Dustydog said:
With a braked trailer I would have thought the tow vehicle is unlikely to bear significant additional pressures under breaking. Certainly my car does not feel heavier even on steep downward inclines. Clutch though, yes!
With a braked trailer I would have thought the tow vehicle is unlikely to bear significant additional pressures under breaking. Certainly my car does not feel heavier even on steep downward inclines. Clutch though, yes!
Find a safe place, test track. Get upto 50 mph and do an emergency stop.Jules_ht said:
Hitch up and repeat with the caravan on the back. The results will speak for themselves.
BHP and torque are important but the final drive ratio and gearing also play a very important part.
Jules_ht said:
Surley you would work up to 50 mph in stages. But if you frightened of jacknifing that doesn't bode well for other road users if a real emergency occurs at 60 mph on a motorway does it?
outdoors said:
Whilst I'm sure you're within 80% what is the kerb weight of your pick up? I have seen figures for the 3.0l double cab as low as 1800kg. Not a good match for a caravan weighted at 2000kg.
Although you may work to 80% the recognised advice for many years has been 85% of kerb weight so I think most people will go with that. Using a figure of 80% would be very restrictive to many even though it is only a guide.
Dusty D, I do similar to you, we keep,our van away from home but on the way from storage to home and on a clear front and back dual carrigeway hit the brakes hard to make sure the vans brakes are working, and all is well.
Dustydog said:
I seem to recall that a set of emergency stops with and without a caravan were carried out, either by one of the clubs or a magazine, and yes the results were interesting, but did not give the result you might have been expecting.
Emergency stops did take some extra distance but not as much extra as you might instinctively think.
The reason the stopping distance didn't increase dramatically is due to the way the trailer breaking system works.
When the car starts to decelerate the inertia of the caravan tries make it catch the car up, but by doing so, it compresses the over-run hitch, which starts to activate the caravans brakes.
As the stopping effect of the caravan brakes is dependant on how hard the overrun is pushed, the brakes apply progressively and according to the closing speed of the caravan to the car.
After a small fraction of a second the caravans brakes will start ****** the caravans speed until it again closely matches that of the car, at which point the caravan brakes will ease off.
The consequence of this is the caravan will only apply a relatively small amount of thrust to the ball coupling even under severe braking.
The movement in the overrun coupling means the actual mass the cars brakes are having are still principally retarding the car, and the caravans brakes are retarding the mass of the caravan.
The car only feels and has to deal with the force necessary to compress the overrun coupling, not the whole weight of the caravan.
If any brakes lock up the situation changes.
outdoors said:
Hello Outdoors,
Your assertion that 80% is the accepted figure is what is fundamentally wrong, the accepted figure is 85%. Not a lot of difference, but the industry has decided on 85% not 80.
However whilst I will repeat it when offering advice about matching, I also stress the importance of other factors which arguably have a greater influence on towing stability than just weight ratios. For example achieving an appropriate nose load, the mechanical condition of the vehicles, and probably the most important is the driving style.
I have driven countless different cars and towed many different trailers, and I firmly believe you can have some combinations of car and trailer and despite all the weights being well within spec. they can be a real handful, and others where the trailer is well over 100% and it tows very comfortably. So I do question the validity and efficacy of having a simplistic weight ratio as being the major criteria used to determine tow matches.
In fact I have a strong suspicion that if we want to eliminate caravan related driving incidents, the advice needs to be reviewed and made more dependant on the known technical specifications we now have for most vehicles. Having looked at some of the research into vehicle and caravan stability, I can assure you it is a very complex issue and would be beyond the realms of reason to expect every caravanner to explore their own outfits specifications and apply them to the many calculations needed to model an outfits stability envelope.
So we are left with the rather simplistic weight ratio guidance, and suck it and see approach.
There is nothing wrong with you adopting an 80% ratio, but it is far from common practice.
I do agree with the Prof that different combinations may look good or bad on paper but in fact do not follow the theory. I have towed caravans for nearly 35 years and have always tried to be responsible with weights but having company cars where you have no choice did mean sometimes the ratio was not what I wished. In practice most cars did well, but there were differences in towing the same caravan with a different car despite similar ratios and towing different caravans with the same car. At no time have any proved to be unstable but from experience in dealing with accident claims, it did appear that too high a weight ratio was a problem in some accidents.
As you cannot test the car and caravan as an outfit before buying my position is that you should err on the side of caution particularly when starting out and the 85% figure looks reasonable for a starter although just how scientific it is I cannot say. It also should be appreciated that this is advice for people starting out towing and a higher ratio is acceptable as you gain experience but the simple fact is the better the ratio the more chance you have of getting a stable outfit.
As you cannot test the car and caravan as an outfit before buying my position is that you should err on the side of caution particularly when starting out and the 85% figure looks reasonable for a starter although just how scientific it is I cannot say. It also should be appreciated that this is advice for people starting out towing and a higher ratio is acceptable as you gain experience but the simple fact is the better the ratio the more chance you have of getting a stable outfit.
ProfJohnL said:
Which was my instint.
otherclive said:
I'm happy planting all 100kg of my weight onto the brakes of my car on a test track, safe in the knowledge that ABS and stability control, combined with my own not insignificant track based driving experience, will have a good stab at controlling any inclination for the car to spin- and that if it doesn't manage it I won't damage anything much.
ProfJohnL said:
Exactly. My van doesn't have ABS, and if the wheels lock and it tries to overtake the car (not something that would be reduced by additional braking capability from the car, incidentally, quite the opposite), all bets are off. Maybe it'll be fine and it'll all come to a nice straight stop. Maybe it won't. I don't fancy rolling my van testing it out though.
I'm comfortable driving defensively and sensibly in the hope that I will never end up in a situation where I have to very seriously plant the brakes at speed. If and when I do though I'll apply the minimum force I feel necessary to stop in whatever distance I have (as opposed to going all out on the brakes).
If that minimum is all the force I have, then so be it- I'll back myself to make the best of a bad situation and try to minimise the damage my outfit does if a collision is inevitable for any reason (not that I expect that to be the case).
I've had to so some fairly decent stops whilst towing (although again much reduced from what they might have been by a sensible approach to driving), and am happy controlling the outfit, but again I'm not going to find an air field and stamp on the brakes as hard as I can at speed just for the sake of finding out what happens. I don't want to have to get all the plates back out of the clothes cupboard for one thing.
seth1 said:
Nearly Funny ! Plenty of hills and slopes and banks in Yorkshire where we normally go , I didn't just mean Holland ! Plenty off hill starts that's what I meant ! Still copes .
https://caravanchronicles.com/guides/understanding-over-run-brake-systems/
This is worth a read.
I believe it is important and responsible to appreciate fully your car's braking performance both solo and hitched. There is a difference but not one which should cause jack knifing assuming the brakes are correctly adjusted.
No amount do defensive driving can avoid the unforeseen idiot who crosses the central reservation or who pulls out right in front of you.
This is worth a read.
I believe it is important and responsible to appreciate fully your car's braking performance both solo and hitched. There is a difference but not one which should cause jack knifing assuming the brakes are correctly adjusted.
No amount do defensive driving can avoid the unforeseen idiot who crosses the central reservation or who pulls out right in front of you.
DD , that's a good article to read for someone to understand how the braking system works what could and could not happen . Most of us on this forum will understand that & appreciate how good you have to be to do what we do but they'll be a certain %'age that will look at that & think yeah no bother !!
I drive a 11 ton bus 8 hrs a day, 15 tonnes or so when full, the amount of idiots that I have to break for everyday is uncountable & scary !
Craig .
I drive a 11 ton bus 8 hrs a day, 15 tonnes or so when full, the amount of idiots that I have to break for everyday is uncountable & scary !
Craig .
Spot on Craig. You will know how important it is to know exactly what your vehicle can do in those unfortunate circumstances we may have to face
Being just outside Glasgow does mean we have plenty of hills. The car copes with them rather than sailing up with a petrol engine but it was a compromise we accepted when buying the car.
Dustydog said:
Indeed, although it contains more information to support my initial comment (which was that impact on braking of towing a braked trailer is nominal, provided the trailer's brakes are rated correctly and the van isn't overloaded) than to dispel it.
The most useful part of that article appeared to me to be the detailed explanation of the (already implicit, one would hope) need to keep your van's running gear in good working order.
If you're concerned about the outfit's overall ability to brake, it's the trailer's brakes you need to be concerned with (the condition of the vehicle's brakes being (a) just as relevant when not towing, as when towing, and should therefore always be a concern, and (b) checked annually at the MOT) .
Dustydog said:
Hello Dusty
I have generally been impressed by the content of the forum in the link you point to, and much of the content parallel's my own thoughts and experiences. There is a lot of detail, and it takes a deal of concentration to assimilate it.
I think it points to the author as someone who, like me, prefers to understand a process rather than simply to accept it, becasue its been the tradition.
There is a link to “Understanding the dynamics of towing“ near the bottom of the page, and there are some slightly of the mark points about hitch height and transfer of load when braking which I take some issue with, but on the whole it may save me writing my own book.
I think that the amount that the prof writes on this forum , he'd be onto his second or third book now ! 
[quote="ProfJohnL
There is a link to “Understanding the dynamics of towing“ near the bottom of the page, and there are some slightly of the mark points about hitch height and transfer of load when braking which I take some issue with, but on the whole it may save me writing my own book.[/quote]
B) Can I have a signed first edition Prof
There is a link to “Understanding the dynamics of towing“ near the bottom of the page, and there are some slightly of the mark points about hitch height and transfer of load when braking which I take some issue with, but on the whole it may save me writing my own book.[/quote]
B) Can I have a signed first edition Prof
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