Safe Speed Forums

Every so often when one's driving, making continuous fine steering adjustments, one of those adjustments seems subjectively to take additional time to have an effect. Some vehicles do it more than others.

I've had a couple this evening. drifting slightly towards the centreline, steer slightly left, still drifting, but I know I've put on enough lock, wait, ah, there it is, I've got my correction.

* I'm pretty sure the effect is real and not purely subjective.
* I'm pretty sure it isn't front wheel slip angle because I'm very sensitive to front wheel slip angles.
* I usually know what's going on and don't wind on extra lock. Somehow I know I have to wait.

I've never seen this effect documented anywhere. Anyone know what's really happening?

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Variable crosswinds?

Had a similar thing when driving on lane 1 of the motorway. Constant truck loads cause shallow endents in the road which cause the front wheels to drift and seem to put lag into the steeering. M1 J23-21 southbound is bad for this

_________________
Speed camera policy Kills

I think so.

Often, you can't tell the strength of the crosswinds because the vegetation hardly moves.

Probably eddy currents or something like that.

I've had this experiance myself, and I agree with Gizmo and Pogo, ruts in the road from lorries, and variation in wind speeds. I often wander if sometimes it might be down to power steering.

_________________
Useless laws weaken necessary laws.

were you driving a sherpa van by any chance (or one of the many rebadged derivatives, leyland, LDV etc?) they appear in my experience to have a certain elastic quality to the steering linkage making constant readjustment neccesary especially on motorway driving.

_________________
Fear is a weapon of mass distraction

Lock to lock turns in the steering and the front wheel toe in (more toe = more responsive) makes a difference. Is toe in what you mean by slip angle? Steering rack wear will also affect how much slop there is before the wheels repsond. Tyre types and makes also respond differently. Some have more of an 'edge' so feel like they turn in faster than others. Tyre pressures also have a bearing on things. Some cars are like barges and seem to take ages to respond. Others, like my lancia, turn the moment you turn the wheel at modest speeds. Still a bit of a barge at car park speeds though!

If you want fun and responsive steering then try a jap car with rear wheel steering

I think you may have hit the nail on the head there.

Vans have a habit of doing strange things like this. I've had to drive with a quater turn of lock in a bad sidewind.

I think what Paul is getting is lag from the higher profile tyres. The wheel has turned but it takes that bit longer for the rubber to change direction.

We've (Claire and I) been talking about it a lot today. The main conclusion is that it's likely to most frequently be caused by road surface irregularities. It might be a white line, a join between tarmac sections or any other 'ridge' type feature. Sometimes the ridge feature may not be obvious...

"Slip angle" is a precise technical term that refers to the difference between wheel direction and path. maximum cornering grip is generated when there's about 10% slip on dry tarmac. Try this google:

http://www.google.com/search?client=ope ... p+angle%22

I'm certainly not talking about an effect that is limited to vehicle type, and certainly not talking about wind. But the effect is more common and more marked with less sophisticated suspensions.

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

nah, its just vans designed in the 60's and tarted up to pass off as 21st centuary items that do it. nothing to do with wind or tyres just an ungodly amount of play in the steering due to sloppy tolerances in manufacture i expect. modern transits, transporters etc are more like cars in terms of responce and handling.

The 10 year old transits were nicer to drive, quieter, more comfortable, handled better and were more reliable than the brand new sherpas* they were replaced with...

*or LDV's or whatever they'll badge them as this year in the hope nobody realises it's a poxy sherpa.

_________________
Fear is a weapon of mass distraction

Disagree 100%. Whilst the tolerance in the newly laid surface course is 6mm, the tolerance for adjoining "rips" of surface course is less than 2mm. This would not affect your path in the way you have said.

Similarly, thermoplastic white lines whilst having a different skid resistance to the surrounding surface course has a difference in level of only 2 or 3 mm.

None of these tolerances are, IMO, sufficient to cause the drag you describe.

Other "ridges" would be picked up on the regular maintenance activity.

I think this is actually a tiny effect but you notice it out of all proportion, which is why you don't really need to correct it. For example, you wish to steer ten degrees to the right, and put on the approximately correct amount of lock to steer that way. Your "feedback loop" is now highly attuned towards verifying that the vehicle is responding as expected, partly for peace of mind, and partly because at some point you need to decide when the manoeuvre is complete and wind the lock off again.

Thus at the instant you begin to steer your senses are on red alert - albeit largely subconsciously - so when some outside influence alters the vehicles course by a relatively small amount (say 1 degree) then it immediately sounds alarm bells in the alert driver.

Of course in reality the effect is very minor, and indeed may well self correct due to the suspension and steering "winding up" and unwinding again as a momentary outside force acts upon it. So you don't actually need to correct for it, or if you do it will be negligible. Perhaps you wind your steering lock back off half a second later than you would otherwise have done, but either way you don't actually make any specific correction.

My car has very taut, stiff suspension and quite direct steering, so in principle goes exactly where you steer it. But it also has low profile tyres so is very prone to "tramlining" and "whitelining". In most cases this is exhibited in exactly the way you describe, ie you steer an "average" course based on where you want to be 100 yards up the road, and largely ignore the fluctuations along the way if there is an irregularity in the road that causes the tyres to "kick".

An analogy is steering a sailing yacht in small waves. You mostly steer an average course and ignore the momentary effects that the waves have, as you know that they will cancel themselves out a second later as you cross the opposite face of the wave. Indeed if you try to correct for each fluctuation you end up steering a wild zig zag course, which in turn leads to more steering and more errors. Good helmsmen "steer small", meaning they are always looking to use minimal control inputs to maintain a smooth course, and to a certain extent the same applies in a car.

_________________
CSCP Latin for beginners...
Ticketo ergo sum : I scam therefore I am!

So you've never experienced tramlining then?

I now think that the 'steering delay' in the first post is largely a tramlining effect.

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Yeah, that's about the same conclusion I've come to. The steering delay effect originally described is simply a minor case of tramlining.

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Don't know if it helps, but a few years back, I went on holiday to France in our Renault 19 RTD, and all was well until we went out for the day, and the car kept veering to the right.
I checked for brake drag, tyre pressures, etc. to no avail.
The tyres were nearing the end of their life, and I had intended replacing them once we had got our continental holiday out of the way, but they were evenly worn.
After three days, with no sign of what was wrong, and gingerly driving in anticipation of a failure of some sort, we took the car into the local Renault dealership.
After my father had translated, it transpired their opinion was that thousands of miles of careful motoring had worn my tyres with a profile which matched the road camber - in Britain.
On reaching France, and being on the opposite side of the road, the tyre was "falling off" the camber (their words).
We had new Michelins put on all round, and voila - end of problem!
Brother-in-law has a scooter which displayed wear on one side - the right.

The other pleasant surprise was the cost of 'home grown' tyres in France - they were equivalent of £90 for all four tyres including fitting and ballancing! (Full exhaust for my Espace the following year was £110 - Kwikfit quoted us £145, and the best quote had been £128 in Carlisle excluding the downpipe from the manifold!)

I know of the ruts in lane 1 on the M6 - if you steer positively out in an overtake, they present no problem, but if you stray slowly out of the centre of lane 1, the steering gives a little wobble, and the car directs ITSELF back int the centre (Peugeot 406 estate - quite a long wheelbase).
It's a little unerving the first time, but you soon get used to it!

_________________
Time to take responsibility for our actions.. and don't be afraid of speaking out!

Is your car front wheel drive, Paul? (If it's a car in subject)

_________________
My friends call me RuFFy

It's every vehicle I've ever owned.

The FWD / RWD score is, I think, about 2:55 in the favour of RWD. I hate it when the power corrupts the steering in FWD.

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Had a similar deal with our family car (V reg Mondeo) that bugged me ever since the day I bought it (a couple of months ago).
The car would constantly veer off to the left if you took your hands off the wheel, even when driving on roads with no apparent camber to them. The other thing that niggled me about it was that it was also very noisy inside when driving (far too much road noise for a car that was only 5 years old IMO).

Anyway, I bit the bullet yesterday and had 4 new Avon ZZ3's fitted and the difference was amazing.
The car now drives in a perfectly straight line with no hands on the wheel (which is what any car should do anyway) and the amount of road noise present is now negligible.

As for handling, I was quite impressed with the cars "chuckability" around the bends with the old rubber, but with the Avons on it has become a completely different car and the road holding ability is definately noticeable.

_________________
What makes you think I'm drunk officer, have I got a fat bird with me?

I've noticed this in my car, too.

There is one particular point in my journey home where it happens every single time. At that one point, it always feels like it's turning less than it should for my steering input, whereas the car normally has extremely direct steering response. I cannot see anything about the road surface that would cause it, but it feels like it has a layer of dust on it.

I've noticed it on motorways, but only when I had my previous set of tyres on. It would completely repeatedly exhibit the delay that you mention, I would turn the wheel and you could actually feel a sudden change in the level of resistance through the steering wheel when the tyre grip behaviour changed. It only happened on motorways, but I don't believe it was tramlining as it was consistent for hundreds of miles. It doesn't do it now that I've had the front tyres replaced, so it's possible my tyres were suffering from some sort of slightly uneven wear.

I think you're feeling front wheel slip angle here. You're describing mild 'understeer'. It's quite possible to learn to use the feeling to measure (estimate?) the level of available grip at any given moment. In fact in low grip conditions, a lightening of the steering and an increase in front wheel slip angles are usually the earliest signs.

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety