The Physics of towed vehicles (1 Viewer)

[olley]

Hi just been reading an interesting post on IRV2.com, about the load a toad can put on your RV/Motorhome if its unbraked or their not set up right.

In an emergency stop from 60mph the toad will push against your vehicle with almost 3 times its normal weight.

See here: The Physics of Towed-Vehicle Braking - Topic Powered by eve community

Olley

 

[davejen]

Very easy answer- use a braked device whether it be a trailer or a frame!
Dave:thumb:

 

[scotjimland]

Interesting article Olley, thanks for posting..

Makes me wonder why some companies still supply and fit unbraked A frames.. irrespective of the towed weight it seems irresponsible...

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[olley]

Hi Jim wondered that myself, and how effective the usual "A" frame cable systems are without servo assistance.

Olley

 

[bobandjanie]

Hi do you think it would be any worse than a trailers brakes. When I had my lorries I used to pick trailers up, and often had to pull the breaks up a bit, or I would be renewing my brakes 3 times a year. Thats my profit gone. Bob.

I give up I know its brakes but I cant change it.

 

[scotjimland]

Hi Jim wondered that myself, and how effective the usual "A" frame cable systems are without servo assistance.

Olley

Good question and one I considered before buying the toad..

I decided to get as light a toad as possible, preferable under 750kg, the Seicento's kerb weight is 730kg (including fuel) it has a braked frame, but how to test or set up isn't easy..

I haven't tried an emergency stop yet but under normal driving and braking I couldn't detect any difference in the stopping distance.. that's not to say there isn't.

It would make an interesting day out if we could hire a disused airfield for testing rigs with trailers and toads.. :Cool:

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[bobandjanie]

Hi dont over do it Jim, my last A frame jamed the breaks on, and boiled the fluid out. Dont do too many test they will ban them. Bob.

 

[scotjimland]

Dont do too many test they will ban them. Bob.

... ever the pessimist.. ... just be my luck..

 

[Braunston]

Hi, Jim

When the "A" frame is attached and the brake cable connected does the "A" frame's hand brake do anything, by that i mean does it apply the brakes or can you still push toad, as I would have thought that would have been a reasonable indication if the brakes do in fact have any effect when connected without the servo.

I would be interested to know the answer

Thanks
Braunston

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[olley]

Hi trailer brakes a designed to work without servo assistance and use soft linings, cars aren't, and use hard linings or disc brakes, just try stopping without the servo working, you will need leg muscles like garth.

I guess that would be the only way to access the braking ability Jim, race down a runway and ram the brakes on, not very scientific but would I think give a decent indication. Wife might not be to pleased about all the broken plates though.

Olley

 

[scotjimland]

Hi, Jim

When the "A" frame is attached and the brake cable connected does the "A" frame's hand brake do anything, by that i mean does it apply the brakes or can you still push toad, as I would have thought that would have been a reasonable indication if the brakes do in fact have any effect when connected without the servo.

I would be interested to know the answer

Thanks
Braunston

Hi Braunston

I will try it out tomorrow and report back, but it won't be very scientific, I tend to think like Olley, brakes without a servo aint going to be very effective.

Hi trailer brakes a designed to work without servo assistance and use soft linings, cars aren't, and use hard linings or disc brakes, just try stopping without the servo working, you will need leg muscles like garth.

Have you seen Jan's leg muscles.. ? I didn't mention she was riding shot gun ..

 

[Braunston]

Hi, Olley

I understand the point you are making but it would be interesting to know if the cable from the "A" frame arrangements can actually exert enough force to actually apply the brakes that are fitted,

Further to your suggestion of needing legs like Garth, isn't that precisely what is being illustratrated by your link, the force that can be exerted by a car being towed is probably more like 2 Garth's and if this was transmitted into an ALKO over run device routed by cable to the cars existing braking system then just perhaps the 2 legs like Garth pressure (or more) may be sufficient to successfully apply them.

hope that make sense.


I just remembered someone on one of the "A" frame discussions saying that when the servo is primed (has vacuum) the braking affect can be very harsh on the towing vehicle, so that may be worth taking into account.

Hi trailer brakes a designed to work without servo assistance and use soft linings, cars aren't, and use hard linings or disc brakes, just try stopping without the servo working, you will need leg muscles like garth.

I guess that would be the only way to access the braking ability Jim, race down a runway and ram the brakes on, not very scientific but would I think give a decent indication. Wife might not be to pleased about all the broken plates though.

Olley

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[bobandjanie]

They might let us try at Ben****ers Airfield. but it would have to be in the day time, because they have UFO's landing at night. Bob.

Why did it do that, is it the fact I said UFO's.

Here: Ben****ers Airfield

Well its near Ipswich.

 

[pappajohn]

i read somewhere if towing a fully loaded unbraked 750kg trailer, the tow car should weigh at least 4000kg.

john.

 

[olley]

Hi brauston, yes I agree, but that means garth is pushing against the RV/motorhome with two of his leg muscles, if their as strong as the mirror made out, you won't stop this side of the north sea.

Ben****ers???? odd one that, totally off topic but I dismantled a sauna out of the fire station at the adjacent Woodbridge base when the yanks left, and took it to the fire station at Alconbury, got lost on the Alconbury base and finished up driving down the main runway

Olley

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[des]

i always thought the reason for (american) unbraked a-frames was for use with auxilliary braking systems e.g. brake buddy.

des

 

[pappajohn]

Hi, Olley

it would be interesting to know if the cable from the "A" frame arrangements can actually exert enough force to actually apply the brakes that are fitted,

there is a long winded way to find out.........

fix a ratchet strap around the hitchhead and a frame to pull the hitchhead back as if braking........try to drive away. you'll get the answer.:thumb:

obviously you need a jockey wheel to get the correct hitch height and to be able to drive.

 

[Geo]

Tomorrow
for the benefit of all you lucky people, I will conduct a few tests on my MoT brake rollers and produce some braking efficiency figures for cars with servo used and engine off IE no servo, should be interesting, i will also note pressure needed to achieve mot pass rate ( if possible) without servo:thumb:
Given the Mot pass rate in efficiency terms is 50% of the testable weight, this will be the bench mark used, also to bare in mind, locked wheels are the maximum effort possible, note i didn't say safest.
Watch this space
Geo

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[pappajohn]

cheers Geo......could be interesting :thumb:

of coarse, a conclusive test would be as my rachet strap method mentioned earlier....:thumb:

 

[davejen]

Reply to Papajon, if you did that ,your servo would be working so you'll get a false result anyway!
Dave:thumb:

 

[olley]

Hi papa what would that prove?? that if you apply enough force you can a) break, the brake cable, or b) lock the wheels.

Olley

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[Geo]

cheers Geo......could be interesting :thumb:

of coarse, a conclusive test would be as my rachet strap method mentioned earlier....:thumb:

Next time we get an MoT failure on brakes I'll try that John, if it works ill give him a ticket, and dump 20 grands worth of test equipment
Geo

 

[pappajohn]

Reply to Papajon, if you did that ,your servo would be working so you'll get a false result anyway!
Dave:thumb:

oh:oh:oh:oh:oh:oh:oh:

 

[pappajohn]

Hi papa what would that prove?? that if you apply enough force you can a) break, the brake cable, or b) lock the wheels.

Olley

yeah! but if you tighten it in stages it will give you some idea whats happening at the brakes, but you can only exert a certain amount of force as the hitchhead will come to its stop. there is very little movement of the cable anyway.

if the servo was active you probably wouldnt have enough travel in the cable to be of any use.....my pedal drops another inch or two when the engines started while pressing the pedal.

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[olley]

Hi geo I would be very interested in the results of your test.

Olley

 

[scotjimland]

Hi geo I would be very interested in the results of your test.

Olley

Me too.. look forward to your report Geo

Jim

 

[paulharrison]

Hi olley
Me and my dolly dont have any braking problems it tows 100% best way to tow behind your Rv as big heavy drum brakes best thing I bought can tow 2 tons if needed and folds down to 30" when I need to store it, you can now buy a bike rack to fit on the towing arm if you get a dolly make sure its the Demco, I have been checked by the police in a lay-by and they admired the complete rig.
Paul

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[olley]

Hi Paul, now I know their not legal.

Olley

 

[paulharrison]

Hi Paul, now I know their not legal.

Olley

promise you wont tellbut everbody in the states uses them?

 

[Geo]

Brake test results

Not exactly laboratory conditions, but..
over all braking % figures without servo were very slightly less than with the servo, it is my considered opinion that in an emergency panic situation the un servo,d brakes would stop the vehicle,in the event of a servo failure, even front wheel lock out was obtained without to much pressure being applied, pressure reqd was approx 2 to 3 times greater and IMHO easily obtainable by the brake overrun system
vehicles with rear disc's as opposed to drums did not perform quite so well on the un servo'd rears and were borderline but passable
Geo
Paul, if the Yanks use Recovery Dolly's it must be ok:thumb:

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