Stopping distance of a motorhome

[BusyBuilder]

We are in litigation with a young lad who pulled out in front of us on a slip road on the A9.

The solicitor wants to know that stopping distance of a 4t Hymer B544 2012, on wet roads.

Basically this young lad pulled out on us and I had to stand on the brakes before we hit him. There wasn't a lot of damage to his car but over £5k to ours, bent inner steel bumper and bent both radiators. Front fibreglass grill was split but not much more, in fact you'd be hard pressed to see any damage looking at the front. His 2005 Vauxhall Corsa had a hole in his bumper where our towing eye punched through it, but not much more.

The accident happened just before Christmas 2023, wet roads with snow on verges. We had very little time to react. We were travelling at an indicated 50mph. I think we had about 15-20m to stop.

So if anyone can give me an idea on stopping distances I'd be interested.

What's really annoying about this accident, is, we are doing all the work for the benefit of Saga insurance who paid out over £5k for our damages. Saga dragged their heels for almost a year before we insisted we used our legal expenses insurance to fight our case. They have basically washed their hands now and left us to do all the work, the solicitor is a bit of a wet blanket too.
I would never recommend Saga insurance going by our claims experiences.

 

[L' Hobo]

Far from having much experience other than as a driver but isn't the concept of wet road etc all a bit passe now as isn't braking achieved by stopping the rotation of the wheels in a controlled manner rather than 'locking' them up....... as in ABS.......?

We did cadence braking on some of the truck testing, basically it's manual ABS and that has been taught for years in Sweden.

 

[bigtwin]

We did cadence braking on some of the truck testing, basically it's manual ABS and that has been taught for years in Sweden.

I once went on a skid pan and the instructor got us all to brake in turn and, of course, most just planted the brake pedal and lost control. On my turn I cadence braked by stabbing the pedal rapidly and I think the instructor was a bit miffed as he told me that I’d done it too fast and was overpowering the system - yeah right! There’s no way a human could cycle the pedal as fast as an anti-lock braking system.

Ian

 

[cyberyacht]

Emergency stopping distances for motorhomes are usually 1 metre more than you have available.

 

[PaulW2]

We are in litigation with a young lad who pulled out in front of us on a slip road on the A9.

The solicitor wants to know that stopping distance of a 4t Hymer B544 2012, on wet roads.

Basically this young lad pulled out on us and I had to stand on the brakes before we hit him. There wasn't a lot of damage to his car but over £5k to ours, bent inner steel bumper and bent both radiators. Front fibreglass grill was split but not much more, in fact you'd be hard pressed to see any damage looking at the front. His 2005 Vauxhall Corsa had a hole in his bumper where our towing eye punched through it, but not much more.

The accident happened just before Christmas 2023, wet roads with snow on verges. We had very little time to react. We were travelling at an indicated 50mph. I think we had about 15-20m to stop.

So if anyone can give me an idea on stopping distances I'd be interested.

What's really annoying about this accident, is, we are doing all the work for the benefit of Saga insurance who paid out over £5k for our damages. Saga dragged their heels for almost a year before we insisted we used our legal expenses insurance to fight our case. They have basically washed their hands now and left us to do all the work, the solicitor is a bit of a wet blanket too.
I would never recommend Saga insurance going by our claims experiences.

He is asking to build an adversarial case.

I wouldn’t reply except through a lawyer.

Any answer you venture to the question is bound to be used against you - that’s why it’s being sought

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[L' Hobo]

I once went on a skid pan and the instructor got us all to brake in turn and, of course, most just planted the brake pedal and lost control. On my turn I cadence braked by stabbing the pedal rapidly and I think the instructor was a bit miffed as he told me that I’d done it too fast and was overpowering the system - yeah right! There’s no way a human could cycle the pedal as fast as an anti-lock braking system.

Ian

Well, I have to say, I wouldn't have described cadence braking as 'rapid stabbing ' but I suppose we're all taught different?

 

[Coolcats]

The type of disc and pads will also affect the ability to stop

 

[Coolcats]

These are the type of pads I have in my bike

Disc Pads - Disc Brake Pads - X-Large Sintered/Steel (Heavy Duty) - Maven 2024+

Sram: DISC BRAKE PADS - X-LARGE SINTERED/STEEL - MAVEN 2024+COMPATIBLE WITHDB-MVN-BRZ-A1, DB-MVN-SLV-A1, DB-MVN-ULT-A1

www.swinnertoncycles.co.uk

 

[bigtwin]

Well, I have to say, I wouldn't have described cadence braking as 'rapid stabbing ' but I suppose we're all taught different?

What do you perceive the objective of cadence braking to be?

How would you describe how ABS works?

I wasn’t taught that approach to cadence braking; my engineer’s brain concluded that was the best way to achieve the desired objective.

Ian

 

[Nanniemate]

We had a similar experience in Morocco, although we hit a sheep that suddenly dashed across the road in front of us. Not a hope in hell of stopping. 41,000 euros and 10 months later (all paid by AXA insurance, no quibble) we are back on the road, but why, with today's level of vehicle technology aren't manufacturers fitting automatic panic braking sensors to the front? This could remove the reaction time completely and save lives, maybe even that stupid lump of mutton that we hit.

They are it will be standard before long
But until they stop braking for shadows and leaves it not a perfect system

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[L' Hobo]

What do you perceive the objective of cadence braking to be?

How would you describe how ABS works?

I wasn’t taught that approach to cadence braking; my engineer’s brain concluded that was the best way to achieve the desired objective.

Ian

Both Cadence and ABS are designed to allow braking in a controlled manner .

Unless the tyre is allowed to turn between braking, this is hard to achieve.
Rapid application, possibly, would not allow time for the brake pads/shoes to release the wheel.

 

[ianp]

He is asking to build an adversarial case.

I wouldn’t reply except through a lawyer.

Any answer you venture to the question is bound to be used against you - that’s why it’s being sought

I think, possibly incorrectly, that it's his lawyer that has requested the information. Not really sure what he's after really..... I know he's in Scotland and things may be different but my understanding is that you wont / can't claim for assumed losses...only what you have lost and as the damage is repaired then unless you lost some pre booked 'things' then your back to where you were..... but again this is just an assumption as I'm no lawyer either......!
Having had a couple of recent incidents with vehicles both car and MH I found it almost impossible to find a lawyer that would get involved in the issue, all of them without exception telling me to use my insurance to sort it......even when one of the incidents happened to our camper while parked up for the winter and on the house drive....!

 

[bigtwin]

Both Cadence and ABS are designed to allow braking in a controlled manner .

Cadence simply means rhythm (or frequency) and can be a slow rhythm, or a fast rhythm. Maximum braking force occurs just before a wheel locks (and skids). ABS uses sensors to detect that one, or more, wheels has stopped turning and releases brake pressure to allow the wheel(s) to start rotating (gripping) again. On surfaces with a low coefficient of friction, this process is repeated at a frequency of between 5 and 20 Hz (times per second), irrespective of the brake pedal pressure applied.

Unless the tyre is allowed to turn between braking, this is hard to achieve.

Agreed. On ABS systems this application and release of brake pressure occurs at up to 20 times a second. I don’t know about you but there’s no way that I could achieve a pumping frequency of 5 times per second never mind 20 times per second (and that’s ignoring my ability to detect a wheel lock quickly enough).

Rapid application, possibly, would not allow time for the brake pads/shoes to release the wheel.

I refer you to my arguments above.

At best, an average human being might achieve a wheel-lock detection, release of brake pressure and reapplication of brake pressure cycle of 1 Hz. Clearly, this is still better than not cadence braking but, in terms of achieving the maximum braking effect (shortest stopping distance), it falls significantly short of an automated system.

Consequently, my engineer’s brain tells me that the faster that I can apply and release the brake pressure (deliberately ignoring the wheel lock detection process) then the shorter will be my braking distance. At best, I might approach a frequency of 5Hz (but more likely around 3Hz). This is not as fast as an automated system which would provide a much greater challenge to the time necessary for the wheel to regain rotation that you have questioned.

If you attempt to include wheel lock detection (as conventionally taught for cadence braking) then that frequency will drop substantially (and remember that detection must occur on every cycle). My approach requires detection only once followed by a rapid release and reapplication of braking force.

Ian

 

[L' Hobo]

Cadence simply means rhythm (or frequency) and can be a slow rhythm, or a fast rhythm. Maximum braking force occurs just before a wheel locks (and skids). ABS uses sensors to detect that one, or more, wheels has stopped turning and releases brake pressure to allow the wheel(s) to start rotating (gripping) again. On surfaces with a low coefficient of friction, this process is repeated at a frequency of between 5 and 20 Hz (times per second), irrespective of the brake pedal pressure applied.

Agreed. On ABS systems this application and release of brake pressure occurs at up to 20 times a second. I don’t know about you but there’s no way that I could achieve a pumping frequency of 5 times per second never mind 20 times per second (and that’s ignoring my ability to detect a wheel lock quickly enough).

I refer you to my arguments above.

At best, an average human being might achieve a wheel-lock detection, release of brake pressure and reapplication of brake pressure cycle of 1 Hz. Clearly, this is still better than not cadence braking but, in terms of achieving the maximum braking effect (shortest stopping distance), it falls significantly short of an automated system.

Consequently, my engineer’s brain tells me that the faster that I can apply and release the brake pressure (deliberately ignoring the wheel lock detection process) then the shorter will be my braking distance. At best, I might approach a frequency of 5Hz (but more likely around 3Hz). This is not as fast as an automated system which would provide a much greater challenge to the time necessary for the wheel to regain rotation that you have questioned.

If you attempt to include wheel lock detection (as conventionally taught for cadence braking) then that frequency will drop substantially (and remember that detection must occur on every cycle). My approach requires detection only once followed by a rapid release and reapplication of braking force.

Ian

You obviously think your correct, I, and your Instructor, disagree, we'll leave it at that.

PS. There is a clue in your second sentence, first paragraph!
It's got little to do with speed of application, it's when that application and release happens that matters.

Like many other things in life, it's all about natural instinct, confidence and practice.

 

[bigtwin]

You obviously think your correct, I, and your Instructor, disagree, we'll leave it at that.

Of course I do, and you likewise. In support of my belief I have presented logical arguments in support of my statement; and you?

It's got little to do with speed of application, it's when that application and release happens that matters.

Agreed. In low grip circumstances there is no question that the wheels will be locking so, by definition, the faster the cycle the more effective the braking process. Do you disagree with this?

Like many other things in life, it's all about natural instinct, confidence and practice.

On the contrary, it is about understanding the principles and adopting an approach that mitigates your own weaknesses.

I’m happy to modify my view if I have missed an important point in relation to this. Are you able to help in this respect or am I simply to accept that your view, without any supporting evidence/argument, is gospel?

Ian

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[Stoosal]

ABS principally allows steering control whilst under emergency braking by adjusting pressure at each wheel to ensure each wheel does not lock up. At the same time it allows each wheel to turn at a speed which ensures maximum deceleration.
It does not necessarily follow that a manual cadence version relies on maximum speed of on/off application. The application must be long enough to ensure that the wheel reaches the point at which it locks or just about locks up then removing application to allow the wheel to continue to turn.
A simple rapid application and release of the brakes at maximum speed may simply be very inefficient and not achieve the aim of minimising braking distance nor steering if required.

 

[bigtwin]

It does not necessarily follow that a manual cadence version relies on maximum speed of on/off application.

Agreed. There will be circumstances where that is the case. The scenario that I have described relates to low grip circumstances. The ability of a driver to detect the point at which the wheel locks is very difficult. By braking in such a way as to ensure that the wheel locks removes that human detection weakness.

The application must be long enough to ensure that the wheel reaches the point at which it locks or just about locks up then removing application to allow the wheel to continue to turn.

Agreed. See my comment above.

A simple rapid application and release of the brakes at maximum speed may simply be very inefficient and not achieve the aim of minimising braking distance nor steering if required.

Agreed. There will be circumstances (where more grip is available) where fewer, longer, cycles would be more effective.

Thank you for your thoughts.

Ian

 

[cyberyacht]

Judging by the amount of smoke at Turn 1, ABS isn't fitted to F1 cars then

 

[L' Hobo]

Judging by the amount of smoke at Turn 1, ABS isn't fitted to F1 cars then

Good drivers shouldn't need them just have to learn a bit of left foot braking.

 

[Silver-Fox]

Judging by the amount of smoke at Turn 1, ABS isn't fitted to F1 cars then

I think they have enough “aids” at their disposal.
About time they went back to a basic machine and a very good driver made the difference

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[dunnah01]

Stopping distance needs to be greater than the distance to something trying to hit you or something you would hit - works for me

 

[Silver-Fox]

Stopping distance needs to be greater than the distance to something trying to hit you or something you would hit - works for me

That the offending car driver failed to account for clearly

 

[PaulW2]

The cadence braking arguments are interesting. My understanding was that it has been pretty much entirely superseded by modern ABS systems that operate at individual wheel level, preventing all wheels from locking up.

If braking force can be maintained to just before the locking-up point this obviously maximises stopping distance.

Manual cadence braking was, I thought, a method for ensuring you can both brake and steer around an obstacle.

As a method of stopping in a straight line, however, it is less clear to me that it necessarily reduces stopping distance.

I apply the brakes, say at 2 second intervals. In each 2 second cycle there is zero braking force, then force to the point of lock-up, then back to zero. Contrast this with judicious constant application of brakes to a point a little before lock-up. Which gives the better stopping distance?

 

[bigtwin]

The cadence braking arguments are interesting. My understanding was that it has been pretty much entirely superseded by modern ABS systems that operate at individual wheel level, preventing all wheels from locking up.

It has.

If braking force can be maintained to just before the locking-up point this obviously maximises stopping distance.

It does. That’s why ABS operates at up to 20 times per second. This rapid cycling provides maximum braking effort and is way faster than even the best driver could ever hope to achieve.

Manual cadence braking was, I thought, a method for ensuring you can both brake and steer around an obstacle.

It is; however the ability to maintain steering is a direct consequence of maximising the time during which the wheels are rotating. Braking, and skidding results in a loss of steering control. By rapidly cycling between wheels being locked and wheels rotating gives a greater time where the wheels are rotating and hence steering is maintained (so far as it can be).

As a method of stopping in a straight line, however, it is less clear to me that it necessarily reduces stopping distance.

It does, that’s it’s primary purpose. The ability to retain some steering effect is a byproduct of this.

I apply the brakes, say at 2 second intervals. In each 2 second cycle there is zero braking force, then force to the point of lock-up, then back to zero.

You are mimicking ABS but at a much reduced cycle frequency.

Contrast this with judicious constant application of brakes to a point a little before lock-up.

This is a single cycle?
Careful, controlled application of the brakes is unlikely to be achieving maximum braking effort and consequently will increase the braking distance. The ability of an average human to detect the point at which wheels are ABOUT to lock up would be very low. Yes, they will, to varying extents, be able to detect that their wheels HAVE locked but they must then release the brakes before judging that they are now rotating before reapplying the brakes.

Which gives the better stopping distance?

Impossible to say because there are too many variables in each case.
What we do know is the the mechanical (and electrical) components within the braking system can cope with cycle frequencies of 20Hz so the faster that a human can emulate that process (on a vehicle not equipped with ABS (or with ABS disabled)) the shorter their braking distance (on low grip surfaces, which, after all, is the raison d’etré for their existence).

Ian

 

[Phill D]

All this discussion just proves how stupid and irrelevant the question posed by the solicitor is!

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[PaulW2]

You are mimicking ABS but at a much reduced cycle frequency.

Doesn't ABS only do the pulsating thing once it notices wheel lock/a difference between wheels though? I thought it was just braking as usual until then, and that it just gives you the peace of mind that it will prevent wheel lock.

So my pulsating entails a reduction in braking efficiency by braking for only half the time (on the downstroke) and even then not at full force all the time; the ABS interferes only to mitigate wheel lock.

 

[bigtwin]

Doesn't ABS only do the pulsating thing once it notices wheel lock/a difference between wheels though?

Yes. However, on a low grip surface (such as snow, or a skid pan) that will be occurring more or less as soon as you touch the brakes.

I thought it was just braking as usual until then, and that it just gives you the peace of mind that it will prevent wheel lock.

It is, and it does. However, much of this discussion relates to the absence of ABS and hence the need for cadence braking (and how to be most effective in achieving the objective of stopping in the shortest possible distance). We are not looking to compete with ABS; there is no requirement for/any point in cadence braking if your vehicle is equipped with ABS.

Ian

 

[Barriesimpson]

In the beginning of ABS there was only one sensor fitted (rear right hand side) and that controlled all the information to the system. This may well have changed now, but I doubt there is a sensor on each wheel. Just thought I'd throw that log on the fire

 

[stuartholmes]

In the beginning of ABS there was only one sensor fitted (rear right hand side) and that controlled all the information to the system. This may well have changed now, but I doubt there is a sensor on each wheel. Just thought I'd throw that log on the fire

I think that log has been pre-soaked in paraffin...

 

[PaulW2]

In the beginning of ABS there was only one sensor fitted (rear right hand side) and that controlled all the information to the system. This may well have changed now, but I doubt there is a sensor on each wheel. Just thought I'd throw that log on the fire

I replaced my LHS front one in my car about 10 days ago. It was a pig of a job trying to reach the damn thing on the drive in the cold.

After this, the computer still kept panicking about ABS and a tyre pressure sensor. This time the RHS front, my OBD reader told me.

I thought I'm not going to do the other one, and as I can't do the tyre pressure sensor anyway - it requires getting the tyre out of the way off the rim and I'm not Kwikfit - I took it to the local BMW specialist who sorted it all out.

I can confirm that there is an ABS sensor in each wheel.

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[Barriesimpson]

I replaced my LHS front one in my car about 10 days ago. It was a pig of a job trying to reach the damn thing on the drive in the cold.

After this, the computer still kept panicking about ABS and a tyre pressure sensor. This time the RHS front, my OBD reader told me.

I thought I'm not going to do the other one, and as I can't do the tyre pressure sensor anyway - it requires getting the tyre out of the way off the rim and I'm not Kwikfit - I took it to the local BMW specialist who sorted it all out.

I can confirm that there is an ABS sensor in each wheel.

Ok, things have changed since I worked in that environment then. Thanks for the update.