Dustydog said:
Mike
This from the Caravan Club is very good
http://www.caravanclub.co.uk/media/1022844/caravan-tyres-and-wheels-mo.pdf
Hello Dusty,
That is a pretty good document, a lot to commend it in its conclusions, but I do find some of its logic off the mark.
It clearly recognises that especially single axle caravans load their tyres aggressively, even alluding to the fact
at times one tyre may be carrying virtually the whole caravan weight when towing, but incongruously it then tries to make out that caravan tyres are less tortured than car tyres, and that is a point I would argue.
I accept that only driven wheels under go the forces associated with putting power down to increase speed, however the forces endured under breaking are far more aggressive. after all most cars can get from 60 to 0 far quicker than 0 to 60. Also if you are increasing speed the whole tread surface is being used thus sharing the energy transfer, where as under braking the wheel has to be under-rotaing or even stopped to effect retardation, this means the energy density through the tread per unit area is higher.
As for lateral loads consider a typical car. When it corners, the side ways force is resisted predominately by the two outer most wheels. But as the mass sits within the wheel base, neither wheel sees more lateral load than the than the maximum mass it carries. But for a caravan, almost half its mass is distributed behind the axle, and when cornering this mass produces a greater lateral force on the outside wheel by virtue of its position behind the axle and hitch, in simplistic terms the pendulum effect.
I venture to suggest that caravan tyres rather than having an easy life just trundling behind a car, actually are subject to several forces that car tyres would not see.
Its important to have explained the forces issue before approaching the subject of directional tyres which has been touched on in earlier postings.
Given a scenario of a large puddle on a motorway, and an outfit travelling at speed towards it. If we assume the tow vehicle has good wet weather tyres and wont be troubled by the puddle, can the same be said for a caravan with poor wet tyres such as a directional tyre(s) fitted the wrong way round.
As the tow vehicle hits the puddle you can feel the cars speed drop as some of its forward kinetic energy is used to lift and throw the water away from the tyres. Now if the caravan tyres are less able to do the same to the water they will loose grip and could start to aquaplane. This means the caravan brakes effectiveness are reduced or completely ineffective. So the car is continuing to slow down, but the caravan is effectively floating on the water and pushing into the tow vehicle. When the hitch is fully compressed where can the caravan go - only sideways.
Its for this reason that I have come to the conclusion that you should have tyes on a trailer that should be at least as good as those on the car, and certainly it would be foolish to have a directional tyre fitted the wrong way round.
As the Caravan Club Document points out, the use of a directional tyre counter rotating should be used with the same caution as a space saver such as minimal distance and speed.and corrected as soon as possible.
Facebook
Twitter