Reduced safety margins due to car modifications

[Darren]

Something that regularly comes to mind about car modification is generally, that although the performance of the car increases, the safety margin decreases. Let me explain.

Inched up Tyres
The process of decreasing the height of the tyre wall, and increasing (inching up) the size of the inner wheel. Usually in relation to adding some nice big alloy wheels.

Although this does have the general advantage of increasing cornering performance (and the look of your nice new ride). It also has the negative effects of making the ride less comfortable, and if you happen to take a bend too quickly you wont get any feedback in the steering, and less rear end twitch before the vehicle slides.

i.e. if it's gonna go...kiss your ass goodbye and hope you get out of the ditch alive...as there will be no warning, compared to a standard vehicle setup.

ESP/ESC - Electronic Stability Program/Control
Used to stabilise a car during cornering by distributing the suspension/wheel traction control to give maximum grip/more control.

The problem with this is similar to above. Although it will generally give the car higher performance when cornering, if you push too hard, you wont get any feedback as to the potential of "losing control".

I believe the problem with the majority of driver's these days, coupled with the inability assess risk, is based around feeling "too safe". Then the one time they push it, using all the latest toys, there is no reality check to say "hey big boy, slow down, or stop doing that because your gonna die".

I suppose, this also contributes significantly to the cost of insurance premiums for modified cars. Where the performance has been altered in one respect, the safety margins built into the car at manufacture have been decreased.

In simple terms, to avoid/prevent a skid...stop doing what caused it in the first place. If there is no feedback to tell you where you sit on the control curve, how does the driver know where they control loop becomes "unstable".

<for anyone who has studies electronics or any type of systems / stability control theory, the above I'm sure will all make perfect sense>

Darren

[manilva15b]

I know that some of this has been covered elsewhere but I had to put an answer here as well.

I agree totally on ESP systems. The problem is for me (in the company car) is that I can't turn the damn thing off! Sure, I can override it in certain circumstances, (e.g. snow, in 1st gear only ) but change up or get to 20 kph and the little beggar turns itself on again.

Another feature I've mentioned is the trend towards ever thicker A-pillars. On the C8 it's between 10cm and 18cm thick. Referring back to Steve Haley's excellent 'Mind Driving' (pages 116-117) this means that hiding a pedrestrian at just 3m distance is easily possible, and a car at only 10m.

I think I'm going to get the beast swapped for a C4 Picasso at the earliest opportunity!

[Big Err]

Risk compensation comes to mind. Make the driver feel safer and they are inclined to take more risks?

I'm sure some psychologists have done studies in this, I certainly have heard and have probably been guilty of it myself. Take high friction surfacing for example, some of the two wheeler community give a quick 'yahoo' when they find it on a bend, before opening up safe in the knowledge of lots of grip.......

Fortunately the stats (around here anyway) point to such surfacing having a positive effect on reported crashes, so although the driver/rider risk increases the improved engineered safety still remains infront with a suitable margin?

Eric

[Gromit37]

Given that my previous career involved spending a lot of time working out the effects of this, the extra grip (which doesn't exist by the way, only the amount of steering needed to achieve maximum grip) effects are normally significantly outweighed by the effects of modifying the suspension to fit the elastic bands into the car. If I had a pound for every Max Power reader with an angle grinder I'd have £4.50...

Oh, and ESP doesn't work like that - it works by creating a positive or negative yaw moment by braking alternate wheels in order to prevent the car from excessively yawing combined with a traction control function to slow you down in circumstances where it detects that the grip level is lower than required for your desired speed and radius combination. A lot of work is going into positive torque devices so you have a controllable differential that does the same thing, leaving the brakes and engine to deal with the traction control.

Thanks for the explanation Dave... but would you be able to put that in to a 'simpleton' format for those of us who didn't go beyond 'O' Level physics? Seriously, I'm not sure I understand the tyre/grip comments. Are you saying that fitting wider, low profile tyres does not increase overall grip?.The performance mods to my car run to a door edge protector on either side I'm not really in to the idea of modding.

Do you have an opinion on traction control systems (positives/negatives) and whether it encourages more reckless driving?

[Susie]

To pick up on Darren's original comments, when the last-but-one Discovery was on the drawing board, the clever people at Land Rover decided to ask their customers how they could improve the cars. The most consistent feedback was that drivers didn't like the 'feel' of the car when cornering - the 'body roll' made the car feel 'wobbly'. So, the clever engineers decided to stiffen the anti rollbars or whatever <technical term>

The Discovery was now able to go round corners quicker and the drivers didn't get any feeling of body roll. Result...well, I leave that to your imaginations

Same thing with the active yaw on Evos. Car goes round on rails until the inevitable happens... something to do with fizzicks I believe

I agree wholeheartedly with our Spanish friend. "A" pillars on modern cars are a nightmare. If you don't move fore and aft of the obstruction during your scan, you can easily miss a pedestrian, motorbike or small sevenesque car.

Over to the Stressed One for proper technicals

S

[ScoobyChris]

The Discovery was now able to go round corners quicker and the drivers didn't get any feeling of body roll. Result...well, I leave that to your imaginations

No feeling of body roll?!?! My P reg Disco had loads of body roll (although less than my friends who took his ARB's off for better offroad ability) :}

Chris

[rlmr]

It all comes back to a phrase BigERR coined in an earlier thread... Risk Compensation.

Add in the electronics etc. to make things "better" for the driver and as the driver "feels safer" they will use up this additional safety margin and be no better off...in fact they will be worse off... rather like pulling back on an elastic band. Further you pull it back before releasing, the harder it whacks your fingers

I recall the introduction of the Ford XR4i. One of the English Police Forces "lost" several in the first few months as the drivers "used" the ABS more and more rather than relying on their inherent skills. Yes you could leave the braking a wee bit later and have the ABS cut in and pull you out of trouble, but the safety margin was gone... and so did many of their cars

[Gromit37]

Thankyou Dave. I am obviously at the lower end of the simpleton scale

So, my next question is... what benefits do the wider tyres provide over the skinny ones on my KA? I'll get my dunces hat now shall I?

Ian

[rlmr]

So, my next question is... what benefits do the wider tyres provide over the skinny ones on my KA?

You will find it easier to slide on wet roads and "aquaplane" on mud, snow and slush... whereas your skinny wee tyres will cut right through the crap and make contact with the road surface.

Rennie

[PeteG]

...Now they can't stop making it...

I thought they'd just forgotten they were making it. Hmm.

Never had the chance to drive one more than a few yards - I've heard that there's a lot of body roll, but it'll grip til the cows come home. Always been impressed by the packaging for someone my size in the front - boot space and rear passengers fare less well.
I'd be interested to take one out sometime... but then that goes for a lot of cars :p

[Gromit37]

Thanks Dave and Rennie. I'll take my dunces hat off now

As for the KA, it's an entertaining little car, with handling that belies it's cute 'city car' image. It's no sports car mind... the engine isn't exactly state of the art, but it doesn't roll too much and grips well. I don't think I'll be changing anything on it. I hear the little Sportka is lots of fun, so I might upgrade if I can.

OMG... i'M TURNING IN TO A CHAV!

But my next question (reaching for my dunces hat again) is...

Why do 'Sports' cars have much wider tyres than most standard road cars? My girlfriend's Renault Scenic has 205mm all round, my Ka has 165mm and the Lotus Elise is 225mm rear. So the benefits are?

Please be gentle. Stupidity is a talent I've worked hard at perfecting

[Nigel]

I have to be honest and say I've not noticed any great differences between tyre sizes makes etc, apart from tramlining on the larger tyres.

My first beemer 525i had 195's on, after I had put the correct wheels on it had 225's, it handled better on the 195's

[Renny]

The Discovery was now able to go round corners quicker and the drivers didn't get any feeling of body roll. Result...well, I leave that to your imaginations

No feeling of body roll?!?! My P reg Disco had loads of body roll (although less than my friends who took his ARB's off for better offroad ability) :}

Chris

I think Susie means the TD5 Discovery from '98 onwards. Our TD5 had ACE (Active Cornering Enhancement) which is hydraulic controlled anti-roll bars front and rear. These have the effect of reducing body roll whilst cornering on-road, but still allowing suspension flex off-road. The result is that fast corners produce very little roll if you are gentle and smooth on entry. The down-side is that you tend not to realise just how close to the limits of adhesion you actually are.

I remember a spirited drive along a twisty back road where oncoming traffic which was using rather too much of my side of the road caused me to gently feather the brakes mid-corner (I know ). The result was that the ABS was triggered, presumably as the lightly loaded inside front wheel approached lock-up. Until that point, I had not realised how close I was to the limit of adhesion as the car was stable and almost level despite the amount of speed I had carried into the corner.

It is technology like this that can and does lead folks to believe that their car is invincible and totally stable in all conditions, that is until either it fails, or the pure mechanical limits are reached (usually at much higher speeds and in worse conditions when the driver does not have the required experience to deal with it). Then the blame is placed on the technology, not the driver accepting responsibility.

There is a lot to be said for learning how a car behaves and handles at the limit. Skinny tyres and low-tech suspension systems allowed some of us to gain this experience at relatively low speed.

[manilva15b]

I think Susie means the TD5 Doscovery from '98 onwards. Our TD5 had ACE (Active Cornering Enhancement) which is hydraulic controlled anti-roll bars front and rear. These have the effect of reducing body roll whilst cornering on-road, but still allowing suspension flex off-road. The result is that fast corners produce very little roll if you are gentle and smooth on entry. The down-side is that you tend not to realise just how close to the limits of adhesion you actually are.

Last year I had a Freelander which from your description probably had the same system fitted. It was actually quite awesome on the twisty back roads near Casares . the Citroen I have at the moment, the C8 has quite a lot of body roll, so I'm not so enthusiastic on these roads

One feature I really did like about that car was the HDC (Hill Descent Control) which it needed because of the lack of low ratio. It made going into town down 'La Espileta' a doddle - I reckon the gradient there is about 30%!

[Renny]

The lack of a Low box is one of the reasons I don't like the Freelander. HDC is good, but you still don't have enough control at very low speeds without abusing the clutch.

We're looking at a Discovery 3 just now to replace the TD5. Oddly enough on the first test drive I was uncomfortable with how much it rolled in corners . It seems the active conrtoll is reduced and the steering responds quicker so you have to be even smoother on turn-in.

The TDV6 diesel is a huge leap forward over the TD5, much quieter and smoother as well as being more powerful. The access mode where the suspension lowers by 50mm is also good for the (getting older) relatives and dogs. The new Freelander is about 200mm higher to the boot floor level.