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SHOCK ABSORBERS

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Minormatt
BobK
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Caraman
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Post by Caraman 29/10/2022, 12:44 pm

road warrior wrote:
Caraman wrote:Paul is correct.  If you have Camping Pneu (CP) tyres (80 psi on the rear), they are much stronger than equivalent Commercial (C) tyres.  This allows them to be run at higher pressures than C tyres.  This is to compensate for the extra demands placed on motorhomes' tyres compared to commercial vehicles' tyres.  The downside is that CP tyres give a firm ride.  If you were to drop a CP tyre's pressures to those of an equivalent C tyre, you would be compromising safety in the interest of comfort and there would be no point in having the CP tyre.
 I disagree, aside from the extra ability to sustain 4 more psi than a " normal " van tyre- that all it is... CP tyres hold their shape better than van tyres - MH tyres spend long periods of inactivity and it is aspect thats is most useful as tyres tend to go oval standing still after long periods of non use - and tends to be felt as a vibration which cant be got rid of by balancing.  Although if you do a few thousand miles you can sometimes " wear" it out up!
The difference in recommended cold tyre pressures between a C and CP tyre varies depending on the size of the tyre and whether it is on the front or rear axle.  Typically on a R15 rear tyre at its maximum load, the difference is 15 psi.  A tyre 'holds it shape' principally due to the air within it.  If a CP tyre's cold tyre pressure is reduced to a C tyre's pressure, there will be less air in it and it will be less able to hold its shape.  During 'long periods of inactivity' tyres should be inflated to their maximum permitted pressure which is 80 psi for all CP tyres and either 65 psi or 69 psi for all C tyres.  At these maximum permitted pressures, CP tyres are more resistant to going oval than C tyres and developing weak spots in their sidewalls which on CP tyres are reinforced.
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Post by Suppersready 29/10/2022, 12:50 pm

road warrior wrote:
Caraman wrote:Paul is correct.  If you have Camping Pneu (CP) tyres (80 psi on the rear), they are much stronger than equivalent Commercial (C) tyres.  This allows them to be run at higher pressures than C tyres.  This is to compensate for the extra demands placed on motorhomes' tyres compared to commercial vehicles' tyres.  The downside is that CP tyres give a firm ride.  If you were to drop a CP tyre's pressures to those of an equivalent C tyre, you would be compromising safety in the interest of comfort and there would be no point in having the CP tyre.
 I disagree, aside from the extra ability to sustain 4 more psi than a " normal " van tyre- that all it is... CP tyres hold their shape better than van tyres - MH tyres spend long periods of inactivity and it is aspect thats is most useful as tyres tend to go oval standing still after long periods of non use - and tends to be felt as a vibration which cant be got rid of by balancing.  Although if you do a few thousand miles you can sometimes " wear" it out up!

I have never experienced an oval tyre …. I have several vehicles that spend a lot of time motionless, one for 5yrs and when driven it was perfectly fine ( I did have precautions to take with the engine before attempting a start up though ). Maybe I’m just lucky or is it a myth ? I’ve never heard of anyone having oval tyres either …

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Post by Caraman 29/10/2022, 1:24 pm

Its not scientific but on my first caravan I always put it on axle stands during out of use periods and during long out of use periods over winter I even removed the wheels.  I had it over 7 years and had no problem with the tyres.  Complacency and laziness set in with my second caravan and I stopped taking the above precautions and when the tyres were about 7 years old, one of them blew out on the sidewall whilst being towed.  On my third caravan I reverted to my previous practice with the first caravan and had no problems.  On my motorhome, each CP tyre's load, pressure and replacement cost is generally higher than with my caravans.  Although my out of use periods are generally shorter than with the caravan, I used to inflate the tyres to their maximum permitted pressure when out of use. I don't do this any more as I jack up the wheels in stead using my recently acquired automatic levelling system.  So I haven't knowingly experienced tyres going oval but I have had a sidewall blowout which I suppose could have been caused by other things.
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Post by road warrior 31/10/2022, 5:40 pm

Tinwheeler wrote:I can only speak from my own experience but I found camper tyres to give the most awful harsh bumpy ride. The only way to tolerate them was to reduce the pressure. I would never have them again.
i can only assume you put the max 80psi in - which frankly is ludicrous
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Post by road warrior 31/10/2022, 5:41 pm

Suppersready wrote:
road warrior wrote:
Caraman wrote:Paul is correct.  If you have Camping Pneu (CP) tyres (80 psi on the rear), they are much stronger than equivalent Commercial (C) tyres.  This allows them to be run at higher pressures than C tyres.  This is to compensate for the extra demands placed on motorhomes' tyres compared to commercial vehicles' tyres.  The downside is that CP tyres give a firm ride.  If you were to drop a CP tyre's pressures to those of an equivalent C tyre, you would be compromising safety in the interest of comfort and there would be no point in having the CP tyre.
 I disagree, aside from the extra ability to sustain 4 more psi than a " normal " van tyre- that all it is... CP tyres hold their shape better than van tyres - MH tyres spend long periods of inactivity and it is aspect thats is most useful as tyres tend to go oval standing still after long periods of non use - and tends to be felt as a vibration which cant be got rid of by balancing.  Although if you do a few thousand miles you can sometimes " wear" it out up!

I have never experienced an oval tyre …. I have several vehicles that spend a lot of time motionless, one for 5yrs and when driven it was perfectly fine ( I did have precautions to take with the engine before attempting a start up though ). Maybe I’m just lucky or is it a myth ? I’ve never heard of anyone having oval tyres either …
so.. you didnt move your van for 5 years and it was still perfect eh ?
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Post by Caraman 31/10/2022, 5:48 pm

The ETRTO used to recommend that all rear CP tyres are inflated to 80 psi regardless of the axle/wheel load.  They no longer make this recommendation so 80 psi is only appropriate now if the rear tyre is at its maximum permitted load, or, if the van is out of use and not on stands.  Unfortunately, TyreSafe continue to apply the old ETRTO recommendation in their on-line calculator which I think is wrong.
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Post by road warrior 31/10/2022, 6:09 pm

cp tyres have a max capacity of 80psi -  MAX , this is akin to driving your car at 150mph cus it says so on the speedo- its max capacity - not your working psi load, if you want to shake your van to pieces and have a rubbish ride,  fine but its not compulsary or recommended. I am very aware if you are convinced otherwise nothing will change your mind and is purely subjective. I learned my knowledge/opinions from Dunlop when I used to make tyres there. The golden rule is on any vehicle on the planet you must have a about a 1-2" flat spot looking at it from a few feet away and looking down on it from above about 1" bulge - no pressure gauge needed for that - just a visual check. As every vehicle is loaded differantly, used differantly and the comfort is subjective anyway its impossible to give a magic number and we all know that, anyway the max for vanco four season 2 tyres 236/65/16 is 76psi and cp tyres are 80psi.
Personally i would terrified to drive around at the max capacity of a tyre. moi
The ETRTO's sole function in life is to harmonise rims and tyres, they dont make anything, and their sole concern is to make sure rims and tyes stay together - they dont give a rat's do-dar about your comfort snigger
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Post by Caraman 31/10/2022, 6:28 pm

I can see when a tyre is significantly under-inflated but beyond that I would always use a tyre pressure gauge and the ETRTO's tables for axle load 'v' pressure to determine if it is correctly inflated.  As I have said before, a tyre's maximum permitted pressure corresponds to its maximum permitted load.  Lower pressures correspond to lower loads as per the ETRTO tables.  CP tyres are different in that they have pressure/load table for the front tyres and different table for the rear tyres.
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Post by road warrior 31/10/2022, 6:45 pm

i was not suggesting you dont use a tyre gauge - i  was trying to show the correlation between a tyre in contact with the road to its max capability ie = if your tyre DOESNT a look how i described its too hard or too soft,  and it cant do its job, as we all do very low mileage you could travel 10k ( which will be years in reality) before you notice the effect of outer or inner wear but will have immediate effect on comfort and safely and roadholding.
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Post by Caraman 31/10/2022, 6:57 pm

road warrior wrote:i was not suggesting you dont use a tyre gauge - i  was trying to show the correlation between a tyre in contact with the road to its max capability ie = if your tyre DOESNT a look how i described its too hard or too soft,  and it cant do its job, as we all do very low mileage you could travel 10k ( which will be years in reality) before you notice the effect of outer or inner wear but will have immediate effect on comfort and safely and roadholding.
I agree, it's all about the contact between the tyre and road.  But I'm not experienced enough to judge whether its right by just looking at it and I would rather not wait to see how it wears.
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Post by Suppersready 1/11/2022, 6:37 pm

road warrior wrote:
Suppersready wrote:
road warrior wrote:
 I disagree, aside from the extra ability to sustain 4 more psi than a " normal " van tyre- that all it is... CP tyres hold their shape better than van tyres - MH tyres spend long periods of inactivity and it is aspect thats is most useful as tyres tend to go oval standing still after long periods of non use - and tends to be felt as a vibration which cant be got rid of by balancing.  Although if you do a few thousand miles you can sometimes " wear" it out up!

I have never experienced an oval tyre …. I have several vehicles that spend a lot of time motionless, one for 5yrs and when driven it was perfectly fine ( I did have precautions to take with the engine before attempting a start up though ). Maybe I’m just lucky or is it a myth ? I’ve never heard of anyone having oval tyres either …
so.. you didnt move your van for 5 years and it was still perfect eh ?

The tyres yes … never mentioned it was my van though !

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Post by road warrior 7/12/2022, 11:07 pm

for the benefit of the OP i think we got distracted by the ever raging tyre and tyre pressure dispute, so i neglected to say i had to all intents and purposes non leaking legal rear shock absorbers but like the OP i was rolling all over the place and feeling every bump in the road,  so i decided to replace them and after some research went for KYB which are regarded as the best of the best from what i was reading. For whatever reason i had great difficulty in finding anybody with stock ( they are japanese ) eventually i sourced some and asked my local garage to fit them - they replied oh no sir while we accept KYB are the best shock absorbers we will not fit them unless we supplied them - bla bla ... and then offered to charge me more to fit a koni subsiderary make which are regarded as low quality - it does annoy me when garages try to take the high ground and simultainiously sell me cheaper stuff = i digress - anyway the KYB shocks were a revelation, i fitted them myself and have transformed the van handling, no more rolling and passing trucks at high speed is a non event now - as i said - i removed the old ones and they felt fine - even better than the ones i was putting on so i was concerned i had wasted my money - but they are a game changer - very happy to recommend.
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