Tyre pressures?

[Pete-B]

Having pumped my tyres up with a Joe Blow stirrup pump to the recommended pressures on my new van I fitted a Tyre Pal system. So far so good, but the problem is, the stirrup pump gives a pressure reading of 62 psi the tyre Pal's reading is 67psi and my Halfords bought gauge shows 64psi. I could go to the local garage to get them checked but who's to say theirs is correct! I'm inclined to think (don't ask me why) that the Tyre Pal is likely to be nearer the correct pressure but I wonder what others would think.

[Billggski]

The only way is to check at a tyre fitter's, I wouldn't trust a supermarket one.

Remember driving there will heat the tyres up and raise the pressure.

[Willy Wonka]

I bought one of these Draper tyre pressure gauges a few years ago, took it to a couple of local tyre depots and had them check how accurate it was.

Both checks came within 1 psi of the figure on the gauge and for ease of use and accuracy I'd recommend it to anyone.

[Brian Kirby]

Pete-B - 2015-12-05 4:07 PM

 

Having pumped my tyres up with a Joe Blow stirrup pump to the recommended pressures on my new van I fitted a Tyre Pal system. So far so good, but the problem is, the stirrup pump gives a pressure reading of 62 psi the tyre Pal's reading is 67psi and my Halfords bought gauge shows 64psi. I could go to the local garage to get them checked but who's to say theirs is correct! I'm inclined to think (don't ask me why) that the Tyre Pal is likely to be nearer the correct pressure but I wonder what others would think.

What is the correct pressure to which the tyres should be inflated? I'm assuming 62psi, as that is where you stopped? However, no difference between front and rear pressures (and lower than the normally recommended "Camping" tyre pressures to boot) seems a bit odd.

 

I wouldn't expect the gauge on the Joe Blow to be that accurate, and I would expect the Halfords gauge to read a bit low as that is the safest error. So, your Tyre Pal may well be the most accurate. They claim accuracy to +/- 1.5psi, which seems pretty good. The most important thing, given reasonable accuracy of measurement, is that the pressures (it is doubtful that any two gauges will give the same results, especially if of different types), are the same nearside and offside across each axle, respect the load on the tyre, and are correct for the type and profile of tyre fitted.

 

The actual pressure should be measured cold, and will in any case fluctuate (generally rising) as the vehicle is driven and the tyres heat up. So, as long as the cold pressure is at least the minimum recommended by the tyre manufacturer, and that the correct tyres relative to load and speed are fitted, there should be no cause for concern.

 

Accuracy of the gauge should be in the range +/- 2% between 25% and 75% of its range. They are most accurate in the middle of their range, meaning that for accuracy at the pressures you are using the maximum pressure on the gauge scale should be approx 125psi. However, even then the accuracy will be only +/- 1.5psi or so, depending on the quality, age, and condition of the gauge.

 

All a bit academic, really. :-) Just make sure the pressures you are using are, if anything, a bit high relative to the load on the axle, which will in any case vary as you use the van and consume the food and water etc. that it contains. Under-inflation is the greater sin!

[mikebeaches]

I have got Tyrepal on my van - and very good it is too IMHO.

 

It has been mentioned in this thread how the pressure is likely to increase as you drive and the tyres heat up. But, the thing that really surprised me was just how much the pressures rise when the vehicle is driven at cruising speed, especially when the ambient air temperature is already warm.

 

Mike

[Tracker]

A Halfords guage did rather well in this test!

 

http://www.autoexpress.co.uk/accessories-tyres/85474/best-tyre-pressure-gauge-2014-group-test

 

 

And I find the motorhome specific section of this guide to be very handy with tyre advice and pressures which have worked well for me for years in the real world.

 

http://www.tyresafe.org/tyre-safety/tyre-safety-information

 

The subject of tyre pressures can become a bit emotive at times on here so best to add that anyone using any other pressures than those ridiculously high figures printed on the van door frame does so at their own risk!

[Brian Kirby]

Tracker - 2015-12-05 7:11 PM...............................The subject of tyre pressures can become a bit emotive at times on here so best to add that anyone using any other pressures than those ridiculously high figures printed on the van door frame does so at their own risk!

Quite true, and if Tracker's somewhat Delphic comment isn't quite transparent to everyone, what he is on about is this.

 

The pressure figures printed (usually) on the van door frame (or in the van converter's user manual), are the appropriate pressures for the maximum permissible load on each axle (or sometimes just the maximum permissible pressure for the tyres themselves without reference to the actual load).

 

However, it is not legal or practical to so load a van that both its axles are simultaneously at their maximum permitted loads. Why? Because if you add together the permitted axle loads for each axle, they total more than the maximum permitted weight (i.e. its MAM) of the van itself. So, if you did this, your van would almost certainly be illegally loaded (i.e. overloaded). (If the MAM has been uprated by a previous owner this could be the case, but it is very unusual.)

 

These are fail-safe pressures, to be used by anyone who doesn't know what load their fully fuelled, laden, and crewed van actually places on each of its axles. (There is a rather obvious problem with this blissful state of ignorance, however, which is that until the van is taken to a weighbridge fully laden etc. and the load on each axle recorded, it is impossible to know whether the van itself, or one of its axles, is over-loaded. Overload is, of course illegal and potentially dangerous.)

 

All tyre manufacturers therefore publish tables of the correct tyre pressures to be used for various axle loads. So, if you visit a weighbridge and obtain the actual axle loads for your fully laden van, you can then apply the tyre manufacturer's recommended tyre pressures for each axle, instead of the van converter's fail-safe pressures. In the process, you will also verify whether your van, or any of its axles, is overloaded. By using the tyre manufacturer's almost invariably lower pressures, you should also gain in ride quality, but also in emergency braking performance, roadholding, and general handling.

 

If you can't obtain or find your specific tyre manufacturer's table of pressures for load, you can, as Tracker links above, download the Tyresafe booklet that includes the generic table of pressures for load that will be applicable to tyres manufactured by their members (basically, as can bee seen from Tracker's link, all the major tyre manufacturers represented on the UK market). Just note that you must exactly match the size, profile, speed, and load ratings for your van's tyres, and check whether they are designated C (for light commercial, or "camionette", or CP for camping). The letter follows the other tyre size and type indications on the tyre sidewall. For example 215/70 R 15 C, or 215/70 R 15 CP.

[Derek Uzzell]

Pete-B - 2015-12-05 4:07 PM

 

Having pumped my tyres up with a Joe Blow stirrup pump to the recommended pressures on my new van...

 

This is just idle curiosity...

 

I believe you own a recent-model Bessacarr E462. This will be Ducato-based and (I would have thought) will have been Fiat factory-fitted with Michelin “Agilis Camping” CP-marked tyres. For ‘recreational’ vehicles with CP-marked tyres Fiat advises tyre pressures of 72psi(front axle) and 80psi(rear axle) or 80psi(front and rear axles) depending on the tyre-size. Swift handbooks say that lower pressures may be used, but the tyre manufacturer should be consulted. But Michelin will normally insist on advising 80psi for their ‘camping’ tyres when fitted to a motorhome’s rear axle, so where did you get the in-the-60s figure from, please?

 

I have three gauges with scales that are able to handle motorhome tyre pressures. This should be the most accurate

 

http://www.ebay.co.uk/itm/ACCU-GAGE-ITC-PROFESSIONAL-TOOLS-PRECISION-TYRE-PRESSURE-GAUGE-0-160-PSI-RDF160X-/380900205560

 

and its readouts closely match those of my Michelin digital gauge. I also have a cheap Chinese-made gauge that reads somewhere near the other two.

 

Although the Accu-Gage is nice to use and (probably!) accurate, I can’t check my 2015 Ducato’s tyre pressures with it without first removing the wheel trims. The Schrader clamp-in valves are pretty short and (besides there being a real risk of dropping the valve-cap inside the wheel trim when removing the cap) the trim prevents the gauge’s ‘chuck’ seating properly on the valve stem. For the same reason I can’t inflate the tyres with my electric tyre pump as the wheel trim won’t allow the pump’s thumb-lock connector to fully attach to the valve stem.

 

[Robbo]

Derek - I had difficult connecting my air compressor to my scooter tyre because of lack of clearance.

 

This seems to be a common problem with motorcyclists. I purchased a right angle adaptor to overcome the problem - available at most motorcycle outlets.

 

This may solve your problem, to avoid having to remove the wheel trims.

[Derek Uzzell]

Thanks for the suggestion - I presume you are referring to this type of adapter

 

http://www.amazon.co.uk/schrader-adapter-motorcycle-caravan-trailer/dp/B006GPIX0M

 

I’d rather not use adapters as I think they’d stick out well proud of the wheel trims and be vulnerable to damage if (when!) I rub the wheels against kerbs. I’m also not sure if it would be possible to fit the wheel trims with the adapters attached to the valves.

 

If the valve stems were just a few millimeters longer (say the same length as the clamp-in valves I chose for my previous Ford Transit-based Hobby motorhome) I’d be able to use the Accu-Gage gauge and my tyre pump. There doesn’t seem to be any compelling need for the valves to be so short, so I suspect it’s because Fiat has chosen to buy only Schrader valves and this is the only length in this valve-design that Schrader markets.

[keninpalamos]

Brian Kirby - 2015-12-05 5:48 PM

 

Pete-B - 2015-12-05 4:07 PM

 

Having pumped my tyres up with a Joe Blow stirrup pump to the recommended pressures on my new van I fitted a Tyre Pal system. So far so good, but the problem is, the stirrup pump gives a pressure reading of 62 psi the tyre Pal's reading is 67psi and my Halfords bought gauge shows 64psi. I could go to the local garage to get them checked but who's to say theirs is correct! I'm inclined to think (don't ask me why) that the Tyre Pal is likely to be nearer the correct pressure but I wonder what others would think.

What is the correct pressure to which the tyres should be inflated? I'm assuming 62psi, as that is where you stopped? However, no difference between front and rear pressures (and lower than the normally recommended "Camping" tyre pressures to boot) seems a bit odd.

 

I wouldn't expect the gauge on the Joe Blow to be that accurate, and I would expect the Halfords gauge to read a bit low as that is the safest error. So, your Tyre Pal may well be the most accurate. They claim accuracy to +/- 1.5psi, which seems pretty good. The most important thing, given reasonable accuracy of measurement, is that the pressures (it is doubtful that any two gauges will give the same results, especially if of different types), are the same nearside and offside across each axle, respect the load on the tyre, and are correct for the type and profile of tyre fitted.

 

The actual pressure should be measured cold, and will in any case fluctuate (generally rising) as the vehicle is driven and the tyres heat up. So, as long as the cold pressure is at least the minimum recommended by the tyre manufacturer, and that the correct tyres relative to load and speed are fitted, there should be no cause for concern.

 

Accuracy of the gauge should be in the range +/- 2% between 25% and 75% of its range. They are most accurate in the middle of their range, meaning that for accuracy at the pressures you are using the maximum pressure on the gauge scale should be approx 125psi. However, even then the accuracy will be only +/- 1.5psi or so, depending on the quality, age, and condition of the gauge.

 

All a bit academic, really. :-) Just make sure the pressures you are using are, if anything, a bit high relative to the load on the axle, which will in any case vary as you use the van and consume the food and water etc. that it contains. Under-inflation is the greater sin!

Surely consuming food and water etc won't alter the load until various waste tanks are drained etc :-) on a serious note garage forecourt tyre gauges that are available for customer use have to be calibrated regularly by weights and measures department

[Robbo]

Hi Derek - I was just thinking about connecting a single adaptor to the end of your compressor to inflate all tyres.

 

As you say, it wouldn't be a good idea to purchase 4 adaptors and leave them permanently in place.

 

The problem you also mention is the confined space around the valve and the high probability of losing the valve cap between wheel and trim. The right angle adaptor screws into the valve so this would also be difficult if space is limited.

[Brian Kirby]

keninpalamos - 2015-12-07 2:36 PM

Surely consuming food and water etc won't alter the load until various waste tanks are drained etc :-)

Does on our van, Ken, we leave it all outside as we go - wherever we are! :-D

 

on a serious note garage forecourt tyre gauges that are available for customer use have to be calibrated regularly by weights and measures department

 

Indeed they do Ken, but none I have yet visited can handle 80psi! I use my own portable mains pump that can comfortably inflate to well above this pressure.

[Pete-B]

Hi,

Thanks for all the replies, very helpful. Regarding the 62 psi, that's the pressure I got to when inflating with the Joe Blow before I checked with the Halfords gauge and fitted the Tyre Pal cap but not the pressure I will be running at.

 

[Brian Kirby]

Understood. Thanks Peter.

[Pete-B]

I spoke to Michelin regarding correct pressure, (that is after going on the weighbridge which showed my weight as, front axle, 1400kg, total weight 3280kg and this was their reply

 

 

The Michelin Agilis Camping tyre is designed especially for motorhomes and would be the preferred fitment on a motorhome.

 

The Agilis Camping tyre boasts a long life by using the same technology as the Michelin Agilis van tyre range. It has a reinforced construction to enable the use of higher pressures, has 8 kerbing protectors built in to each sidewall to increase resistance of sidewall scuffing and is M+S (mud and snow) marked to give sufficient grip when occasionally travelling in difficult conditions such as unsurfaced roads, mud and snow.

 

The suggested tyre pressure for the rear of a motorhome running on the Agilis Camping is 80psi.

 

This is due to the construction of the tyre with 2 casing plies enabling the use of higher pressures. Its construction and the use of higher pressures is designed to cope with continual heavy loads sometimes found on Motorhomes and can help with wear pattern issues if lower pressures are used particularly on the rear axle.

 

The front pressures however can be adjusted according to accurately weighed axle loads for a more comfortable ride and optimum performance. This recommended pressure is 51ps.

 

I hope this is of some help to others

[Tracker]

I shudder to think what 51psiF and 80psiR would do to the ride and handling?

[Brian Kirby]

Four assumptions. First, that your van has an MAM of 3,500kg. Second, that the maximum permissible axle loads are 1,850kg front and 2,000kg rear. Three, that it was absolutely fully laden, with all passengers on board, when you weighed it. Four, that the tyres fitted are 215/70 R 15 CP.

 

The rear axle load, as weighed, was 1,880kg, the front 1,400kg, and the total 3,280kg.

 

Just for comparison, and using those loads, and applying them to Continental's Technical databook for VancoCamper tyres of the same size, would give pressures of 3.0BAR (44PSI) front and 5BAR (72PSI) rear. Using the maximum permissible axle loads as above, the pressures would be 4.25BAR (62PSI) and 5.5BAR(80PSI)rear. However, I am not suggesting you should adopt those pressures for you tyres.

 

As a further comparison, the TyreSafe Motorhome Tyres booklet, published by the British Tyre Manufacturers Association (BTMA), of which both Michelin and Continental are members, publishes recommended tyre pressures for CP rated tyres which agree with Continental/Michelin data that the correct pressure at the rear, for a maximum load of 2,000kg, should be 5.5 BAR, and for your load of 1,880kg should be 5BAR (72PSI). However, they do not list a pressure for a front axle load below 1,795kg, for which load they recommend 4.0BAR (58PSI). So, no further help there.

 

If your van is a Bessacarr E462, it has a quite long rear overhang, meaning that the rear axle will tend to take the majority of the habitation load, and will be sensitive to load fluctuations.

 

Our van runs fully laden at 1,640kg front and 1,870 rear, for which I use Continental's pressures (215/70 R 15 CP Conti VancoCamper tyres fitted) of 3.75BAR front and 5.0BAR rear.

 

I would suggest you adopt the Michelin recommended pressures for now, and see how the van drives. If you still find it unsatisfactory, try visiting an ATS (owned by Michelin) tyre depot, and see if they have access to any additional data on pressures for load from Michelin for your Agilis Camping tyres. They have become very conservative in quoting any rear tyre pressures for CP tyres, other than those for the maximum permissible rear axle load, because these represent the fail-safe position. They are aware of a tendency on the part of motorhomers to overload their vans, especially at the rear, and now recommend only rear pressures that err on the safe side, both to protect users from their own innocence and to protect Michelin's reputation.

 

It hardly needs saying, but the only person able to recommend the correct pressures to use for a given tyre at a given load, is its manufacturer.

[Pete-B]

Sorry, I should have given the size of my tyres which are, Michelin Agilis 225/75R/16CP. Regarding my going to weighbridge I was fully loaded, with 3/4 tank of water, full tank of diesel and the duchess in the navigators seat.

[Brian Kirby]

Hello Pete

 

Silly question, perhaps, but how do you know you had only 3/4 tank of fresh water? :-) The gauge is not reliable enough to be sure and, unless you brim the tank, will be the equivalent of a guess. Fully loaded means absolutely full on all scores (water, fuel, and gas), so that it is weighed in the heaviest condition in which it is ever be likely to travel. Then, it will always be likely to run lighter than the weighbridge result, which builds in a safety margin.

 

Otherwise, the logic for setting the correct pressures is the same whatever size is fitted. I have only info for Conti 225/75 R 16 CP, but 1,400kg is off the bottom of their scale. 3BAR is rated correct for 1730kg at the front, and 5.5BAR for 2,500 kg at the rear. I don't think you will get better than the Michelin advice anywhere, except perhaps from ATS.

[Tracker]

If the water tank is say 120 litres then 30 litres, 30kg, either way ain't gonna make a lot of difference in the grand scheme of real world weight variables now is it Brian!

[Pete-B]

Re water

 

I know how much the tank holds so put 3/4 in from empty?