825 GPS.
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| 10th May 2008 5:05 am |
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