Insurance and the 85% rule

[xtrailman]

It is a proven fact that braking distance is actually shorter when towing a trailer than when the car is solo (on condition that both the car's brakes and those of the caravan are properly adjusted and maintained). This is due to the fact that when the caravan's overrun brake is deployed, the caravan will tend to tip forward and the increased noseload will push the back end of the car down. This, in turn, increases rear axle load of the car, thereby improving the braking efficiency of that axle. This doesn't mean to say that I think that exceeding the kerbweight would actually be beneficial (there are other effects which are equally counteractive) but I strongly question whether the insurers' assessment of the risk is based on actual accident data. Only 0.9% of all accidents involve cars which are towing so there cannot be very much reliable and differentiated data to form the basis of a justifiable restriction on a 85%+ weight ratio

Lutz.

You are confusing two issues, Allan. I am not saying that car plus caravan would stop as quickly as a lightly laden car with just the driver. What I am saying is that it would stop as quickly as a solo car which is fully laden up to its max. GVW

Lutz

No Colin, you've got it wrong. The caravan doesn't have to brake harder than the car in order for the outfit to be able to stop more quickly. As you rightly say, it couldn't because then its overrun brake would be released.

The reason why stopping distance is shorter is because the car is actually braking harder than when solo. This is because there's more weight on the back axle. More weight, more friction, better braking, it's as simple as that.

Lutz.

Tests have proved that stopping distances for solo cars are increased when ABS is fitted.

Not reduced.

This argument has been debated on the honest john forum some years ago.

However ABS will allow you to steer round a hazard under heavy braking.

Ray

RAY, Your quote:

"Tests have proved that stopping distances for solo cars are increased when ABS is fitted.

Not reduced.

Tests have proved that stopping distances for solo cars are increased when ABS is fitted.

Not reduced.

However ABS will allow you to steer round a hazard under heavy braking."

Please state the source of this incorrect information. Judging by the last statement regarding steering around a hazard, I think someone has confused ABS with ESP.

Lutz

this goes some way towards explaining the point re abs brakes i was trying to get across.

see this link

http://www.telegraph.co.uk/motoring/main.jhtml?xml=/motoring/2002/08/02/emrip03.xml
Take a brake

From my physics course I seem to remember that maximum braking efficiency occurs just before the wheel stops rotating and then begins to skid or slide. I don't think a non-ABS car would stop sooner on a dry surface with the wheels locked and almost certainly an ABS car will stop better on contaminated surfaces unless the driver is very skilful.

J.A.P., Esher

Drivers are not skilful enough, they just believe they are. In the UK alone, more than 90 per cent of all accidents are caused by human error and it's a sad fact that current basic training standards aren't up to the job of ensuring safety on the road. You are correct in your understanding about when braking is at its most efficient - just prior to the wheels locking. Manually braking like this in an emergency, however, is one of the hardest things to learn. It is known as threshold braking, whereby a driver generates the maximum braking force just prior to wheel lock-up. The sensitivity and cool head required for this are expert-only qualities.

Most drivers faced with an emergency will simply stand on the brake pedal, which does two things in a non-ABS car. First it removes all steering control and second, on anything other than a dry, smooth surface, or freshly fallen snow, it increases the braking distance. By repeatedly stamping on the brake pedal (cadence braking), drivers can mimic the effect of ABS and retain steering control, but again this is a technique that requires expert tuition and much practice and it is never as efficient as ABS.

Best by far is a modern ABS system with electronic brake force distribution, which uses wheel sensors and a computer to measure how near to lock-up each wheel is. It then modulates the brake line hydraulic pressure around the point of lock-up, maintaining almost maximum stopping power to each wheel while retaining steering control. In a critical emergency, braking distance is often academic; it is the ability to steer round a hazard that can save the day, yet few drivers understand this or how to use their ABS brakes to enhance safety.

Ray

lutz

I'm sorry if you understood my replies to be blanket statements. They were never meant to be. All I intended to get over was that in a straight line and on a dry road, with all brakes working correctly, a fully laden car fitted with ABS and towing a caravan would be able to stop in a shorter distance than the same fully laden car not towing. Anything that deviates from these conditions could, under adverse circumstances (such as having to swerve at the same time to avoid a hazard for example) have the opposite effect

Lutz

I still await you comments re ABS brakes from my last post.

May I also add that I consider all the above posts, including my own to be blanket statements, unless conditions are attached.

 

[Lutz]

I'm a bit baffled by the above reply. Are you expecting an answer from me? If so, to what question? I thought that the whole issue has been reasonably well clarified now that everyone has accepted that different sets of circumstances may result in different consequences. That, to me, means that everybody is satisfied that no blanket statements are being made which are meant to cover all eventualities.

 

[ProfAlGoogle]

Your confused Lutz, none more so than me I can assure you!

Best by far is a modern ABS system with electronic brake force distribution, which uses wheel sensors and a computer to measure how near to lock-up each wheel is. It then modulates the brake line hydraulic pressure around the point of lock-up, maintaining almost maximum stopping power to each wheel while retaining steering control. In a critical emergency, braking distance is often academic; it is the ability to steer round a hazard that can save the day, yet few drivers understand this or how to use their ABS brakes to enhance safety.

Ray

Why do most people refer to emergency braking & ABS as if it is going to happen under ideal conditions, most times Emergency braking happens when you least expect it, so no amount of electronic wizardry is going to steer you safely around three blocked lanes (& hard shoulder) of standing traffic on a motorway, to name but one scenario.

Once again 100% concentration & complete respect for the vehicle you are driving & the conditions you are driving in. Prevention is better than cure.(defensive driving)

"More than 90 per cent of all accidents are caused by human error and it's a sad fact that current basic training standards aren't up to the job of ensuring safety on the road."

Now that above statement I can wholeheartedly agree with, driver training should be made compulsory for all who tow a trailer, be it that they have held there license for 1year or 30 years, and to cover all aspects, both practical & theory.

And finally I agree with Lutz, this topic has been well & truly debated, and all we are doing now is covering old ground, there might be a little more debating on the subject when Lutz returns home at Easter and has a look for the magazine that carried the original information.

Allan.

 

[ProfAlGoogle]

Forgot to mention,

"More than 90 per cent of all accidents are caused by human e

error"

We do not have accidents on our roads any more! (RTA)

According to the police we have "Road traffic incidents" (RTI)

Food for thought.

Allan.

 

[Berty3]

The most serious design fault in 99% of trailers in the class 750kg to 3500kg is the brakes. These are "Over run" brakes. They work when the tow car brakes and the trailer catches up with the tow car and so pushes on a lever which applies the trailer brakes. This works very well as long as the trailer and tow car are in a straight line. When this is not the case you are in effect operating with no brakes at all (including your tow car), as the consequences of applying the brakes can be so disasterous. Take a look at this site Lutz it makes for very good comon sense reading

http://20six.co.uk/caravanaccidents
Berty

 

[Lutz]

While the blog quoted gives some food for thought, it also contains a lot of rubbish, especially further down the page on the subject of aerodynamics. (I found the call for a wind speed indicator in towing vehicles particularly funny).

However, the author did have a point concerning the fitment of service brakes on trailers under 3500kg (they are already a legal requirement over that limit anyway). But, even then, these brakes do not act when the towcar is slowing down using engine braking only. This puts extra load on the towcar brakes when descending a long hill, for example. Without an overrun brake, the brakes on the towing vehicle would therefore have to be uprated to take this condition into account. (This is probably one of the reasons why many American cars have such surprisingly low towload limits for their size and power.) Service brakes on the trailer would also require significant changes to the electrics on the towcar, as the information to apply the brakes on the trailer must come from the towcar. This would result in the need for additional wiring to the trailer or caravan.

A combination of an overrun and a service brake would be ideal but the complexity and cost would probably be out of all proportion. I therefore go along with Allan's suggestion that driver training should be improved so that people towing are aware of additional risk and act accordingly by demonstrating appropriate extra due care.

Regarding loss of braking when snaking, the author has not taken modern developments in ESP (or DSC or whatever you want to call it) into account. This will automatically apply the brakes on the car as soon as it recognises a swaying motion transmitted through the towbar. Also, the electronic stabiliser like the one I have on my caravan works on the same principle but applies the brakes on the caravan instead of on the towcar. Here again, the ideal system would be ESP on the car plus an electronic stabiliser plus a friction stabiliser, like the AlKo or the Winterhoff. With all three systems fitted, the chance of a getting into an snake is minimal because all three will act early on to prevent uncontrollable instability.

 

[ProfJohnL]

Hello Allan,

I fully support the re designation of what is colloquially called and accident as an incident.

The reason being is that accidents do not happen; there is always an underlying cause, and that means that someone has either under estimated an effect, or has chosen to ignore it.

In some cases the underlying cause may not have previously been identified, so that means who ever should have considered the risk has been negligent.

 

[Terry_5112949]

Very interesting, I can agree and disagree with a lot of comments on this thread but one point I have not noticed is that if under heavy braking an outfit and more weight is put onto the rear axle then surely this is taking some of the weight off the front axle brakes which are the most effective brakes on any vehicle. I also much prefer to tow at less than 85% and always have done, my tow vehicle`s kerb weight is 1420kg of which 85%= 1207kg, my van has a MTPLM of 11000kg can anyone calculate as to what that equates to?

 

[Lutz]

No, the additional load on the rear axle is not accompanied by an equivalent reduction of the load on the front axle. Because the towbar is (usually) relatively close to the rear axle, the increase in noseload acts almost 100% on the rear axle only and has a negligible effect on the front axle.

 

[joeby]

Very interesting, I can agree and disagree with a lot of comments on this thread but one point I have not noticed is that if under heavy braking an outfit and more weight is put onto the rear axle then surely this is taking some of the weight off the front axle brakes which are the most effective brakes on any vehicle. I also much prefer to tow at less than 85% and always have done, my tow vehicle`s kerb weight is 1420kg of which 85%= 1207kg, my van has a MTPLM of 11000kg can anyone calculate as to what that equates to?

i worked it out that you are towing at 77.5%

 

[cris_408518]

Well I actually carry a windmeter when caravanning, how the **** it would work on route with caravan in to I'm not quite sure.

As for Incident V Accident , when it goes wrong it is likely to

Effingham well hurt you and your finances and also any one else that is with you.

So call it what you like but try your best to avoid at call

cost ;-)

 

[ProfAlGoogle]

http://people.bath.ac.uk/en8cjk/Caravan.pdf
Makes for very interesting reading,

your thoughts.

Allan.

 

[Lutz]

It does make for interesting reading, yes, but it doesn't really contain any surprises. It is noteworthy that while concurring with the general recommendation that a heavy car and a light caravan is of advantage, it does appreciate the complexity of the issue and not once does it suggest that a weight ratio limit of 85% is particularly desirable.

However, the report is not comprehensive. There are several issues which would have been interesting but which weren't touched on. One is a comparison of single and twin axles of the same weight (genuine interest on my part, Cris, no irony meant) and another the effect of side-to-side weight distribution. I have read caravan tests where stability of the caravans was not as good as expected and in every case there was a relatively large difference between wheel load left to right. Whether this is coincidence or of significance would be informative.

Also, the tests were performed using an older Mondeo which, of course, did not have second generation ESP. A comparison between an ESP-equipped car and a similar non-ESP one would be interesting.

Under 2.7.2.2 "Active caravan braking", mention is made of a virtual braking system without appreciating that such a system is already on the market (I have one on my caravan).

Interpreting the results concerning critical speed at which a snake starts to occur, one gets the impression that outfits of the setup tested should be limited to 55mph and not 60mph, as is currently the case.

A further omission is the failure to include the effect of crosswinds or going downhill but that would probably have made the study just too complex.

 

[ProfAlGoogle]

To be honest Lutz I always limit my max speed to around 55mph (chicken) but I think you already know my thoughts on caravans and there unpredictability. A few years ago if memory serves me right there used to be a company in the UK that manufactured a device that was wired into the brake light circuit, and operated via a servo, or servos on the brake rods, and hence you got immediate caravan retardation as soon as the brake circuit was energised. Would this be of a similar (but updated) system to the one that you use?

Allan.

 

[Lutz]

I don't think you're chicken at all. I find that attitude most responsible. I always get the shudders when people boast that they tow their caravan at the legal limit (130km/h) in France. Even if everything has gone alright in the past, to me it's like playing Russian roulette.

What you are referring to, Allan, is an electric brake (or electric brake assist) not an electronic stabiliser. The electronic stabiliser has a small electronic circuit which includes an accelerometer that measures the sway in the event of a snake. As soon as the lateral acceleration of back of the caravan exceeds a preset threshold value (I think it's a 0.6g swing once in each direction) it applies the brakes on the caravan until stability is recovered and the lateral acceleration is down to zero again.

 

[RichardS1]

I can relate to Allan's comment regarding towing speed. I find towing at 55mph far more relaxing and comfortable than sitting at 60. I work with several people who are also caravanners and we often comment that if you undertake a business journey at the legal speed limits these days you hardly get there any quicker than you would towing. With this in mind 5mph will hardly make a difference in the journey time towing.

 

[cris_408518]

I really can't beleive what I've just read!

If you are not comfortable or not happy towing at 60mph when all is well you are often a manace to other road users and no wonder we caravanners get so much flak.

Trucks have to find a way past you and you are trevlling at about 20 mph less than the average car on the M Way and 30 or so mph less in France.

There are times of course when we need to reduce speed when towing, but quite frankly if you are not comfortable or happy at 60 mph but are at 55 I think you need to look at the rig you are using and maybe yourself and your driving!

I know this will not make me many friends here, but I feel its time for a reality check and thought for all road users.

 

[ProfAlGoogle]

Thanks for the information Lutz, who manufactures the electronic stabilizer, and in your opinion are they any good? Are they available in the UK? (web address) We are off down to Biarritz latter in the year and there is no way on this earth I will see 130km/ph (about 80mph) with my caravan on tow, Absolute madness, yes fine if all stays stable and in a straight line, but god help them & other road users if things get out of hand, the chance of recovery at those kinds of speed must be pretty slim. I spend most of the working year chasing round and trying to beat deadlines (not on the road) so when it comes for time to get the van out, my attitude is sit back & relax take your time and try as best as you can to enjoy the journey, but as I mentioned before the best time is when those four legs are down on terra firma.

Allan.

 

[Terry_5112949]

Thanks for the information Lutz, who manufactures the electronic stabilizer, and in your opinion are they any good? Are they available in the UK? (web address) We are off down to Biarritz latter in the year and there is no way on this earth I will see 130km/ph (about 80mph) with my caravan on tow, Absolute madness, yes fine if all stays stable and in a straight line, but god help them & other road users if things get out of hand, the chance of recovery at those kinds of speed must be pretty slim. I spend most of the working year chasing round and trying to beat deadlines (not on the road) so when it comes for time to get the van out, my attitude is sit back & relax take your time and try as best as you can to enjoy the journey, but as I mentioned before the best time is when those four legs are down on terra firma.

Allan.

Cheers Joby 77.5% OK by me, car is a Vectra 2.0DTi pulls well and cruises at 60mph no problem and with very good fuel economy

 

[Terry_5112949]

Thanks for the information Lutz, who manufactures the electronic stabilizer, and in your opinion are they any good? Are they available in the UK? (web address) We are off down to Biarritz latter in the year and there is no way on this earth I will see 130km/ph (about 80mph) with my caravan on tow, Absolute madness, yes fine if all stays stable and in a straight line, but god help them & other road users if things get out of hand, the chance of recovery at those kinds of speed must be pretty slim. I spend most of the working year chasing round and trying to beat deadlines (not on the road) so when it comes for time to get the van out, my attitude is sit back & relax take your time and try as best as you can to enjoy the journey, but as I mentioned before the best time is when those four legs are down on terra firma.

Allan.

Sorry this comment should have been to an earlier posting and not to Allan sorry.

 

[ProfAlGoogle]

In reply to Cris

1, Trucks have to find a way past me? Not very difficult on a three lane motorway!

2, Never ever encountered any problems in over 35 yrs driving in France at those speeds.

3, traveling at 20mph less than the average car on the Motorway? When did they increase the limit to 75?

4. Why all the fuss about 5mph? On a single carriageway we are restricted to 50mph, cars 60 mph so there you have a 10 mph difference + a lot more difficult to overtake (and yes before you mention it I do pull over) and no problems with Lgv's they are restricted to 40mph

5, The most important factor is the ability to maintain my 55 mph, up hill or down dale, which I can do quite comfortably, the biggest problem with some outfits (Rig!that normally applies to a caravanner who thinks he is a big trucker) is there inability to maintain a constant speed, you know the ones 70mph+ down hill then crawl up the next slight incline, there the ones Cris that get carravaners as you put it so much flak

6, when all is well? If you adopt that attitude you are an accident waiting to happen, you should know my

Feelings on caravans by now, 100% concentration all of the time, and expect the worse.

7, When did you last maintain an average speed of 55mph solo or towing on our congested roads, the computer on my car at present reads at about 37mph.

8, "I know this will not make me many friends here, but I feel its time for a reality check and thought for all road users"

Easy that one Cris, and you do not need me to give you the answer.................

 

[Lutz]

I think you'll find that HGV's are governed at 90km/h (=56mph). I really don't think that it's worth quibbling about 1mph.

 

[ProfAlGoogle]

Normally between 56/57 so they can have whacky races on the motorway, totally blocking lanes 1 & 2,for mile after mile, so I just sit there happily doing my comfortable 55mph while the rest of the traffic builds up behind Mr HGV in lane 2. woops forgot to mention, thats on a good day when the traffic is actually moving when NCP are not using it as acar park.

Allan.

 

[Lutz]

Thanks for the information Lutz, who manufactures the electronic stabilizer, and in your opinion are they any good? Are they available in the UK? (web address) We are off down to Biarritz latter in the year and there is no way on this earth I will see 130km/ph (about 80mph) with my caravan on tow, Absolute madness, yes fine if all stays stable and in a straight line, but god help them & other road users if things get out of hand, the chance of recovery at those kinds of speed must be pretty slim. I spend most of the working year chasing round and trying to beat deadlines (not on the road) so when it comes for time to get the van out, my attitude is sit back & relax take your time and try as best as you can to enjoy the journey, but as I mentioned before the best time is when those four legs are down on terra firma.

Allan.

Here's a link to the feature article in the July 2004 issue of PC magazine describing the LEAS electronic stabiliser.

It has since been improved and the price of the latest Mark 3 has also been reduced slightly to 655_ (

 

[cris_408518]

Most UK motorways are pretty full. "Maintaining good progress" is an important safety matter and aids traffic flow and any repsonsible driver should make good progress to aid all road users.

If you've had your eye on motoring for 35+ years you should have noticed that average UK motorway speed is over 75mph.

Forcing large trucks out to use the middle lane is a no brainer I'm afraid and if that if you think that is good driving God help us if that is what you do!

France is a slightly different case with lower traffic flow, but with two lane Motorways at bust times you are rolling chicane.

Motorways are our main motoring arteries and we all need our arteries to flow freely and that was one reason why the towing limit was raised to 60.

We all know that motorways have some very bad accidents, holding up traffic flow at an indicated 55 does little for other drivers frustrations and has nothing to do with single carriageways with limited overtaking opportunities.

If your outfit can't maintain all the legal limits up hill and down dale again you are a potential menace and should look at your rig and maybe take some action about what you drive or what you tow!

If you take note of your average speed, consider that your average would be better if some truck was not forcing his way into the middle lane to pass a caravan causing tail lights to repeat down miles of motorways until three lanes is at stand still.

When I drive, I take a lot of measures be it business or pleasure mileage to average as near to the speed limit as I can.

Driving is a business due to the dangers of road use.

Pootling along looking at the birdies and the hedge rows or naming the type of cows or pigs in the feilds on a balmy Sunday heading for Robin Hod bay or whilst heading on route with the caravan is something that belongs in a bygone age.

We should all respct other road users and make good progress and let others get on with their business as quickly and effortlessly as possible and then the roads wuld be safer and flow more freely.

Quite frankly if on a motorway you do not feel at ease and towing safely at 60 mph rather than ONLY 5 mph less maybe its time to give up towing or change for a safer set-up.