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Turning noise

raypollock

raypollock

New member
I notice a noise from the front wheels when I'm on or near full lock and driving very slowly. It's like the wheels are moving over small rocks. As my car is a C4S I thought it might be one wheel driving at slightly a different speed than its mate and the noise might me the tread moving on the tyre. Any need for me to worry?




2006 C4S. Seal Grey.
 
It's because of the low profile tyres and the camber changes at extreme lock, happens with most sports cars, nowt to worry about :)
 
All quite normal. [:)]

It's all to do with wide tyres and the Ackerman angles of the steering, when the tyres have to skip across the road surface in tight turns.[;)]

Regards,

Clive
 
I notice it more this time of year, I think it may get more pronounced as the temperature drop.

I normally take it as one of the signals it is time for the winter tyres to go on.
 

A perennial posting on the forum at this time of the year Ray.

As others have said, wide tyres, low ambient temperatures and Ackerman, castor and camber angles all come into play to make the front wheels skip over the surface. Just have a quick look at your wheels from the front of the car when you're on full lock.

I must say that, for me, it's most noticeable when I'm reversing on full lock.

Jeff
 
OK, lets clear this up, Caster and Camber have nothing to do with it at all, nor does low profile tyres.

The phenomonon is indeed as others have said - the Ackerman Principal, as you will be aware but have not thought about the two front wheels when turning corners have to turn in two different radius, the outer wheel has a larger circle and the inner one a smaller circle, Ackerman engineered his principal to ensure that steering systems have a compensatory element built into the engineering to provide the wheels are parallel when runing straight and different angles when on a full lock, this provides a tighter turning angle for the inner wheel.
However, this can only be a perfect angle for a given point on the tyre and as the tyres are so wide either side of this given point will be scrubbing, as you can appreciate the very outer edge of the tyre and the very inner edge of the tyre would in fact need a different angle to be perfectly planted on the road.

Without Ackermans principal tyres would wear out at an alarming rate and whilst its not a perfect system it is the very best even today.

What you describe is perfectly normal but for piece of mind you should be confident that your tracking is correct as an error here will increase the tyre scrub on full lock
 

ORIGINAL: Glyn

The phenomonon is indeed as others have said - the Ackerman Principle.......

Without Ackermans principal tyres would wear out at an alarming rate and whilst its not a perfect system it is the very best even today.
Click to expand...

That's certainly true Glyn, but modern cars don't employ pure Ackerman steering geometry because suspension compliance and other dynamic effects in the suspension and tyres need to be taken into account. After all, I guess that the suspension and steering system on our cars is optimised more for high-speed handling and not for performing 3-point turns at 5mph..!

Remember also that owing to wheel camber the tyre is not exactly perpendicular to the road surface, which defines the nominal contact point of the tyre with the road, and there is a complex interplay between suspension compliance, steering angle, camber angle, castor angle and toe - which makes an analysis of what's going on up front even more complex for what we're discussing in this post.

Just having my two-pence worth really..!

Jeff
 
ORIGINAL: Motorhead
A perennial posting on the forum at this time of the year Ray.
Click to expand...
Correct, January 2009 since we were asked the same question... and I wrote an article in the club magazine last December - sort of proving this does seem to be more prominent an occurrence in the colder times of the year...[:)]

Maybe a FAQ time...

garyw
 
acker-bilk_tickets_13043318635995.png


ackerbilk
 
Sincerest apologies to dear old Rudolph. Many manuals make the same mistake.

Anyway, here's the principle (principal [:D]) explained:


243px-Ackermann_simple_design_svg.png

Ackermann_turning_svg.png


Regards,

Clive.
 
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