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UK Caravanning (uk.rec.caravanning) A forum for the discussion of caravanning undertaken by residents of the United Kingdom, whether in the UK or abroad. It encourages the interchange of views on the merits of models of caravan, makes of tow car, accessories, caravan sites, caravan clubs, and other related topics. The term caravan is to include trailer vans, motor caravans and trailer tents.

Tyre Pressures (again)



 
 
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  #1 (permalink)  
Old July 3rd 05, 02:43 PM posted to uk.rec.caravanning
Mr W Z Boson
external usenet poster
 
Posts: 142
Default Tyre Pressures (again)

I've just replaced the (2) tyres on my van.

The van has a max. laden wt. of 850Kg i.e. 425Kg per wheel.

The tyres show a max loading of 605Kg at 65 psi and my problem is -
what's the proper inflation pressure?

I've done some ferreting around and there seems to be 3 main schools of
thought ...

1. Inflate the tyres to the caravan manufacturer's recommendation (in
my case that would be 35psi)

2. If the van is fully loaded - inflate to the tyre's maximum (i.e.
65psi)

3. Take the "loaded wt/max wt ratio" the tyres are under (i.e. 425/605)
and set the pressure to give the same ratio to the max. pressure (i.e
65 x 425/606, or about 46psi)

My instinct is to adopt the last method - so I applied the same
calculation to my car's tyres - for a fully laden car, the "result"
from method 3 gave 42psi - but the car manufacturer's "maximum loaded"
figure is 37psi - Hmmm.

I don't want to underinflate (overheating) or overinflate (too rough a
ride) also I don't think tyre wear is an issue - I do about 4000 miles
a year and the tyres I took off (after 5 years) had no wear at all.

As an aside, the tyre fellow said "caravan tyres are always either 35
or 42psi, so I've inflated yours to 40"

I wonder if anyone has any thoughts .....

Ads
  #2 (permalink)  
Old July 3rd 05, 03:11 PM posted to uk.rec.caravanning
David
external usenet poster
 
Posts: 1,622
Default Tyre Pressures (again)


"Mr W Z Boson" wrote in message
oups.com...
I've just replaced the (2) tyres on my van.

The van has a max. laden wt. of 850Kg i.e. 425Kg per wheel.

The tyres show a max loading of 605Kg at 65 psi and my problem is -
what's the proper inflation pressure?

I've done some ferreting around and there seems to be 3 main schools of
thought ...

1. Inflate the tyres to the caravan manufacturer's recommendation (in
my case that would be 35psi)

2. If the van is fully loaded - inflate to the tyre's maximum (i.e.
65psi)

3. Take the "loaded wt/max wt ratio" the tyres are under (i.e. 425/605)
and set the pressure to give the same ratio to the max. pressure (i.e
65 x 425/606, or about 46psi)

My instinct is to adopt the last method - so I applied the same
calculation to my car's tyres - for a fully laden car, the "result"
from method 3 gave 42psi - but the car manufacturer's "maximum loaded"
figure is 37psi - Hmmm.

I don't want to underinflate (overheating) or overinflate (too rough a
ride) also I don't think tyre wear is an issue - I do about 4000 miles
a year and the tyres I took off (after 5 years) had no wear at all.

As an aside, the tyre fellow said "caravan tyres are always either 35
or 42psi, so I've inflated yours to 40"


Just looked in my CC handbook and it says the caravan tyre pressure should
be as the makers handbook.

You do not say what size and type of tyre you have bought, I've allways
found Reinforced Van tyres have been specified for my caravans with pressure
in the region of 45psi.

--
Regards,
David

Please reply to News Group.


  #3 (permalink)  
Old July 3rd 05, 03:11 PM posted to uk.rec.caravanning
David
external usenet poster
 
Posts: 1,622
Default Tyre Pressures (again)


"Mr W Z Boson" wrote in message
oups.com...
I've just replaced the (2) tyres on my van.

The van has a max. laden wt. of 850Kg i.e. 425Kg per wheel.

The tyres show a max loading of 605Kg at 65 psi and my problem is -
what's the proper inflation pressure?

I've done some ferreting around and there seems to be 3 main schools of
thought ...

1. Inflate the tyres to the caravan manufacturer's recommendation (in
my case that would be 35psi)

2. If the van is fully loaded - inflate to the tyre's maximum (i.e.
65psi)

3. Take the "loaded wt/max wt ratio" the tyres are under (i.e. 425/605)
and set the pressure to give the same ratio to the max. pressure (i.e
65 x 425/606, or about 46psi)

My instinct is to adopt the last method - so I applied the same
calculation to my car's tyres - for a fully laden car, the "result"
from method 3 gave 42psi - but the car manufacturer's "maximum loaded"
figure is 37psi - Hmmm.

I don't want to underinflate (overheating) or overinflate (too rough a
ride) also I don't think tyre wear is an issue - I do about 4000 miles
a year and the tyres I took off (after 5 years) had no wear at all.

As an aside, the tyre fellow said "caravan tyres are always either 35
or 42psi, so I've inflated yours to 40"


Just looked in my CC handbook and it says the caravan tyre pressure should
be as the makers handbook.

You do not say what size and type of tyre you have bought, I've allways
found Reinforced Van tyres have been specified for my caravans with pressure
in the region of 45psi.

--
Regards,
David

Please reply to News Group.


  #4 (permalink)  
Old July 3rd 05, 03:36 PM posted to uk.rec.caravanning
Mr W Z Boson
external usenet poster
 
Posts: 142
Default Tyre Pressures (again)



David wrote:
"Mr W Z Boson" wrote in message
oups.com...
I've just replaced the (2) tyres on my van.

The van has a max. laden wt. of 850Kg i.e. 425Kg per wheel.

The tyres show a max loading of 605Kg at 65 psi and my problem is -
what's the proper inflation pressure?

I've done some ferreting around and there seems to be 3 main schools of
thought ...

1. Inflate the tyres to the caravan manufacturer's recommendation (in
my case that would be 35psi)

2. If the van is fully loaded - inflate to the tyre's maximum (i.e.
65psi)

3. Take the "loaded wt/max wt ratio" the tyres are under (i.e. 425/605)
and set the pressure to give the same ratio to the max. pressure (i.e
65 x 425/606, or about 46psi)

My instinct is to adopt the last method - so I applied the same
calculation to my car's tyres - for a fully laden car, the "result"
from method 3 gave 42psi - but the car manufacturer's "maximum loaded"
figure is 37psi - Hmmm.

I don't want to underinflate (overheating) or overinflate (too rough a
ride) also I don't think tyre wear is an issue - I do about 4000 miles
a year and the tyres I took off (after 5 years) had no wear at all.

As an aside, the tyre fellow said "caravan tyres are always either 35
or 42psi, so I've inflated yours to 40"


Just looked in my CC handbook and it says the caravan tyre pressure should
be as the makers handbook.

You do not say what size and type of tyre you have bought, I've allways
found Reinforced Van tyres have been specified for my caravans with pressure
in the region of 45psi.

--
Regards,
David

Please reply to News Group.


Wheel 155R13, load rating 91, speed rating N

  #5 (permalink)  
Old July 3rd 05, 03:36 PM posted to uk.rec.caravanning
Mr W Z Boson
external usenet poster
 
Posts: 142
Default Tyre Pressures (again)



David wrote:
"Mr W Z Boson" wrote in message
oups.com...
I've just replaced the (2) tyres on my van.

The van has a max. laden wt. of 850Kg i.e. 425Kg per wheel.

The tyres show a max loading of 605Kg at 65 psi and my problem is -
what's the proper inflation pressure?

I've done some ferreting around and there seems to be 3 main schools of
thought ...

1. Inflate the tyres to the caravan manufacturer's recommendation (in
my case that would be 35psi)

2. If the van is fully loaded - inflate to the tyre's maximum (i.e.
65psi)

3. Take the "loaded wt/max wt ratio" the tyres are under (i.e. 425/605)
and set the pressure to give the same ratio to the max. pressure (i.e
65 x 425/606, or about 46psi)

My instinct is to adopt the last method - so I applied the same
calculation to my car's tyres - for a fully laden car, the "result"
from method 3 gave 42psi - but the car manufacturer's "maximum loaded"
figure is 37psi - Hmmm.

I don't want to underinflate (overheating) or overinflate (too rough a
ride) also I don't think tyre wear is an issue - I do about 4000 miles
a year and the tyres I took off (after 5 years) had no wear at all.

As an aside, the tyre fellow said "caravan tyres are always either 35
or 42psi, so I've inflated yours to 40"


Just looked in my CC handbook and it says the caravan tyre pressure should
be as the makers handbook.

You do not say what size and type of tyre you have bought, I've allways
found Reinforced Van tyres have been specified for my caravans with pressure
in the region of 45psi.

--
Regards,
David

Please reply to News Group.


Wheel 155R13, load rating 91, speed rating N

  #6 (permalink)  
Old July 3rd 05, 03:49 PM posted to uk.rec.caravanning
David
external usenet poster
 
Posts: 1,622
Default Tyre Pressures (again)


"Mr W Z Boson" wrote in message
ups.com...




Wheel 155R13, load rating 91, speed rating N


See
http://www.towitall.co.uk/NTTA_law/t...d_pressure.htm

Looks to me 35psi for normal tyre
and 42psi for reinforced


Also http://www.towitall.co.uk/NTTA_law/trailers/tyres.htm
will show how to read markings.


--
Regards,
David

Please reply to News Group.




  #7 (permalink)  
Old July 3rd 05, 03:49 PM posted to uk.rec.caravanning
David
external usenet poster
 
Posts: 1,622
Default Tyre Pressures (again)


"Mr W Z Boson" wrote in message
ups.com...




Wheel 155R13, load rating 91, speed rating N


See
http://www.towitall.co.uk/NTTA_law/t...d_pressure.htm

Looks to me 35psi for normal tyre
and 42psi for reinforced


Also http://www.towitall.co.uk/NTTA_law/trailers/tyres.htm
will show how to read markings.


--
Regards,
David

Please reply to News Group.




  #8 (permalink)  
Old July 3rd 05, 05:56 PM posted to uk.rec.caravanning
Hitch Lock
external usenet poster
 
Posts: 692
Default Tyre Pressures (again)

In an earlier contribution to this discussion,
David wrote:


Wheel 155R13, load rating 91, speed rating N


See
http://www.towitall.co.uk/NTTA_law/t...d_pressure.htm

Looks to me 35psi for normal tyre
and 42psi for reinforced

How do you work that out? I assume that you have simply looked at the table
and quoted the *maximum* pressure for normal and re-inforced tyres of the
specified size?

But those figures *only* apply when the tyre is running at its max. rated
load - which the OP's caravan certainly isn't!

Question to OP: Have you replaced like with like? Your van is nearly light
enough for a standard tyre, but would probably have been factory fitted with
re-inforced tyres. However, a load rating of 91 is way off the scale for
either of these in a 155R13 - and is almost certainly an 8-ply rated tyre -
intended for a commercial vehicle. You will be running it way below its
rated load, and won't need anything like the max permissible 65psi (unless
you want to shake your van to bits!)

If the caravan manufacturer recommeded a pressure to go with whatever tyres
were originally fitted, that *same* pressure won't be far out when you fit
over-specified tyres, which you seem to have done.
--
Cheers,
Hitch Lock
______
Please reply to newsgroup. Reply address is invalid.


  #9 (permalink)  
Old July 3rd 05, 05:56 PM posted to uk.rec.caravanning
Hitch Lock
external usenet poster
 
Posts: 692
Default Tyre Pressures (again)

In an earlier contribution to this discussion,
David wrote:


Wheel 155R13, load rating 91, speed rating N


See
http://www.towitall.co.uk/NTTA_law/t...d_pressure.htm

Looks to me 35psi for normal tyre
and 42psi for reinforced

How do you work that out? I assume that you have simply looked at the table
and quoted the *maximum* pressure for normal and re-inforced tyres of the
specified size?

But those figures *only* apply when the tyre is running at its max. rated
load - which the OP's caravan certainly isn't!

Question to OP: Have you replaced like with like? Your van is nearly light
enough for a standard tyre, but would probably have been factory fitted with
re-inforced tyres. However, a load rating of 91 is way off the scale for
either of these in a 155R13 - and is almost certainly an 8-ply rated tyre -
intended for a commercial vehicle. You will be running it way below its
rated load, and won't need anything like the max permissible 65psi (unless
you want to shake your van to bits!)

If the caravan manufacturer recommeded a pressure to go with whatever tyres
were originally fitted, that *same* pressure won't be far out when you fit
over-specified tyres, which you seem to have done.
--
Cheers,
Hitch Lock
______
Please reply to newsgroup. Reply address is invalid.


  #10 (permalink)  
Old July 3rd 05, 06:23 PM posted to uk.rec.caravanning
Mr W Z Boson
external usenet poster
 
Posts: 142
Default Tyre Pressures (again)

Hitch Lock wrote:
In an earlier contribution to this discussion,
David wrote:


Wheel 155R13, load rating 91, speed rating N


See
http://www.towitall.co.uk/NTTA_law/t...d_pressure.htm

Looks to me 35psi for normal tyre
and 42psi for reinforced

How do you work that out? I assume that you have simply looked at the table
and quoted the *maximum* pressure for normal and re-inforced tyres of the
specified size?

But those figures *only* apply when the tyre is running at its max. rated
load - which the OP's caravan certainly isn't!

Question to OP: Have you replaced like with like? Your van is nearly light
enough for a standard tyre, but would probably have been factory fitted with
re-inforced tyres. However, a load rating of 91 is way off the scale for
either of these in a 155R13 - and is almost certainly an 8-ply rated tyre -
intended for a commercial vehicle. You will be running it way below its
rated load, and won't need anything like the max permissible 65psi (unless
you want to shake your van to bits!)

If the caravan manufacturer recommeded a pressure to go with whatever tyres
were originally fitted, that *same* pressure won't be far out when you fit
over-specified tyres, which you seem to have done.
--
Cheers,
Hitch Lock
______
Please reply to newsgroup. Reply address is invalid.


I can't remember the spec. of the original tyres - but not reinforced
if I remember rightly & the van's been through a few replacements (last
time reinforced @ 42psi)

I've been trying to find a loading-inflation table for commercial tyres
(I should have said that the tyres are 155R13C), but I can't find one.
I've seen this kind of linear relationship between actual/maximum
loading for working out the pressure in a couple of places and wondered
if it had any basis or was simply snake oil.

I'll perhaps try a couple of experiments and look at the laid-down
tread patterns at 35 and 45 psi and see if there's any difference. I've
also read that a properly inflated tyre should increase its pressure by
about 4psi when running "normally" warm, so maybe I'll try that as
well.

I'm sure there must be an answer somewhere!

 



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