Tyre Pressure Calculator (1 Viewer)

[Margaritaman]

Edited with correct link to Mohos

Corrected link http://www.tyresafe.org/check-your-pressures/motorhomes/

Gives the same recommended pressures as my Motorhome manufacturer's handbook does.

Thanks to @Wagoneer for the correct link

 

[Wagoneer]

This one MH specific http://www.tyresafe.org/check-your-pressures/motorhomes/

 

[funflair]

This one MH specific http://www.tyresafe.org/check-your-pressures/motorhomes/

Thats better, the other one didn't work for me, and it agrees with what I am running basically.

Martin

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[Margaritaman]

Sorry for sending you on a wild goose chase @Wagoneer and Martin @funflair

 

[funflair]

Some people think that the pressure is tyre specific but in reality you just need axle loads tyre size and load rating, as this web site uses

Martin

 

[Infinity31]

Some people think that the pressure is tyre specific but in reality you just need axle loads tyre size and load rating, as this web site uses

Martin

I know for sure you're right but somehow I don't trust the figures I came up with:


225 75R 16CP 118 1800kg 2400kg 53psi 80psi 1500kg 2000kg 51psi 80psi

225 75R 16CP 116 1800kg 2400kg 51psi 80psi 1500kg 2000kg 44psi 80psi


Just random choices that don't to my mind don't add up.

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[funflair]

I know for sure you're right but somehow I don't trust the figures I came up with:


225 75R 16CP 118 1800kg 2400kg 53psi 80psi 1500kg 2000kg 51psi 80psi

225 75R 16CP 116 1800kg 2400kg 51psi 80psi 1500kg 2000kg 44psi 80psi


Just random choices that don't to my mind don't add up.

Back to the drawing board then

Martin

 

[Fletton]

It states....

."CP-type tyre construction enables the use of higher inflation pressures to provide resistance to the difficult conditions of use encountered on motorhomes. Therefore, when CP-type tyres are fitted on the rear axle in a single formation set the inflation pressures to 5.5 bar (80 psi) for all loads"

But when I got printed info from tyre manuf... they advised pressure dependant on load for both axles.... !??

Ps ...I posted the above in the resources section some time ago...

 

[Infinity31]

Interesting that it seems from that chart it also depends which axle the tyres are on (do driven wheels also come into the equation?) not withstanding the recommendation to use 80psi in the rear whatever the load.

Front axle load 1730kg = 3.0 Bar
Rear axle load 1740kg = 3.5 Bar

So the formula, if there is one, is different for front and rear even if the load is the same.

I've seen this: (Max pressure, as marked on tyre / weight for load index) x 1/2 the axle wt = pressure in psi, but think that was for caravans/trailers.

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[peterc10]

I just trust the manufacturers of the tyres. They know better than anyone else what their tyres are capable of. So I weigh my motorhome fully loaded and use Continental's chart for my tyres to determine the pressures. It is one of the reasons that I will always use their tyres.

 

[Infinity31]

Michelin recommend 80psi for the rear no mater what the load.

From what I have read many Michelin users choose to ignore that and make an informed decision as to the rear pressure.

 

[peterc10]

Michelin recommend 80psi for the rear no mater what the load.

From what I have read many Michelin users choose to ignore that and make an informed decision as to the rear pressure.

That's why I don't want to buy their tyres

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[Mr Chrysalis]

I have Continental Vanco Tyres. The tyre has 69psi written on it, but both the calculator and some advice from Continental for the same tyres reproduced in this forum advise 79 or 80 psi for rear tyres. Can the 69 be safely exceeded? My Fiat Ducati manual also says 5.5 bar for camping tyres (80psi). My tyres are 215/70R15CP 109R and my weights are 1850 kg front and 2000kg rear (single axle). It's a Rapido 109F

 

[peterc10]

I have Continental Vanco Tyres. The tyre has 69psi written on it, but both the calculator and some advice from Continental for the same tyres reproduced in this forum advise 79 or 80 psi for rear tyres. Can the 69 be safely exceeded? My Fiat Ducati manual also says 5.5 bar for camping tyres (80psi). My tyres are 215/70R15CP 109R and my weights are 1850 kg front and 2000kg rear (single axle). It's a Rapido 109F

Are those the actual axle weights or the maximum? Continental's figures are based upon the actual weights, so best to get onto a weighbridge fully loaded if you have not yet done so.

 

[Mr Chrysalis]

Are those the actual axle weights or the maximum? Continental's figures are based upon the actual weights, so best to get onto a weighbridge fully loaded if you have not yet done so.

Those are the max. I have not yet found a weighbridge but by estimation of weight of everything in the van, I am approaching the max

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[peterc10]

Those are the max. I have not yet found a weighbridge but by estimation of weight of everything in the van, I am approaching the max

My guess will be that you motorhome has a 3500 limit. If so if you are maxing out on both axles you are overweight. Usually it is not possible to max out on the front axle, as most of the payload tends to be put rearwards. That is why the pressures on our front tyres are a lot lower than on the rear.

When we followed Fiats suggested tyre pressures on both our motorhomes our fillings nearly fell out. Once we used the more sensible settings from Continental we got a much better ride quality.

 

[Mr Chrysalis]

My guess will be that you motorhome has a 3500 limit. If so if you are maxing out on both axles you are overweight. Usually it is not possible to max out on the front axle, as most of the payload tends to be put rearwards. That is why the pressures on our front tyres are a lot lower than on the rear.

When we followed Fiats suggested tyre pressures on both our motorhomes our fillings nearly fell out. Once we used the more sensible settings from Continental we got a much better ride quality.

No it's plated for 3650, though the front and back axles add up to 3850. I know we have to comply wth both, and we do by weight estimation. I haven't measured front and back but suspect more at the rear. I've asked Continental for specific advice but not had it yet

 

[peterc10]

No it's plated for 3650, though the front and back axles add up to 3850. I know we have to comply wth both, and we do by weight estimation. I haven't measured front and back but suspect more at the rear. I've asked Continental for specific advice but not had it yet

The trouble with weight estimation is that it assumes that your motorhome started at the weight the maker or dealer says it is. That is rarely correct, unless your actual motorhome has been checked on a weighbridge to start with. And even then I have never seen any info on the individual axle weights, rather than overall unladen weight.

I suspect Continental's advice will be to take it to a weighbridge and check your actual axles loads when fully loaded with people and stuff and ready to go. Then use their chart for your tyre to set the pressures. That is what they told me.

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[Fletton]

I have Continental Vanco Tyres. The tyre has 69psi written on it, but both the calculator and some advice from Continental for the same tyres reproduced in this forum advise 79 or 80 psi for rear tyres. Can the 69 be safely exceeded? My Fiat Ducati manual also says 5.5 bar for camping tyres (80psi). My tyres are 215/70R15CP 109R and my weights are 1850 kg front and 2000kg rear (single axle). It's a Rapido 109F

@Mr Chrysalis .....

The above chart is for 116R's .... yours are 109R's....

That's important....

 

[peterc10]

@Mr Chrysalis .....

The above chart is for 116R's .... yours are 109R's....

That's important....

And they are a smaller size as well. 215/70R15 instead of 225/75R16 for the chart. That will make a lot of difference to.

 

[Mr Chrysalis]

@Mr Chrysalis .....

The above chart is for 116R's .... yours are 109R's....

That's important....

I've not been able to find the chart online

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[DBK]

I think the link is a good guide if you don't have any specific advice from your tyre manufacturer. Based on my axle loadings, Continental recommend 3.0 bar at the front and 3.25 at the rear. The link suggests 3.5 and 4.0 respectively, which is a lot closer than than the handbook suggestion of 5.5 bar all round. I've done over 20K on these reduced pressures and all is fine - and I still have all my fillings.

 

[peterc10]

I've not been able to find the chart online

Try phoning their technical helpline 0844 630 0011. They can email you the chart for your sized tyre.
Edited the phone number

 

[Mr Chrysalis]

Try phoning their technical helpline 0844 630 0011. They can email you the chart for your sized tyre.
Edited the phone number

Thank you

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[Wagoneer]

Google "continental tire data sheet" and download the PDF file.

Goto pages 78 & 79. First table shows tyre details and second tyre pressures related to axle load.

Assuming OP is up to max on rear axle, 2000Kg, front axle would be 1650Kg to keep within MAM of 3650kg. Resulting pressures from the table indicate 50psi/3.5bar front and 65psi/4.5bar rear. Obviously, confirm axle loads on weighbridge in fully loaded condition.

 

[Mr Chrysalis]

Google "continental tire data sheet" and download the PDF file.

Goto pages 78 & 79. First table shows tyre details and second tyre pressures related to axle load.

Assuming OP is up to max on rear axle, 2000Kg, front axle would be 1650Kg to keep within MAM of 3650kg. Resulting pressures from the table indicate 50psi front and 65psi rear. Obviously, confirm axle loads on weighbridge in fully loaded condition.

Thank you. I'll do that

 

[peterc10]

Google "continental tire data sheet" and download the PDF file.

Goto pages 78 & 79. First table shows tyre details and second tyre pressures related to axle load.

Assuming OP is up to max on rear axle, 2000Kg, front axle would be 1650Kg to keep within MAM of 3650kg. Resulting pressures from the table indicate 50psi/3.5bar front and 65psi/4.5bar rear. Obviously, confirm axle loads on weighbridge in fully loaded condition.

I don't get the same figures as you.

You need to use the figures in the bottom block of data on page 79. That is because for camper contact tyres (CP) used on motorhomes Continental recommend higher pressures on the rear axle to the front for the same axle load. That is, they say, to allow for the likelihood of overloading and uneven weight distribution on the rear axle. That is why they have FA and RA with different figures. The last line is for twin wheel axles so should be ignored.

The front axle pressure for 1650kg load is 3.75bar (need to go up to the next above). And for the rear axle load of 2000kg it is 5.5bar.

All of this is explained in the tyre specific chart they will email you if you speak to their technical department. I have checked the chart they sent me for my size of tyres with the equivalent figures on page 83 for those tyres and they are the same.

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[Mr Chrysalis]

Thanks for all the advice. The bit I don't quite get is that all the rear axle figures appear to be above the 69psi written in the tyre, and if it is safe to exceed that

 

[Wagoneer]

I don't get the same figures as you.

You need to use the figures in the bottom block of data on page 79. That is because for camper contact tyres (CP) used on motorhomes Continental recommend higher pressures on the rear axle to the front for the same axle load. That is, they say, to allow for the likelihood of overloading and uneven weight distribution on the rear axle. That is why they have FA and RA with different figures. The last line is for twin wheel axles so should be ignored.

The front axle pressure for 1650kg load is 3.75bar (need to go up to the next above). And for the rear axle load of 2000kg it is 5.5bar.

All of this is explained in the tyre specific chart they will email you if you speak to their technical department. I have checked the chart they sent me for my size of tyres with the equivalent figures on page 83 for those tyres and they are the same.

Yes, you are correct @peterc10 . I should have used the pressures relating to the FA & RA for the 8 ply tyre.

 

[Wagoneer]

Thanks for all the advice. The bit I don't quite get is that all the rear axle figures appear to be above the 69psi written in the tyre, and if it is safe to exceed that

My Vanco 2 tyres which are C (not CP) have a max pressure of 69psi. But my recommended pressures are lower anyway, so it's not a problem.

If your CP tyres also have this same max pressure, you need to speak with someone at Continental and explain the apparent anomaly. I'd be interested to learn what they say.

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